|
|
|
|
Demand response
|
| |
|
| |
In electricity grids, demand response (DR) 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. The difference is that demand response mechanisms respond to explicit requests to shut off, whereas dynamic demand devices passively shut off when stress in the grid is sensed.
Discussion
Ask a question about 'Demand response' Start a new discussion about 'Demand response' Answer questions from other users |
Encyclopedia
In electricity grids, demand response (DR) 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. The difference is that demand response mechanisms respond to explicit requests to shut off, whereas dynamic demand devices passively shut off when stress in the grid is sensed. Demand response can involve actually curtailing power used or by starting on site generation which may or may not be connected in parallel with the grid.This is a quite different concept from energy efficiency, which means using less power to perform the same tasks, on a continuous basis or whenever that task is performed. Current demand response schemes are implemented with large commercial customers, often through the use of dedicated control systems to shed loads in response to a request by a utility or market price conditions. Services (lights, machines, air conditioning) are reduced according to a preplanned load prioritization scheme during the critical timeframes. An alternative to load shedding is on-site generation of electricity to supplement the power grid. Under conditions of tight electricity supply, demand response can significantly reduce the peak price and, in general, electricity price volatility.
Demand response is generally used to refer to mechanisms used to encourage consumers to reduce demand, thereby reducing the peak demand for electricity. Since electrical systems are generally sized to correspond to peak demand (plus margin for error and unforeseen events), lowering peak demand reduces overall plant and capital cost requirements. Depending on the configuration of generation capacity, however, demand response may also be used to increase demand (load) at times of high production and low demand. Some systems may thereby encourage energy storage to arbitrage between periods of low and high demand (or low and high prices).
Smart grid application
Demand response could be extended from large industrial customers to a substantial portion of the system load in a smart grid. During times of peak demand, smart grid enabled air conditioning and refrigerators would receive a digital message from the grid requesting them to curtail power usage. As the proportion of intermittent power sources such as wind power in a system grows, the magnified impact of demand response in a smart grid may become increasingly important to effective management of the electric grid. For example with a region heavily relying on wind, rather than building expensive grid energy storage schemes to deposit excess power, demand response may be used to absorb the excess- for example by recharging vehicle batteries during times of excess wind, and shedding demand (delaying activation of the refrigeration compressor, or hot water heater coils) when the wind dies down.
Electricity pricing
In many electric systems, some or all consumers pay a fixed price per unit of electricity independent of the cost of production at the time of consumption. The consumer price may be established by the government, a regulator, or represent an average cost per unit of production over a given timeframe (for example, a year). Consumption therefore is not sensitive to the cost of production in the short term. In economic terms, consumers' consumption of electricity is inelastic in short time frames since they do not face the "real" price of production; if consumers were to face actual prices in short periods, they would (presumably) increase and decrease their use of electricity in reaction to price signals.
Electricity producers, however, are (implicitly or explicitly) paid according to a system intended to encourage priority usage of lower-cost sources of generation (in terms of marginal cost). In many systems that use market-based pricing, the wholesale cost will vary according to demand and available supply. The variation in pricing can be significant: for example, in Ontario between August and September 2006, wholesale prices paid to producers ranged from a peak of C$318 per MW·h to a minimum of negative $C3.10 per MW·h,; in the latter case, the negative price indicates that producers were being charged to provide electricity to the grid (and consumers paying real-time pricing may have actually received a rebate for consuming electricity during this period). Variations in price within a 24-hour period of two to five times are not unusual, due to daily demand cycles .
In cases where consumers do not face actual market prices, they have little or no incentive to reduce consumption (or defer consumption to later periods) during times when production costs are significantly higher. Since costs may be substantially higher at these times, the potential for savings should not be overlooked.
Two Carnegie Mellon studies in 2006 looked at the importance of demand response for the electricity industry in general terms and with specific application of real-time pricing for consumers for the PJM Interconnection Regional Transmission authority. The latter study found that even small shifts in peak demand would have a large effect on savings to consumers and avoided costs for additional peak capacity: a 1% shift in peak demand would result in savings of 3.9%, billions of dollars at the system level. An approximately 10% reduction in peak demand (achievable depending on the elasticity of demand) would result in systems savings of between $8 to $28 billion.
A study carried out in 2007 by The Brattle Group for the United States showed that even a 5 percent drop in peak demand would yield substantial savings in generation, transmission, and distribution costs – enough to eliminate the need for installing and running some 625 infrequently used peaking power plants and associated power delivery infrastructure. This would yield an annual savings of $3 billion which translates into a present value of $35 billion over the next two decades.
In Ontario, Canada, the Independent Electricity System Operator has noted that in 2006, peak demand exceeded 25,000 megawatts during only 32 system hours (less than 0.4% of the time), while maximum demand during the year was just over 27,000 megawatts. The ability to "shave" peak demand based on reliable commitments would therefore allow the province to reduce built capacity by approximately 2,000 megawatts.
