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Load management, also known as demand-side management (DSM), is the process of balancing the supply of electricity on the network with the electrical load by adjusting or controlling the load rather than the power station output. This can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering the circuit breakers (ripple control), by time clocks, or by using special tariffs to influence consumer behavior. Load management allows utilities to reduce demand for electricity during peak usage times (peak shaving), which can, in turn, reduce costs by eliminating the need for
peaking power plant Peaking power plants, also known as peaker plants, and occasionally just "peakers", are power plants that generally run only when there is a high demand, known as peak demand, for electricity. Because they supply power only occasionally, the power ...
s. In addition, some peaking power plants can take more than an hour to bring on-line which makes load management even more critical should a plant go off-line unexpectedly for example. Load management can also help reduce harmful emissions, since peaking plants or backup generators are often dirtier and less efficient than
base load power plant The base load (also baseload) is the minimum level of demand on an electrical grid over a span of time, for example, one week. This demand can be met by unvarying power plants, dispatchable generation, or by a collection of smaller intermittent en ...
s. New load-management technologies are constantly under development — both by private industry and public entities.


Brief history

Modern utility load management began about 1938, using ripple control. By 1948 ripple control was a practical system in wide use. The Czechs first used ripple control in the 1950s. Early transmitters were low power, compared to modern systems, only 50 kilovolt-amps. They were rotating generators that fed a 1050 Hz signal into transformers attached to power distribution networks. Early receivers were electromechanical relays. Later, in the 1970s, transmitters with high-power semiconductors were used. These are more reliable because they have no moving parts. Modern Czech systems send a digital "telegram." Each telegram takes about thirty seconds to send. It has pulses about one second long. There are several formats, used in different districts. In 1972, Theodore George “Ted” Paraskevakos, while working for
Boeing The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and product ...
in
Huntsville, Alabama Huntsville is a city in Madison County, Limestone County, and Morgan County, Alabama, United States. It is the county seat of Madison County. Located in the Appalachian region of northern Alabama, Huntsville is the most populous city in t ...
, developed a sensor monitoring system which used digital transmission for security, fire, and medical alarm systems as well as meter-reading capabilities for all utilities. This technology was a spin-off of his patented automatic telephone line identification system, now known as
caller ID Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call is ...
. In, 1974, Paraskevakos was awarded a U.S. patent for this technology. At the request of the
Alabama Power Company Alabama Power Company, headquartered in Birmingham, Alabama, is a company in the southern United States that provides electricity service to 1.4 million customers in the southern two-thirds of Alabama. It also operates appliance stores. It is one ...
, Paraskevakos developed a load-management system along with automatic meter-reading technology. In doing so, he utilized the ability of the system to monitor the speed of the watt power meter disc and, consequently, power consumption. This information, along with the time of day, gave the power company the ability to instruct individual meters to manage water heater and air conditioning consumption in order to prevent peaks in usage during the high consumption portions of the day. For this approach, Paraskevakos was awarded multiple patents.


Advantages and operating principles

Since electrical energy is a form of
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
that cannot be effectively stored in bulk, it must be generated, distributed, and consumed immediately. When the load on a system approaches the maximum generating capacity, network operators must either find additional supplies of energy or find ways to curtail the load, hence load management. If they are unsuccessful, the system will become unstable and blackouts can occur. Long-term load management planning may begin by building sophisticated models to describe the physical properties of the distribution network (i.e. topology, capacity, and other characteristics of the lines), as well as the load behavior. The analysis may include scenarios that account for weather forecasts, the predicted impact of proposed load-shed commands, estimated time-to-repair for off-line equipment, and other factors. The utilization of load management can help a power plant achieve a higher
capacity factor The net capacity factor is the unitless ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. The theoretical maximum energy output of a given installation is def ...
, a measure of average capacity utilization. Capacity factor is a measure of the output of a power plant compared to the maximum output it could produce. Capacity factor is often defined as ''the ratio of average load to capacity'' or ''the ratio of average load to peak load in a period of time''. A higher load factor is advantageous because a power plant may be less efficient at low load factors, a high load factor means fixed costs are spread over more kWh of output (resulting in a lower price per unit of electricity), and a higher load factor means greater total output. If the power load factor is affected by non-availability of fuel, maintenance shut-down, unplanned breakdown, or reduced demand (as consumption pattern fluctuate throughout the day), the generation has to be adjusted, since
grid energy storage Grid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage on a large scale within an electrical power grid. Electrical energy is stored during times when electricity is plentiful and inexp ...
is often prohibitively expensive. Smaller utilities that buy power instead of generating their own find that they can also benefit by installing a load control system. The penalties they must pay to the energy provider for peak usage can be significantly reduced. Many report that a load control system can pay for itself in a single season.


