One of the biggest drawbacks with electricity produced by windmills is that the price per Kw falls the harder and longer the wind blows. Since there is no way to regulate the output from windmills it would be nice to be able to somehow store the energy until prices are high enough.

This is an interesting design challenge as well as a huge business opportunity.

The price the electrical utilities pay per kW of electricity from windmills fluctuates considerably minute by minute. During peak loads the prices are higher, at night time the prices are lower. Power stations conserve energy by turning production down at night, (un)fortunately nobody can increase or decrease the wind to regulate the output of windmills. The consequence is that windmills sell a large portion of their output at very cheap rates.

To encourage investment in windmills and windmill parks most governments subsidize the price of electricity produced by windmills. This means that it is taxpayers who are bearing the burden of this CO2 friendly energy source.

The big design issue here is how we can store the energy from windmills. By creating an energy buffer we can wait until prices are favorable before selling the electricity to the power utilities.

One solution is to convert the electricity into compressed air and store it underground. When its time to sell the the stored up energy, the process is reversed, the compressed air is used to power turbines that generate electricity. Voila, an energy buffer!

This is exactly what they are doing at Iowa's compressed air energy storage (CAES) project. When finished in 2011 it will be able to store 20 weeks worth of air supply from the 268-megawatt windmill park.