What hydroelectricity is:

Hydroelectricity is electricity that is produced by moving water.

How hydroelectricity is made:

If you’ve been following along on this series, you’re probably familiar with the goal: turning a magnet inside a coil of wire. To produce hydroelectricity, the moving water spins the turbine (and thus the magnet) directly. No need to heat and pump water around because it’s already moving.

The moving water can come in a variety of forms. The most conventional form is a dam. The weight of the water in the reservoir is the source of energy. At the bottom of the reservoir there is a drainpipe. The gravity pulls the water from the reservoir through the drainpipe, and spins the turbines as it flows past.

Another possible source of hydroelectricity is a river. The turbine is submerged in the river, spinning as the water flows past (think a modern day water mill). These “run-of-the-river” generators are small scale and the electricity must be used as it is produced. But no damming is needed, so the environmental impacts are much lower.

How much of our current electricity is hydroelectricity:

Hydroelectricity is currently the largest source of renewable energy. World wide, hydroelectricity accounts for 16% of electricity production. However, in the U.S. only 7% of our electricity is hydroelectricity.

Potential energy supply: 

According to the US Department of Energy, building generators on currently non-powered dams in the U.S. could meet 16% of the US electricity demands. This would more than double our current supply.

Materials and how we get them:

Moving water! As explained above, this can either be naturally occurring – such a a river or waterfall for small scale production, or through man-made dams. In the case of the dam, massive amounts of concrete are needed, but the power plants actually require less materials than coal power. Remember, hydroelectricity doesn’t need pumps, furnaces, or fuel.

Waste produced and how we deal with it:

Once the dam and plant are built, hydroelectricity produces essentially no waste. However, constructing dams uses tons of cement, a huge source of CO2 emissions.


The cost of electricity from a large scale hydroelectric plant is about $0.03-0.05/Kwh


Hydroelectricity sounds pretty great so far! Simple to produce, and pretty low impact.  Sure there is the issue of making all of that cement, but dams last for 50-100 years easily without requiring much maintenance. The CO2 emissions from building a dam are actually the least of any of the renewable energy sources.

However, damming rivers can cause great distress to the environment and to the ecosystems and communities that rely on the river. The reservoir that is produced by damming floods and submerges the land around it, destroying habitats. Dams disrupt the natural aquatic ecosystems in the river, too (e.g. blocking salmon and other migratory animals). The change in current also has dramatic effects downstream, for example not being strong enough for irrigation or to flush out salt water in deltas.

The far less impacting run-of-the-river production is not scaleable. It’s great for local needs where it’s available, but can’t meet greater demands.


For an introduction on sources of electricity, look here.

For an explanation of how we make electricity, look here.

Clean Coal

Nuclear Energy


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