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Water and Energy, Energy and Water


We use water to create usable energy and energy to create usable water.

Water and energy, energy and water – inextricably linked.

Energy needs water

In the United States, we predominately generate electricity in large power plants that burn fossil fuels (coal and natural gas) to generate heat. This heat is used to boil water to make steam and it is this steam that is used to generate electricity by turning a turbine linked to a generator. In this process we end up with a lot of excess heat, which we can’t use in the turbine (they only work with super high-quality steam, meaning we end up with a lot of steam that they can’t use without being damaged). To get rid of this heat, cooling is required.

While this process is fascinating, let’s get to the bottom line –

getting rid of heat = cooling = lots and lots of water

Getting rid of all of the excess heat generated in power generation requires water – and even though we’ve become very efficient at condensing this water to prevent excess evaporation, some of this water will be consumed. This water will be evaporated into the air and will eventually rain down to the earth again at some other location. But, it is highly unlikely that this water will rain down in the same area in which it was evaporated. As our power plants aren’t easily relocated, this shifting of water resources is quite a hefty price.

The end result – we consume a LOT of water to make electricity. What do I mean by a lot?

An average household in Austin uses 1,000 kilowatt-hours (kWh) of electricity every month. If this electricity came from a natural gas plant, this household would have also consumed 223 gallons of water during the same month. For coal, this almost doubles to 426 gallons. Nuclear – 600 gallons. Every time we turn on our computer, heat up leftovers or turn on the lights, we are evaporating water.

Ouch.

The Sweetwater coal plant that I wrote about on Tuesday will use a dry cooling system, meaning it uses air instead of water for its cooling needs. While this method of cooling saves water, it also decreases power plant efficiency meaning you have to burn more fuel (for example coal) to get the same amount of electricity. For water constrained areas, this may still be an acceptable tradeoff. However, this increase in fuel use has a corresponding increase in greenhouse gas emissions and in the final cost of the electricity generated. This plant will still need water to run its carbon capture system.

As we move into our energy future, we cannot forget the water implications of our choices. The good news is that renewable energy sources like solar and wind take little or no water to generate electricity. We can shift our energy use to preserve our precious water resources.

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