Tesla Inc.’s solar panels and roof will only be sold together with its Powerwall battery, according to Chief Executive Officer Elon Musk, as the company seeks to convince investors and users of its viability in the residential energy technology sector.

Solar power from these panels will feed exclusively to Powerwall, he said in a series of tweets. The Powerwall will only interface between utility meter and house main breaker panel for simple installation and backups during utility dropouts, Musk said.

His comments follow a Twitter interaction with Ark Investment Management’s director of research, Brett Winton, who said his solar installed by Tesla since January “hasn’t generated a single watt-hour" and that he was waiting for his utility to approve the connection.

Winton said his Tesla-installed solar system could have powered Bitcoin mining and generated $1,500 over the three months it laid idle.

Musk tweeted at Winton to ask if he had a Powerwall to accompany his solar installation, saying utility permission is not required to use electricity stored in its battery.

Cathie Wood’s Ark Investment has been one of Tesla’s most ardent supporters, holding significant stakes in the company through its flagship fund and setting big price targets. Last month, Ark Investment predicted Tesla stock would hit $3,000 by 2025, although this week it has been selling some shares.

While Tesla is known for its battery-powered electric vehicles, it has been spending years expanding into energy technology for homes. Back in March 2015, Musk unveiled the Powerwall. A year later Tesla acquired SolarCity, the solar-panel installer founded by Musk and his cousins.

Musk then hawked a solar roof that has gone through several iterations without becoming a strong contender in the market.