Storage of Wind Energy using Weights on the Tower

A thought experiment. What if you suspended a large mass from a wind tower, cranking it up when there is surplus wind, and letting it fall when electricity is needed. How much weight would you need to make this useful?

Well, from http://en.wikipedia.org/wiki/Kilogram-force, we get the measure of magnitude of the force exerted on one kilogram of mass by a 9.80665 m/s2 gravitational field = 9.8 Newtons (N), or to make things easier, 10 N. The potential energy stored by raising this one meter is F * D = 10 Nm, or 10 Joules (J). Now, there are 3600 J in a Watt-hour (since 1 Watt-second = 1 J).

Wind towers are typically 60-90m tall ( http://en.wikipedia.org/wiki/Wind_turbine ). Let's assume 75m for this calculation. Raising our 1kg mass 75 meters would store 750J, or 750/3600 = 0.208 Wh, not a heck of a lot. Another way to phrase this is we would need 4.8kg to store 1 Wh. Assuming a 1MW turbine, to store one hour of 1MW output would require a weight of 4.8 million kilograms - or 4800 metric tons.

Say that we wanted to use concrete for this. Density of concrete is about 2400kg/m3. (http://www.simetric.co.uk/si_materials.htm). We would need then:

4,800,000/2400 = 2000m3 of concrete, or a block about 10m x 10m x 20m, or about as big as my house. Probably not practical, but you never know...

I guess this is why batteries, air compression, etc are more practical.