A photovoltaic system, also PV system or solar power system, is an
electric power system
An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of a power system is the electrical grid that provides power to homes and industries within an extended area. The e ...
designed to supply usable
solar power
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic e ...
by means of
photovoltaics
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...
. It consists of an arrangement of several components, including
solar panel
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
s to absorb and convert sunlight into electricity, a
solar inverter
A solar inverter or photovoltaic (PV) inverter is a type of power inverter which converts the variable direct current (DC) output of a photovoltaic solar panel into a utility frequency alternating current (AC) that can be fed into a commercial ...
to convert the output from
direct
Direct may refer to:
Mathematics
* Directed set, in order theory
* Direct limit of (pre), sheaves
* Direct sum of modules, a construction in abstract algebra which combines several vector spaces
Computing
* Direct access (disambiguation), a ...
to
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
, as well as
mounting,
cabling, and other electrical accessories to set up a working system. It may also use a
solar tracking system
A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, lenses or the mirrors of a heliostat.
For flat-panel photovoltaic systems, trackers are used to mi ...
to improve the system's overall performance and include an
integrated battery.
PV systems convert light directly into electricity, and are not to be confused with other solar technologies, such as
concentrated solar power
Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated when ...
or
solar thermal
Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors.
Solar thermal collectors are classified by the United Sta ...
, used for heating and cooling. A solar array only encompasses the ensemble of solar panels, the visible part of the PV system, and does not include all the other hardware, often summarized as
balance of system The balance of system (BOS) encompasses all components of a photovoltaic system other than the photovoltaic panels.
This includes wiring, switches, a mounting system, one or many solar inverters, a battery bank and battery charger.
Other optiona ...
(BOS). PV systems range from small,
rooftop-mounted or
building-integrated systems with capacities from a few to several tens of kilowatts, to large
utility-scale power stations of hundreds of megawatts. Nowadays, most PV systems are
grid-connected, while off-grid or
stand-alone systems account for a small portion of the market.
Operating silently and without any moving parts or
environmental emissions, PV systems have developed from being niche market applications into a mature technology used for mainstream electricity generation. A rooftop system
recoups the invested energy for its manufacturing and installation within 0.7 to 2 years and produces about 95 percent of net clean
renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
over a 30-year service lifetime.
Due to the
growth of photovoltaics
Worldwide growth of photovoltaics has been close to exponential between 1992 and 2018.
During this period of time, photovoltaics (PV), also known as solar PV, evolved from a niche market of small-scale applications to a mainstream electricit ...
, prices for PV systems have rapidly declined since their introduction; however, they vary by market and the size of the system. In 2014, prices for residential 5-kilowatt
systems in the United States were around $3.29 per watt, while in the highly penetrated
German market, prices for rooftop systems of up to 100 kW declined to €1.24 per watt. Nowadays, solar PV modules account for less than half of the system's overall cost, leaving the rest to the remaining BOS-components and to soft costs, which include customer acquisition, permitting, inspection and interconnection, installation labor and financing costs.
Modern system
Overview
![From a solar cell to a PV system](https://upload.wikimedia.org/wikipedia/commons/a/a0/From_a_solar_cell_to_a_PV_system.svg)
A
photovoltaic
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...
system converts the Sun's
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
, in the form of light, into usable
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
. It comprises the solar array and the balance of system components. PV systems can be categorized by various aspects, such as,
grid-connected vs.
stand alone
''Stand Alone'' is a 1985 American action drama film directed by Alan Beattie and starring Charles Durning.
Plot
An older war hero witnesses a murder. He is reluctant to identify the killers. When they come after him, he ends up having to pro ...
systems, building-integrated vs. rack-mounted systems, residential vs. utility systems,
distributed Distribution may refer to:
Mathematics
*Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations
*Probability distribution, the probability of a particular value or value range of a varia ...
vs. centralized systems, rooftop vs. ground-mounted systems, tracking vs. fixed-tilt systems, and new constructed vs.
retrofitted
Retrofitting is the addition of new technology or features to older systems. Retrofits can happen for a number of reasons, for example with big capital expenditures like naval vessels, military equipment or manufacturing plants, businesses or go ...
systems. Other distinctions may include, systems with microinverters vs. central inverter, systems using
crystalline silicon
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semicondu ...
vs.
thin-film technology, and systems with modules.
About 99 percent of all European and 90 percent of all U.S. solar power systems are connected to the
electrical grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
, while off-grid systems are somewhat more common in Australia and South Korea.
PV systems rarely use battery storage. This may change, as government incentives for distributed energy storage are implemented and investments in storage solutions gradually become economically viable for small systems.
[
] A typical residential solar array is rack-mounted on the roof, rather than integrated into the roof or facade of the building, which is significantly more expensive. Utility-scale
solar power stations are ground-mounted, with fixed tilted solar panels rather than using expensive tracking devices. Crystalline silicon is the predominant material used in 90 percent of worldwide produced solar modules, while its rival thin-film has lost market-share.
[
] About 70 percent of all solar cells and modules are produced in China and Taiwan, only 5 percent by European and US-
manufacturers.
The installed capacity for both small rooftop systems and large solar power stations is growing rapidly and in equal parts, although there is a notable trend towards utility-scale systems, as the focus on new installations is shifting away from Europe to sunnier regions, such as the
Sunbelt
The Sun Belt is a region of the United States generally considered to stretch across the Southeast and Southwest. Another rough definition of the region is the area south of the 36th parallel. Several climates can be found in the region — des ...
in the U.S., which are less opposed to ground-mounted solar farms and cost-effectiveness is more emphasized by investors.
Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of photovoltaics is declining continuously.
There are several million PV systems distributed all over the world, mostly in Europe, with 1.4 million systems in Germany alone
– as well as North America with 440,000 systems in the United States. The energy
conversion efficiency
Energy conversion efficiency (''η'') is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radi ...
of a conventional solar module increased from 15 to 20 percent since 2004
and a PV system recoups the energy needed for its manufacture in about 2 years. In exceptionally irradiated locations, or when thin-film technology is used, the so-called
energy payback time decreases to one year or less.
Net metering
Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly importa ...
and financial incentives, such as preferential
feed-in tariffs
A feed-in tariff (FIT, FiT, standard offer contract,Couture, T., Cory, K., Kreycik, C., Williams, E., (2010)Policymaker's Guide to Feed-in Tariff Policy Design National Renewable Energy Laboratory, U.S. Dept. of Energy advanced renewable tariff, ...
for solar-generated electricity, have also greatly supported installations of PV systems in many countries. The
levelised cost of electricity
The levelized cost of electricity (LCOE), or levelized cost of energy, is a measure of the average net present cost of electricity generation for a generator over its lifetime. It is used for investment planning and to compare different methods ...
from large-scale PV systems has become competitive with conventional electricity sources in an expanding list of geographic regions, and
grid parity
Grid parity (or socket parity) occurs when an alternative energy source can generate power at a levelized cost of electricity (LCOE) that is less than or equal to the price of power from the electricity grid. The term is most commonly used wh ...
has been achieved in about 30 countries.
As of 2015, the
fast-growing global PV market is rapidly approaching the 200 GW mark – about 40 times the installed capacity in 2006. These systems currently contribute about 1 percent to worldwide electricity generation.
Top installers of PV systems in terms of capacity are currently China, Japan and the United States, while half of the world's capacity is installed in Europe, with Germany and Italy supplying 7% to 8% of their respective domestic electricity consumption with solar PV.
The International Energy Agency expects
solar power
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic e ...
to become the world's largest source of electricity by 2050, with solar photovoltaics and
concentrated solar thermal
Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated when ...
contributing 16% and 11% to the global demand, respectively.
Solar grid-connection
![PV-system-schematics-residential-Eng](https://upload.wikimedia.org/wikipedia/commons/2/20/PV-system-schematics-residential-Eng.png)
A grid connected system is connected to a larger independent grid (typically the public electricity grid) and feeds energy directly into the grid. This energy may be shared by a residential or commercial building before or after the revenue measurement point, depending on whether the credited energy production is calculated independently of the customer's energy consumption (
feed-in tariff
A feed-in tariff (FIT, FiT, standard offer contract,Couture, T., Cory, K., Kreycik, C., Williams, E., (2010)Policymaker's Guide to Feed-in Tariff Policy Design National Renewable Energy Laboratory, U.S. Dept. of Energy advanced renewable tariff, ...
) or only on the difference of energy (
net metering
Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly importa ...
