Wind power supplies a large proportion of the electricity in countries like Denmark, Germany, and Spain, and its use is growing at an explosive pace around the world. Government incentives and the high cost of fossil fuels have combined to make wind farms a good investment for power-generation companies. But that investment comes at a price: the potentially expensive systems needed to make transmission grids run reliably, regardless of wind’s famous fickleness. The question is, how much does that cost? To date, power grid studies have produced widely divergent estimates. Conclusions differ, for instance, about how much reserve generating capacity must be built to keep the lights on when the wind dies down. The uncertainties are a big problem for policy-makers, because such grid-related costs will ultimately determine how much wind power is too much.
The International Energy Agency (IEA) in Paris created a research team to do a metaâ''analysis of 19 national or regional wind and grid studies, under the direction of Hannele Holttinen, a senior research scientist at the Technical Research Center of Finland, in Espoo. The first draft of that analysis, issued in November, found that in some cases for every 100 megawatts of wind power, you need 100 MW of fossil, nuclear, or hydroelectric as a backup. But in general, the analysis argues, reserves can be much lower where there’s ready access to a large electricity grid. Much depends, therefore, on the size of the region studied.
The IEA found that the larger the area examined, the greater the number of power plants available to fill the gap when the wind wanes. Mainly as a result of this issue, projections of how much it would cost to add needed reserve capacity differ by a factor of 10 or more—swinging from an extra 0.50 to 4 (about US $0.74 to $5.88) per megawatt-hour in regions that use 20 percent wind power.
Holttinen’s team found that those models yielding the highest costs tend to ignore the modeled grid’s interconnections with neighboring grids—an oversimplification that exaggerates the variability caused by wind farms and thus the cost of reserve power to balance it out, Holttinen believes. Whether those interconnections are up to the task of stabilizing wind-tossed electric grids is a real question.
Wind-farm installation in Europe grew an estimated 38 percent last year, up from 19 percent in 2006, bringing the total capacity to about 67 gigawatts (roughly the equivalent of 20 to 25 standard-size nuclear power plants). At those rates, European grid operators report, windmill construction is outstripping growth in transmission capacity. The result is that in wind-farm-rich countries such as Germany and Denmark, high winds cause large and unanticipated power flows that saturate the grids of neighboring nations. In recent years this has forced grid operators to curtail scheduled transfers of power between grids. In 2008, the grid operators warn, the unanticipated power flows could overload lines anywhere from the Czech Republic to the Netherlands.
Europe’s grid operators bet they can prevent most of the wind-related overloads by adjusting their control schemes and further limiting power trades, while a pair of new 380-kilovolt transmission lines in northeastern Germany expected on line in 2009 will prevent the rest. Until then, operators say they might be forced to shut down some wind farms when the wind blows strong.