Tesla Motors chief executive Elon Musk has won shareholder approval for a $2.6bn (£2.1bn) deal to buy solar panel company SolarCity, in which he is the largest shareholder.
The takeover will expand the electric car maker’s clean energy business.
Some investors had opposed the move, citing a conflict of interest.
But Tesla said the tie-up was “overwhelmingly” approved by 85% of shareholders not affiliated with the energy business.
Earlier this month Mr Musk made an appeal to investors, predicting that SolarCity could add $1bn of extra revenue to Tesla next year, despite it having been loss-making until now.
He said the two firms would move towards “accelerating the world’s transition to sustainable energy” by generating and storing clean energy and providing transport that uses it.
Tesla has had a tricky 2016, with its share price tumbling 20% since the start of the year.
There are concerns US president-elect Donald Trump will follow through on a pledge to strip away government subsidies for electric vehicles, which have allowed the firm to compete better on price against petrol and diesel cars.
And it also suffered a setback in May when a man was killed driving a Tesla Model S while using the Autopilot function – though a preliminary US National Transportation Safety Board report into the incident said the driver had been speeding moments before he collided with a lorry.
It is also having to ramp up vehicle production ahead of the launch of its Model 3 sedan next year, which is aimed at the mass market.
The firm faces competition from other similarly priced electric cars that will become available first, including General Motors’ Chevy Bolt and BYD’s Qin EV300.