Wind Generation's Performance during the July 2006 California Heat Storm

9.8.06 David Dixon, Nuclear Engineer, US DOE, Oakland Operations


In considering energy policy issues, it is helpful to remember there are a variety of different, and sometimes conflicting, imperatives to be balanced. These include: 1) Assurance of Supply - avoiding blackouts and lines for gasoline; 2) Low Total Cost : where total costs include building costs and utilization, fuel costs, operating costs and other grid costs; 3) Environmental Issues : pollutants, green house gases, nuclear waste, land use issues, etc; and 4) Energy Independence - the political, foreign policy, military and balance of trade concerns with energy imports. In general, wind generated electricity meets these needs fairly well. Certainly with tax credits its cost is acceptable; there are some bird kill and land use issues, but these are modest compared to the environmental concerns with others energy sources; and wind has significant energy independence benefits. All of these strengths have been reflected in a truly dramatic growth of planned and installed wind generation facilities during this first decade of the 21st century.

While wind generation has the benefits outlined above and is enjoying wide success, there has been a remaining controversy about its availability 24/7. It is virtually a cliché that the wind is fickle; it blows in different directions and different strengths seemingly at random. As such there has been some concern about how often will the wind blow and produce electricity, and when electricity is needed will the wind be there? Everyone has experienced a really hot day when the air is absolutely still, or a really cold, still night. This concern with the 24/7 availability of wind generation translates to questions about backup capacity to satisfy peak demand, i.e. the first energy policy imperative - Assurance of Supply. This question may be academic most of the year when there is adequate back up capacity and even if the wind is still for a while other electric plants will pick up the slack. But during periods of peak demand, typically in mid-summer or mid-winter the question is very important. That was certainly the case this July during the record heat waves in California, then the East Coast and finally the Southern States. Each region in turn experienced record demand and issued pleas for conservation; commentators expressed concern about blackouts. Under these conditions, the 24/7 availability of wind generation is not an academic question.

Over the last few years, two schools of thought have developed about wind's 24/7 availability. The first : 'this is really not a problem'. Proponents argue, yes the wind is fickle, but wind turbines are being installed in many, many windy locations and when one location is still, you may expect others to be gusty. Thus wind will have excellent 24/7 availability'. Others are concerned, 'blackouts are very dangerous and simply not acceptable. Maybe we need to build back-up generation for wind assets and maybe include such backup in cost calculations, or otherwise significantly discount wind generation when analyzing total grid capacity vs. peak demand?' Both schools have their advocates, and to date the controversy is unresolved.

With this understanding of the 24/7 availability controversy in mind, the recent experience of California is interesting. California has been a pioneer in alternative electricity generation with many decades of service from significant geothermal and wind facilities. The Alamont Pass area, about 50 miles south east of San Francisco was the nation's first significant wind facility. With that start, California today has 2,500 MW of installed wind capacity. That is, these facilities are not being planned or under construction, they are built and on line. 2,500 MW is a big number; a large nuclear plant is 1,000 MW, a large coal plant is 500 to 800 MW, individual wind turbines are 2 to 20 MW. Most significantly, wind is now approaching 5% of California's total electric generating capacity. California's electric grid planners want 7% to 15% of reserve capacity between predicted total demand and total generating capacity; as such the 24/7 reliability of their wind capacity, again 5% of California's total capacity, is important.

So what happened in California during the mid-July heat storm when that electric grid was put to the test, and California avoided rolling blackouts amid a Level 1 Emergency in which Californian's were asked to raise their thermostats to 77 and many manufactures and business voluntarily shutdown? By most people's analysis, wind's performance was disappointing. Specifically during this period of peak demand, statewide wind often operated at only 5% of capacity, or less. The specific data is plotted in the attached graph.

The upper line shows the peak daily electric demand as recorded by the California Independent System Operator, CASIO, during the heat storm. Daily peak power usage increased fairly steadily in mid July, reaching its peak on July 24 at 50,270 MW. Wind's availability during this same period is presented in the lower line. Specifically this is the percent of the CASIO available wind capacity, 2,500MW, which was actually putting electricity into the CASIO grid at the time of peak demand on each day plotted.

By most measures these numbers are disappointing. On the day of peak demand, August 24, 2006, wind power produced at 254.6 MW at the time of peak demand. 254.6 MW represents only 10.2% of wind's rated capacity of 2,500MW. Another perspective on the data, over the preceding seven days, August 17 to 23, wind produced at 89.4 to 113.0 MW, averaging only 99.1 MW at the time of peak demand or just 4% of rated capacity.

This data presents wind's performance during roughly two week's of only one heat storm, California's July '06 storm. This author recommends caution in reaching larger conclusions about its significance. However as a minimum the data suggests that analysis of wind's performance during periods of peak demand in other grid systems with different wind sited facilities would be useful. And until other such data is available, this experience implies caution in assuming a significant fraction of wind capacity will be available for periods of peak demand such as California's July level 1 emergency.