Electricity grids and peak demand response
In an electricity grid, electricity consumption and production must balance at all times; any significant imbalance could cause grid instability or severe voltage fluctuations, and cause failures within the grid. Total generation capacity is therefore sized to correspond to total peak demand with some margin of error and allowance for contingencies (such as plants being off-line during peak demand periods). Operators will generally plan to use the least expensive generating capacity (in terms of marginal cost) at any given period, and use additional capacity from more expensive plants as demand increases. Demand response in most cases is targeted at reducing peak demand to reduce the risk of potential disturbances, avoid additional capital cost requirements for additional plant, and avoid use of more expensive and/or less efficient operating plant. Consumers of electricity will also pay lower prices if generation capacity that would have been used is from a higher-cost source of power generation.
Demand response may also be used to increase demand during periods of high supply and/or low demand. Some types of generating plant must be run at close to full capacity (such as nuclear), while other types may produce at negligible marginal cost (such as wind and solar). Since there is usually limited capacity to store energy, demand response may attempt to increase load during these periods to maintain grid stability. For example, in the province of Ontario in September 2006, there was a short period of time when electricity prices were negative for certain users. Energy storage such as Pumped-storage hydroelectricity is a way to increase load during periods of low demand for use during later periods. Use of demand response to increase load is less common, but may be necessary or efficient in systems where there are large amounts of generating capacity that cannot be easily cycled down.
Some grids may use pricing mechanisms that are not real-time, but easier to implement (users pay higher prices during the day and lower prices at night, for example) to provide some of the benefits of the demand response mechanism with less demanding technological requirements. For example, in 2006 Ontario began implementing a "Smart Meter" program that implements "Time-of-Use" (TOU) pricing, which tiers pricing according to on-peak, mid-peak and off-peak schedules. During the winter, on-peak is defined as morning and early evening, mid-peak as mid-day to late afternoon, and off-peak as night-time; during the summer, the on-peak and mid-peak periods are reversed, reflecting air conditioning as the driver of summer demand. In 2007, prices during the off-peak were C$0.034 per KWh and C$0.097 during the on-peak demand period, or just less than three times as expensive. As of 2007, few utilities had the meters and systems capability to implement TOU pricing, however, and most customers are not expected to get smart meters until 2008-2010. Eventually, the TOU pricing (or real-time pricing) is expected to be mandatory for most customers in the province.
Incentives to shed loads
Energy consumers need some incentive to respond to such a request from a Demand Response Provider (see list of Providers below). Demand Response incentives can be formal or informal. For example, the utility might create a tariff-based incentive by passing along short-term increases in the price of electricity. Or they might impose mandatory cutbacks during a heat wave for selected high-volume users, who are compensated for their participation. Other users may receive a rebate or other incentive based on firm commitments to reduce power during periods of high demand , sometimes referred to as negawatts.
Commercial and industrial power users might impose load shedding on themselves, without a request from the utility. Some businesses generate their own power and wish to stay within their energy production capacity to avoid buying power from the grid. Some utilities have commercial tariff structures that set a customer's power costs for the month based on the customer's moment of highest use, or peak demand. This encourages users to flatten their demand for energy, known as energy demand management, which sometimes requires cutting back services temporarily.
Smart metering has been implemented in some jurisdictions to provide real-time pricing for all types of users, as opposed to fixed-rate pricing throughout the demand period. In this application, users have a direct incentive to reduce their use at high-demand, high-price periods. Many users may not be able to effectively reduce their demand at various times, or the peak prices may be lower than the level required to induce a change in demand during short time periods (users have low price sensitivity, or elasticity of demand is low). Automated control systems exist, which, although effective, may be too expensive to be feasible for some applications.
Technologies for demand reduction
Technologies are available, and more are under development, to automate the process of demand response. Such technologies detect the need for load shedding, communicate the demand to participating users, automate load shedding, and verify compliance with demand-response programs. GridWise and EnergyWeb are two major federal initiatives in the United States to develop these technologies. Universities and private industry (including EnergyConnect, Inc., Energy Curtailment Specialists, North America Power Partners, EnerNOC, Inc., Site-Controls, LLC., Powerit Solutions and RTP Controls, Inc) are also doing research and development in this arena. Scalable and comprehensive software solutions for DR (such as platforms by Ziphany, LLC) enable business and industry growth.
Some utilities are considering and testing automated systems connected to industrial, commercial and residential users that can reduce consumption at times of peak demand, essentially delaying draw marginally. Although the amount of demand delayed may be small, the implications for the grid (including financial) may be substantial, since system stability planning often involves building capacity for extreme peak demand events, plus a margin of safety in reserve. Such events may only occur a few times per year.
