Electrical devices are considered grid friendly if they operate in a manner that supports electrical grid reliability through

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 ...

. Basic grid-friendly devices may incorporate features that work to offset short-term undesirable changes in line

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

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 ...

; more sophisticated devices may alter their operating profile based on the current market price for electricity, reducing load when prices are at a peak. Grid-friendly devices can include

major appliance A major appliance, also known as a large domestic appliance or large electric appliance or simply a large appliance, large domestic, or large electric, is a non-portable or semi-portable machine used for routine housekeeping tasks such as cookin ...

s found in homes, commercial building systems such as

HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HV ...

, and many industrial systems.

Frequency Response

Most electric systems use

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 ...

with a nominal frequency of 50 or 60 Hz (

hertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...

) to deliver

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 ...

produced by

electrical generator In electricity generation, a generator is a device that converts motive power (mechanical energy) or fuel-based power (chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, gas ...

s to the electricity consumers. When the amount of

electric power Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...

produced by the generators exceeds the power used by the customers, the frequency of the electricity rises. Conversely, when the amount of electric power produced is less than what is consumed, the frequency drops. Therefore frequency is an accurate indicator of the system-wide (called ''global'') balance between supply and demand. Without grid-friendly

frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and phase of the output as a function of input frequency. The frequency response is widely used in the design and analysis of sy ...

, the rate at which the frequency changes is dependent principally on the system's total

inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...

(which is not very controllable) and the aggregate response of the generators'

control system A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loops. It can range from a single home heating controller using a thermostat controlling a domestic boiler to large industrial c ...

s (which can only be controlled relatively slowly). In contrast, grid-friendly devices can act very quickly. A grid-friendly device can respond to changes in frequency by reducing or interrupting the demand for electric power (called ''load'') when the frequency drops below a certain threshold, and/or increasing load when the frequency rises. Although a single grid-friendly device may be a very small load, the fraction of the total load that can be controlled by frequency at any time is usually sufficient to provide under-frequency protection to the system before more drastic measures like black-outs are required. The advantage of grid-friendly frequency response is that frequency is ubiquitous on an electric system. When a generator shuts down in one part of the system, all the loads everywhere in the system can simultaneously detect the change and respond instantly and appropriately without the need for a control system to detect the problem, a control center to make a decision, or a

telecommunications network A telecommunications network is a group of nodes interconnected by telecommunications links that are used to exchange messages between the nodes. The links may use a variety of technologies based on the methodologies of circuit switching, message ...

to deliver commands to millions of devices. This type of behavior changes frequency from a simple

electrodynamic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...

and control systems input to an

emergent property In philosophy, systems theory, science, and art, emergence occurs when an entity is observed to have properties its parts do not have on their own, properties or behaviors that emerge only when the parts interact in a wider whole. Emergence ...

. While there is still some controversy on the subject, it is believed that

complex systems A complex system is a system composed of many components which may interact with each other. Examples of complex systems are Earth's global climate, organisms, the human brain, infrastructure such as power grid, transportation or communication s ...

utilizing self-regulation through emergence are generally more resilient and flexible than are simpler top-down command and control systems.

Voltage Response

In contrast to frequency, voltage varies widely throughout electric systems, because it is the voltage difference between two devices that largely determines the direction and magnitude of the

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 ...

(hence the power) that flows between them. Therefore voltage is a more local phenomenon, and grid-friendly devices that respond to voltage will support more local aspects of the electric delivery system. However, load types such as thermally protected induction motors and power electronics can respond poorly to significant voltage changes. When a sufficient fraction of the power demand in a region is composed of such loads, their collective response can lead to fault-induced delayed voltage recovery behavior, which may have adverse effects on transmission system reliability and may require mitigation to avoid initiating system outages.

Price Response

While frequency and voltage respond to physical phenomena on the electric system, grid-friendly price response is designed to address economic phenomena. With the increasing application of electricity markets to manage the efficient distribution of electric power, more consumers are exposed to electricity prices that change over time, rather than fixed for months or years. In general, higher prices occur at times when the electric system is running short of supply. The purpose of grid-friendly price response is to promote demand response among electricity consumers. Demand response is one means of reducing the

market power In economics, market power refers to the ability of a firm to influence the price at which it sells a product or service by manipulating either the supply or demand of the product or service to increase economic profit. In other words, market powe ...

of electricity suppliers when production runs short. Grid-friendly response to price also allows consumers to reduce their energy costs by using less electricity when prices are high, and more electricity when prices are low.

Demonstrated Results

A demonstration of grid-friendly technology was conducted for the

United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United Stat ...

in 2006 and 2007 in the Northwest region of the United States. Participants included local utilities, residential and commercial customers, industrial loads belonging to municipalities, and a number of vendors and researchers. The grid-friendly technology demonstration showed that common residential appliances did automatically detect grid problems expressed as frequency deviations and reduced energy consumption at critical moments. The Olympic Peninsula demonstration showed that residential, commercial, and industrial loads did adjust their consumption patterns based on price signals emanating from a distribution-level market operated as a double action. Both of these projects showed how grid-friendly technologies can and do reduce pressure on the electric grid during time of peak demand.D. Hammerstrom et al. (2007). Pacific Northwest GridWise Testbed Demonstration Projects Part II. Grid Friendly Appliance Project. PNNL no. 17079, Pacific Northwest National Laboratory, Richland, Washingto

/ref>

Sources and additional resources

* US Department of Energy, Office of Electricity Delivery and Energy Reliabilit

* Grigsby, L. L., et al. The Electric Power Engineering Handbook. USA: CRC Press. (2001). * S. Stoft. Power System Economics. Wiley Interscience. IEEE Press. (2002). * D. J. Morrow, et al. (1991). Low-cost under-frequency relay for distributed load-shedding. In proc. of 3rd Int. Conf. on Power System Monitoring and Control. 273-275. * Z. Zhang, et al. (1999). An adaptive microcomputer-based load shedding relay. In conf. rec. of 34th IAS Annual Mtg. Industrial Applications. 3: 2065–2071. * D. P. Chassin, et al. (2005). Estimation of WECC system inertia using observed frequency transients. IEEE Transactions on Power Systems. 20:2 1190–1192. * Pacific Northwest National Laboratory (2007). GridWise Demonstration Project Fast Facts

* D. Hammerstrom et al. (2007). Pacific Northwest GridWise Testbed Demonstration Projects Part II. Grid Friendly Appliance Project. PNNL no. 17079, Pacific Northwest National Laboratory, Richland, Washingto

* D. Hammerstrom et al. (2007). Pacific Northwest GridWise Testbed Demonstration Projects Part I. Olympic Peninsula Project. PNNL no. 17167, Pacific Northwest National Laboratory, Richland, Washingto

References