At 2 pm on August 18th the combined output of renewables in Germany amounted to 41 GW, enough to provide 75% of all the domestic power needed at that time. While such high shares of renewables are a positive testament of the energy transition, they are also evidence of the upcoming challenges.
Yesterday was neither an extremely windy nor a very sunny Sunday in Germany. However, at 2 pm wind power peaked at 18.6 GW, coinciding with 13.5 GW of solar power. Adding about 4 GW of hydro power and approx. 4.9 GW from biomass, to those 32 GW of variable renewable power (VRE), the total renewable output amounted to 41 GW at that hour. At the same time domestic power demand was 53.5 GW, thus renewables did in theory meet 75% of the German demand and only 13.4 GW of additional conventional power was needed. However, in reality conventional power was only throttled back to 21.4 GW.
The chart above shows the hourly power generation from renewable and conventional power sources. In this chart conventional power plants greater than 100 MW provide the electricity that is being exported. As we can see electricity was exported all day, indicating foreign demand for cheap electricity from Germany. At the time of high renewable generation, exports soared. In line with the definition of residual load, this should be attributed to a lack of flexibility in the power supply. In other words large conventional power stations were unable to reduce their output, leading to higher exports  driven by negative wholesale power prices (-5.9 cent / kWh at 4 pm). Increasing flexibility and reducing power plant capacity that cannot reduce its output as required, is thus the big technical challenge of the coming years.
Source: Renewables International. Reproduced with permission.