Comparisons to demand response

When the decision is made to curtail load, it is done so on the basis of system ''reliability''. The utility in a sense "owns the switch" and sheds loads only when the stability or reliability of the electrical distribution system is threatened. The utility (being in the business of generating, transporting, and delivering electricity) will not disrupt their business process without due cause. Load management, when done properly, is non-invasive, and imposes no hardship on the consumer. The load should be shifted to off peak hours.
Demand response Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Until the 21st century decrease in the cost of pumped storage and batteries electric energy could not be ...
places the "on-off switch" in the hands of the consumer using devices such as 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 ...
controlled
load control switch Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Until the 21st century decrease in the cost of pumped storage and batteries electric energy could not be ...
. While many residential consumers pay a flat rate for electricity year-round, the utility's costs actually vary constantly, depending on demand, the distribution network, and composition of the company's electricity generation portfolio. In a free market, the wholesale price of energy varies widely throughout the day. Demand response programs such as those enabled by smart grids attempt to incentivize the consumer to limit usage based upon ''cost'' concerns. As costs rise during the day (as the system reaches peak capacity and more expensive peaking power plants are used), a free
market economy A market economy is an economic system in which the decisions regarding investment, production and distribution to the consumers are guided by the price signals created by the forces of supply and demand, where all suppliers and consumers ...
should allow the price to rise. A corresponding drop in demand for the commodity should meet a fall in price. While this works for predictable shortages, many crises develop within seconds due to unforeseen equipment failures. They must be resolved in the same time-frame in order to avoid a
power blackout A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricity ...
. Many utilities who are interested in demand response have also expressed an interest in load control capability so that they might be able to operate the "on-off switch" before price updates could be published to the consumers. The application of load control technology continues to grow today with the sale of both
radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...
and powerline communication based systems. Certain types of
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 ...
systems can also serve as load control systems.
Charge control Charge control is a technology that lets an electric utility control, in real time, the charging of a ''gridable'' (plug-in) vehicle, such as a plug-in hybrid (PHEV) or a battery electric vehicle (BEV). Through charge control, the utility is able t ...
systems can prevent the recharging of electric vehicles during peak hours.
Vehicle-to-grid Vehicle-to-grid (V2G), also known as Vehicle-to-home (V2H) or Vehicle-to-load (V2L) describes a system in which plug-in electric vehicles (PEV) sell demand response services to the grid. Demand services are either delivering electricity or by red ...
systems can return electricity from an electric vehicle's batteries to the utility, or they can throttle the recharging of the vehicle batteries to a slower rate.


Ripple control

Ripple control is a common form of load control, and is used in many countries around the world, including the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
,
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
,
Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...
,
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, the
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, and
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
. Ripple control involves superimposing a higher-frequency signal (usually between 100 and 1600 Hz) onto the standard 50–60 Hz of the main power signal. When receiver devices attached to non-essential residential or industrial loads receive this signal, they shut down the load until the signal is disabled or another frequency signal is received. Early implementations of ripple control occurred during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
in various parts of the world using a system that communicates over the electrical distribution system. Early systems used rotating generators attached to distribution networks through transformers. Ripple control systems are generally paired with a two- (or more) tiered pricing system, whereby electricity is more expensive during peak times (evenings) and cheaper during low-usage times (early morning). Affected residential devices will vary by region, but may include residential electric hot-water heaters, air conditioners, pool pumps, or crop-irrigation pumps. In a distribution network outfitted with load control, these devices are outfitted with communicating controllers that can run a program that limits the duty cycle of the equipment under control. Consumers are usually rewarded for participating in the load control program by paying a reduced rate for energy. Proper load management by the utility allows them to practice
load shedding Demand response is a change in the power consumption of an electric utility customer to better match the demand for power with the supply. Until the 21st century decrease in the cost of pumped storage and batteries electric energy could not be ...
to avoid
rolling blackout A rolling blackout, also referred to as rota or rotational load shedding, rota disconnection, feeder rotation, or a rotating outage, is an intentionally engineered electrical power shutdown in which electricity delivery is stopped for non-overla ...
s and reduce costs. Ripple control can be unpopular because sometimes devices can fail to receive the signal to turn on comfort equipment, e.g. hot water heaters or baseboard electrical heaters. Modern electronic receivers are more reliable than old electromechanical systems. Also, some modern systems repeat the telegrams to turn on comfort devices. Also, by popular demand, many ripple control receivers have a switch to force comfort devices on. Modern ripple controls send a digital telegram, from 30 to 180 seconds long. Originally these were received by electromechanical relays. Now they are often received by
microprocessors A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
. Many systems repeat telegrams to assure that comfort devices (e.g. water heaters) are turned on. Since the broadcast frequencies are in the range of human hearing, they often vibrate wires, filament light-bulbs or transformers in an audible way. The telegrams follow different standards in different areas. For example, in the Czech Republic, different districts use "ZPA II 32S", "ZPA II 64S" and Versacom. ZPA II 32S sends a 2.33 second on, a 2.99 second off, then 32 one-second pulses (either on or off), with an "off time" between each pulse of one second. ZPA II 64S has a much shorter off time, permitting 64 pulses to be sent, or skipped. Nearby regions use different frequencies or telegrams, to assure that telegrams operate only in the desired region. The transformers that attach local grids to interties intentionally do not have the equipment (bridging capacitors) to pass ripple control signals into long-distance power lines. Each data pulse of a telegram could double the number of commands, so that 32 pulses permit 2^32 distinct commands. However, in practice, particular pulses are linked to particular types of device or service. Some telegrams have unusual purposes. For example most ripple control systems have a telegram to set clocks in attached devices, e.g. to midnight.
Zellweger off-peak Zellweger is the brand name of an electric switching device also known as a Ripple Control Receiver used to load management, control off-peak electrical loads such as water heaters by switching these loads OFF over peak energy use times of the day ...
is one common brand of ripple control systems.


