Every time I get into a debate about “alternative” energy I point out it can’t be used for baseline power because it can’t provide reliable power, and it can’t provide reliable power because you can’t store the electricity that it episodically generates.
Immediately, someone will say, “We can use hydraulic storage!”
Hydraulic storage is basically a hydroelectric dam on a small or large scale, except instead of using water brought by a watershed, the water is pumped up behind the dam with pumps powered by the generator whose energy output you want to store. For example, you would have electric pumps powered by solar panels or wind turbines, the idea being that when the wind or cloud-free days produced a surplus of power (or you built in surplus capacity) the pumps would pump water from a lower reservoir uphill into a higher storage reservoir. The electricity would be stored as the potential energy in the elevated water. When you needed the power back, you would drain the water back downhill through turbines just like a hydroelectric damn.
Now, this certainly works and it has been done on a small scale. However, it will never, ever be a real-world, large-scale solution that can make alternative power work.
Why? Well, let’s just do some back-of-the-envelope calculations.
(Note: Below when I say “conservative assumption” I mean an assumption biased in favor of alternative power.)
Let’s say we want alternative power to produce just 30% of our current baseline power needs. Let’s make a very conservative estimate that we only need to have a 25% stored reserve. (This very optimistically assumes that alternative power will otherwise be able to provide sufficient power, when it’s needed, 75% of the time.) So, 25% of 30% equals 7.5 % of the total (0.30*0.25=0.075).
By happenstance, hydroelectric power today produces 8% of the nation’s electricity. This means that if we want to use hydraulic storage to make alternative power work, we will have to recreate the 93% of the generating capacity of every currently existing hydroelectric facility in this country. That’s right, Hoover Dam, the entire TVA, all the damns in the Rock Mountains, all the rest, all duplicated.
That alone raises the question: Where the hell are we going to put these dang dams anyway? All the places with the geography and the water supply to produce hydroelectric power are already in use. Worse, all the places that produce significant amounts of solar and wind power are simultaneously the worst places to build hydroelectric facilities. Solar energy is produced most abundantly in, wait for it, the desert, and wind power is produced most abundantly in very, very flat places. So any hydroelectric storage facilities will have to be a long, long way off from the point of generation.
[Update: 2010-6-19-8:43am Joseph Somsel, provides an article that says that the very best hydroelectric storage produces 75% effeciency. However, these plants are massive and have to be located in specific terrain.
The highest differential between high and low reservoirs in the U.S. is the Helms pumped storage facility. This 1,050 MW capacity installation, located in the Sierra Nevada Mountains in Northern California has a 1,630 foot elevation difference between reservoirs connected through an underground equipment hall carved out of solid granite.
We aren’t going to building a lot of those.
My figures below are for the much less efficient low-head generators, the ones that don’t require mountains to work. More importantly, it really doesn’t matter how efficient the storage is. Even if hydroelectric storage was 100% efficient we would still need to duplicate every existing hydroelectric dam in North America in addition to building all the alternative power generators. All that to avoid a building a few nuclear plants.
It gets even sillier. Hydroelectric storage is only around 25% efficient. This mean that to get 1 watt back out of the system you have to put 4 watts in. This in turn means that in order to create a 25% energy store of 30% of total power, you have to actually generate 30% of total power just to get 8% of total power back out. All that in addition to 30% of the total power that goes straight into the grid.
So, to get 30% of total power from an alternative power system you actually have to build the generating capacity to supply
60% 40% of total power! Half of the alternative power will go into immediate consumption and half will be stored.
On a good day.
In the best-case scenario.
Even if alternative power’s cost is equivalent to nuclear’s at the point of generation, once you double the needed capacity to make it reliable and then build the equivalent of every existing hydroelectric plant in the country, you’re talking about a system 3-4 times more costly per watt at the point of consumption. Even if you assume that the point-of-generation cost of alternative power is half of that of nuclear, it still ends up costing twice as much at the point of consumption.
All the proposed energy storage schemes that are utterly necessary to give alternative power a hope of working have the same type of scale problem. Yeah, they might work for one small-scale facility, but when you start to scale them up to the size and geographic distribution that you actually need for them to provide baseline power, they become ridiculous.
It doesn’t even help if you use several different technologies. Hydroelectric store is the best possible large-scale technology. The others are even more less efficient, more costly and more difficult to implement on a large scale.
Scale matters. The sad thing is, our political class doesn’t understand this so now we’re seriously trying to base our long-term energy generation on a hopeless technology.
Honestly, the stupid and expensive things that we try in order to avoid building nuclear plants never cease to amaze me.