Electric power supplies fueled directly by the sun, such as wind power and solar cells, require significant backup capability because the wind or sun are not always available. It is argued by proponents of wind power that a widespread grid increases the availability significantly, and reduces the standby capacity required. That may be true to some degree, but it increases the capital cost of the system since billions of dollars worth of transmission lines are necessary. In any event both wind and solar require significant standby power that can be brought online rapidly. This rules out nuclear and coal fueled plants since both of these respond to load changes slowly, so gas fired turbines are indicated. Energy storage systems can be used in some places, but those require a significant increase in the primary generating capability. Where the terrain permits, water can be pumped uphill while the wind is blowing and the sun is shining, and then flowed downhill through water turbines to generate electricity when the wind is not blowing or the sun is not shining. But, in places like the Texas Panhandle, where there is good wind and a lot of sunshine, the land is flat and water is scarce. One approach in such a place is to store compressed air in natural underground caverns. When the primary source is not available, the compressed air is mixed with natural gas, burned, and expanded through a gas turbine. This approach doesn't seem to me to have much advantage over a regular gas-fired electric generating station. At any rate, it is obvious that the "free energy" systems require substantially more capital structure than other electric generation systems. And, people seem to not appreciate that the electric conversion devices are more susceptible to weather related damage than conventional systems, require more maintenance, and have a limited useful life.