Wind turbines are supposed to provide electric power without adding CO2 to the atmosphere. This would be accomplished if our electric power requirements varied with time to match the availability of wind power. But a wind farm in any given location will face periods of low or no wind. There are also times when the wind velocity is too high and the wind turbine's blades must be feathered and braked to prevent damage. It might be hoped that the distribution of wind farms throughout a geographic area might be such that power can be dispatched from a wind farm that is producing power to a load area that is temporarily without wind power. A monumental scheduling problem would result from attempting to supply one area exclusively with wind power produced in various places scattered over a wide geographic area. The total sum of available wind power might be more constant than the power available from one farm, but there will be some unmatched surpluses. Moreover, the present transmission infrastructure is not adequate to tie all these areas together, so we must look for ways to fill in locally when wind power is not adequate.
Solar power suffers from diurnal variation as well as local weather and seasonal variation, so it merely adds to the variability of wind power. The variability is ideally filled in with stored energy: vanadium ion flow batteries, other batteries, kinetic energy inertia storage, potential energy (pumped storage and river dam reservoirs). But these are limited in size. Reservoirs are large, but because of drought, little water is available for wind power fill in.
So as we add more wind turbines, we are forced to fill in the wind deficits with power from our base load coal, gas, oil, geothermal, and nuclear plants. There are gas turbine peaking plants, but these are inefficient. When the base load plants are operated as backups for wind and solar, they are not running at their design load and their efficiency is reduced. This means that the combustion plants will put more CO2 into the atmosphere, thus decreasing the greenhouse gas reductions from wind power. Also, getting them to increase and decrease power fast enough to match the wind and solar variations is a problem. I do not have a good quantitative assessment of how well we are reducing CO2 emissions with wind and solar power, but I guess we are falling short of our goal. Therefore, when we build a wind farm and tie it into the power grid, our work is only beginning. We have to improve the efficiency and flexibility of the backup power generation so that it does not erode the reduction in greenhouse gas emissions.
Wind turbines themselves are not as innocent as we have pictured them. Their blades kill birds and bats. The bats suffer lung damage from flying into low pressure regions in the blade wakes. We cannot afford to lose the insect control provided by the bats. Bird and bat migratory patterns impose restrictions on wind turbine siting and hours of operation. Another problem is the hardship imposed on human neighbors due to air pressure pulsations caused by the large blades swooshing upstream. This may require power reduction or complete shutdown when people need to sleep.
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