). These systems vary in size from residential (2–10 kW
p) to solar power stations (up to 10s of MW
p). This is a form of
decentralized electricity generation. Feeding electricity into the grid requires the transformation of DC into AC by a special, synchronising
grid-tie inverter
A grid-tie inverter converts direct current (DC) into an alternating current (AC) suitable for injecting into an electrical power grid, normally 120 V RMS at 60 Hz or 240 V RMS at 50 Hz. Grid-tie inverters are used between local electrica ...
. In kilowatt-sized installations the DC side system voltage is as high as permitted (typically 1000 V except US residential 600 V) to limit ohmic losses. Most modules (60 or 72 crystalline silicon cells) generate 160 W to 300 W at 36 volts. It is sometimes necessary or desirable to connect the modules partially in parallel rather than all in series. An individual set of modules connected in series is known as a 'string'.
Scale of system
Photovoltaic systems are generally categorized into three distinct market segments: residential rooftop, commercial rooftop, and ground-mount utility-scale systems. Their capacities range from a few kilowatts to hundreds of megawatts. A typical residential system is around 10 kilowatts and mounted on a sloped roof, while commercial systems may reach a megawatt-scale and are generally installed on low-slope or even flat roofs. Although rooftop mounted systems are small and have a higher
cost per watt than large utility-scale installations, they account for the largest share in the market. There is, however, a growing trend towards bigger utility-scale power plants, especially in the "sunbelt" region of the planet.
Utility-scale
![Perovosolarstation](https://upload.wikimedia.org/wikipedia/commons/7/7b/Perovosolarstation.jpg)
Large utility-scale
solar parks or farms are
power station
A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.
Many p ...
s and capable of providing an energy supply to large numbers of consumers.
Generated electricity is fed into the transmission grid powered by central generation plants (grid-connected or grid-tied plant), or combined with one, or many, domestic electricity generators to feed into a small
electrical grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
(hybrid plant). In rare cases generated electricity is stored or used directly by island/standalone plant. PV systems are generally designed in order to ensure the highest energy yield for a given investment. Some large photovoltaic power stations such as
Solar Star
Solar Star is a 579-megawatt ( MWAC) photovoltaic power station near Rosamond, California, United States, that is operated and maintained by SunPower Services. When completed in June 2015, it was the world's largest solar farm in terms of instal ...
,
Waldpolenz Solar Park
The Waldpolenz Solar Park is a 52-megawatt (MW) photovoltaic power station built by German developer and operator Juwi at a former military air base near Leipzig, Eastern Germany. When completed by the end of 2008, it was the world's largest ...
and
Topaz Solar Farm
Topaz Solar Farm is a 550 megawatt ( MWAC) photovoltaic power station in San Luis Obispo County, California, United States. Construction on the project began in November 2011 and ended in November 2014. It is one of the world's largest sola ...
cover tens or hundreds of hectares and have power outputs up to hundreds of
megawatt
The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units, International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), ...
s.
Rooftop, mobile, and portable
![Solar panels on house roof](https://upload.wikimedia.org/wikipedia/commons/8/8e/Solar_panels_on_house_roof.jpg)
A small PV system is capable of providing enough AC electricity to power a single home, or an isolated device in the form of AC or DC electric. Military and civilian Earth observation
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
s,
street lights
A street light, light pole, lamp pole, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or path. Similar lights may be found on a railway platform. When urban electric power distribution ...
, construction and traffic signs,
electric car
An electric car, battery electric car, or all-electric car is an automobile that is propelled by one or more electric motors, using only energy stored in batteries. Compared to internal combustion engine (ICE) vehicles, electric cars are quie ...
s, solar-powered tents, and
electric aircraft
An electric aircraft is an aircraft powered by electricity.
Electric aircraft are seen as a way to reduce the environmental effects of aviation, providing zero emissions and quieter flights.
Electricity may be supplied by a variety of methods, ...
may contain integrated photovoltaic systems to provide a primary or
auxiliary power
Auxiliary power is electric power that is provided by an alternate source and that serves as backup for the primary power source at the station main bus or prescribed sub-bus.
An offline unit provides electrical isolation between the primary pow ...
source in the form of AC or DC power, depending on the design and power demands. In 2013, rooftop systems accounted for 60 percent of worldwide installations. However, there is a trend away from rooftop and towards utility-scale PV systems, as the focus of new PV installations is also shifting from Europe to countries in the sunbelt region of the planet where opposition to ground-mounted solar farms is less accentuated.
Portable and mobile PV systems provide electrical power independent of utility connections, for "off the grid" operation. Such systems are so commonly used on
recreational vehicle
A recreational vehicle, often abbreviated as RV, is a motor vehicle or trailer that includes living quarters designed for accommodation. Types of RVs include motorhomes, campervans, coaches, caravans (also known as travel trailers and camper ...
s and boats that there are retailers specializing in these applications and products specifically targeted to them. Since recreational vehicles (RV) normally carry batteries and operate lighting and other systems on nominally 12-volt DC power, RV systems normally operate in a voltage range that can charge 12-volt batteries directly, so addition of a PV system requires only panels, a charge controller, and wiring. Solar systems on recreation vehicles are usually constrained in wattage by the physical size of the RV's roof space.
Building-integrated
![Façana Fotvoltaica MNACTEC](https://upload.wikimedia.org/wikipedia/commons/0/0f/Fa%C3%A7ana_Fotvoltaica_MNACTEC.JPG)
In urban and suburban areas, photovoltaic arrays are often used on rooftops to supplement power use; often the building will have a connection to the
power grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
, in which case the energy produced by the PV array can be sold back to the
utility
As a topic of economics, utility is used to model worth or value. Its usage has evolved significantly over time. The term was introduced initially as a measure of pleasure or happiness as part of the theory of utilitarianism by moral philosopher ...
in some sort of
net metering
Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly importa ...
agreement. Some utilities use the rooftops of commercial customers and telephone poles to support their use of PV panels. Solar trees are arrays that, as the name implies, mimic the look of trees, provide shade, and at night can function as
street light
A street light, light pole, lamp pole, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or path. Similar lights may be found on a railway platform. When urban electric power distribution ...
s.
Performance
Uncertainties in revenue over time relate mostly to the evaluation of the solar resource and to the performance of the system itself. In the best of cases, uncertainties are typically 4% for year-to-year climate variability, 5% for solar resource estimation (in a horizontal plane), 3% for estimation of irradiation in the plane of the array, 3% for power rating of modules, 2% for losses due to dirt and
soiling, 1.5% for losses due to snow, and 5% for other sources of error. Identifying and reacting to manageable losses is critical for revenue and O&M efficiency. Monitoring of array performance may be part of contractual agreements between the array owner, the builder, and the utility purchasing the energy produced. A method to create "synthetic days" using readily available weather data and verification using the
Open Solar Outdoors Test Field The Open Solar Outdoors Test Field (OSOTF) is a project organized under open source principles, which is a fully grid-connected test system that continuously monitors the output of many solar photovoltaic modules and correlates their performance to ...
make it possible to predict photovoltaic systems performance with high degrees of accuracy. This method can be used to then determine loss mechanisms on a local scale - such as those from snow
or the effects of surface coatings (e.g.
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
or
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are no ...
) on soiling or snow losses. (Although in heavy snow environments with severe ground interference can result in annual losses from snow of 30%.)
Access to the Internet has allowed a further improvement in energy monitoring and communication. Dedicated systems are available from a number of vendors. For solar PV systems that use
microinverters
A solar inverter or photovoltaic (PV) inverter is a type of power inverter which converts the variable direct current (DC) output of a photovoltaic solar panel into a utility frequency alternating current (AC) that can be fed into a commercial ...
(panel-level DC to AC conversion), module power data is automatically provided. Some systems allow setting performance alerts that trigger phone/email/text warnings when limits are reached. These solutions provide data for the system owner and the installer. Installers are able to remotely monitor multiple installations, and see at-a-glance the status of their entire installed base.
Components
![Balance of System](https://upload.wikimedia.org/wikipedia/commons/0/05/Balance_of_System.svg)
A photovoltaic system for residential, commercial, or industrial energy supply consists of the solar array and a number of components often summarized as the
balance of system The balance of system (BOS) encompasses all components of a photovoltaic system other than the photovoltaic panels.
This includes wiring, switches, a mounting system, one or many solar inverters, a battery bank and battery charger.
Other optiona ...
