Hydroelectric Power Plants

Turning water into electricity.

Feb 18, 2021

A lot of things have happened the past few weeks: GameStop went to the moon, the US still hasn’t in 45 years, and Jeff Bezos stepped down from all of his CEO responsibilities but still has 180 billion dollars. Shame. Through all of this chaos, however, we’ve still had lights, TVs, and running water. All things that in some way need electricity.

The US consumes about 100 quadrillion Btu’s of energy each year. This number includes electricity generation, heating, and transportation (cars and things using fuel). Zooming in on just electricity, the two largest sources are Natural Gas and Coal power plants. Nuclear isn’t far behind. Then comes all of our renewable energy sources combined. They account for 17.6% of all electricity annually. [1] Now that’s pretty good when compared to some countries, but very bad when compared to others. Norway is able to meet 98% of its energy demands with renewable sources. [2] When we talk about renewables, the three largest ones currently are hydroelectric, wind, and solar. You may have heard about geothermal as well – this is when you literally drill a hole extremely deep into the earth and use the natural heat that the earth generates to heat your home. This unfortunately is only viable in certain areas with a lot of geothermal activity – and is why Iceland is able to meet almost 100% of their energy needs with renewable sources. [2]

A lot of these sources of electricity generate it the same way: use mechanical energy to spin a generator to create electricity. But how does this actually work? In comes the world of electricity and magnetism. Consider the picture below. You induce a magnetic field through a coil of wires. Induce in this case means to change it (i.e., Go from no field, to a magnetic field, back to no field). This change in magnetic field induces an electric current in the coil of wires. [3]

Now the question is, how do we use this? If we want to generate electricity through the wire, we have to continuously change the magnetic field going through it. To achieve this, we can strap some magnets onto our spinning shaft from earlier. As they spin, they continuously induce a current through the wires. We can control this spinning to get exactly the right type of electricity.

Quick aside: what would happen if you did the opposite? As in what if you flowed this type of current through a wire and had magnets waiting for it? That’s right! It would move the magnets. Put it into a similar geometry as before and you can get magnets on a shaft to spin when you expose them to the right current. There you go, we just stumbled upon how electric motors work.

So, in most cases, to generate electricity you need to spin something. Picture wind turbines: wind spins the blades and they generate electricity. The nuances and special circumstances surrounding wind power will be explored in a future newsletter. Traditional power plants use coal, natural gas, or nuclear decay to heat water into steam, then use this steam to spin a turbine, which generates power. Lastly, the reason I’ve gathered you all here today: hydroelectric.

Hydroelectric power plants are typically found in dams. As dams allow some water through, they direct it through many pipes accelerating it from the top to the bottom of the dam. Once it gains some speed, it passes through a set of blades. This flow causes rotation, similar to a very high-speed wind turbine. [4]

Just as this diagram blurr-ily says, the larger the height difference between the water source and the turbine, the more power that can be generated. Depending on the power need at any given time, the water flow can be regulated to obtain the right output. Keep in mind that the power needs of the area are not constant. In the afternoon and very late at night people use less power, and thus power plants don’t need to generate as much electricity. Hydroelectric plants have a very reliable way of controlling how they meet the demand. Compare this to, say, wind or solar energy, the two other largest renewable energy sources. They can’t control when they’re able to produce power. Either the sun is out, and the wind is blowing, or it’s not.

Hydroelectric power plants can power entire cities. The Hoover Dam’s hydroelectric plant has a capacity of over 2 Gigawatts with a peak flow of 1,000 cubic meters per second – 264,000 gallons every second. New York City has a power demand of around 16 GW, which places the Hoover Dam at being capable of meeting ~12% of NYC’s demand. [5] There are hydroelectric plants that can produce more than this, up to 6.5 GW, but unfortunately this still won’t cut it. Hydro power is more efficient than any other source of power, renewable or otherwise, but there just aren’t enough places that are viable to place a plant. As a result, we settle for a combination of multiple different sources.

In general, the path towards renewable energy lies in capacity. Renewable energy sources either lack vast placement locations or are extremely expensive to develop. When the push for electricity first occurred, cost didn’t matter—people just wanted electrons. Now we have an alternative, it’s just a blatantly harmful one. So, at this point, either cost is driven down so renewables can be competitive, or public opinion needs to shift to not care what it costs.

You’d be surprised as to how much overlap there is in hydro and aero – it’s just engineering two different types of liquids, so we’ll count it as being rocket science. Thank you for reading, I appreciate your continued support, and have a great rest of your week!

It's Not Rocket Science

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