It is desired to store the energy from a 2 MW wind turbine by mechanical means.

Question

It is desired to store the energy from a 2 MW wind turbine by mechanical means. The idea is to build a deep shaft and have a heavy weight hanging in the shaft to store the energy. The wind turbine would raise the weight during windy conditions and the weight would release energy when the energy is needed. Assume: That the weight is 10x10x10 ft box filled with lead. That it is desired to store lOMw-hrs of energy (the equivalent of operating the turbine at maximum power for 5 hours) How deep would the shaft have to be to store this amount of energy? Explain the practicality of this device or the lack of practicality.

Explanation / Answer

Desired storage of energy = 10 Mw - hrs = 10* 106 J/s * 3600 s = 3.6 * 1010J

Volume of box = 1000ft3 = 1000 * (0.3048)3 m3 = 28.316 m3

Density of Lead = 11340 kg/m3

Mass of lead = Density * Volume = 11340 * 28.316 = 321103.44 kg

Potential Energy = m*g*h

321103.44 * 9.81 * h = 3.6 * 1010

h = 11428.48 m = 11.43 km

Device is impractical

1) Depth of shaft is very large ( statically impossible to develop)

2) Lead is poisonous

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