If you think you see that one of the world’s answers to the challenges of the future is clean energy, you might be willing to dismiss a skeptical response to your latest acquisition. Elon Musk, CEO of Tesla Motors (NASDAQ:TSLA),has disdained both the analysts and the journalists from raining on his corporate acquisition parade, and his ambition.

Yesterday he set out publicly the details of an agreement to pay $2.6 billion in stock for SolarCity (NASDAQ:SCTY), the solar power company where he is Chairman.

It has been only a couple of months since he first proposed such a deal, without much of an enthusiastic response at the time from analysts on Wall Street and beyond. When it was first mooted, he said, “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 went on to connect the individual consumer with the global goals. “With your Model S, Model X, or Model 3, your solar panel system, and your Powerwall all in place, you would be able to deploy and consume energy in the most efficient and sustainable way possible, lowering your costs and minimizing your dependence on fossil fuels and the grid,” said the company release.

Yesterday’s announcement took it a step further. “Solar and storage are at their best when they're combined. As one company, Tesla (storage) and SolarCity (solar) can create fully integrated residential, commercial and grid-scale products that improve the way that energy is generated, stored and consumed,” it said.

“Now is the right time to bring our two companies together: Tesla is getting ready to scale our Powerwall and Powerpack stationary storage products and SolarCity is getting ready to offer next-generation differentiated solar solutions. By joining forces, we can operate more efficiently and fully integrate our products, while providing customers with an aesthetically beautiful and simple one-stop solar + storage experience: one installation, one service contract, one phone app,” it went on.

SolarCity says it expects to achieve cost synergies of $150 million in the first full year after closing. “We also expect to save customers money by lowering hardware costs, reducing installation costs, improving our manufacturing efficiency and reducing our customer acquisition costs. We will also be able to leverage Tesla's 190-store retail network and international presence to extend our combined reach,” said the announcement.

“Given Mr. Musk’s personal stake of around 20 percent in both companies, the offer also raised questions about whether he was using Tesla to bail out the struggling power company, whose shares had fallen by nearly two-thirds from a year ago. However, the hit that Mr. Musk’s Tesla stock suffered when he suggested the deal has more than cancelled out his potential gain from selling SolarCity,” reported the Financial Times.

There are conflicts of interest concerns from a corporate governance perspective.

But SolarCity has said that an independent committee of its board has approved the deal and would have a 45-day period to consider other offers. The deal also needs the approval of a majority of shareholders on both sides. Mr. Musk has agreed not to vote his shares, according to the FT.

But Standard & Poor’s has now warned that it could cut Tesla’s credit rating following this acquisition.

S&P put Tesla’s credit on review for a downgrade — citing “significant risks related to the sustainability of the company’s capital structure following the proposed transaction”.

Dina Medland is an independent writer, editor and commentator with a strong focus on issues around corporate governance, ethics, the workings of the boardroom and sustainable business. She is on the team of contributors to @ForbesEurope and is an ex-Financial Times staff member who has been a regular contributor in recent years. Further details about her background and a portfolio of work – including her commercially sponsored blog ‘Board Talk’ are available on her website http://www.dinamedland.com