Evaporation engines like the drinking bird operate on the other half of the water cycle (surface water -> vapor -> cloud water). A 'cloud sponge elevator' woul

Evaporation engines like the drinking bird operate on the other half of the water cycle (surface water -> vapor -> cloud water). A 'cloud sponge elevator' would operate on essentially the same half of the water cycle that we already tap into with hydroelectric dams (cloud water -> rain -> surface water). We could get the same increase in energy per unit water by building dams almost as high as the clouds. Now, that would be a huge capital expense (but probably look pretty awesome), but I'm not sure it would be more of a capital expense per watt than a cloud sponge elevator. One of the reasons why people are interested in evaporation engines is to try to tap into the energy in the water cycle, like dams do, without the high capital expense. Of course, dipping birds aren't efficient, but they also aren't the only possible design.