Tesla has launched a Powerwall 3 heat pump optimisation feature across European markets, allowing residential battery systems to signal compatible heating units to store surplus solar electricity and cheap off-peak power as domestic hot water. The update began rolling out to European installations on 2 November 2026.
Key points
- The new firmware lets Tesla Powerwall 3 and 3P units send hardwired control signals to boost water heating when solar generation peaks or electricity tariffs drop.
- A standard 300-litre domestic water cylinder can absorb roughly 10.5 kWh of thermal energy, preserving the home battery capacity for other household loads.
- The system requires physical SG-Ready relay wiring installed by a certified technician rather than an internet-based cloud integration.
Turning domestic water cylinders into thermal storage
The feature, named Heat Pump Optimization, changes how Tesla home energy storage hardware interacts with household heating. Instead of storing all excess midday solar energy in the battery cells or exporting it to the local grid, the Powerwall monitors real-time production and grid tariff prices to run heating units harder during surplus periods.
According to Tesla’s support page for the feature, the battery system communicates directly with the heat pump by issuing one of two commands: normal operation or boost. When switched into boost mode, the heat pump raises the temperature of a domestic hot water tank or dedicated buffer cylinder beyond immediate demand.
That thermal reserve keeps the building supplied during peak evening hours, allowing the heat pump compressor to scale back when electricity tariffs rise. The automation relies on two primary battery operating profiles within the Tesla ecosystem.
In Self-Powered mode, the Powerwall triggers a boost cycle only when on-site photovoltaic generation exceeds the active electrical demand of the property. In Savings mode, the algorithm schedules a boost based on available solar production or when wholesale electricity drops to its lowest rate over a rolling 24-hour tariff forecast.
Tesla Energy described the system on social media: “Heat Pump Optimization allows your Powerwall to boost heating when there’s surplus solar or energy is inexpensive.”
The SG-Ready interface and hardware rules
Tesla has bypassed cloud application programming interfaces in favour of a physical relay circuit. The integration depends on SG-Ready, a hardware and signalling standard established in 2012 by the German Heat Pump Association, known as the Bundesverband Wärmepumpe, alongside 17 equipment manufacturers.
The German standard defines four distinct operating states using relay contacts on the heat pump control board, ranging from complete utility lockouts to forced activation. Tesla uses two of these states to issue normal and boosted heating instructions through a hardwired connection.
To run the system, customers must have a Powerwall 3 or three-phase Powerwall 3P operating on firmware version 26.26 or higher, along with version 4.59.1 or later of the mobile app. The property must also feature an SG-Ready-certified heat pump with an exposed SG-2 digital input contact.
Because the signalling relies on physical contacts, a certified installer must run a cable between the Powerwall and the heat pump terminal block before commissioning the system. Once wired, the feature functions continuously without an on-off toggle in the user application.
Operational boundaries remain tied to the underlying German specification. Each signal transmitted by the battery must persist for at least 10 minutes to meet SG-Ready compliance rules and protect the compressor from short-cycling. The heating unit’s internal safety limiters and thermostatic controls also retain priority, meaning the appliance can override boost commands if storage cylinders reach maximum design temperatures.
During an electrical outage, the Powerwall automatically suspends boost signals and returns the heating circuit to baseline operation, preserving its remaining lithium-ion reserves for critical domestic circuits.
The physics of hot water energy storage
The mechanical efficiency of water storage explains Tesla’s European focus. A standard 300-litre domestic hot water tank raised by 30 degrees Celsius stores approximately 10.5 kilowatt-hours of thermal energy.
Because modern residential heat pumps operate with a typical coefficient of performance of around 3, the machine requires only 3.5 kWh of electrical input to produce that heat. Capturing midday generation in water allows a homeowner to bank significant energy without drawing deeply on the battery.
The approach leaves the Powerwall’s 13.5 kWh usable electrical capacity available for evening electronics, lighting, cooking and vehicle charging, which cannot run on stored hot water. Thermal storage also incurs far less cyclic degradation than electrochemical battery cells.
European heating markets and competition
Tesla enters a segment where regional manufacturers and local inverter makers have operated for several years. German energy storage provider sonnen released an update in 2023 allowing its sonnenBatterie hardware to modulate NIBE heat pumps using surplus rooftop generation, while standalone solar energy managers in Central Europe have offered SG-Ready dry-contact relays for more than a decade.
The timing aligns with swift changes in how homes across the Continent heat their living spaces. Germany recorded sales of 299,000 hydronic heating heat pumps in 2025, an increase of 55 percent over the prior year, according to data from the Bundesverband Wärmepumpe. Heat pumps accounted for nearly half of all newly installed domestic heating systems across Germany during that period.
Tesla has targeted this transition with specific regional hardware. Earlier in 2026, the company introduced the Powerwall 3P, integrating a native three-phase inverter tailored to domestic grid architectures in Germany, Austria and Switzerland. Having crossed one million total Powerwall installations worldwide in 2025, the company is using local firmware features to retain customers who are pairing home electrification with rooftop solar.
Tesla has not announced plans to release the capability in North America, where split-phase electrical panels dominate and heating typically relies on ducted air systems rather than the hydronic buffer tanks common to European housing.
