Filed under: Utilities
By Seth Masia
On March 14, NPR’s Science Friday did an hour on concentrating solar power, with Mark Mehos (NREL), Fred Morse (Abengoa) and David Mills (Ausra). A listener called in with a question: What’s the effect of excess heat bounced back from the mirrors into the atmosphere?
The answer is that there’s none. The solar array creates no new heat — it simply intercepts some of the sun’s heat and converts it to other forms.
Waste heat is in fact a legitimate issue for most forms of electrical power. The typical coal, gas or nuclear-powered electric generating station is only about 35% efficient, which means that most of the energy produced goes out not as electricity but as hot water dumped into a river, lake or ocean, or as hot water vapor pumped into the air. Worldwide, this year, it appears that electrical plants will dump the heat equivalent of 2.4 trillion watts into the air and groundwater every year, over and above any heat retained through greenhouse gas emissions.
I talked to Chuck Kutscher of NREL about thermal pollution from power plants. He calculates that powerplant thermal pollution amounts to about 4% of the heating effect due to greenhouse gases.
“That’s just my back-of-the-envelope calculation and, to be honest, it’s a bit larger term than I expected,” Kutscher said. “That is, it’s not completely negligible.”
Concentrating solar power (CSP) does require large flows of of cooling air or water to condense the steam exiting the turbine, and that can constitute a local water-use issue. The discharged heat is not, however, waste heat, in the sense that it’s converted solar radiation that would have entered the biosphere anyway.
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