El Salvador is going all in on bitcoin. One month after the country made the cryptocurrency legal tender, President Nayib Bukele announced another first. In a tweet on Friday, he revealed that the country had mined its first bitcoin from an interesting source: clean energy from volcanoes.

It was a project that had been in the works for a while, and Bukele said that El Salvador was “still testing and installing” it. But this is a pretty big milestone for cryptocurrency mining, which uses a whole lot of energy. Bitcoin mining alone uses more power in a single year than the Philippines, so the ability to mine any of it with clean energy is a big upside for the industry.