Rather than directly converting photons into electricity, concentrated solar energy uses mirrors to turn sunlight into heat, which can then be used to drive traditional generating turbines. Up to about a decade ago, there was a case to be made that concentrated solar energy had a bright future, as improvements in heat storage had turned it into a way to generate power around the clock.
It wasn’t to be. While concentrated solar costs fell enough to compete with nuclear power, the price of photovoltaics plunged, making solar panels the cheapest source of power in most locations. Currently, if you have a good site to generate solar power, then the economics of PV panels are hard to beat.
That has left us needing to build a mixture of other facilities—typically batteries and natural gas facilities—to handle overnight needs or weather-driven shortfalls. But a small company is promising that it can help avoid the need to build a separate facility. Its version of concentrated solar is designed so that a fossil-fueled backup system shares most of the generating hardware with the solar side.
Back to the future?
Concentrated solar, also called solar thermal, is pretty simple in principle. Most of the site is covered with heliostats, devices that incorporate mirrors and a motorized tracking system that can keep their focus on a single point as the Sun moves across the sky. The point of focus is in a tower, where sunlight heats a working fluid. The hot fluid can then be used to power a traditional steam turbine, or its heat can be stored and used to generate power overnight.
There are many potential variations, however: different working fluids and methods of heat storage, trough-shaped mirrors that eliminate the need for a tower, and so on. All of those variants are meant to reduce some of the issues inherent to solar thermal: lots of moving parts, potentially corrosive fluids, and so on. Those issues and the lack of standardization have helped ensure that the costs of these plants haven’t come close to keeping pace with photovoltaics.