Frequency-based decentralized demand control

Greater loads physically slow the rotors of a grid's synchronized generators. This causes AC mains to have a slightly reduced frequency when a grid is heavily loaded. The reduced frequency is immediately sensible across the entire grid. Inexpensive local electronics can easily and precisely measure mains frequencies and turn off sheddable loads. In some cases, this feature is nearly free, e.g. if the controlling equipment (such as an electric power meter, or the thermostat in an air-conditioning system) already has a microcontroller. Most electronic electric power meters internally measure frequency, and require only demand control relays to turn off equipment. In other equipment, often the only needed extra equipment is a
resistor divider In electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage (''V''out) that is a fraction of its input voltage (''V''in). Voltage division is the result of distributing the in ...
to sense the mains cycle and a
schmitt trigger In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input si ...
(a small integrated circuit) so the microcontrollers' digital input can sense a reliable fast digital edge. A schmitt trigger is already standard equipment on many microcontrollers. The main advantage over ripple control is greater customer convenience: Unreceived ripple control telegrams can cause a water heater to remain off, causing a cold shower. Or, they can cause an airconditioner to remain off, resulting in a sweltering home. In contrast, as the grid recovers, its frequency naturally rises to normal, so frequency-controlled load control automatically enables water heaters, air-conditioners and other comfort equipment. The cost of equipment can be less, and there are no concerns about overlapping or unreached ripple control regions, mis-received codes, transmitter power, etc. The main disadvantage compared to ripple control is a less fine-grained control. For example, a grid authority has only a limited ability to select which loads are shed. In controlled war-time economies, this can be a substantial disadvantage. The system was invented in
PNNL Pacific Northwest National Laboratory (PNNL) is one of the United States Department of Energy national laboratories, managed by the Department of Energy's (DOE) Office of Science. The main campus of the laboratory is in Richland, Washington. O ...
in the early 21st century, and has been shown to stabilize grids.


Examples of schemes

In many countries, including
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
,
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
and
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
, the power grids routinely use privately held, emergency diesel generators in load management schemes


Florida

The largest residential load control system in the world is found in Florida and is managed by
Florida Power and Light Florida Power & Light Company (FPL), the principal subsidiary of NextEra Energy Inc. (formerly FPL Group, Inc.), is the largest power utility in Florida. It is a Juno Beach, Florida-based power utility company serving roughly 5 million customers ...
. It utilizes 800,000 load control transponders (LCTs) and controls 1,000 MW of electrical power (2,000 MW in an emergency). FPL has been able to avoid the construction of numerous new power plants due to their load management programs.


Australia and New Zealand

Since the 1950s, Australia and New Zealand have had a system of load management based on ripple control, allowing the electricity supply for domestic and commercial water storage heaters to be switched off and on, as well as allowing remote control of nightstore heaters and street lights. Ripple injection equipment located within each local distribution network signals to ripple control receivers at the customer's premises. Control may either done manually by the local distribution network company in response to local outages or requests to reduce demand from the transmission system operator (i.e. Transpower), or automatically when injection equipment detects mains frequency falling below 49.2 Hz. Ripple control receivers are assigned to one of several ripple channels to allow the network company to only turn off supply on part of the network, and to allow staged restoration of supply to reduce the impact of a surge in demand when power is restored to water heaters after a period of time off. Depending on the area, the consumer may have two electricity meters, one for normal supply ("Anytime") and one for the load-managed supply ("Controlled"), with Controlled supply billed at a lower rate per kilowatt-hour than Anytime supply. For those with load-managed supply but only a single meter, electricity is billed at the "Composite" rate, priced between Anytime and Controlled.


