You won't be able to buy cars from Tesla with Bitcoin again until miners adopt clean energy mining methods.

Tesla CEO Elon Musk said Sunday the automaker would resume accepting Bitcoin for vehicle purchases when it's confirmed that miners have adopted clean energy methods to mine the cryptocurrency.

"Tesla only sold ~10% of holdings to confirm BTC could be liquidated easily without moving market," Musk said in the tweet. "When there's confirmation of reasonable (~50%) clean energy usage by miners with positive future trend, Tesla will resume allowing Bitcoin transactions."

Tesla officially started accepting bitcoins back in March but said in May it would no longer take bitcoins for vehicle purchases and suspended its policy of trading the bitcoins it already has until the currency transitions to a more efficient, sustainable energy source.

Climate scientists have concerns about the electricity use required to mine bitcoin. Mining the currency requires high levels of computing power, which solve mathematical puzzles to earn new coins. In 2018, researchers suggested an increase in the cryptocurrency's popularity could create a demand for electricity that would generate excessive carbon emissions.