Sandia’s concentrating solar quarterly seminar addresses paradigms in thermal energy storage

Dr. Forsberg will discuss the Crushed Rock Ultra-large Stored Heat (CRUSH) system, which uses crushed rock for sensible heat storage with oil or nitrate salt for transfer of heat into or out of the crushed rock. The capital cost goals are $2-4/kWh of heat at scales many gigawatt hours. The low cost enables long-duration storage from hours to weeks. The crushed rock is 20 to 40 meters high with sloped sides and multiple drain pans under the rock. Rock is heated by sprinkling hot nitrate salt or oil on top of the crushed rock that then trickles by gravity through the rock to the drain pans below. Heat is recovered by sprinkling cold nitrate salt or oil on top of the crushed rock with the fluid heated as it trickles through the crushed rock to drain pans below. The system is located within a large building with insulation on inside walls. CRUSH couples with Concentrated Solar Power (CSP), nuclear or other heat sources to enable dispatchable electricity with base-load operation of the heat source. If applied to CSP, it changes CSP designs to favor larger systems.

Dr. Charles Forsberg is a principal research scientist at MIT. His research areas include Fluoride-salt-cooled High-Temperature Reactors (FHRs) with nitrate salt intermediate loop and utility-scale heat storage including Firebrick Resistance-Heated Energy Storage (conductive firebrick) and CRUSH systems. He teaches the fuel cycle and nuclear chemical engineering classes. Before joining MIT, he was a Corporate Fellow at Oak Ridge National Laboratory. He is a Fellow of the American Nuclear Society (ANS), a Fellow of the American Association for the Advancement of Science, and recipient of the 2005 Robert E. Wilson Award from the American Institute of Chemical Engineers for chemical engineering contributions to nuclear energy, including his work in waste management, hydrogen production and nuclear-renewable energy futures.

Nathan Schroeder will discuss the transition from dispatchable fossil-fuel-based energy generation to intermittent renewable sources and how it will require energy storage to match the energy supply with demand. Packed-bed thermal energy storage utilizes a bed of gravel or rocks that is heated by a stream of heat-transfer fluid (HTF) (air in this case, heated by solar thermal or electricity). When needed, the heat is recovered by flowing the HTF in reverse through the packed bed to generate process heat and/or pressurized steam or supercritical CO2 to generate electricity via a turbine-generator power block. This is an attractive solution because it is composed of inexpensive geomaterials, can store energy for days to weeks, and can be retrofitted into existing thermal generation stations such as coal power plants. The design and testing of a 100 kWh radially charged/discharged packed bed thermal energy storage system will be presented.