Tesla formally announced its $2.6 billion acquisition of SolarCity Monday morning, but it has been discussing the deal, and dividing opinions about it, since late June.
And the skepticism over the wisdom of combining the two companies continues.
Speaking Monday on CNBC's "Closing Bell," Oppenheimer analyst Colin Rusch said Tesla and SolarCity would be better off as two separate companies.
"We are very bullish on solar," Rusch said, "but I am not convinced that this is the best use of cash for Tesla."
He added that he thinks "the cash generation off this platform, the leverage, could be 20-25 plus for Tesla," while investors would be "lucky to get high-single digits from a combined company."
Once entirely focused on high-end electric sports cars, Tesla appears to be moving toward a broader product line that would make the company a one-stop-shop for sustainable energy.
Tesla already manufactures battery packs for stationary power storage — the Powerwall is meant for homes, and the much larger PowerPack is meant for commercial or industrial clients. Tesla Chief Executive Elon Musk has maintained that formally combining the two companies will make it easier to develop a complete system that can be sold as a package to a customer.
"The idea is that there is one sales process, one installation process, one service contact, one phone app to monitor things," Musk said on a conference call on Monday.
But the company has had some difficulty ramping up production enough to meet demand for its cars, and plans to release a new model next year.
"At the end of the day, they have a tremendous amount to overcome with respect to the Model 3 launch," said Consumer Edge analyst James Albertine in the same segment. "The production line as we understand it has not broken ground yet. So to take this on, I think is going to beg a lot more questions around" regarding what the company's future capital needs will be, and where Tesla will get capital, he said.
But other analysts think that Tesla's plan could pay off in the long run.
"Over time I think it will be a smart move, I think it is taking analysts and investors quite a bit of time to digest why it is a smart move," said Baird analyst Ben Kallo in an interview with CNBC.
Kallo said he can see why the deal seems to worry some investors and analysts.
"Solar carries with it a tough reputation, to be nice," he told CNBC. "We have had a lot of bankruptcies in the space, SolarCity has not been a clean story from an execution standpoint."
He also noted that the relationship Musk already has with SolarCity have "raised question marks" for some investors and analysts. Musk is chairman of SolarCity, owns a 22 percent stake, and counts family members among top SolarCity executives.
But Kallo said he expects that "investors and analysts, as they have dug in, and done more homework, over time they have begun see how this could be additive to Tesla."
To be fair, Musk has been hinting at grouping the two companies' products for at least a decade. In 2006, Musk's "Secret Tesla Motors Master Plan," posted on Tesla's website, closed by saying the company planned to "co-market" other sustainable energy products along with its cars, specifically referring to a solar panel package from SolarCity. Installing the system, meant to be "modest" in both size and price, would allow Tesla car owners to produce more energy than they used.
Tesla expects the deal to close in the fourth quarter of 2016.