Off-Peak Chilled Water Storage: Tariff Arbitrage and Load Shifting Off-peak chilled water storage is the commercial heart of TES: charge the tank with cheap night power, discharge during expensive day peaks, and let the tariff delta pay for the steel. For a data center where cooling is a large, steady load, the arbitrage case can be stronger than the PUE story. This article focuses on the bill, not the ratio. Off-peak chilled water storage cuts data center cooling cost by