A waterfall can compress air for mines with no moving parts
In 1910, on the Montreal River near Cobalt, Ontario, engineers built a trompe. Water tumbled down a shaft dragging air bubbles into an underground chamber, where the trapped air was squeezed by the weight of the falling column. With no pistons or turbines at all, it sent 5,000 horsepower worth of compressed air to nearby mines.
Hydropower means harnessing falling or fast-flowing water, from the Greek root for water. Watermills have ground grain, sawn timber, driven trip hammers and even worked dock cranes and domestic lifts. Its roots are ancient: water wheels appear in the Near East by the 4th century BC, the idea seems to have arisen independently in China around the same era, and irrigation machinery reaches back to Sumer and Babylonia.
The physics is pleasingly simple. Available power depends on how much water flows and how far it drops. Take a turbine that is 85 percent efficient, feed it 80 cubic metres of water per second falling 145 metres, and it delivers roughly 97 megawatts. Some water wheels tap moving water without any fall, using only its motion, while overshot wheels capture both the drop and the flow. Because rivers swell and shrink with the seasons, planners may study decades of flow records before choosing a site, and dams must be built to survive the worst flood the location could plausibly see.
Generating electricity is now the main use, supplying about 15 percent of the world's power and at least half the electricity in more than 35 countries. Yet the drawbacks are serious. Dams block migrating animals, send cold, oxygen-poor water downstream and trap the sediment that rebuilds river deltas. Rotting matter in stagnant reservoir depths releases methane, estimated to equal almost a billion tonnes of carbon dioxide a year. Residents may be displaced, and sacred or cultural sites can stand in the way.
Researchers are even trying to tap rain. A French study in 2008 estimated that piezoelectric devices might wring 12 milliwatts from a single raindrop, adding up to under one watt-hour per square metre in a year. Channelling roof runoff through a small turbine does better; three students in Mexico built a system called Pluvia that charges 12-volt batteries this way.
Source: Hydropower