(BOS). This term is synonymous with "
Balance of plant" q.v. BOS-components include power-conditioning equipment and structures for mounting, typically one or more DC to
AC power converters, also known as
inverters
A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...
, an energy storage device, a racking system that supports the solar array, electrical wiring and interconnections, and mounting for other components.
Optionally, a balance of system may include any or all of the following:
renewable energy credit
A Renewable energy credit (REC) is a certificate corresponding to the environmental attributes of energy produced from renewable sources such as wind or solar. RECs were created as a means to track progress towards and compliance with states' Rene ...
revenue-grade meter,
maximum power point tracker
Maximum power point tracking (MPPT) or sometimes just power point tracking (PPT), is a technique used with variable power sources to maximize energy extraction as conditions vary. The technique is most commonly used with photovoltaic (PV) solar s ...
(MPPT),
battery
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
system and
charger
Charger or Chargers may refer to:
* Charger (table setting), decorative plates used to fancify a place setting
* Battery charger, a device used to put energy into a cell or battery
* Capacitor charger, typically a high voltage DC power supply ...
,
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
solar tracker
A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, lenses or the mirrors of a heliostat.
For flat-panel photovoltaic systems, trackers are used to mi ...
,
energy management software
Energy Management Software (EMS) is a general term and category referring to a variety of energy-related software applications which may provide utility bill tracking, real-time metering, building HVAC and lighting control systems, building simulat ...
,
solar irradiance
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/ ...
sensors,
anemometer
In meteorology, an anemometer () is a device that measures wind speed and direction. It is a common instrument used in weather stations. The earliest known description of an anemometer was by Italian architect and author Leon Battista Alberti ( ...
, or task-specific accessories designed to meet specialized requirements for a system owner. In addition, a
CPV system requires
optical lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a #Compound lenses, compound lens consists of several simple lense ...
es or mirrors and sometimes a cooling system.
The terms "solar array" and "PV system" are often incorrectly used interchangeably, despite the fact that the solar array does not encompass the entire system. Moreover, "solar panel" is often used as a synonym for "solar module", although a panel consists of a string of several modules. The term "solar system" is also an often used
misnomer
A misnomer is a name that is incorrectly or unsuitably applied. Misnomers often arise because something was named long before its correct nature was known, or because an earlier form of something has been replaced by a later form to which the name ...
for a PV system.
Solar array
![Turisme de parcs fotovoltaics](https://upload.wikimedia.org/wikipedia/commons/2/29/Turisme_de_parcs_fotovoltaics.JPG)
The building blocks of a photovoltaic system are solar cells. A solar cell is the electrical device that can directly convert photons energy into electricity. There are three technological generations of solar cells: the first generation (1G) of
crystalline silicon cells (c-Si), the second generation (2G) of
thin-film
A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ap ...
cells (such as
CdTe
Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with cadmi ...
,
CIGS,
Amorphous Silicon
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films onto ...
, and
GaAs
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circui ...
), and the third generation (3G) of
organic,
dye-sensitized,
Perovskite
Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure as (XIIA2+VIB4+X2−3), known as ...
and
multijunction cells.
Conventional
c-Si solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. s, normally wired in series, are encapsulated in a solar module to protect them from the weather. The module consists of a
tempered glass
Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tension. ...
as cover, a soft and flexible
encapsulant, a rear backsheet made of a weathering and fire-resistant
material
Material is a substance or mixture of substances that constitutes an object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical and chemical properties, or on their geologi ...
and an aluminium frame around the outer edge. Electrically connected and mounted on a supporting structure, solar modules build a string of modules, often called solar panel. A solar array consists of one or many such panels. A photovoltaic array, or solar array, is a linked collection of solar modules. The power that one module can produce is seldom enough to meet requirements of a home or a business, so the modules are linked together to form an array. Most PV arrays use an
inverter
A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...
to convert the DC power produced by the modules into
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
that can power
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...
s, motors, and other loads. The modules in a PV array are usually first connected in
series
Series may refer to:
People with the name
* Caroline Series (born 1951), English mathematician, daughter of George Series
* George Series (1920–1995), English physicist
Arts, entertainment, and media
Music
* Series, the ordered sets used in ...
to obtain the desired
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
; the individual strings are then connected in
parallel
Parallel is a geometric term of location which may refer to:
Computing
* Parallel algorithm
* Parallel computing
* Parallel metaheuristic
* Parallel (software), a UNIX utility for running programs in parallel
* Parallel Sysplex, a cluster of ...
to allow the system to produce more
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
. Solar panels are typically measured under STC (standard test conditions) or PTC (PVUSA test conditions), in
watt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s. Typical panel ratings range from less than 100 watts to over 400 watts. The array rating consists of a summation of the panel ratings, in watts, kilowatts, or megawatts.
Modules and efficiency
A typical 150 watt
PV module
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a pho ...
is about a square meter in size. Such a module may be expected to produce 0.75
kilowatt-hour
A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...
(kWh) every day, on average, after taking into account the weather and the latitude, for an insolation of 5 sun hours/day. Module output degrades faster at increased temperature. Allowing ambient air to flow over, and if possible behind, PV modules reduces this problem. Effective module lives are typically 25 years or more. The payback period for an investment in a PV solar installation varies greatly and is typically less useful than a calculation of
return on investment
Return on investment (ROI) or return on costs (ROC) is a ratio between net income (over a period) and investment (costs resulting from an investment of some resources at a point in time). A high ROI means the investment's gains compare favourably ...
. While it is typically calculated to be between 10 and 20 years, the financial payback period can be far shorter with
incentives
In general, incentives are anything that persuade a person to alter their behaviour. It is emphasised that incentives matter by the basic law of economists and the laws of behaviour, which state that higher incentives amount to greater levels of ...
.
The temperature effect on photovoltaic modules is usually quantified by means of some coefficients relating the variations of the open‐circuit voltage, of the short‐circuit current, and of the maximum power to temperature changes. In this paper, comprehensive experimental guidelines to estimate the temperature coefficients.
Due to the low voltage of an individual
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. (typically ca. 0.5V), several cells are wired ''(see
Copper in renewable energy#Solar photovoltaic power generation)'' in series in the manufacture of a "laminate". The laminate is assembled into a protective weatherproof enclosure, thus making a photovoltaic module or
solar panel
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
. Modules may then be strung together into a photovoltaic array. In 2012, solar panels available for consumers had an efficiency of up to about 17%, while commercially available panels can go as far as 27%. By concentrating the sunlight it is possible to achiev higher efficiencies. A group from The
Fraunhofer Institute for Solar Energy Systems
The Fraunhofer Institute for Solar Energy Systems ISE (or Fraunhofer ISE) is an institute of the Fraunhofer-Gesellschaft. Located in Freiburg, Germany, The Institute performs applied scientific and engineering research and development for all a ...
has created a cell that can reach 44.7% efficiency using the equivalent of "297 suns".
Shading and dirt
Photovoltaic cell electrical output is extremely sensitive to shading (the so-called "Christmas light effect"). When even a small portion of a cell or of a module or array of cells in parallel is shaded, with the remainder in sunlight, the output falls dramatically due to internal 'short-circuiting' (the electrons reversing course through the shaded portion). When connected in series, the current drawn from a string of cells is no greater than the normally small current that can flow through the shaded cell, so the current (and therefore power) developed by the string is limited. If the extermal load is of low enough impedance, there may be enough voltage available from the other cells in a string to force more current through the shaded cell by breaking down the junction. This breakdown voltage in common cells is between 10 and 30 volts. Instead of adding to the power produced by the panel, the shaded cell absorbs power, turning it into heat. Since the reverse voltage of a shaded cell is much greater than the forward voltage of an illuminated cell, one shaded cell can absorb the power of many other cells in the string, disproportionately affecting panel output. For example, a shaded cell may drop 8 volts, instead of adding 0.5 volts, at a high current level, thereby absorbing the power produced by 16 other cells.
[Ursula Eicker, ''Solar Technologies for Buildings'', Wiley 2003, , page 226] It is thus important that a PV installation not be shaded by trees or other obstructions. There are techniques to mitigate the losses with diodes, but these techniques also entail losses.
Several methods have been developed to determine shading losses from trees to PV systems over both large regions using
LiDAR
Lidar (, also LIDAR, or LiDAR; sometimes LADAR) is a method for determining ranges (variable distance) by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be ...