The process may involve turning down or off certain appliances or sinks (and, when demand is unexpectedly low, potentially increasing usage). For example, heating may be turned down or air conditioning or refrigeration may be turned up (turning up to a higher temperature uses less electricity), delaying slightly the draw until a peak in usage has passed. In the city of Toronto, certain residential users can participate in a program (Peaksaver AC) whereby the system operator can automatically control air conditioning during peak demand; the grid benefits by delaying peak demand (allowing peaking plants time to cycle up or avoiding peak events), and the participant benefits by delaying consumption until after peak demand periods, when pricing should be lower. Although this is an experimental program, at scale these solutions have the potential to reduce peak demand considerably. The success of such programs depends on the development of appropriate technology, a suitable pricing system for electricity, and the cost of the underlying technology. Bonneville Power experimented with direct-control technologies in Washington and Oregon residences, and found that the avoided transmission investment would justify the cost of the technology.
Other methods to implementing demand response approach the issue of subtlely reducing duty cycles rather than implementing thermostat setbacks. These can be implemented using customized building automation systems programming, or through swarm-logic methods coordinating multiple loads in a facility (e.g. REGEN Energy's EnviroGrid controllers).
It was recently announced that electric refrigerators will be sold in the UK fitted with a frequency sensing device which will delay or advance the cooling cycle based on monitoring grid frequency.
Short-term inconvenience for long-term benefits
Shedding loads during peak demand is important because it reduces the need for new power plants. To respond to high peak demand, utilities build very capital-intensive power plants and lines. Peak demand happens just a few times a year, so those assets run at a mere fraction of their capacity. Electric users pay for those idle "spinning reserves" with rate hikes. DR is a way for utilities to avoid large capital expenditures, and thus keep rates lower overall.
Importance for the operation of electricity markets
It is estimated that a 5% lowering of demand would have resulted in a 50% price reduction during the peak hours of the California electricity crisis in 2000/2001. With consumers facing peak pricing and reducing their demand, the market should become more resilient to intentional withdrawal of offers from the supply side.
Residential and commercial electricity use often vary drastically during the day, and demand response attempts to reduce the variability based on pricing signals. There are three underlying tenets to these programs: 1) unused electrical production facilities represent a less efficient use of capital (little revenue is earned when not operating); 2) electric systems and grids typically scale total potential production to meet projected peak demand (with sufficient spare capacity to deal with unanticipated events); and 3) by "smoothing" demand to reduce peaks, less investment in operational reserve will be required, and existing facilities will operate more frequently. In addition, significant peaks may only occur rarely, such as two or three times per year, requiring significant capital investments to meet infrequent events.
Initiative of the US Energy Policy Act of 2005
The US Energy Policy Act of 2005 has mandated the Secretary of Energy to submit to the US Congress "a report that identifies and quantifies the national benefits of demand response and makes a recommendation on achieving specific levels of such
benefits by January 1, 2007." Such a report was published in February 2006 .
The report estimates that in 2004 potential demand response capability equaled about 20,500 megawatts (MW), 3% of total U.S. peak demand, while actual delivered peak demand reduction was about 9,000 MW (1.3% of peak), leaving ample margin for improvement. It is further estimated that load management capability has fallen by 32% since 1996. Factors
affecting this trend include fewer utilities offering load management services,
declining enrollment in existing programs, the changing role and responsibility of
utilities, and changing supply/demand balance.
Available Markets
SDG&E San Diego
- Real Time Demand Response
- Real Time Price Response
- Day-Ahead Option
- Emergency Demand Response Program
SCE SoCal
- Real Time Demand Response
- Real Time Price Response
- Day-Ahead Option
- Emergency Demand Response Program
- Real Time Demand Response
- Real Time Price Response
- Day-Ahead Option
NYISO
- Day Ahead Demand Response Program
- Emergency Demand Response Program
- Special Case Resources
- Real Time Demand Response
- Real Time Price Response
- Day-Ahead Option
- Interruptible Load for Reliability
- Synchronous Reserve
See also
External links
- Ways for businesses to reduce their electric requirements when the electric grid is unstable due to high demands
- Article and audio interviews
- Alison Silverstein, former Senior Energy Policy Advisor at FERC, thoughts on EPAct 2005, AMI-MDM, and demand response
- Demand Response research information
- Turnkey Demand Response Provider
- Bonneville Power Administration research initiative
- Overcoming industry challenges for demand response providers
- Pacific Northwest National Laboratories research initiative
-
-
-
-
-
-
-
- EnerNOC
- M2M Communications
- Ken Sinclair interviews Ahmad Faruqui on Dynamic Pricing, September 2008
- Demand Response and Advanced Metering, Regulation, Spring 2006
|
| |
|
|
