From a grid-optimization point of view a hot water storage is almost as good as a battery. You can "charge" it whenever unreliable local energy sources (wind,

From a grid-optimization point of view a hot water storage is almost as good as a battery. You can "charge" it whenever unreliable local energy sources (wind, the solar panel on your roof) are producing in excess. This helps to consume electricity more locally, and reduces the losses and infrastructure required to transport electricity.