Fickle renewables are a problem, especially for network operators. “Compared to hydropower or fossil power sources such as gas and coal, wind power, for example, has a very large statistical forecast error of an average of five percent,” explains Hövelhaus. In simple words: The 100 megawatts of wind power forecast for the coming day that are traded on the Leipzig Stock Exchange can turn into 105 at any time – or just 95. The grid operators, however, need plannable power in order to keep the frequency and voltage in their grids stable. If this does not succeed, control reserve power plants have to start up, usually expensive gas. If that is not enough, the load has to be “shed”, as it is called in the jargon: some consumers get less electricity for a few hours. “That is why the network operators have to compensate for renewable electricity if it is not certain that it can meet the acute demand 100 percent,” explains Hövelhaus. However, if the renewable electricity can be fed in flexibly, it has a big effect: Because the network operators can compensate for the five percent forecast errors with the electricity from the flexible biogas, they can purchase a lot more renewables and integrate them into the electricity system. This relieves the network and saves CO.
