Backup generation

From Interwest Energy Alliance Wiki

It is a common myth that wind energy requires “backup” generation and that wind’s variability will keep it from being a major electricity contributor.

The fact is, while wind energy’s variable output can pose challenges, these can be successfully managed with the right procedures.

Any generation technology has its special characteristics, and so utility and transmission system operators have always adapted to accommodate them. For example, when nuclear power was introduced, system managers had to adjust operations to ease the integration of a large, non-dispatchable, single source of electricity that could suddenly trip off-line; in fact, even today, utilities typically set their “reserve margin” at the level of the largest nuclear plant on their system. That doesn’t mean nuclear energy is unreliable or that this characteristic limits its potential, just that modest steps need to be made to manage its integration. Coal-fired plants are also relatively inflexible. Nuclear, coal, and gas plants all occasionally suddenly trip offline and contribute to the need for reserves. Wind is similar. Modest changes including adding additional reserves are sometimes needed to integrate wind energy and this can be done reliably and at modest cost.

Wind power is not typically used for its capacity to meet peak electric loads but it makes a large contribution to the amount of electric energy that is generated and consumed over time. Wind’s benefit is in providing energy, diversifying supply, saving fuel, and reducing carbon and other emissions. This important role should be clarified because all generation types make different contributions and wind should be valued for what it does, and not expected to do what it cannot.

It is sometimes claimed that due to variability, every wind farm requires its own “back-up” or “storage.” This is false. The power system is operated as a pool where reserve needs are based on what the whole system needs rather than what every individual coal, nuclear, gas, or wind plant needs. The claim is just as false as applied to wind as it would be if applied to coal, gas, or nuclear. Typically only a modest amount of additional reserves are needed to handle wind’s variability.

Most people are not aware that with or without wind, utilities are already expert at managing variability. Along with supply variability from resources shutting down or rising and falling, electricity demand variability is something utilities have learned to deal with quite well. Demand, or “load,” moves up and down with limited predictability. Further, a utility also must stand ready to deal with the sudden disconnection of any of the major components of the energy supply system. Utilities also regularly plan for new high-usage consumers, such as manufacturing plants, connecting to their systems.

Now let’s return to the supply side of the equation, where wind energy and the rest of the energy sources reside. Keeping in mind the analogy concerning the variability of electricity demand, it is helpful to think of wind power as “negative demand” or “negative load.” That is, wind energy reduces the need for the rest of the system to provide power. Wind, then, is a positive addition to the overall energy picture on a given system.

The European countries that lead in wind have successfully built up this clean energy source to the point where it provides 20% or more of the electricity supply in Denmark and some states in Western Germany and Spain. What’s more, these countries have done so without a high degree of integration planning. It is only now, at these levels, that utility managers and operators in some of those regions are finding that preparation for the integration of more wind power be-comes more important. Such preparations include improved forecasting, expansion of transmission capacity, adding load following and reserves, and cooperation between regional power markets.

With wind supplying under 1% of total U.S. electricity generation and 10% or less of any individual utility’s generation, the U.S. has not yet reached similar levels of wind penetration. However, many wind integration studies have been performed in the U.S. The studies confirm that wind’s variability can be successfully managed, and that the larger the control area, the more diverse the generation mix, and the less discriminatory the transmission access and distribution rules, the more wind the region can accommodate.

A good summary of these studies was assembled by the Utility Wind Integration Group in coordination with the three associations that together represent all of the nation’s electric utilities: the Edison Electric Institute, the American Public Power Association, and the National Rural Electric Cooperative Association. The short paper is available along with many other resources at the Utility Wind Integration Group’s web site, www.uwig.org

According to the utility summary, wind resources can have impacts on the system, but those impacts “can be managed through proper plant interconnection, integration, transmission planning, and system and market operations.” As for cost associated with 20% wind penetration of system peak demand, “system operating cost increases arising from wind variability and uncertainty amounted to about 10% or less of the wholesale value of the wind energy.”

The report also addresses compatibility and other technical issues: “Wind power plant terminal behavior is different from that of conventional power plants, but can be compatible with existing power systems,” it states. “With current technology, wind-power plants can be designed to meet industry expectations such as riding through a three-phase fault, supplying reactive power to the system, controlling terminal voltage and participating in SCADA system operation.”

Finally, the report suggests that overall, “...with new equipment design and the proper plant engineering, wind generation can actually improve system stability in response to a major plant or line outage.”

Other reports around the country have offered similar evidence of wind’s reliability. A study conducted for the New York State Energy Research and Development Authority and the New York Independent System Operator (NYISO) examined possible impacts of integrating wind power capacity equal to 10% of the state’s peak load. The study found that, given NYISO’s large balancing area, mix of resources, and existing processes, such an increase could be accommodated in the state without special measures—and even would reduce system operating costs, largely due to fuel savings.

Meanwhile, results of the Midwest Wind Integration Study, which was required by the Minnesota legislature in 2005 to evaluate reliability and other impacts of higher levels of wind generation, show that with the right procedures in place, utilities can incorporate wind power into their resource portfolios in an amount comprising up to one-fourth of their delivered energy without sacrificing reliability and with only minor costs.

These are just a few of the studies, in fact, confirming wind power’s reliability and feasibility on a large scale. Studies and experiences are pointing in the same direction, to a reliable U.S. power system with wind penetration up to 20% and beyond in many regions.

—Adapted from June 2006 “Windletter,” from the American Wind Energy Association.

Also see Interwest wiki entry on Reliability of wind