In deregulated energy markets, the price of electricity varies with time. This creates large incentives for electricity storage. CANES is been examining a nuclear-geothermal energy storage system for daily to seasonal energy storage. At times of low electricity demand, heat from light-water reactors is used to heat rock a kilometer underground to create a geothermal hot-rock zone. A geothermal power plant is used to recover this heat for production of electricity at times of high electricity demand. Rock is the only storage media cheap enough for seasonal energy storage. The technology may enable base-load nuclear plants to provide variable electricity to the grid to match electricity demand.