A common lament of those analysts wishing to get to grips with the real-world performance of solar thermal power plants has been, well… an absence of data. Trainer noted, in ‘Solar Thermal Questions‘:
It would be great to get some actual data on their year round performance. I have found it fiendishly difficult to get such data out of anyone; they seem not to want to make it public, and this makes evaluation of claims very difficult.
During the Equinox Energy 2030 summit, Jay Apt noted some issues with utility-scale PV farm performance, as illustrated in the figure below (from this paper):
Note that this is from a solar PV farm in the Arizona desert — one of the best locations in the US for this type of facility. The associated commentary said:
Observed rapid and deep fluctuations at time scales of 10 seconds to several minutes may indicate that a component of the intermittency is due to low, scattered clouds with significant opacity. We observe a number of examples of output power rising above nameplate capacity before and after deep drops in power. This may be due to focusing of sunlight around the edges of low clouds. If PV becomes economically attractive enough to be deployed at large scale, intermittency is likely to be matched with dispatchable power, storage, and / or demand response
The implied ramp rates to compensate for these types of fluctuations will be challenging. Indeed, some form of large-scale battery energy storage seems vital to maintain quality of the electricity output.
That is PV. Now, at last, I have some data on solar thermal performance. It comes from the final report of the Colorado Integrated Solar Project, which you can download here (25-page PDF).
First though, some details on the facility:
The world’s first hybrid solar/coal power plant has been built near Palisade in Colorado. Xcel Energy and Abengoa Solar are partnering on the demonstration project which uses solar parabolic trough technology to supplement the use of coal. Initially, it’s expected to reduce the emissions generated by the Cameo Station’s Unit 2 plant by three to five percent, but it’s thought that this could increase to up to ten percent.
The system focuses solar energy on mineral oil, which is then passed through a heat exchanger where it’s used to preheat the water used by the coal-powered part of the 49MW plant.
You can also go to its National Renewable Energy Laboratory page for further technical specifications on the plant. In short, the expected generation was 49 MWh per year for the 6 acre parabolic trough facility, with a 2 MW turbine capacity. The NREL page says: