Thermal storage refers to a large tank that holds hot water or chilled water and functions as a thermal battery. This technology allows a district cooling system to chill water at night, using off-peak electricity, and then store the water for distribution to customers during the day.
At District Energy St. Paul, most of the chilled water provided is produced at night using off-peak electricity and stored in two larger thermal storage tanks, located at the Kellogg and 10th Street plants (respectively – 2.5 million and 4.2 million gallons of capacity). Chilled water stored in these tanks is dispatched to customers as needed, particularly to meet higher demand, such as high humidity and high temperature conditions.
Thermal storage provides a critical solution to district heating, district cooling, and electric grid systems. Tanks of varying scale are used within integrated systems to shave peaks, increase system stability, and allow greater flexibility in energy production from alternative fuels. District cooling systems integrate the use of thermal storage to enable the system to shift a significant portion of the cooling load to off-peak hours. District heating systems can utilize thermal storage to reduce the temperature of the loop and incorporate waste heat, solar, and other alternatives. Thermal storage capacity benefits customers and electric utilities on high peak-loading days and is an ideal solution for data centers that demand reliable cooling.