Toyota on Thursday unveiled a home battery energy storage system similar in concept to Tesla's Powerwall.

The automaker has started pre-orders for its O-Uchi Kyuden System in Japan, with sales expected to begin in August through home builders and general construction companies, a Toyota press release said.

The system has a storage capacity of 8.7 kwh. That's significantly less than Tesla's currently listed Powerwall capacity of 13.5 kwh. But while the Powerwall can deliver up to 5 kw of continuous power (7 kw peak), Toyota claims 5.5 kw for the O-Uchi Kyuden. And just as with Powerwall battery packs, it's likely homeowners or builders might be able to use multiple battery units.

Toyota O-Uchi Kyuden energy storage system

Toyota O-Uchi Kyuden energy storage system

Toyota also claims its system can draw power from electrified vehicles at 100 volts—the normal household AC voltage in Japan—allowing hybrids, plug-in hybrids, or battery-electric vehicles to serve as emergency backup power sources. But Toyota notes that "electrified vehicles" can only supply 1.1 kwh of energy—likely because most of Toyota's hybrids have battery packs not much larger than that.

In 2015, Tesla estimated that the demand for energy storage could be about twice the energy demand of Tesla's vehicles. That's of course changed dramatically since then—but the point being that Toyota could find a significant market here.

Toyota O-Uchi Kyuden energy storage system

Toyota O-Uchi Kyuden energy storage system

Tesla isn't the only other automaker intending to create its own energy storage. Hyundai introduced its Home ecosystem, due to span solar, charging, and energy storage—although United States details are still missing.

Ford isn't directly selling energy storage, but through hardware sold with partner Sunrun the F-150 Lightning can become a power broker in the same way as a Powerwall—provided it stays plugged-in.

Lucid and Rivian are also aiming to introduce energy storage, and it's part of a broader convergence between home solar and electric cars.