Reasons for interest in electric power generation from wind are multifold. First, wind is a renewable energy source. It is not likely to deplete over time, which is not the case for oil, coal, and natural gas.
Second, wind electric power generators use no water, which is in declining supply in many places in the world.
Third, there are no atmospheric pollutants emitted during the operation of wind electric power generators. Here’s where simple thinking fails, because wind electric turbines require near 100 percent fossil fuel backup in order to provide electric power on demand, which the public requires.
Wind blows at variable speeds and sometimes not at all. The physics of wind electric power generation tell us that the electric output varies as the third power of the wind speed, so a factor of two difference in wind speed means a factor of eight difference in electric power generation. Small or no wind means no electric power generation.
The nameplate capacity of a wind electric generator is the maximum that it can produce, which is much higher than its average electrical output, because average wind speed is always less than the maximum wind speed that a wind turbine is designed for. In the best geographical regions for wind, the difference between wind turbine nameplate power and its average electric output is in the 30-40% range; elsewhere the average can be much less.
There are numerous examples of electric power from wind not being available when needed. For instance, in a “heat storm” in California in July 2006, the electric power system was strained due to the unusually high demand for electric power for air conditioning. At the time, the wind was blowing at low levels in the areas where wind turbines were located, so available wind power was well below rated capacity. Because the local electric power grid had enough reserve power, the grid did not fail, and wide-area blackouts were avoided. However, had wind accounted for a larger fraction of the local electrical grid capacity, blackouts would have occurred.
Low electric power production from wind has been a problem in Texas, which has an aggressive wind power program. In recent forecasts, the regional electric power authority determined that during hot summer demand periods, less than 10% of the state’s wind power capacity could be counted on as reliable.
The Pacific Northwest is another region with an aggressive wind program. The region’s experience is that when electric power is needed most, wind is either not blowing or only weakly available. For example, during the cold days of January 5 – 28, 2009, wind electric power generation in the region was virtually non-existent. The Bonneville Power Authority stated that over a full 56-week period, nearly a quarter of the time total wind generation was less than 3% of total wind electric nameplate capacity.
Consumers require electric power on-demand – power must be available when we want it. If electric power is to be available on-demand, the fact that wind power is variable means that there must always be ready backup power available for when the wind fades or dies. In other words, other power sources must be standing by, ready to quickly make up for declines in wind power. These backup options must be able to respond very quickly to wind variations if power-on-demand is to be maintained. Four options for providing backup are prominently discussed:
1) Dedicated fossil fuel power plants
2) An existing grid with significant reserve capacity
3) Long transmission lines to interconnect wind turbines in far-flung regions
4) Hydroelectric storage
Using dedicated fossil fuel power plants can result in a wind/fossil fuel generation complex that is “dispatchable,” providing power-on-demand. In this option, the fossil plant must “run hot” so it is able to quickly ramp up to make up for rapidly declining wind power. In utility jargon, that hot-running operation is called “spinning reserve” and it means that a small amount of fossil fuel is consumed even when the wind turbines are operating at their maximum rated output. Overall costs in this case are the capital and operating costs for both the wind electric generators and one or more backup fossil fuel plants plus the fossil fuel cost required to maintain the spinning reserve. In this option, wind is in effect acting as a fuel-saver for the fossil plant, because when wind electric power is being generated, less fossil fuel is consumed. Total electrical power costs for the combination are clearly much higher than for the wind turbines alone.
In this situation, the reduction in the generation of carbon dioxide and other emissions is not 100%, because fossil fuels are consumed to maintain the needed spinning reserve. The electric generation cost of the so-called backup power plant is less than that of the wind turbines, and since near 100 percent backup is required, the wind turbines represent added cost, making the resultant electric power from the combination more expensive than it would have been without the wind turbines. This is a losing proposition economically.
Another backup option utilizes fossil fuel generators already on the electric grid as backup. Many existing grids have significant fossil fuel electric generation in spinning reserve, ready to make up for the loss of electric power when winds subside. The costs of this backup option are similar or lower than the first option, and wind power is acting as a fuel saver for existing fossil fueled plants. Since the backbone of this method of operation is fossil fuel electric power generators, wind again is simply acting as a fuel saver. If fossil fuels remain inexpensive, the cost of fuel saving is small, but the overall costs for the combined system are much higher, because of the added cost of the wind turbines. This is also a losing proposition economically.
The bottom line is that important purported advantages of wind electric power are not what are often assumed.
PS. Consideration of long transmission lines and hydroelectric storage options are dealt with in our book, “The Impending World Energy Mess.” Note that the fuel saver story for wind also applies to electric power from solar cells.
Dr. Robert L. Hirsch, Ph.D. is a former senior energy program adviser for Science Applications International Corporation and is a Senior Energy Advisor at MISI and a consultant in energy, technology, and management. Hirsch has served on numerous advisory committees related to energy development, and he is the principal author of the report Peaking of World Oil Production: Impacts, Mitigation, and Risk Management, which was written for the United States Department of Energy.