On July 1, 2014, UCLA’s MAE Department began its DOE Sunshot Award project “Solar Thermochemical Storage with Anhydrous Ammonia.” The participants from the department are Professors Adrienne Lavine (the PI), Richard Wirz, and Pirouz Kavehpour, and Dr. Gopinath Warrier.
In Concentrating Solar Power (CSP) plants, there is a need to store energy to generate electricity at night or for cloudy periods. The current state-of-the-art is to store energy “thermally” by heating up molten salt. This technology requires large volumes of molten salt, at considerable expense. In contrast, “thermochemical” storage stores energy in chemical bonds; this allows energy to be stored in a much smaller volume and consequently has the potential for lower costs. The team will conduct research on using the ammonia dissociation and synthesis reactions for energy storage in a CSP plant. Solar energy would be used to dissociate ammonia (NH3) into nitrogen (N2) and hydrogen (H2). These gases would be stored and recombined at night to synthesize ammonia, giving off heat to power a turbine and generate electricity.
In an interview with Climate Wire, Prof. Lavine was quoted about the program:
“In general, thermochemical storage has a potential to use a smaller volume because you can store more energy in chemical bonds for a given mass than you can in just raising the temperature of a fluid,” explained Adrienne Lavine, a professor of mechanical and aerospace engineering at the University of California, Los Angeles.
“The advantages [of ammonia] are mainly that it’s a very simple reaction and very plentiful materials are involved,” Lavine said. Though the process is mature, she noted that gases are not as energy-dense as other thermochemical approaches, so her team is investigating the feasibility of storing these gases underground.
On the experimental side, Lavine is looking into how to run the ammonia storage process around 650 degrees Celsius, the target temperature for supercritical steam. “Even though it is a well-understood process, it has not [yet] been run at the high temperatures that we want to achieve,” she said.