Grid friendly
Encyclopedia
Electrical devices are considered grid friendly if they operate in a manner that supports electrical power grid
reliability. Basic grid-friendly devices may incorporate features that work to offset short-term undesirable changes in line frequency
or voltage
; 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
s found in homes, commercial building systems such as HVAC
, and many industrial systems.
with a nominal frequency of 50 or 60 Hz (hertz
) to deliver energy
produced by electrical generator
s to the electricity consumers. When the amount of electric power
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, the rate at which the frequency changes is dependent principally on the system's total inertia
(which is not very controllable) and the aggregate response of the generators' control system
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
to deliver commands to millions of devices. This type of behavior changes frequency from a simple electrodynamic and control systems input to an emergent property. While there is still some controversy on the subject, it is believed that complex systems
utilizing self-regulation through emergence are generally more resilient and flexible than are simpler top-down command and control systems.
among electricity consumers. Demand response is one means of reducing the market power
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.
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.
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
reliability. Basic grid-friendly devices may incorporate features that work to offset short-term undesirable changes in line frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
or voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
; 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
Major appliance
A major appliance, or domestic appliance, is usually defined as a large machine which accomplishes some routine housekeeping task, which includes purposes such as cooking, or food preservation, whether in a household, institutional, commercial or industrial setting...
s found in homes, commercial building systems such as HVAC
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
, and many industrial systems.
Frequency Response
Most electric systems use alternating currentAlternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
with a nominal frequency of 50 or 60 Hz (hertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
) to deliver energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
produced by electrical generator
Electrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
s to the electricity consumers. When the amount of electric power
Electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
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, the rate at which the frequency changes is dependent principally on the system's total inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
(which is not very controllable) and the aggregate response of the generators' control system
Control system
A control system is a device, or set of devices to manage, command, direct or regulate the behavior of other devices or system.There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls...
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
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...
to deliver commands to millions of devices. This type of behavior changes frequency from a simple electrodynamic and control systems input to an emergent property. While there is still some controversy on the subject, it is believed that complex systems
Complex systems
Complex systems present problems in mathematical modelling.The equations from which complex system models are developed generally derive from statistical physics, information theory and non-linear dynamics, and represent organized but unpredictable behaviors of systems of nature that are considered...
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 (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.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 responseDemand response
In electricity grids, demand response is similar to dynamic demand mechanisms to manage customer consumption of electricity in response to supply conditions, for example, having electricity customers reduce their consumption at critical times or in response to market prices...
among electricity consumers. Demand response is one means of reducing the market power
Market power
In economics, market power is the ability of a firm to alter the market price of a good or service. In perfectly competitive markets, market participants have no market power. A firm with market power can raise prices without losing its customers to competitors...
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 EnergyUnited States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
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.
Sources and additional resources
- US Department of Energy, Office of Electricity Delivery and Energy Reliability http://www.electricdistribution.ctc.com/index.htm
- Grigsby, L. L., et al. The Electric Power Engineering Handbook. USA: CRC Press. (2001). ISBN 0-8493-8578-4
- S. Stoft. Power System Economics. Wiley Interscience. IEEE Press. (2002). ISBN 0-471-15040-1
- 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. http://gridwise.pnl.gov/docs/pnnl_gridwiseoverview.pdf.
- 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, Washington http://gridwise.pnl.gov/docs/gfa_project_final_report_pnnl17079.pdf.
- D. Hammerstrom et al. (2007). Pacific Northwest GridWise Testbed Demonstration Projects Part I. Olympic Peninsula Project. PNNL no. 17167, Pacific Northwest National Laboratory, Richland, Washington http://gridwise.pnl.gov/docs/op_project_final_report_pnnl17167.pdf.