Tesla Powerwall 3 Stores Solar as Hot Water in Europe — SkimNews
Get the Energy newsletter
Daily energy & climate — solar, EVs, oil, the policy fights and tech bets shaping the transition. Free.
- Tesla launched Heat Pump Optimization in Europe only for the Powerwall 3 and three-phase Powerwall 3P, while compatible heat pumps run harder during surplus-solar or low-price periods to bank heat in hot-water or buffer tanks; Tesla has not said whether the feature will reach the US or Canada.
- Heat Pump Optimization uses wired SG-Ready control rather than cloud integration; Tesla sends 'normal' or 'boost' recommendations using two of the standard’s four operating states, and each recommendation must be held for at least 10 minutes.
- SG-Ready compatibility requires the Powerwall 3 or Powerwall 3P on firmware 26.26 or later, an SG-Ready-certified heat pump with an accessible SG-2 contact, physical wiring commissioned by a Tesla-certified installer, and Tesla app version 4.59.1 or later.
- Powerwall 3 can leave its 13.5 kWh capacity for other loads while a 300-liter hot-water tank heated an extra 30°C stores about 10.5 kWh of thermal energy, requiring around 3.5 kWh of electricity at a heat-pump COP of 3.
- BWP introduced SG-Ready in 2012 with 17 manufacturers, while sonnen launched a 2023 sonnenBatterie update that let heat pumps run on surplus solar, starting with NIBE units.
- Germany sold 299,000 heating heat pumps in 2025, up 55% year over year, and they accounted for nearly half of all new heating systems sold in the country for the first time.
- Heat Pump Optimization has no on/off toggle in the Tesla app once wired; a heat pump’s thermostat can override its recommendations, and the feature returns to normal during an outage so the Powerwall prioritizes backup loads.
Why it matters: European Powerwall owners can use hot-water tanks as low-cost thermal storage: a 300-liter tank stores about 10.5 kWh of heat for roughly 3.5 kWh of electricity, preserving the Powerwall’s 13.5 kWh for other loads. Tesla gains a software-based way to improve its installed base’s value, but the feature remains dependent on SG-Ready-compatible heat pumps and certified installers.
Ask SkimNews