, but also at an individual system level using
3D modeling
In 3D computer graphics, 3D modeling is the process of developing a mathematical coordinate-based representation of any surface of an object (inanimate or living) in three dimensions via specialized software by manipulating edges, vertices, an ...
software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
.
Most modules have bypass diodes between each cell or string of cells that minimize the effects of shading and only lose the power that the shaded portion of the array would have supplied, as well as the power dissipated in the diodes. The main job of the bypass diode is to eliminate hot spots that form on cells that can cause further damage to the array, and cause fires.
Sunlight can be absorbed by dust, snow, or other impurities at the surface of the module (collectively referred to as
soiling). Soiling reduces the light that strikes the cells, which in turn reduces the power output of the PV system. Soiling losses aggregate over time, and can become large without adequate cleaning. In 2018, the global annual energy loss due to soiling was estimated to at least 3–4%.
However, soiling losses vary sisgnificantly from region to region, and within regions.
Maintaining a clean module surface will increase output performance over the life of the PV system. In one study performed in a snow-rich area (
Ontario
Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...
), cleaning flat mounted solar panels after 15 months increased their output by almost 100%. However, 5° tilted arrays were adequately cleaned by rainwater.
In many cases, especially in
arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...
regions, or in locations in close proximity to deserts, roads, industry, or agriculture, regular cleaning of the solar panels is
cost-effective
Cost-effectiveness analysis (CEA) is a form of economic analysis that compares the relative costs and outcomes (effects) of different courses of action. Cost-effectiveness analysis is distinct from cost–benefit analysis, which assigns a monetar ...
. In 2018, the estimated soiling-induced revenue loss was estimated to between 5 and 7 billion euros.
The long‐term reliability of photovoltaic modules is crucial to ensure the technical and economic viability of PV as a successful energy source. The analysis of degradation mechanisms of PV modules is key to ensure current lifetimes exceeding 25 years.
Insolation and energy
Solar insolation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
is made up of direct, diffuse, and reflected
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
. The absorption factor of a PV cell is defined as the fraction of incident solar irradiance that is absorbed by the cell. When the sun is at the zenith on a cloudless day, the power of the sun is about 1
kW/m
2, on the Earth's surface, to a plane that is perpendicular to the sun's rays. As such, PV arrays can
track the sun through each day to greatly enhance energy collection. However, tracking devices add cost, and require maintenance, so it is more common for PV arrays to have fixed mounts that tilt the array and face due south in the northern hemisphere or due north in the southern hemisphere. The tilt angle from horizontal can be varied for season, but if fixed, should be set to give optimal array output during the peak electrical demand portion of a typical year for a stand-alone system. This optimal module tilt angle is not necessarily identical to the tilt angle for maximum annual array energy output. The optimization of the photovoltaic system for a specific environment can be complicated as issues of solar flux, soiling, and snow losses should be taken into effect. In addition, later work has shown that spectral effects can play a role in optimal photovoltaic material selection. For example, the spectrum of the
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
of the surroundings can play a significant role in output depending on the surface around the photovoltaic system and the type of solar cell material. A photovoltaic installation in the northern latitudes of Europe or the United States may expect to produce 1 kWh/m
2/day. A typical 1 kW photovoltaic installation in Australia or the southern latitudes of Europe or United States, may produce 3.5–5 kWh per day, dependent on location, orientation, tilt, insolation and other factors. In the
Sahara
, photo = Sahara real color.jpg
, photo_caption = The Sahara taken by Apollo 17 astronauts, 1972
, map =
, map_image =
, location =
, country =
, country1 =
, ...
desert, with less cloud cover and a better solar angle, one could ideally obtain closer to 8.3 kWh/m
2/day provided the nearly ever present wind would not blow sand onto the units. The area of the Sahara desert is over 9 million km
2. 90,600 km
2, or about 1%, could generate as much electricity as all of the world's power plants combined.
Mounting
![Pellworm Solarkrftanlage MS P4140082](https://upload.wikimedia.org/wikipedia/commons/b/bb/Pellworm_Solarkrftanlage_MS_P4140082.JPG)
Modules are assembled into arrays on some kind of mounting system, which may be classified as ground mount, roof mount or pole mount. For
solar park
A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building- ...
s a large rack is mounted on the ground, and the modules mounted on the rack.
For buildings, many different racks have been devised for pitched roofs. For flat roofs, racks, bins and building integrated solutions are used. Solar panel racks mounted on top of poles can be stationary or moving, see Trackers below. Side-of-pole mounts are suitable for situations where a pole has something else mounted at its top, such as a light fixture or an antenna. Pole mounting raises what would otherwise be a ground mounted array above weed shadows and livestock, and may satisfy electrical code requirements regarding inaccessibility of exposed wiring. Pole mounted panels are open to more cooling air on their underside, which increases performance. A multiplicity of pole top racks can be formed into a parking carport or other shade structure. A rack which does not follow the sun from left to right may allow seasonal adjustment up or down.
Cabling
Due to their outdoor usage, solar cables are designed to be resistant against
UV radiation and extremely high temperature fluctuations and are generally unaffected by the weather. Standards specifying the usage of
electrical wiring
Electrical wiring is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure.
Wiring is subject to safety standards for design and installation. Allowable ...
in PV systems include the
IEC 60364
IEC 60364 ''Electrical Installations for Buildings'' is the International Electrotechnical Commission (IEC)'s international standard on ''electrical installations of buildings''. This standard is an attempt to harmonize national wiring standards ...
by the
International Electrotechnical Commission
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
, in section 712 "Solar photovoltaic (PV) power supply systems", the British Standard
BS 7671
British Standard BS 7671 "Requirements for Electrical Installations. IET Wiring Regulations", informally called in the UK electrical community "The Regs", is the national standard in the United Kingdom for electrical installation and the safet ...
, incorporating regulations relating to
microgeneration
Microgeneration is the small-scale production of heat or electric power from a "low carbon source," as an alternative or supplement to traditional centralized grid-connected power.
Microgeneration technologies include small-scale wind turbin ...
and photovoltaic systems, and the US UL4703 standard, in subject 4703 "Photovoltaic Wire".
![PV connectors 01 Pengo](https://upload.wikimedia.org/wikipedia/commons/b/b1/PV_connectors_01_Pengo.jpg)
A solar cable is the interconnection
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
used in
photovoltaic
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...
power generation. Solar cables interconnect
solar panels
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a phot ...
and other electrical components of a photovoltaic system. Solar cables are designed to be
UV resistant and
weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
resistant. They can be used within a large temperature range.
Specific performance requirements for material used for wiring a solar panel installation are given in national and local
electrical code {{Electrical Wiring Sidebar
An electrical code is a set of regulations for the design and installation of electrical wiring in a building.
The intention of a code is to provide standards to ensure electrical wiring systems that are safe for peopl ...
s which regulate electrical installations in an area. General features required for solar cables are resistance to ultraviolet light, weather, temperature extremes of the area and insulation suitable for the voltage class of the equipment. Different jurisdictions will have specific rules regarding grounding (earthing) of solar power installations for electric shock protection and lightning protection.
Tracker
![ZomeworksTrackerHead5816](https://upload.wikimedia.org/wikipedia/commons/1/12/ZomeworksTrackerHead5816.jpg)
A
solar tracking system
A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, lenses or the mirrors of a heliostat.
For flat-panel photovoltaic systems, trackers are used to mi ...
tilts a solar panel throughout the day. Depending on the type of tracking system, the panel is either aimed directly at the Sun or the brightest area of a partly clouded sky. Trackers greatly enhance early morning and late afternoon performance, increasing the total amount of power produced by a system by about 20–25% for a single axis tracker and about 30% or more for a dual axis tracker, depending on latitude.
Trackers are effective in regions that receive a large portion of sunlight directly. In diffuse light (i.e. under cloud or fog), tracking has little or no value. Because most
concentrated photovoltaics
Concentrator photovoltaics (CPV) (also known as concentration photovoltaics) is a photovoltaic technology that generates electricity from sunlight. Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight on ...
systems are very sensitive to the sunlight's angle, tracking systems allow them to produce useful power for more than a brief period each day. Tracking systems improve performance for two main reasons. First, when a solar panel is perpendicular to the sunlight, it receives more light on its surface than if it were angled. Second, direct light is used more efficiently than angled light. Special
anti-reflective coatings can improve solar panel efficiency for direct and angled light, somewhat reducing the benefit of tracking.
