Addressing the Variability Factor: Can Wind Power Reliably Be Part of the Electricity Mix?

A new AWEA fact sheet aims to promote greater understanding of one of the most complex and frequently confused aspects of wind energy: how wind and other variable energy sources are reliably integrated into electric grid operations.

The fact sheet, entitled “20% Wind Energy by 2030: Wind, Backup Power, and Emissions,” points out that variability is nothing new for the men and women who operate the electric grid. Grid operators already accommodate significant variability in electricity supply and demand, whether from millions of consumers turning appliances on and off or from the sudden failure of a conventional power plant.

Instead of backing up each power plant with a dedicated second generation facility to be used in the event that the first plant suddenly fails, grid operators pool reserves for the whole system to allow them to respond to a variety of potential changes in electricity supply and demand. The same generation reserves that are used to accommodate variability in supply and demand can also be used to accommodate wind energy’s variability. Thus, one does not need dedicated backup power for wind plants any more than one would need a dedicated backup plant for each fossil-fuel or nuclear facility.

As the fact sheet explains, system operators use two main types of generation reserves: “spinning reserves,” (regulation reserves plus contingency spinning reserves) that can be activated quickly to respond to abrupt changes in electricity supply and demand, and “non-spinning reserves,” (including supplemental reserves) that are used to respond to slower changes.

Spinning reserves are typically operating power plants that are held below their maximum output level so that they can rapidly increase or decrease their output as needed. Hydroelectric plants are typically the first choice of system operators for spinning reserves, because their output can be changed rapidly without any fuel use. When hydroelectric plants are not available, natural gas plants can also be used to provide spinning reserves because they can quickly increase and decrease their generation with only a slight loss of efficiency. Studies show that using natural gas plants or even coal plants as spinning reserves increases emissions and fuel use by only 0.5% to 1.5% above what it would be if the plants were generating power normally.

Non-spinning reserves are inactive power plants that can start up within a short period of time (typically 10-30 minutes) if needed. Hydroelectric plants are frequently the top choice for this type of reserve as well because of their speedy response capabilities, followed by natural gas plants. The vast majority of the time, non-spinning reserves that are made available are not actually used, as they only operate if there is a large and unexpected change in electricity supply or demand. As a result, the emissions and fuel use of non-spinning reserves are very low, given that they only rarely run, the fact that hydroelectric plants (which have zero emissions and fuel use) often serve as non-spinning reserves and the very modest efficiency penalty that applies when reserve natural gas plants actually operate.

Analysis included in the fact sheet illustrates that the emissions associated with maintaining reserves for wind are typically less than 1/1000 th of the emissions reductions achieved through the use of wind energy in the first place. Thus, there is no basis for wind opponents’ frequent claim that the need for backup power significantly erodes the emissions and fuel use savings of wind energy.

AWEA produced the fact sheet to help eliminate such common misconceptions about wind energy and ensure that public discussions about wind energy are based on solid information.

Click to download the new fact sheet, “20% Wind Energy by 2030: Wind, Backup Power, and Emissions.” 

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Michael Goggin joined AWEA in February 2008. He represents the wind industry on transmission and grid integration matters, coordinates member input on the development of policy positions, facilitates the exchange of information between members, handles press inquiries on transmission-related issues, and advocates policy positions that advance wind industry interests. Through these activities, he works to promote transmission investment and advance changes in transmission rules and operations to better accommodate wind energy in the power system while maintaining system reliability. Prior to joining AWEA, he worked for two environmental advocacy groups and a consulting firm supporting the U.S. Department of Energy's renewable energy programs. Michael holds a B.A. with honors in Social Studies from Harvard College.

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