Pumped storage hydropower won’t save the planet
Medium’s articles on climate change are bipolar.
We’ve got the apocalyptic articles telling us we’re all going to die in 12 years.
And then we’ve got the overly optimistic ones. Will Lockett writes a lot of these, here’s a recent one:
“Solve climate change with this one easy trick!”
I think the reality is somewhere in between. Climate change isn’t going to kill us all, at least not any time soon.
But it’s also going to keep getting worse, because it’s really hard to replace fossil fuels.
In a previous piece, I went over the difficulties of going green — we could probably build enough solar panels to power the country, but lithium batteries would be really expensive, about 120 trillion dollars at current prices.
The revolutionary CO₂ batteries that Lockett promotes are half as costly as lithium, so that would be a mere 60 trillion dollars!
In another piece, Lockett hypes hydro storage:
He describes a pumped storage hydropower plant in Switzerland,
This plant consists of two massive reservoirs, one at the foot of the Alps and one way up at the top, with a series of pipes, pumps and turbines connecting them. When charging, water is pumped from the lower reservoir to the higher one. To discharge, water from the top is let back into the lower reservoir via an enormous turbine, which spins and creates power.
A schematic would look something like this:
Since we previously described building a nation sized solar array or wind farm, let’s look at what it would take to make a national pumped storage facility.
It’s going to be cheaper if we build this somewhere we already have a reservoir to fill and drain.
The biggest reservoir in the US is Lake Mead, near Las Vegas.
Water from the Colorado river flows through the Grand Canyon, then fills Lake Mead:
The lake ends at Hoover Dam, a large hydropower plant that can make 2 GW of electricity, about the strength of two nuclear reactors.
Could we use that giant reservoir to store enough power for the whole country?
The energy stored in water is pretty simple. Remember potential energy, from high school physics?
Energy = mass * gravity * height
So, we just need to know how much the water weighs, how far it flows downhill, and gravity is 9.8 m/s².
Lake Mead’s volume is listed as 19.2 million acre feet.
That’s equal to 2.4*10¹³ liters of water. (I’m lazy, I just use Google to convert units for me)
A liter of water weighs 1 kilogram.
The national battery we’re trying to build stores 240 billion kWh or 8.6*10¹⁷ Joules.
The number we don’t know is height. We need to drop Lake Mead’s water down into a lower reservoir and gain some energy in the process.
Rearrange the equation:
height = Energy/(mass*gravity) = 8.6*10¹⁷ J / (9.8 m/s² * 2.4*10¹³ kg)
Solving for height, we get 3,656 meters, or 12,000 feet.
Hoover Dam is only 730 feet tall. Lake mead’s surface is only 1,229 feet above sea level. We’d need to drop the water much further than that.
It’s not going to work.
We need a bigger lake, and it needs to be at high elevation so there’s room to drop the water.
There’s one lake in the US that might work:
Lake Tahoe is 6 times larger than lake Mead, and it’s at a higher elevation. The surface is 6,300 feet high. The lake is very deep, 1,600 feet at the bottom. But that’s still 4,700 feet above sea level. We could drill a giant tunnel from the bottom of the lake, down to another reservoir in the Sierra foothills, something like that.
Running the numbers again, it looks possible. We would only have to drop the water from Lake Tahoe by 1,900 feet.
We lose a little power in conversion. But we could just move the bottom reservoir down further, make it 2,500 lower to compensate.
If we drained the entire lake through some pipes and generators, that would generate enough power for the whole country, for 3 days. That gets us through a snowstorm in Arizona where the national solar farm is covered or a cloudy week where the panels are making half as much power.
When the weather in Arizona improves, we can use the excess power to pump water uphill to refill lake Tahoe.
The pipes flowing out would be intensely large. Hoover Dam only makes 2 GW of electricity. We would need to make 3,000 GW while draining the lake, so we’d need 1,500 times as many tunnels and turbines.
I don’t know what this would do to the environment.
Tahoe has a weird drainage system. 63 small rivers flow into the lake, but only one flows out.
The Truckee river doesn’t flow to the ocean, it goes to Pyramid Lake, in Nevada, then the water evaporates — that’s a salty lake with no outflow.
Reno would have to get a new water supply, or we could just get rid of Reno. Small price to pay for solving climate change.
Pyramid Lake would gradually dry up, but that wouldn’t be terrible.
Pyramid Lake is the last remnant of prehistoric Lake Lahontan, which was much larger about 12,000 years ago, near the end of the last ice age:
Parts of North America had bigger lakes during that cooler era:
Most of them evaporated as the world warmed up.
Today, people use the dried-up lake bed of Lake Lahontan for Burning Man.
Maybe we can have an art festival once Pyramid Lake dries up.
We’d deserve a celebration because we solved global warming. Sounds like a good excuse to light things on fire.
I have no idea if we could really build that many tunnels, whether they’d survive the water pressure, or what this would cost. It’s sounding more like mad science than a real engineering project.
Also, California voters won’t tolerate a single nuclear plant operating in the state, they’re not going to vote for draining Lake Tahoe.
Could we just build small reservoirs all over the country?
Maybe. In the end we would have to build a distributed system that’s just as big as Lake Tahoe —with just as much water and just as much elevation. To get a lot of power from the water, the reservoirs need to be built somewhere in the mountains. Will Lockett’s article is about a reservoir in the Swiss Alps.
Lockett’s article says the Swiss reservoir stores 20 million kWh.
A nation sized battery for the US power grid would store 240 billion kWh.
We would need 12,000 of those reservoirs.
His article says each one costs 2 billion dollars, so the full cost would be 24 trillion dollars. That is much cheaper than lithium ion batteries.
But the cost and feasibility depends on having enough natural locations that work well for storage. If we don’t have enough of natural lakes, we’d need lots of excavation or very large dams. The cost would go up dramatically.
We have some pumped storage already, but it’s 1,000 times less than we need. We can probably build some more, but it wouldn’t be easy to build 1000 times more.
Pumped storage hydropower won’t save the planet.
