According to Interesting Engineering, on May 16th, from 10 AM to 7 PM, mainland Spain was powered exclusively by solar, wind and hydro power, without having to cut on any services or commodities.
This was possible thanks to two important factors, one being the fact that more solar and wind capacity have been added recently to the country's total share. The other aspect was that on that day, the wind blew strong enough and the sun shined with power, which means that both sources operated at pretty much peak power.
Nuclear, gas and coal power plants were still operational during that time, though, but it was noted that this was done only to allow for energy exports to take place.
While hydro power plants played a role in Spain's renewable-only achievement, the country may not be able to rely on that resource for too long, as it is the European country that's at the highest risk of desertification by mid-century.
To avoid lack of water in the future, Spain authorities recently announced a 2 billion euros plan to create the important necessary infrastructure in order to mitigate the effects of droughts. This includes building multiple desalinization plants, which should be able to provide clean water to the country's citizens and various industries.