Nathan Bomey

USA TODAY

Tesla Motors said Monday that it had reached a deal to acquire SolarCity, putting the companies one step closer to a marriage that has drawn scrutiny from Wall Street but which Tesla CEO and SolarCity Chairman Elon Musk has vigorously defended.

Tesla (TSLA) said the stock acquisition is worth $2.6 billion, including the assumption of debt, valuing SolarCity shares at $25.37, or 5% lower than Friday's close.

SolarCity (SCTY) will get 45 days to seek an alternative suitor in a provision known as a "go-shop" period.

Musk calls Tesla's SolarCity deal 'no-brainer'; investors disagree

Musk argued that the deal would accelerate Tesla's transition from electric-vehicle automaker into a renewable-energy products company. With solar-panel installer SolarCity on board, Tesla could pair solar panels with its new energy storage products.

"This is really all part of solving the sustainable energy problem," Musk said on a conference call.

For an executive who has long viewed Tesla's trajectory through an ambitious lens aimed at combating climate change by ushering in a renewable energy world, the SolarCity deal is a key part of the puzzle.

"This is an action now which is anticipating several moves ahead," Musk said.

Musk has thrown the full force of his persuasive personality behind the acquisition. But Tesla said the independent board members of both companies voted to authorize the deal, meaning Musk did not cast a ballot.

A majority of each company's independent shareholders must also vote to approve the acquisition, which Tesla expects to close in the fourth quarter.

Theodore O'Neill, senior analyst for Ascendiant Capital Markets, who tracks Tesla, said the company presented "a lot more rational arguments for the transaction than I expected" on the conference call.

"I'm not sure there's a need there to do this right away, but that being said, I do understand the big vision," O'Neill said.

Musk said Monday that if SolarCity finds another buyer at a higher price, "I guess the independent board members would be compelled to accept that."

Tesla shares fell 2% to close at $231.01, while SolarCity shares slumped 7.4% to close at $24.72.

Musk distanced himself from the price of the deal, which has put him in the spotlight because of his close involvement in both companies. "I was fully recused from the matter, so I know about as much as you do about how this price was obtained," he told an analyst on the call.

O'Neill said it made sense for Musk to promote the accord.

"If anyone's gonna get out there and talk about the strategic vision, it has to be him," O'Neill said. "I think the disconnect for investors was he never articulated his vision until after he shook hands with SolarCity."

Tesla said it expects to shed $150 million in costs in the first full year following the deal's completion. Chief Financial Officer Jason Wheeler said the "efficiencies" would include opportunities to use Tesla's stores and website to sell and market SolarCity services, lower the price of shared parts and reduce the costs of installation and services.

Musk said $150 million is "conservative" and based on his "gut feel."

"I think we’ll significantly exceed that in the first year," he said.

It won't be enough to erase SolarCity's red ink. With SolarCity posting an operating loss of $768.8 million in 2015, Tesla is putting shareholders' appetite for losses to the test.

Tesla itself is not profitable and yet recently raised another $1.5 billion in a public offering to fund its investments, including a massive battery factory that Musk now says will someday employ 10,000 employees, up from a previously projected 5,000.

S&P Global Market Intelligence analyst Efraim Levy said in a research note that the SolarCity deal is still likely to win shareholder approval though it's still a questionable deal.

"We see benefits from a combined solar/storage offering and manufacturing efficiencies, but remain concerned about cash flow and capital needs,” Levy said.

SolarCity CEO Lyndon Rive told investors that the company needs Tesla's manufacturing expertise and retail strength to lower its costs and accelerate its growth.

"We’ll be able to provide energy at a lower cost than traditional forms of energy," he said.

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.