Hydrel

Meet Hydrel, a concrete dam who turns falling water into electricity.

Water held behind a dam has gravitational potential energy. When it falls through the turbines, that energy becomes motion, and generators turn it into electricity. The power depends on how much water flows each second and how far it falls.

The power is P = ηρgQh. Here ρ is the density of water, Q is the flow in cubic metres per second, h is the height the water falls, and η is the efficiency of the turbines and generators, often around 90 percent.

A small dam with a 50 m drop and a flow of 20 m³/s produces about 0.9 × 1000 × 9.8 × 20 × 50 ≈ 8.8 MW, enough for several thousand homes.

The Three Gorges Dam in China has a capacity of about 22 GW, the largest in the world. Pumped hydro stations run the idea in reverse, pumping water uphill when power is cheap and letting it fall again when it is needed.