Czech Republic

The Czechs have operated ripple control systems since the 1950s.


France

France has an EJP tariff, which allows it to disconnect certain loads and to encourage consumers to disconnect certain loads. This tariff is no longer available for new clients (as of July 2009). The ''Tempo'' tariff also includes different types of days with different prices, but has been discontinued for new clients as well (as of July 2009). Reduced prices during nighttime are available for customers for a higher monthly fee.


Germany

The distribution system operator Westnetz and gridX piloted a load management solution. The solution enables the grid operator to communicate with local energy management systems and adjust the available load for EV charging in response to the state of the grid.


United Kingdom

Rltec in the UK in 2009 reported that domestic refrigerators are being sold fitted with their dynamic load response systems. In 2011 it was announced that the Sainsbury supermarket chain will use dynamic demand technology on their heating and ventilation equipment. In the UK, night storage heaters are often used with a time-switched off-peak supply option -
Economy 7 Economy 7 is the name of a differential tariff provided by United Kingdom electricity suppliers that uses base load generation to provide cheap off-peak electricity during the night. Houses using the Economy 7 tariff require a special electricity ...
or
Economy 10 Economy 10 is the name of a tariff provided by United Kingdom electricity suppliers created in 2004. Similar to the Economy 7 this is designed to be used with high thermal mass heating such as storage heaters, underfloor heating, and is also used w ...
. There is also a programme that allows industrial loads to be disconnected using circuit breakers triggered automatically by frequency sensitive relays fitted on site. This operates in conjunction with Standing Reserve, a programme using diesel generators.Commercial Opportunities for Back-Up Generation and Load Reduction via National Grid, the National Electricity Transmission System Operator (NETSO) for England, Scotland, Wales and Offshore.
/ref> These can also be remotely switched using BBC Radio 4 Longwave
Radio teleswitch A radio teleswitch is a device used in the United Kingdom primarily to allow electricity suppliers to switch large numbers of electricity meters between different tariff rates, by broadcasting an embedded signal in broadcast radio signals. Radio ...
. SP transmission deployed Dynamic Load Management scheme in Dumfries and Galloway area using real time monitoring of embedded generation and disconnecting them, should an overload be detected on the transmission Network.


See also

*
Energy management system An energy management system (EMS) is a system of computer-aided tools used by operators of electric utility grids to monitor, control, and optimize the performance of the generation or transmission system. Also, it can be used in small scale syste ...
*
Energy storage as a service Energy storage as a service (ESaaS) allows a facility to benefit from the advantages of an energy storage system by entering into a service agreement without purchasing the system. Energy storage systems provide a range of services to generate reven ...
(ESaaS) * National Grid (Great Britain): Estimating costs per kWh of transmission * Calculating the cost of back up: See
spark spread The spark spread is the theoretical gross margin of a gas-fired power plant from selling a unit of electricity, having bought the fuel required to produce this unit of electricity. All other costs (operation and maintenance, capital and other financ ...
*
Energy in the United Kingdom Energy in the United Kingdom came mostly from fossil fuels in 2021. Total energy consumption in the United Kingdom was 142.0milliontonnes of oil equivalent (1,651TWh) in 2019. In 2014, the UK had an energy consumption ''per capita'' of 2.78ton ...
*
National Grid Reserve Service To balance the supply and demand of electricity on short timescales, the UK National Grid has contracts in place with generators and large energy users to provide temporary extra power, or reduction in demand. These reserve services are needed if ...
*
Cost of electricity by source Different methods of electricity generation can incur a variety of different costs, which can be divided into three general categories: 1) wholesale costs, or all costs paid by utilities associated with acquiring and distributing electricity to ...
* Diesel-electric transmission *
Motor–generator A motor–generator (an M–G set) is a device for converting electrical power to another form. Motor–generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electr ...
*
Three-phase electric power Three-phase electric power (abbreviated 3φ) is a common type of alternating current used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires (or four including an optional neutral ...
*
Load bank A load bank is a piece of electrical test equipment used to simulate an electrical load, to test an electric power source without connecting it to its normal operating load. During testing, adjustment, calibration, or verification procedures ...
*
Wet stacking Wet stacking is a condition in diesel engines in which unburned fuel passes on into the exhaust system. The word "stacking" comes from the term "stack" for exhaust pipe or chimney stack. The oily exhaust pipe is therefore a "wet stack". This condi ...


References


External links


Load Manager for automotive applications

Distributed Energy Resources Customer Adoption Model (DER-CAM)

Center for Energy and innovative Technologies

All about ripple control in the Netherlands. Ales over Toonfrequent in Nederland
{{DEFAULTSORT:Load Management Electric power transmission Electrical power control