Trackers and sensors to optimise the performance are often seen as optional, but they can increase viable output by up to 45%. Arrays that approach or exceed one megawatt often use solar trackers. Considering clouds, and the fact that most of the world is not on the equator, and that the sun sets in the evening, the correct measure of solar power is
insolation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
– the average number of kilowatt-hours per square meter per day. For the weather and latitudes of the United States and Europe, typical insolation ranges from 2.26 kWh/m
2/day in northern climes to 5.61 kWh/m
2/day in the sunniest regions.
For large systems, the energy gained by using tracking systems can outweigh the added complexity. For
very large systems, the added maintenance of tracking is a substantial detriment. Tracking is not required for flat panel and low-concentration
photovoltaic system
A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and co ...
s. For high-concentration photovoltaic systems, dual axis tracking is a necessity. Pricing trends affect the balance between adding more stationary solar panels versus having fewer panels that track.
As pricing, reliability and performance of single-axis trackers have improved, the systems have been installed in an increasing percentage of utility-scale projects. According to data from WoodMackenzie/GTM Research, global solar tracker shipments hit a record 14.5 gigawatts in 2017. This represents growth of 32 percent year-over-year, with similar or greater growth projected as large-scale solar deployment accelerates.
Inverter
![Vermont Law School Solar Panel Array-4](https://upload.wikimedia.org/wikipedia/commons/2/28/Vermont_Law_School_Solar_Panel_Array-4.JPG)
Systems designed to deliver
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(AC), such as grid-connected applications need an inverter to convert the
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
(DC) from the solar modules to AC. Grid connected inverters must supply AC electricity in sinusoidal form, synchronized to the grid frequency, limit feed in voltage to no higher than the grid voltage and disconnect from the grid if the grid voltage is turned off. Islanding inverters need only produce regulated voltages and frequencies in a sinusoidal waveshape as no synchronisation or co-ordination with grid supplies is required.
A
solar inverter
A solar inverter or photovoltaic (PV) inverter is a type of power inverter which converts the variable direct current (DC) output of a photovoltaic solar panel into a utility frequency alternating current (AC) that can be fed into a commercial ...
may connect to a string of solar panels. In some installations a
solar micro-inverter
A solar inverter or photovoltaic (PV) inverter is a type of power inverter which converts the variable direct current (DC) output of a photovoltaic solar panel into a utility frequency alternating current (AC) that can be fed into a commercial ...
is connected at each solar panel. For safety reasons a circuit breaker is provided both on the AC and DC side to enable maintenance. AC output may be connected through an
electricity meter
North American domestic analog electricity meter.
Electricity meter with transparent plastic case (Israel)
North American domestic electronic electricity meter
An electricity meter, electric meter, electrical meter, energy meter, or kilowa ...
into the public grid. The number of
module
Module, modular and modularity may refer to the concept of modularity. They may also refer to:
Computing and engineering
* Modular design, the engineering discipline of designing complex devices using separately designed sub-components
* Mo ...
s in the system determines the total DC watts capable of being generated by the solar array; however, the inverter ultimately governs the amount of AC watts that can be distributed for consumption. For example, a PV system comprising 11
kilowatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s DC (kW
DC) worth of PV modules, paired with one 10-kilowatt AC (kW
AC) inverter, will be limited to the inverter's output of 10 kW. As of 2019, conversion efficiency for state-of-the-art converters reached more than 98 percent. While string inverters are used in residential to medium-sized commercial PV systems, central inverters cover the large commercial and utility-scale market. Market-share for central and string inverters are about 44 percent and 52 percent, respectively, with less than 1 percent for micro-inverters.
Maximum power point tracking
Maximum power point tracking (MPPT) or sometimes just power point tracking (PPT), is a technique used with variable power sources to maximize energy extraction as conditions vary. The technique is most commonly used with photovoltaic (PV) solar sy ...
(MPPT) is a technique that grid connected inverters use to get the maximum possible power from the photovoltaic array. In order to do so, the inverter's MPPT system digitally samples the solar array's ever changing power output and applies the proper impedance to find the optimal ''maximum power point''.
Anti-islanding
Islanding is the condition in which a distributed generation, distributed generator (DG) continues to power a location even though external electrical grid power is no longer present. Islanding can be dangerous to utility workers, who may not reali ...
is a protection mechanism to immediately shut down the inverter, preventing it from generating AC power when the connection to the load no longer exists. This happens, for example, in the case of a blackout. Without this protection, the supply line would become an "island" with power surrounded by a "sea" of unpowered lines, as the solar array continues to deliver DC power during the power outage. Islanding is a hazard to utility workers, who may not realize that an AC circuit is still powered, and it may prevent automatic re-connection of devices. Anti-Islanding feature is not required for complete Off-Grid Systems.
Battery
Although still expensive, PV systems increasingly use rechargeable batteries to store a surplus to be later used at night.
Batteries used for grid-storage also stabilize the
electrical grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
by
leveling out peak loads, and play an important role in a
smart grid
A smart grid is an electrical grid which includes a variety of operation and energy measures including:
*Advanced metering infrastructure (of which smart meters are a generic name for any utility side device even if it is more capable e.g. a f ...
, as they can charge during periods of low demand and feed their stored energy into the grid when demand is high.
Common battery technologies used in today's PV systems include the
valve regulated lead-acid battery
A valve regulated lead–acid (VRLA) battery, commonly known as a sealed lead–acid (SLA) battery, is a type of lead–acid battery characterized by a limited amount of electrolyte ("starved" electrolyte) absorbed in a plate separator or formed ...
– a modified version of the conventional
lead–acid battery
The lead–acid battery is a type of rechargeable battery first invented in 1859 by French physicist Gaston Planté. It is the first type of rechargeable battery ever created. Compared to modern rechargeable batteries, lead–acid batteries have ...
–
nickel–cadmium and
lithium-ion
A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also sees ...
batteries. Compared to the other types, lead-acid batteries have a shorter lifetime and lower energy density. However, due to their high reliability, low self discharge as well as low investment and maintenance costs, they are currently (as of 2014) the predominant technology used in small-scale, residential PV systems, as lithium-ion batteries are still being developed and about 3.5 times as expensive as lead-acid batteries. Furthermore, as storage devices for PV systems are stationary, the lower energy and power density and therefore higher weight of lead-acid batteries are not as critical as, for example, in
electric transportation Other rechargeable batteries considered for distributed PV systems include
sodium–sulfur and
vanadium redox batteries, two prominent types of a
molten salt
Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.[< ...]
and a
flow battery, respectively.
In 2015, Tesla Motors launched the
Powerwall
A powerwall is a large, ultra-high-resolution display that is constructed of a matrix of other displays, which may be either monitors or projectors. It is important to differentiate between powerwalls and displays that are just large, for exam ...
, a rechargeable lithium-ion battery with the aim to revolutionize energy consumption.
PV systems with an integrated battery solution also need a
charge controller
A charge controller, charge regulator or battery regulator limits the rate at which electric current is added to or drawn from electric batteries to protect against electrical overload, overcharging, and may protect against overvoltage. , as the varying voltage and current from the solar array requires constant adjustment to prevent damage from overcharging. Basic charge controllers may simply turn the PV panels on and off, or may meter out pulses of energy as needed, a strategy called PWM or
pulse-width modulation
Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...
. More advanced charge controllers will incorporate
MPPT
Maximum power point tracking (MPPT) or sometimes just power point tracking (PPT), is a technique used with variable power sources to maximize energy extraction as conditions vary. The technique is most commonly used with photovoltaic (PV) solar sy ...
logic into their battery charging algorithms. Charge controllers may also divert energy to some purpose other than battery charging. Rather than simply shut off the free PV energy when not needed, a user may choose to heat air or water once the battery is full.
Monitoring and metering
The metering must be able to accumulate energy units in both directions, or two meters must be used. Many meters accumulate bidirectionally, some systems use two meters, but a unidirectional meter (with detent) will not accumulate energy from any resultant feed into the grid. In some countries, for installations over 30
kWp a frequency and a voltage monitor with disconnection of all phases is required. This is done where more solar power is being generated than can be accommodated by the utility, and the excess can not either be exported or
stored. Grid operators historically have needed to provide transmission lines and generation capacity. Now they need to also provide storage. This is normally hydro-storage, but other means of storage are used. Initially storage was used so that baseload generators could operate at full output. With
variable renewable energy
Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating nature, such as wind power and solar power, as opposed to controllable renewable ener ...
, storage is needed to allow power generation whenever it is available, and consumption whenever needed.
