Energy and emissions analysis of ice thermal energy storage in the western US

Abstract

Energy storage systems provide a variety of benefits to the electricity sector, including taking better advantage of renewable electricity when available and smoothing demand by shifting peaks to times when electricity prices and demand are lower. When low electricity demand occurs during the nighttime, additional benefits of overnight energy storage can also occur. Lower nighttime ambient temperatures can lead to efficiency improvements throughout the grid, including power generators, transmission and distribution systems, and chillers. For ice thermal energy storage, these benefits have even been shown to enable net reductions in primary energy consumption compared to normal cooling operations. The energy and emissions impacts of ice storage depend strongly on the diurnal temperature variation and power fleet characteristics in a given region, but previous analysis only examined a single location with relatively high humidity. This study extends the previous analysis to arid regions with high diurnal temperature variation, using Phoenix, AZ and Flagstaff, AZ as case studies, and to a region with high solar penetration, using Los Angeles, CA as a case study. This study demonstrates that the larger temperature variations in Arizona lead to higher round-trip efficiencies, with average primary energy-based effective round-trip efficiencies of 127% in Flagstaff, 107% in Phoenix, and 90% in Los Angeles, with site round-trip efficiencies of 133%, 127%, and 99%, respectively. These high round-trip efficiencies result in net reductions in carbon emissions of 34% in Flagstaff and 24% in Phoenix, but an increase of 53% in Los Angeles due to the absence of solar production overnight. Additionally, the lower icemaking efficiency during warm daytime temperatures makes ice storage poorly-suited for storing excess solar generation compared to other storage approaches. However, the presence of a mature commercial market and the possibility of gaining over 100% effective round-trip efficiency create a strong case for ice thermal energy storage as an energy storage approach for reducing both primary energy consumption and carbon emissions, particularly if fleet efficiencies are higher and carbon intensities are lower overnight.