Scientists in China and the United States are working on a novel way to kill two birds with one stone: capturing carbon-dioxide pollution to use in an energy-storage system that can back up clean sources like solar and wind.
Compressed air is already employed in one of the cheapest forms of energy storage. When windmills are spinning and the sun is shining, excess energy is used to compress air that later, when the air is still and the sky dark, is blasted through turbines mixed with natural gas. But that method produces a lot of waste heat and its own carbon footprint.
Using CO2 in a different way could avoid those problems.
“Now, we have been thinking about how to use CO2 for energy storage,” Curtis M. Oldenberg, a senior scientist at Lawrence Berkeley National Laboratory, told me via email, “and came up with the idea of using it as the working fluid in a closed loop and having the gas spin a turbine without combustion.”
Working with colleagues at LBL and the North China Electric Power University in Beijing, Oldenburg proposed a system in which captured CO2 is compressed—when the wind is blowing or the sun is shining—to a supercritical fluid state and pumped into a reservoir in a deep saline aquifer. When there’s no wind or the sky is dark, the CO2 can be released to a more shallow, low-pressure reservoir. As it rushes from the high-pressure reservoir to the low-pressure reservoir, it spins a turbine, producing electricity.
Their model achieved higher energy-storage density than conventional compressed-air systems, the scientists contend in a paper they published last July in the journal Energy Conversion and Management.
Chinese scientists had already considered using CO2 to smooth the intermittency of Chinese wind farms. In 2015, scientists from Xi’an Jiaotong University published a performance analysis of a system using liquid carbon dioxide.
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