![Stromzähler in Kanada](https://upload.wikimedia.org/wikipedia/commons/f/f0/Stromz%C3%A4hler_in_Kanada.JPG)
The two variables a grid operator has are storing electricity for ''when'' it is needed, or transmitting it to ''where'' it is needed. If both of those fail, installations over 30kWp can automatically shut down, although in practice all inverters maintain voltage regulation and stop supplying power if the load is inadequate. Grid operators have the option of curtailing excess generation from large systems, although this is more commonly done with wind power than solar power, and results in a substantial loss of revenue. Three-phase inverters have the unique option of supplying reactive power which can be advantageous in matching load requirements.
Photovoltaic systems need to be monitored to detect breakdown and optimize operation. There are several
photovoltaic monitoring strategies depending on the output of the installation and its nature. Monitoring can be performed on site or remotely. It can measure production only, retrieve all the data from the inverter or retrieve all of the data from the communicating equipment (probes, meters, etc.). Monitoring tools can be dedicated to supervision only or offer additional functions. Individual inverters and battery charge controllers may include monitoring using manufacturer specific protocols and software. Energy metering of an inverter may be of limited accuracy and not suitable for revenue metering purposes. A third-party data acquisition system can monitor multiple inverters, using the inverter manufacturer's protocols, and also acquire weather-related information. Independent
smart meter
A smart meter is an electronic device that records information such as consumption of electric energy, voltage levels, current, and power factor. Smart meters communicate the information to the consumer for greater clarity of consumption beha ...
s may measure the total energy production of a PV array system. Separate measures such as satellite image analysis or a solar radiation meter (a
pyranometer A pyranometer is a type of actinometer used for measuring solar irradiance on a planar surface and it is designed to measure the solar radiation flux density (W/m2) from the hemisphere above within a wavelength range 0.3 μm to 3 μm. The name pyran ...
) can be used to estimate total insolation for comparison.
Data collected from a monitoring system can be displayed remotely over the World Wide Web, such as
OSOTF The Open Solar Outdoors Test Field (OSOTF) is a project organized under open source principles, which is a fully grid-connected test system that continuously monitors the output of many solar photovoltaic modules and correlates their performance to ...
.
Sizing of the photovoltaic system
Knowing the annual energy consumption in Kwh
of an institution or a family, for example of 2300Kwh, legible in its electricity bill, it is possible to calculate the number of photovoltaic panels necessary to satisfy its energy needs. By connecting to the site https://re.jrc.ec.europa.eu/pvg_tools/en/ , after selecting the location in which to install the panels or clicking on the map or typing the name of the location, you must select "Grid connected" and "Visualize results" obtaining the following table for example relating to the city of Palermo:
Provided inputs:;
Location
at/Lon;38.111,13.352
Horizon:;Calculated
Database used:;PVGIS-SARAH2
PV technology:;Crystalline silicon
PV installed
Wp;1
System loss
;14
Simulation outputs:;
Slope angle
;35
Azimuth angle
;0
Yearly PV energy production
Wh;1519.1
Yearly in-plane irradiation
Wh/m2;1944.62
Year-to-year variability
Wh;47.61
Changes in output due to:;
Angle of incidence
;-2.68
Spectral effects
;0.88
Temperature and low irradiance
;-7.48
Total loss
;-21.88
PV electricity cost
er kWh;
Using the
wxMaxima program, the number of panels required for an annual consumption of 2300 kWh and for a crystalline silicon technology with a slope angle of 35°, an azimut angle of 0° and total losses equal to 21.88 % is 6 rounded up:
E_d : 2300 ;
E_s : 1519.1 ;
P : 300 ;
Number_panels : 1000 * E_d / ( P * E_s ) ;
5.046847914335243
On average, each family manages to consume 30% of energy directly from the photovoltaic. The storage system can bring its self-consumption to a maximum of 70%, therefore the battery storage capacity that should be in the specific case is: 4.41 Kwh which rounded up is 4.8 Kwh
Battery_capacity : 0.70 * E_d/365 ;
4.410958904109589
If the price of energy is 0.5 €/Kwh then the cost of energy excluding taxes will be 1150€ per year:
Energy_cost : E_d * 0.5;
1150.0
So if a 300W panel costs €200, the 4.8Kwh battery costs €3000, the inverter to convert the direct current into alternating current €1000, the charge regulator €100, the installation costs €1000 the total cost will be €6,300 :
Total_cost : 200*6 + 3000 + 1000 + 100 + 1000 ;
3150
which are amortized over 5.46 years:
Years : Total_cost / Energy_cost ;
5.46...
having the battery a life of 10 years and the panels 25-30 years
Other systems
This section includes systems that are either highly specialized and uncommon or still an emerging new technology with limited significance. However,
standalone Standalone or Stand-alone may refer to:
*Stand-alone DSL, a digital subscriber line without analog telephone service; also known as ''naked DSL''
*Stand-alone expansion pack, an expansion pack which does not require the original game in order to us ...
or off-grid systems take a special place. They were the most common type of systems during the 1980s and 1990s, when PV technology was still very expensive and a pure niche market of small scale applications. Only in places where no electrical grid was available, they were economically viable. Although new stand-alone systems are still being deployed all around the world, their contribution to the overall installed photovoltaic capacity is decreasing. In Europe, off-grid systems account for 1 percent of installed capacity. In the United States, they account for about 10 percent. Off-grid systems are still common in Australia and South Korea, and in many developing countries.
CPV
![Concentració Fotovoltaica](https://upload.wikimedia.org/wikipedia/commons/b/b4/Concentraci%C3%B3_Fotovoltaica.jpg)
Concentrator photovoltaics (CPV) and ''high concentrator photovoltaic'' (HCPV) systems use
optical lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a #Compound lenses, compound lens consists of several simple lense ...
es or curved mirrors to concentrate sunlight onto small but highly efficient solar cells. Besides concentrating optics, CPV systems sometime use solar trackers and cooling systems and are more expensive.
Especially HCPV systems are best suited in location with high solar irradiance, concentrating sunlight up to 400 times or more, with efficiencies of 24–28 percent, exceeding those of regular systems. Various designs of systems are commercially available but not very common. However, ongoing research and development is taking place.
CPV is often confused with CSP (
concentrated solar power
Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated when ...
) that does not use photovoltaics. Both technologies favor locations that receive much sunlight and directly compete with each other.
Hybrid
![Hybrid Power System](https://upload.wikimedia.org/wikipedia/commons/b/bf/Hybrid_Power_System.gif)
A hybrid system combines PV with other forms of generation, usually a diesel generator. Biogas is also used. The other form of generation may be a type able to modulate power output as a function of demand. However more than one renewable form of energy may be used e.g. wind. The photovoltaic power generation serves to reduce the consumption of non renewable fuel. Hybrid systems are most often found on islands.
Pellworm
( da, Pelvorm; North Frisian ''Polweerm'') is a municipality in the district of Nordfriesland, in Schleswig-Holstein, Germany.
The municipality is located on the island of Pellworm – one of the North Frisian Islands on the North Sea coast of ...
island in Germany and
Kythnos
Kythnos ( el, Κύθνος), commonly called Thermia ( el, Θερμιά), is a Greek island and municipality in the Western Cyclades between Kea and Serifos. It is from the Athenian harbor of Piraeus. The municipality Kythnos is in area and has a ...
island in Greece are notable examples (both are combined with wind). The Kythnos plant has reduced diesel consumption by 11.2%.
In 2015, a case-study conducted in seven countries concluded that in all cases generating costs can be reduced by hybridising mini-grids and isolated grids. However, financing costs for such hybrids are crucial and largely depend on the ownership structure of the power plant. While cost reductions for state-owned utilities can be significant, the study also identified economic benefits to be insignificant or even negative for non-public utilities, such as
independent power producers.
There has also been work showing that the PV penetration limit can be increased by deploying a distributed network of PV+CHP hybrid systems in the U.S. The temporal distribution of solar flux, electrical and heating requirements for representative U.S. single family residences were analyzed and the results clearly show that hybridizing CHP with PV can enable additional PV deployment above what is possible with a conventional centralized electric generation system. This theory was reconfirmed with numerical simulations using per second solar flux data to determine that the necessary battery backup to provide for such a hybrid system is possible with relatively small and inexpensive battery systems. In addition, large PV+CHP systems are possible for institutional buildings, which again provide back up for intermittent PV and reduce CHP runtime.
