Tesla Rolls Out Solar EV Charging for Powerwall Users

The growing adoption of Tesla’s electric vehicles and home energy systems has prompted a new solar-charging feature for users hooked on both products. The Texas-based EV giant recently rolled out “Charge on Solar,” which allows owners of Models S, 3, X, and Y with on-site solar panels/roofs to harness excess solar energy for home charging through their Powerwall system. 

 

Tesla charging. Image used courtesy of Tesla

 

Users can set a charge limit and location through the Tesla app to automatically charge their vehicles using only extra solar energy. An in-app slider enables charging as usual (via both solar and the grid) for daily driving purposes or limiting charging only when excess solar is available. 

Tesla’s website describes a typical Charge on Solar scenario where an EV is plugged in at a house with a Powerwall installed. The vehicle adjusts its charge power every 10 seconds to match the excess solar power and consumption running elsewhere in the home. It also notes that the vehicle may delay charging until at least 1.2 kilowatts of stable excess solar is free. In addition to boosting the efficiency and lifetime of the charging equipment, Tesla says this function can help account for variability in solar power and home loads. 

Scheduled charging allows users to charge the battery with excess solar power during the day when sun availability is high and from the grid at night when energy costs are lower. 

 

Charge on Solar feature in the Tesla mobile app. Image used courtesy of Tesla

 

All of Tesla’s solar systems integrate its Powerwall compact home battery, which allows users to store solar energy for backup power. Charge on Solar brings this functionality to its growing base of EV customers. The feature is only available to Tesla and Powerwall owners in the U.S. and Canada. 

 

EV Market Context

The feature gets users roped into the ecosystem as Tesla continues expanding its EV, solar, and energy storage segments. Interestingly, Tesla’s top three EV markets are some of the sunniest states in America, further reinforcing the idea of integrating its solar and EV charging businesses. 

California has the most Tesla owners by far. According to the California Energy Commission, there were over 212,000 new sales for Model 3, Y, X, and S EVs in 2022 alone, giving Tesla a leading market share of the total 292,495 battery-EV sales in the state. Cumulative Tesla sales in California through the first quarter of 2023 now stand at 692,544. (For scale, consider this: Nationwide, Tesla’s four models claimed over 484,000 new all-electric vehicle registrations in 2022, according to the U.S. Department of Energy.) 

Other states with high Tesla penetration include Florida and Texas, but specific and up-to-date sales data for these states is hard to find. According to the Dallas-Fort Worth Clean Cities Coalition, Tesla’s Model 3, Y, S, and X have 123,605 cumulative registrations in Texas. In Florida, World Population Review pegs 2021-2022 estimated Tesla sales at 62,166 out of 95,640 total EV registrations. 

As for its energy products, it’s unclear exactly how many Tesla drivers also have a solar roof or panels installed. However, the company said earlier this year that its energy storage deployments (home and utility scale) grew to a record 6.5 gigawatt-hours (GWh) in 2022. In December, it shared a milestone of 500,000 solar panel and roof installations to date, equal to 4 GW. And in a since-deleted tweet last month, Tesla Energy reported surpassing over 500,000 Powerwall installations globally. 

The new Charge on Solar feature comes as Tesla aims to become an electricity retailer, expanding the scope of its electric service business. Its “Tesla Electric” plan in Texas essentially allows customers to be their own utilities, offering real-time solar and Powerwall dispatch capabilities for homes with competitive retail electricity. The company also recently revealed plans to add VPP services in Texas and Puerto Rico, enabling Powerwall owners to earn money by selling backup power to the grid in emergencies. 

 

Powerwall Modes and Options

The Charge on Solar utility supports several Powerwall modes: “Storm Watch” prioritizes charging from any source in preparation for an outage during severe weather before allocating excess solar power for EV charging. “Backup Reserve” prioritizes charging to the set backup percentage before dispatching the excess solar. 

“Self-Powered” charges on excess solar power according to the fixed charge limit while accounting for changes in home loads and solar production until the vehicle’s charging power adjusts. Upon meeting that limit, Powerwall charges on excess solar as usual (Tesla recommends this mode to maximize the new feature.).

 

Charge on Solar settings on a Tesla vehicle’s touchscreen. Image used courtesy of Tesla

 

A “Time-Based Control” function lets Powerwall store energy when costs are low. It may also sell that energy back to the grid when costs are higher instead of using the excess solar power for EV charging. Tesla mentions this behavior can apply during virtual power plant (VPP) or utility program events. In peak periods, the vehicle will pause charging to prioritize total savings or charge the Powerwall from excess solar while charging the vehicle in off-peak hours from the grid. 

Finally, “Go Off-Grid” continues charging the vehicle on extra solar unless Powerwall prioritizes saving energy for home use during an outage.