Tuesday, February 06, 2007

Trapped Wind

The problem with wind power is matching supply with demand. High winds at night can produce more power than needed while on cold, still days the turbines produce nothing at all. Storing electricity has always been difficult and most systems, like flywheels, capacitors or lead-acid batteries are either too expensive or too small. Pump storage is a large-capacity solution. It uses surplus power to pump water up to a reservoir. This water is released to turn hydro-electric turbines at times of high demand. Pump storage is expensive, and needs the right kind of geography with mountains and lakes.

Research in Australia (New Scientist 13th January 2007) has developed the flow battery. This uses electrolytes consisting of chemical solutions based on the element vanadium. The electrolytes are pumped into the flow cell where they are charged by the wind turbines and then pumped out to storage tanks. The size of the battery is therefore only limited by the size of the tanks. When the wind drops the electrolytes are pumped back into the flow cell where they release their electricity. Systems have already been successfully installed and improved the productivity of wind farms by buffering the differences between supply and demand. So far the flow battery is too large to fit in a vehicle, but research continues with alternative chemical compounds for the electrolyte.

At this stage the system is expensive and the future success of flow storage batteries must depend on the cost and availability of vanadium.

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