*
PVT system (hybrid PV/T), also known as photovoltaic thermal hybrid solar collectors, convert solar radiation into thermal and electrical energy. Such a system combines a solar (PV) module with a
solar thermal collector
A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and sola ...
in a complementary way.
*
CPVT system. A ''concentrated photovoltaic thermal hybrid'' (CPVT) system is similar to a PVT system. It uses
concentrated photovoltaic
Concentrator photovoltaics (CPV) (also known as concentration photovoltaics) is a photovoltaic technology that generates electricity from sunlight. Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight on ...
s (CPV) instead of conventional PV technology, and combines it with a solar thermal collector.
* CPV/CSP system is a proposed novel solar hybrid system, combining concentrator photovoltaics with the non-PV technology of
concentrated solar power
Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated when ...
(CSP), or also known as concentrated solar thermal.
*
PV diesel system
Hybrid power are combinations between different technologies to produce power.
In power engineering, the term 'hybrid' describes a combined power and energy storage system.
Examples of power producers used in hybrid power are photovoltaics, ...
combines a photovoltaic system with a
diesel generator
A diesel generator (DG) (also known as a diesel Genset) is the combination of a diesel engine with an electric generator (often an alternator) to generate electrical energy. This is a specific case of engine generator. A diesel compression- ...
. Combinations with
other renewables are possible and include
wind turbine
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...
s.
Floating solar arrays
Floating solar
Floating solar or floating photovoltaics (FPV), sometimes called floatovoltaics, is solar panels mounted on a structure that floats on a body of water, typically a reservoir or a lake.
The market for this renewable energy technology has grown rap ...
arrays are PV systems that float on – or are built over – the surface of drinking water reservoirs, quarry lakes,
irrigation canals
Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...
or remediation and tailing ponds. These systems are called "floatovoltaics" when used only for electrical production or "aquavoltaics" when such systems are used to synergistically enhance
aquaculture
Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
. A small number of such systems exist in France, India, Japan, South Korea, the United Kingdom, Singapore and the United States.
The systems are said to have advantages over photovoltaics on land. The cost of land is more expensive, and there are fewer rules and regulations for structures built on bodies of water not used for recreation. Unlike most land-based solar plants, floating arrays can be unobtrusive because they are hidden from public view. They achieve higher efficiencies than PV panels on land, because water cools the panels. The panels have a special coating to prevent rust or corrosion.
In May 2008, the Far Niente Winery in Oakville, California, pioneered the world's first floatovoltaic system by installing 994 solar PV modules with a total capacity of 477 kW on to 130 pontoons and floating them on the winery's irrigation pond. The primary benefit of such a system is that it avoids the need to sacrifice valuable land area that could be used for another purpose. In the case of the Far Niente Winery, it saved that would have been required for a land-based system. Another benefit of a floatovoltaic system is that the panels are kept at a cooler temperature than they would be on land, leading to a higher efficiency of solar energy conversion. The floating PV array also reduces the amount of water lost through evaporation and inhibits the growth of algae.
Utility-scale floating PV farms are starting to be built. The multinational electronics and ceramics manufacturer
Kyocera
is a Japanese multinational ceramics and electronics manufacturer headquartered in Kyoto, Japan. It was founded as in 1959 by Kazuo Inamori and renamed in 1982. It manufactures industrial ceramics, solar power generating systems, telecommuni ...
will develop the world's largest, a 13.4 MW farm on the reservoir above Yamakura Dam in
Chiba Prefecture
is a prefecture of Japan located in the Kantō region of Honshu. Chiba Prefecture has a population of 6,278,060 (1 June 2019) and has a geographic area of . Chiba Prefecture borders Ibaraki Prefecture to the north, Saitama Prefecture to the ...
using 50,000 solar panels. Salt-water resistant floating farms are also being considered for ocean use, with experiments in Thailand. The largest so far announced floatovoltaic project is a 350 MW power station in the Amazon region of Brazil.
Direct current grid
DC grids are found in electric powered transport: railways trams and trolleybuses. A few pilot plants for such applications have been built, such as the tram depots in Hannover Leinhausen, using photovoltaic contributors and Geneva (Bachet de Pesay). The 150 kW
p Geneva site feeds 600 V DC directly into the tram/trolleybus electricity network whereas before it provided about 15% of the electricity at its opening in 1999.
Standalone
A
stand-alone or off-grid system is not connected to the
electrical grid
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:Kaplan, S. M. (2009). Smart Grid. Electrical Power ...
. Standalone systems vary widely in size and application from
wristwatches
A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached by ...
or
calculators
An electronic calculator is typically a portable electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics.
The first solid-state electronic calculator was created in the early 1960s. Pocket-size ...
to remote buildings or
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
. If the load is to be supplied independently of solar
insolation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
, the generated power is stored and buffered with a battery. In non-portable applications where weight is not an issue, such as in buildings,
lead acid batteries
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut ...
are most commonly used for their low cost and tolerance for abuse.
A charge controller may be incorporated in the system to avoid battery damage by excessive charging or discharging. It may also help to optimize production from the solar array using a maximum power point tracking technique (
MPPT
Maximum power point tracking (MPPT) or sometimes just power point tracking (PPT), is a technique used with variable power sources to maximize energy extraction as conditions vary. The technique is most commonly used with photovoltaic (PV) solar sy ...
). However, in simple PV systems where the PV module voltage is matched to the battery voltage, the use of MPPT electronics is generally considered unnecessary, since the battery voltage is stable enough to provide near-maximum power collection from the PV module.
In small devices (e.g. calculators, parking meters) only
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
(DC) is consumed. In larger systems (e.g. buildings, remote water pumps) AC is usually required. To convert the DC from the modules or batteries into AC, an
inverter
A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...
is used.
In
agricultural
Agriculture or farming is the practice of cultivating Plant, plants and livestock. Agriculture was the key development in the rise of Sedentism, sedentary human civilization, whereby farming of Domestication, domesticated species created food ...
settings, the array may be used to directly power DC
pump
A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...
s, without the need for an
inverter
A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...
. In remote settings such as mountainous areas, islands, or other places where a power grid is unavailable, solar arrays can be used as the sole source of electricity, usually by charging a
storage battery
A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or prima ...
. Stand-alone systems closely relate to
microgeneration
Microgeneration is the small-scale production of heat or electric power from a "low carbon source," as an alternative or supplement to traditional centralized grid-connected power.
Microgeneration technologies include small-scale wind turbin ...
and
distributed generation
Distributed generation, also distributed energy, on-site generation (OSG), or district/decentralized energy, is electrical generation and storage performed by a variety of small, grid-connected or distribution system-connected devices referred to ...
.
Costs and economy
The cost of producing photovoltaic cells has dropped because of
economies of scale
In microeconomics, economies of scale are the cost advantages that enterprises obtain due to their scale of operation, and are typically measured by the amount of output produced per unit of time. A decrease in cost per unit of output enables ...
in production and technological advances in manufacturing. For large-scale installations, prices below $1.00 per watt were common by 2012. A price decrease of 50% had been achieved in Europe from 2006 to 2011, and there was a potential to lower the generation cost by 50% by 2020. Crystal silicon
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. s have largely been replaced by less expensive multicrystalline silicon solar cells, and thin film silicon solar cells have also been developed at lower costs of production. Although they are reduced in energy conversion efficiency from single crystalline "siwafers", they are also much easier to produce at comparably lower costs.
The table below shows the total (average) cost in US cents per kWh of electricity generated by a photovoltaic system. The row headings on the left show the total cost, per peak kilowatt (kW
p), of a photovoltaic installation. Photovoltaic system costs have been declining and in Germany, for example, were reported to have fallen to USD 1389/kW
p by the end of 2014.
The column headings across the top refer to the annual energy output in kWh expected from each installed kW
p. This varies by geographic region because the average
insolation
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre (W/m ...
depends on the average cloudiness and the thickness of atmosphere traversed by the sunlight. It also depends on the path of the sun relative to the panel and the horizon.
Panels are usually mounted at an angle based on latitude, and often they are adjusted seasonally to meet the changing solar
declination
In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...
.
Solar tracking
A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, lenses or the mirrors of a heliostat.
For flat-panel photovoltaic systems, trackers are used to m ...
can also be utilized to access even more perpendicular sunlight, thereby raising the total energy output.
The calculated values in the table reflect the total (average) cost in cents per kWh produced. They assume a 10% total capital cost (for instance 4%
interest rate
An interest rate is the amount of interest due per period, as a proportion of the amount lent, deposited, or borrowed (called the principal sum). The total interest on an amount lent or borrowed depends on the principal sum, the interest rate, th ...
