AUSTIN, Texas — Tesla has given the Powerwall a clever new trick: turning a home's hot-water tank into a second battery. A feature called Heat Pump Optimization, now rolling out in Europe, lets the Powerwall 3 and three-phase Powerwall 3P tell a compatible heat pump to run harder when solar is plentiful or electricity is cheap, banking that surplus energy as stored heat.
How It Works
The idea is elegantly simple. The Powerwall sends a heat pump one of two signals — "normal" or "boost" — based on electricity prices and solar production. In boost mode, the heat pump heats water beyond the home's immediate needs, usually into a domestic hot-water or buffer tank, so that stored heat can carry the household through expensive grid hours.
The behavior adapts to how owners run their systems. In Self-Powered mode, boosting kicks in only when solar is left over after household loads are met. In Savings mode, it fires when solar is available or when grid power hits its cheapest point, drawing on 24-hour tariff forecasts. "Heat Pump Optimization allows your Powerwall to boost heating when there's surplus solar or energy is inexpensive," Tesla Energy wrote on X. It is the kind of software-only upgrade that has made Tesla's energy division a standout, fresh off a record Megapack quarter as its factories ramp.
The Numbers That Make It Work
The physics are compelling. A 300-liter tank heated an extra 30°C stores roughly 10.5 kWh of heat. At a heat-pump coefficient of performance of 3, banking that heat takes only about 3.5 kWh of electricity — leaving the Powerwall's full 13.5 kWh capacity free for loads that can't be stored as hot water. In effect, the system stretches a home's total storage well beyond the battery alone, using water as an inexpensive thermal reservoir.
