You Asked:

Is hydropower a viable long-term green energy alternative? — Adnan, Rawalpindi, Pakistan

Marshall Brain Answers:

As long as it keeps raining, and as long as gravity keeps pulling water downhill, hydropower will be a viable way to generate electricity. This video offers a nice description of what goes on in a typical hydroelectric dam:

Here is an example of a much smaller turbine. You can see that it consists of a turbine wheel, a water jet and an alternator on top that generates the electricity:

In this case, the turbine wheel is called a Turgo turbine. It captures the kinetic enegy from the water jet and uses it to spin the alternator.

There is one problem with hydropower: dams are not necessarily green. Dams have a big effect on river ecosystems and fish. As an example, this video discusses some of the advantages of eliminating dams on the Elwha river:

More info on the Elwha river project: Washington will destroy dams to revive a river

The Elwha River project, which won state approval in March, could be a model for how to bring a river back to life, environmentalists and biologists say. Hundreds of small dams have been torn out around the country in recent years, but none as high as the 210-foot-high Glines Canyon, the taller of the two on the Elwha.

Newer technology is trying to capture the energy of flowing water without needing a dam. That would be a “greener” way to harvest the energy. Think of a wind turbine, but it uses water instead of the wind to turn the blades – that is one way to generate what is known as hydrokinetic power. If you jump to the 5 minute point in this video, there is a discussion of hydrokinetic power: How Hydrokinetic Lab’s HyPEG System Works.