Electricity is something many take for granted, except in those rare instances when the power goes out. It’s not an overstatement to say that electricity is an invisible, ubiquitous and essential part of modern life; it keeps our homes and businesses well-lit, comfortable and safe, and it powers the various devices we use for work and leisure.
Whenever we flip a switch, adjust the thermostat, go online, recharge our smartphone, or drive through an intersection with a traffic light, we are counting on the power system to always be ready and able to reliably meet our needs.
Highly dependable utility service is no accident – instead, it is provided by complex and sophisticated power grids that are the largest machines in the world. These electric utility systems consist of multiple parts, including power plants, transmission lines, local distribution facilities, and associated control and communication systems.
As our consumption of electricity fluctuates from moment to moment, hour to hour, day to day, and month to month, an equal amount of power needs to be produced and delivered to match the load. If at any given point in time not enough juice is being produced, the stuff we’re using starts to shut down. Conversely, if there’s too much juice, things start to overheat. So a continuous re-balancing of loads and resources takes place, like an intricately-choreographed, ongoing dance that enables modern life.
What is resource adequacy?
Simply defined, resource adequacy means having sufficient power resources available when needed to reliably serve electricity demands across a range of reasonably foreseeable conditions.
Electricity consumption is measured using two metrics – peak demand and energy load. Peak demand is the maximum amount of power used at a specific point in time, such as in the evening during very cold or very hot weather after people have arrived home and are using multiple power-consuming devices. The second metric, energy load, is the amount of power consumed over a period of time, such as the monthly energy amount shown on your electric bill.
To keep the lights on, the utility system has to do three things. First, it needs to have enough generating capacity available to meet the peak demands when they occur. Second, it needs generating resources that can produce energy to serve loads across time, from day-to-day, month-to-month, and season-to-season. Third, the utility system needs to have enough operating flexibility to follow upward and downward fluctuations in electricity demands. If the system has sufficient resources to do all of these things reliably, then it is deemed to have resource adequacy (including additional resources to protect against sudden unplanned outages).
What types of resources contribute to resource adequacy?
Traditionally, utilities have used three basic types of generating resources to perform the load-resource balancing act described above. The three types of power plants are known as baseload, peaking and midrange generators. All three types are needed to achieve resource adequacy.
Baseload generators can produce power at a constant rate for extended periods of time, and usually have a relatively low variable cost of production. Examples of baseload generation include nuclear power plants, as well as coal-fired plants. Baseload generators
are the workhorses that produce large amounts of energy, along with steady, dependable capacity.
At the other end of the spectrum are peaking generators, which can quickly provide capacity to help meet peak loads and to follow short-term fluctuations in loads. Peaking generators also tend to have higher variable operating costs. A common type of peaking generation is single-cycle combustion turbines. These are basically large jet engines that can burn either natural gas or liquid fuels. Peaking generators are good sources of capacity and flexibility, but due to their relatively high operating costs, they are not used to produce large amounts of energy.
Midrange generators have more operating flexibility than baseload generators but less than peaking generators. Midrange generators also have variable operating costs that are higher than baseload generators but lower than peaking generators. The most prominent example of midrange generation is combined-cycle combustion turbines, which produce power in two stages. In the first stage, natural gas is burned in a combustion turbine and used to turn a generator. In the second stage, exhaust heat from the combustion turbine is used to make steam and turn a steam turbine-generator. Typically, midrange generators are used to help supply moderate amounts of capacity, energy and flexibility.
Okay, by now you are probably wondering: What about all the hydroelectric power we have in the Northwest? Traditionally, hydro generation has helped meet the region’s needs for all three types of power. It is a particularly effective, low-cost resource for meeting peak demands and following fluctuations in demand. As a result, the Northwest has historically not needed as much fossil-fueled peaking and midrange generation as other regions of the U.S. Our Northwest hydro power also produces significant amounts of annual energy, but not as much as could be produced from an equal amount of baseload generating capacity.
How do utilities decide which resources to use?
When deciding how to operate their resources to meet consumers’ demands for electricity, utilities seek to provide reliable service at the lowest possible cost.
The resources that a utility normally decides to use, or “dispatch,” first are its resources that have the lowest variable operating cost. These include baseload resources such as Columbia Generating Station. Next, the utility dispatches its resources that have the next highest variable operating cost; often these are midrange generators. Finally, if its loads are relatively high or may be subject to rapid fluctuations, the utility will dispatch its more expensive peaking resources.
Columbia Generating Station is one of the key resources that BPA uses to deliver clean, reliable power to public power utilities across the Northwest. Columbia produces 1,190 gross megawatts of baseload power, including both firm energy and capacity.
For wind power to produce the same amount of energy on an annual basis, more than 3,500 megawatts of wind turbines would be needed. Also, Columbia is not subject to the fluctuations that affect generation from wind and solar-PV. As a result, Columbia provides capacity that is much more firm, and does not require other forms of generating capacity to be held to provide incremental and decremental reserves to integrate wind and other intermittent forms of generation.
How do renewables and other alternative forms of resources fit In?
During the last 15 years, large amounts of new renewable resources have been developed in the Northwest. To date, the predominant share of renewable resource additions in the region have been wind power, totaling over 8,000 megawatts of installed capacity. In more recent years, falling costs and government incentives have also begun to make solar photovoltaic power more attractive.
Wind and solar-PV differ from other existing power resources. In particular, wind and solar-PV produce power intermittently. This limits their ability to contribute to resource adequacy. However, both also have very low variable operating costs. This means that to the extent they can be integrated into the system, it is economically desirable to dispatch them early in the utility’s stack of resources.
To date, the Bonneville Power Administration has integrated over 5,000 megawatts of wind power onto its system. To do so, BPA has dedicated significant hydro resources to mirror changes in production from the wind fleet. BPA maintains 900 megawatts of generating reserves that can be rapidly increased or decreased to offset wind resource fluctuations. This illustrates how a portion of BPA’s hydro generating resources that could be used for other resource adequacy purposes are diverted and used to integrate wind power.
Other steps are being taken to deal with the greater variability created by renewable resources. These include implementing shorter, intra-hour scheduling and dispatching practices, as well as developing new energy imbalance markets.
Demand response is another type of resource that has potential to contribute to resource adequacy. Demand response is not a generating resource; instead it works by adjusting customer use of electricity to help maintain the overall supply-demand balance on the power system. For example, if overall electric loads are increasing rapidly toward peak levels, a demand response can be used to reduce certain loads of customers who have volunteered to participate, typically in exchange for compensation.
Energy Northwest partnered with the City of Richland, Cowlitz County Public Utility District, Pend Oreille County PUD and BPA on the Aggregated Demand Response Pilot Project. This project is using 35 megawatts of aggregated fast-response demand-side resources to test their use to help meet capacity needs as well as flexibility needs on the BPA grid.
Tools – We need them all
Maintaining resource adequacy requires responsible energy policy decisions, at the local, state and federal levels, policy not driven by whims and fads. For instance, having a resource like Columbia Generating Station during the Western U.S. Energy Crisis of 2000 and 2001 saved the region approximately $1.4 billion according to the Public Power Council. That could not have been anticipated in 1999.
(Post by Charlie Black)