In a low-carbon world (nuclear, wind, solar, and hydro) there is the need for assured dispatchable electricity to replace the historical role of fossil fuels. Base-load reactors can provide variable electricity to the grid by (1) sending some of their output (steam) to storage at times of low electricity prices and (2) using stored heat to produce added peak electricity at times of high electricity prices. Heat storage (steam accumulators, sensible heat, etc.) is less expensive than electricity storage (batteries, hydro pumped storage, etc.). The added cost of incrementally larger or standalone turbine generators for peak electricity production is small. However, energy storage systems (heat or electricity) can’t provide assured capacity for extreme events, be it supply side (extended low-wind or low-solar conditions in systems with high wind or solar capacity) or demand side (long periods of cold or hot weather). With heat storage systems there is the option to provide peak electricity output when heat storage is depleted by heat addition with a water-tube boiler using natural gas, biofuels, or ultimately hydrogen. Fuel consumption for assured peaking capacity is small because most of the time the heat storage system meets peak electricity demands. The same systems enable reliable low-cost heat production for industry. Such systems enable an all nuclear or nuclear/hydro/wind/solar/geothermal low-carbon electricity grid.