Why CSP Should Not Try to be Coal
Joe Romm, at the influential Climate Progress blog, has hit on a formula for countering the coal industry's claims that we need baseload power sources. Since Concentrating Solar Power (CSP) in conjunction with thermal storage can be used to generate 24/7 or baseload power Joe has renamed it "Solar Baseload." This is win-the-battle-lose-the-war thinking. While it does neatly counter the argument we need coal or nuclear, since there are renewable power sources which can produce baseload, such as CSP, Geothermal, and Biomass. I fell into this coal-industry trap myself in a 2007 article about Geothermal, as did AltEnergyStocks Editor Charles Morand in an article on CSP.
Dispatchable Solar, not Solar Baseload.
Continuous power from solar energy was first demonstrated at the Department of Energy's (DOE) Solar Two project in the late 1990s. I recently interviewed Bill Gould, CTO of CSP company Solar Reserve. Solar Reserve is now working to commercialize the molten salt thermal storage and solar receiver technology demonstrated at Solar Two, where Bill Gould served as project manager.
According to Gould, DOE's intent at the Solar Two project was to demonstrate dispatchable power, not baseload power. Dispatchable power is power that can be called on when needed, in contrast to baseload power, which is essentially always on. As a demonstration, Gould's team throttled back the output from Solar Two to 10% of capacity, and this allowed the plant to produce power continuously for a couple weeks until it was interrupted by several consecutive days of cloudiness. But, in essence, it was a stunt: baseload power is far less valuable than dispatchable power.
The coal industry says that we need baseload power because our refrigerators still come on in the middle of the night. This is like saying we should have the water running constantly in the kitchen sink because we may get thirsty at any time and want a drink. Put in these terms, the assertion that we need baseload power is clearly nuts: what we need is controllable power that's there when we need it, but is not wasted when the lights are off and the fridge is not running.
The Problem With Baseload
Last spring, I discussed one of the problems with baseload power. The more baseload power you have, the harder it is to use variable generation such as photovolatic (PV) solar and wind power. Or, from the baseload generator's perspective, the more variable generation on the grid, the less baseload power can be added. This fact has not been lost on the UK's nuclear industry, which is fighting to get wind targets lowered.
To illustrate the incompatibility of baseload and variable energy sources, I downloaded 4 days of real demand data (January 1-4, 2008) from ERCOT's website. I then simulated production curves for two variable sources, one designed to mimic solar PV (only on during the day, with some variability due to clouds) and a more random type of generation to simulate wind. I then fixed the amount of baseload power at 25,000 MW (68% of demand) and 5,000 MW (14% of demand) in each of two scenarios, and saw how much wind and PV the remaining demand could accommodate with the constraint that total generation could not exceed demand.
As you can see, when I dropped baseload power from 68% to 14% of demand, I was able to increase the power of variable sources from 10% to 36% of demand. Almost half of the drop in baseload power was filled by variable power sources, with the balance requiring an increase in dispatchable generation. If you'd like to try your own scenarios, you can download my Excel spreadsheet here.
Better than Baseload
It should be clear that dispatchable generation is a truly premium power source. Dispatchable generation, like energy storage, long distance transmission, and demand response, all allow the grid to accommodate more variation in both power supplies and in demand. In a carbon-constrained world, where we want to use as much variable generation such as wind and PV as possible, zero carbon, dispatchable power from CSP can do far more to help us decarbonize the grid than CSP baseload.
Baseload power is part of the problem; it's not the solution. We should not denigrate CSP by pretending it is only a substitute for coal or nuclear.
Concentrating Solar Power is much better than baseload.
Tom Konrad, Ph.D.