Most of Germany's coal-fired power stations were not in operation that day, the energy lobby group said (link in German), and those that were online were only operational for one hour and produced less than 8 gigawatts (GW) of energy, well below their maximum output of about 50GW. Nuclear energy sources were also reduced over the weekend of the 30th, Agora Energiewende said.
Renewable energy sources, on the other hand, produced a maximum of 55.2 GW at noon on Sunday and a low of 16Gw at midnight on the same day, with an average of 35.7GW, or 64% of the electricity consumer in Germany that day. At its peak, between 4pm and 5pm, renewable power was providing 85% of the country's electricity, Agora Energiewende said.
The peak in renewable use did, however, bring negative prices for several hours at the electricity exchange.
"This is a sign that there are still too many power stations in the market," said Patrick Graichen, director of Agora Energiewende.
With the growth in renewal energy sources, increasingly independent of government subsidies, this weekend's situation will happen more frequently and should be "normal by 2030", the body said.
Dusseldorf-based energy expert Thorsten Volz of Pinsent Masons, the law firm behind Out-Law.com said: "The power use on 30 April was a good example of how renewable sources influence the German electricity market and that Germany has made a significant step forward in reducing carbon emissions and transferring its power production from conventional sources to renewables."
"However, it also shows how the fact that renewable sources are still being supported by a higher revenue scheme influences the market and its price building mechanism. The challenge will be to avoid or significantly reduce days with negative electricity prices in the future and at the same time to secure supply on days with significant less renewable production, such as on cloudy or windless days in autumn or spring. On those days we still depend on conventional sources to secure our supply, and we will do as long as we are not able to store significant amounts of electricity," he said.
"The aim has to be to find the right balance between extending renewables and keeping conventional sources for securing our supply until we have efficient storage facilities," Volz said.
The UK's National Grid said on 21 April that "For the past 24 hours National Grid has supplied Great Britain's electricity without the need for coal generation as part of the energy mix" in what it said was "the first working day in Britain without coal power since the industrial revolution".