SolarCity shares popped more than 15 percent after-hours on the offer of $26.50 per share to $28.50 per share, while Tesla shares dropped as much as 10 percent, trading below $200 per share for the first time since March.
SolarCity's controlling shareholder, Elon Musk, is also the CEO of electric car company Tesla. The two sets of shareholders will vote on the merger independent of Musk after a due diligence process, the Tesla CEO said.
While Tesla has considered the deal "blindingly obvious" for a while, the timing seemed right as the companies released products that were increasingly aligned, Musk said in a conference call.
"It improves the efficiency of the setup," Musk said, focusing on lowering both cost of sales and cost of implementation."Instead of having, say, three different trips to a house to put in a car charger and solar power and a battery pack, you can actually integrate that into a single business."
The merger would allow Tesla customers, who drive electric vehicles, to harness the power of the sun in an "end-to-end clean energy product" as soon as next year, Tesla said. It builds on an existing partnership between the two companies under which SolarCity uses Tesla battery packs as part of its solar projects, according to Tesla.
The deal comes on the heels of Tesla Energy, a renewable energy storage solution that launched in March 2015.
"It's now time to complete the picture," Tesla said in a blog post. The SolarCity products would fall under the Tesla brand if the deal is approved, Musk said.
SolarCity intends to carefully evaluate the proposal, it said in an SEC filing. The company is increasingly focused toward product, Lyndon Rive, co-founder and CEO of SolarCity, said in a conference call.
"There are tremendous synergies between these two companies," Rive wrote in an email to SolarCity employees. "You should know that the board and the shareholders will be considering this, and so while I am personally excited, I will be recusing myself from the decision-making process. Ultimately, the shareholders will decide."
SolarCity shares have been under pressure, down more than 58 percent year to date. But executives said that didn't influence the terms of the deal.
Tesla shares, meanwhile, are down 8.5 percent so far this year, even as buzz grows around the new Model 3 car, which will also be unaffected by the deal, executives said on a conference call.
"I don't think this creates additional financial risk for Tesla," Musk said, saying the deal would not add significant debt to the Tesla balance sheet. Rive said that SolarCity remains on schedule to be cash flow positive on Q4. "I think it actually amplifies the opportunity for both companies," Musk added.
Musk said he's always seen Tesla as focused on sustainable energy, not an automotive company. He said he didn't know how many of Tesla's customers had solar power already or expressed interest in it.
"The world does not lack for automotive companies — the world lacks for sustainable energy companies," Musk said.