Tesla Motors agreed in August to buy SolarCity, the US’s largest rooftop solar installer for $2.6 billion. Although not finalized as Batteries International went to press, the acquisition offers a more comprehensive business model for energy storage in the future.

Elon Musk, the chief executive of Tesla and also chairman of SolarCity, says he expects two-thirds of shareholders to approve the deal which should be finalized in the last quarter of the year.

“Essentially it’s yet another step in the evolution of Tesla. Initially it was a car company making high-end electric vehicles, it then morphed — probably predictably — into that of a lithium ion contract battery manufacturer capable of feeding the Teslas with the EV batteries at a competitive (if as yet unproven) rate,” says one commentator.

“As part of the volumes required to realise the economies of scale needed for the EV side to work, the company moved the excess volumes — these are potential volumes — into the residential side of the renewables business with its PowerWall.

“It may have been effective but it wasn’t a particularly subtle move on Tesla’s part, the market for residential storage of renewables, at least in the last year or so has been swept by competitors. Sonnen, for example, is disposing of something like 10,000 units this year.”

According to Elon Musk, the chief executive of Tesla and chairman of SolarCity — he owns roughly a fifth in each company according to S&P’s Global Market Intelligence — the deal was a “no brainer” in what it provided.

“We would be the world’s only vertically integrated energy company offering end-to-end clean energy products to our customers. This would start with the car that you drive and the energy that you use to charge it, and would extend to how everything else in your home or business is powered,” he said.

More simply, it would be one-stop shopping for renewables — you’d buy the panels for the roof and their installation, store their energy in the PowerWall, which would then look after the house’s power needs — and then plug in your Tesla, or EV, to take you to work or shopping.

Which sounds brilliantly simple. However, there are too many variants in the business model that cause complications from the price of energy. Predictably analysts have a huge range of opinions over the acquisition. Some say Tesla should focus more on making its car products successful before assuming more debt. Others talk about it being a bail-out of SolarCity.

Initial reaction to the talk of the merger was negative and Tesla stock fell 10% in the week of the announcement.

Both companies “are burning cash at a furious rate,” according to the Wall Street Journal. “SolarCity went through $2.6 billion in 2015 while Tesla spent $2.2 billion.” But that was well known already. Another analyst called the acquisition a bail out of what was effectively a sister firm to Tesla.

In one sense the debt levels are a side issue — albeit an important one. SolarCity has over $6 billion in liabilities, according to Reuters, the news agency, but these are balanced by regular and predictable income streams. SolarCity is however the largest player in the US residential market with roughly a third of all the business.

There are synergies too. A joint company might be able to achieve cost savings of over $150 million in the first full year after closing the transaction, Musk said. The merger could fix this, transforming Tesla’s roughly 200 showrooms around the world into one-stop shops for homeowners and motorists.

The biggest area of savings may come from lowering SolarCity’s cost to obtain customers by using Tesla’s strong brand recognition on top of its retail store locations.

Moreover, it’s the potential income that continue to stop Tesla’s buoyant share price from slipping too far.

Musk’s vision — and a noble one, despite the excessive hype — is dependent on a host of variables varying from the appetite of consumers wanting to move to an electric vehicle and also adopting a home residential system and the price of solar at the time.

As a brand name, and one of a small group of market leaders, the acquisition is more related to the reputation of Musk as the great innovator rather than the vulnerability his companies have in terms of sales, the arrival of new technologies, and at its simplest, its affordability.

From SolarCity’s viewpoint it can only succeed if it gets bigger. In a June interview Lyndon Rive, chief executive of SolarCity said the company wants to function at some point as a distributed power plant that, using its network of panels and batteries. To do that, it needs a lot of SolarCity panels and Tesla batteries in a lot of homes.