Feeding heat from the sun into coal-fired power stations could turn out to be the cheapest way to simultaneously expand the use of solar energy and trim coal plants' oversize carbon footprints.
At least that's what the Electric Power Research Institute (EPRI), a nonprofit organization backed by the electricity industry, is hoping. Last week, the institute launched a nine-month, $640,000 study to pin down the scale of the opportunity and the engineering challenges involved with making these seemingly disparate technologies work together. The study will examine the potential use of solar-thermal technology at a pair of coal-fired power stations, in New Mexico and North Carolina.
Retrofitting existing power plants is a low-cost option for solar-thermal projects because the steam turbines that are needed come for free. But the overall efficiency of retrofitted hybrid solar-gas plants is still limited. That's because a gas steam turbine that has been modified to accommodate waste heat plus solar heat will suffer an efficiency penalty from running at partial load whenever the sun goes down. This is part of the reason why none of the solar-gas hybrid plants under construction rely on solar for more than 15 percent of their power.
In contrast, coal-fired power plants do not suffer from this efficiency cap because they already produce electricity primarily using a steam turbine. As the sun waxes and wanes, the coal feed to the boilers can be adjusted to keep heat production steady and the steam turbine running at full tilt.
Large coal plants could easily absorb 200 to 400 megawatts of solar-thermal power, rivaling the largest stand-alone solar-thermal power projects under construction and dwarfing photovoltaic installations by an order of magnitude. And thanks to coal's carbon intensity, the emissions benefit will be higher.
EPRI says that reducing carbon output is the motivation behind the nine-month feasibility study. The idea is to define a low-cost option for EPRI's industrial members to meet renewable portfolio standards implemented by many states, and to prepare for federal carbon regulations expected to put a price on every ton of CO2 that their plants release.
Dr. Gopal Rao
Web Science Editor
Editor, Meeting Scene
Materials Research Society (MRS)