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Most people think of their water heater as a device designed solely for heating bath water or helping to wash a sink full of dishes. But electric water heaters can provide some of the most rapidly responding, flexible, scalable, and cost-effective energy storage available.

By adding bidirectional control to electric resistance water heaters, GIWHs enable a utility or third-party aggregator to quickly and repeatedly turn the devices off and on. Bidirectional control is a much more powerful tool than standard direct load control, which only allows devices to be turned off, because it effectively turns the water heater into a battery. Traditional batteries supply power when generation is low and absorb power when generation is high. In this way, they help modulate the supply of electricity to follow the load. GIWHs can’t supply electricity, but they provide exactly the same functionality by reversing this equation: They can modulate the load in order to follow generation. In times of overgeneration, fleets of water heaters can be switched on to absorb excess power, and in times of undergeneration, they can be switched off to shed load and redistribute the existing electricity on the grid. Thus, aggregated GIWHs can act as virtual power plants to quickly and effectively control the amount of power on the grid. Moreover, these fleets are completely scalable and can perform this functionality within seconds.