, 1% operating and maintenance cost, and
depreciation
In accountancy, depreciation is a term that refers to two aspects of the same concept: first, the actual decrease of fair value of an asset, such as the decrease in value of factory equipment each year as it is used and wear, and second, the a ...
of the capital outlay over 20 years). Normally, photovoltaic modules have a 25-year warranty.
Learning curve
Photovoltaic systems demonstrate a learning curve in terms of
levelized cost of electricity
The levelized cost of electricity (LCOE), or levelized cost of energy, is a measure of the average net present cost of electricity generation for a generator over its lifetime. It is used for investment planning and to compare different methods ...
(LCOE), reducing its cost per kWh by 32.6% for every doubling of capacity.
From the data of LCOE and cumulative installed capacity from
International Renewable Energy Agency (IRENA) from 2010 to 2017,
the learning curve equation for photovoltaic systems is given as
* LCOE : levelized cost of electricity (in USD/kWh)
* Capacity : cumulative installed capacity of photovoltaic systems (in MW)
Regulation
Standardization
Increasing use of photovoltaic systems and integration of photovoltaic power into existing structures and techniques of supply and distribution increases the need for general standards and definitions for photovoltaic components and systems. The standards are compiled at the
International Electrotechnical Commission
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
(IEC) and apply to efficiency, durability and safety of cells, modules, simulation programs, plug connectors and cables, mounting systems, overall efficiency of inverters etc.
National regulations
United Kingdom
In the UK, PV installations are generally considered permitted development and do not require planning permission. If the property is listed or in a designated area (National Park, Area of Outstanding Natural Beauty, Site of Special Scientific Interest or Norfolk Broads) then planning permission is required.
United States
In the United States, article 690 of the National Electric Code provides general guidelines for the installation of photovoltaic systems; these may be superseded by local laws and regulations. Often a permit is required necessitating plan submissions and structural calculations before work may begin. Additionally, many locales require the work to be performed under the guidance of a licensed electrician.
The
Authority Having Jurisdiction
Construction is a general term meaning the art and science to form objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and co ...
(AHJ) will review designs and issue permits, before construction can lawfully begin. Electrical installation practices must comply with standards set forth within the
National Electrical Code
The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Prote ...
(NEC) and be inspected by the AHJ to ensure compliance with
building code
A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permission ...
,
electrical code {{Electrical Wiring Sidebar
An electrical code is a set of regulations for the design and installation of electrical wiring in a building.
The intention of a code is to provide standards to ensure electrical wiring systems that are safe for peopl ...
, and
fire safety
Fire safety is the set of practices intended to reduce the destruction caused by fire. Fire safety measures include those that are intended to prevent the ignition of an uncontrolled fire and those that are used to limit the development and eff ...
code. Jurisdictions may require that equipment has been tested, certified, listed, and labeled by at least one of the
Nationally Recognized Testing Laboratories
Nationally Recognized Testing Laboratory is the term used by the United States Occupational Safety and Health Administration to identify third-party organizations that have the necessary qualifications to perform safety testing and certification o ...
(NRTL).
[Solar Power World](_blank)
/ref> Many localities require a permit to install a photovoltaic system. A grid-tied system normally requires a licensed electrician to connect between the system and the grid-connected wiring of the building. Installers who meet these qualifications are located in almost every state. Several states prohibit homeowners' association
A homeowner association (or homeowners' association, abbreviated HOA, sometimes referred to as a property owners' association or POA), or a homeowner community, is a private association-like entity often formed either ''ipso jure'' in a building ...
s from restricting solar devices.
Spain
Although Spain generates around 40% of its electricity via photovoltaic and other renewable energy sources, and cities such as Huelva and Seville boast nearly 3,000 hours of sunshine per year, in 2013 Spain issued a solar tax to account for the debt created by the investment done by the Spanish government. Those who do not connect to the grid can face up to a fine of 30 million euros (US$40 million). Such measures were finally withdrawn by 2018, when new legislation was introduced banning any taxes on renewable energy self-consumption.
Limitations
Impact on electricity network
With the increasing levels of rooftop photovoltaic systems, the energy flow becomes two-way. When there is more local generation than consumption, electricity is exported to the grid. However, electricity network traditionally is not designed to deal with the two-way energy transfer. Therefore, some technical issues may occur. For example, in Queensland, Australia, there have been more than 30% of households with rooftop PV by the end of 2017. The famous Californian 2020 duck curve
The duck curve is a graph of power production over the course of a day that shows the timing imbalance between peak demand and renewable energy production. Used in utility-scale electricity generation, the term was coined in 2012 by the Califor ...
appears very often for a lot of communities from 2015 onwards. An over-voltage issue may come out as the electricity flows back to the network. There are solutions to manage the over voltage issue, such as regulating PV inverter power factor, new voltage and energy control equipment at electricity distributor level, re-conductor the electricity wires, demand side management, etc. There are often limitations and costs related to these solutions.
Implication onto electricity bill management and energy investment
Customers have different specific situations, e.g. different comfort/convenience needs, different electricity tariffs, or different usage patterns. An electricity tariff may have a few elements, such as daily access and metering charge, energy charge (based on kWh, MWh) or peak demand charge (e.g. a price for the highest 30min energy consumption in a month). PV is a promising option for reducing energy charge when electricity price is reasonably high and continuously increasing, such as in Australia and Germany. However, for sites with peak demand charge in place, PV may be less attractive if peak demands mostly occur in the late afternoon to early evening, for example residential communities. Overall, energy investment is largely an economic decision and investment decisions are based on systematical evaluation of options in operational improvement, energy efficiency, onsite generation and energy storage.
See also
* Copper conductor
*Polyolefin
A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More speciali ...
*Low smoke zero halogen
Low smoke zero halogen or low smoke free of halogen (LSZH or LSOH or LS0H or LSFH or OHLS or ZHFR) is a material classification typically used for cable jacketing in the wire and cable industry. LSZH cable jacketing is composed of thermoplastic or ...
*MC4 connector
MC4 connectors are single-contact electrical connectors commonly used for connecting solar panels. The MC in MC4 stands for the manufacturer Multi-Contact (now Stäubli Electrical Connectors) and the 4 for the 4 mm diameter contact pin.
...
*Solar micro-inverter
A solar inverter or photovoltaic (PV) inverter is a type of power inverter which converts the variable direct current (DC) output of a photovoltaic solar panel into a utility frequency alternating current (AC) that can be fed into a commercial ...
*Tinning
Tinning is the process of thinly coating sheets of wrought iron or steel with tin, and the resulting product is known as tinplate. The term is also widely used for the different process of coating a metal with solder before soldering.
It is most ...
* Energy demand management
Energy demand management, also known as demand-side management (DSM) or demand-side response (DSR), is the modification of consumer demand for energy through various methods such as financial incentives and behavioral change through education.
Us ...
* List of photovoltaic power stations
The following is a list of photovoltaic power stations that are larger than 300 megawatts (MW) in current net capacity.Note that nominal power may be AC or DC, depending on the plant, and therefore any totals quoted are hybrid. SeAC-DC conundru ...
* List of rooftop photovoltaic installations
A rooftop solar power system, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a syste ...
* Photovoltaic power station
A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building- ...
* Renewable energy
Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...
* Rooftop photovoltaic power station
A rooftop solar power system, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a syste ...
* Solar energy
Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy (including solar water heating), and solar architecture. It is an essenti ...
* Solar vehicle
A solar vehicle or solar electric vehicle is an electric vehicle powered completely or significantly by direct solar energy. Usually, photovoltaic (PV) cells contained in solar panels convert the sun's energy directly into electric energy. T ...
References
Further reading
*
External links
Summary of Photovoltaic Wire Requirements as Outlined in UL 4703
Photovoltaic Energy Factsheet
by the University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
'
Center for Sustainable Systems
Home Power Magazine
Solar project management
Best Practices for Siting Solar Photovoltaics on Municipal Solid Waste Landfills: A Study Prepared in Partnership with the Environmental Protection Agency for the RE-Powering America's Land Initiative: Siting Renewable Energy on Potentially Contaminated Land and Mine Sites
National Renewable Energy Laboratory
The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development of renewable energy, energy efficiency, energy systems integration, and sustainable transportation. NREL is a federally funded research and d ...
{{Authority control
Photovoltaics