Elon Musk, the billionaire head of Tesla Inc., said Bitcoin mining is “shifting towards renewable energy” and his company will likely resume accepting the cryptocurrency as payment for its electric cars.

Tesla suspended purchases using Bitcoin in May on concerns about fossil fuel use in mining, triggering a slide in the digital currency.

“The expectation is not that energy production is pure as the driven snow, but it can’t be using the world’s dirtiest coal,” Musk said at “The B Word” conference hosted by the Crypto Council for Innovation.

Hydropower, geothermal and nuclear are all good energy sources for Bitcoin mining, Musk said, adding that once he confirms mining uses 50 per cent or more renewable energy, Tesla will start accepting the cryptocurrency again.

Jack Dorsey, chief executive officer of Twitter Inc. and Square Inc., and Cathie Wood, head of Ark Investment Management, also spoke about the digital currency’s carbon footprint. Dorsey said Bitcoin is encouraging innovation in the energy sector, citing a company that converts flared natural gas into electricity to power mining rigs.

“I do believe that Bitcoin will be much more environmentally friendly” than gold mining or the existing financial sector, said Wood, adding, “In many ways it already is.”