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Tesla Motors founder Elon Musk is "pretty optimistic" shareholders will approve a $2.6bn (£2.1bn) deal to buy solar panel company SolarCity.

The billionaire, who is chairman of both companies, said he would be surprised if the deal did not go through next month.

The takeover will expand the electric car maker's clean energy business.

But some shareholders oppose the deal, arguing it is a conflict to combine two of Mr Musk's firms.

"I'm pretty optimistic about where the vote's going," Mr Musk, who owns large stakes in both businesses, told analysts on Tuesday.

"The early votes so far have been overwhelmingly in favour... I would find it quite strange if that didn't turn out to be the case."

Mr Musk was speaking after the car maker released further details about the deal, including estimates that SolarCity could add $1bn of extra revenue to Tesla next year.

'A few naysayers'

Together, the two firms will move towards "accelerating the world's transition to sustainable energy", Tesla said, by generating and storing clean energy and providing transport that uses it.

Tesla also sought to address concerns about SolarCity's financial standing by revealing that the solar panel installer had raised about $1bn in funds in the last four months.

Mr Musk said there had been "quite a few naysayers", including big hedge funds, about Tesla's expansion into the energy business.

But he questioned how good they had been at predicting the outcome for Tesla in the past.

"If they have a batting average of zero, you should really question whether their future predictions are going to be better," he said.

Investors will vote on the deal on 17 November.