At roughly midday on Monday, April 28, the lights went out in Spain. The grid blackout, which extended into parts of Portugal and France, affected tens of millions of people—flights were grounded, cell networks went down, and businesses closed for the day.

Over a week later, officials still aren’t entirely sure what happened, but some (including the US energy secretary, Chris Wright) have suggested that renewables may have played a role, because just before the outage happened, wind and solar accounted for about 70% of electricity generation. Others, including Spanish government officials, insisted that it’s too early to assign blame.