Tesla will pay approximately $2.6 billion for solar panel maker SolarCity in an all-stock deal.

While electric car maker Tesla Motors Inc. has said that the transaction would create a one-stop shop for cleaner energy, some have questioned the motives behind the deal. 

Elon Musk is the chairman and biggest shareholder of both companies. And SolarCity is run by his cousin, Lyndon Rive. Musk has insisted he's just showing good business sense.

The deal is expected to close in the fourth quarter, The Los Angeles Times reports.