Energy Storage Investigation at Groundwater Banks
Two different technologies were assessed. Aquifer Pumped Hydro (APH) involved using the aquifer as the lower storage reservoir and a surface storage reservoir as the upper reservoir and retrofitting thegroundwater wells with reversible pump generators. Pumped Storage (PS) involved using a surface storage reservoir as the lower reservoir, an upper elevation reservoir as the upper reservoir, and pumps and hydroelectric generator to connect the two. The Willow Springs Water Bank (WSWB) in Southern California was the facility chosen for the investigation.
Due to the California hydrologic cycle, three different operating modes were assessed. During Wet Years the WSWB is recharging the aquifer and the projects were evaluated as a hydroelectric generators. During Idle Years the WSWB is neither recharging nor withdrawing water and projects were evaluated as pumped storage. During Dry Years the WSWB is withdrawing water continuously and the projects were evaluated as demand response (curtailing pumping load in response to electrical system needs).
The results of the analysis are that, for both technologies, the ability to curtail/adjust pumping and participate in demand response was the most valuable resource, more valuable than the ability to generate electricity. This can be accomplished by adding a surface storage reservoir to balance out water delivery needs when the pumps are curtailed without adding a generation component.
The Aquifer Pumped Hydro was not cost effective, due to technology costs and aquifer transmissivity making the round-trip efficiency dismal.
For Pumped Storage the ability to participate in fast ramping and demand response was significantly more valuable than operating as a bulk energy supplier but this option option needed the Dry Year demand response to be cost effective.
