Integration of renewable energies, flexible loads and storages into the German power grid: Actual situation in German change of power system

摘要

Starting from the late 1990's,the German government decided to change the national electric power supply system dramatically.The main stimulating instrument was the German Law on Renewable Energies (Emeuerbare Energien Gesetz (EEG)),which guaranteed a fixed feed-in tariff to everyone who was willing to invest into renewable generation.Based on the year of commissioning,defined revenues per kWh were fixed for the next 20 years.Due to a very attractive over-funding,more than 1.5 million renewable generation units were connected to the German grid up to the end of 2015.According to the EEG,renewable generation units can feed to the grid wherever they are located and whenever they are able to produce.The old physical principle was and is still neglected,which clearly stated that generation always has to follow the demand-simply due to the limited availability of storages in the power system.Only in cases,when temporarily renewable overproduction exceeds the tolerable loading of lines or transformers respectively endangers the system stability in total,are German grid operators allowed to announce curtailments by emergency measures.Even in such cases,the "not produced energy" from renewable sources has to be funded.Although the installed capacity from renewables is much higher than the peak load in Germany,it contributes only about 32％ to German average annual energy.Unfortunately,the regional distribution of renewable generation and load is very different,e.g.in the northeast of Germany,this Renewable Energy (RE)-ratio meanwhile exceeds 100％ due to the high RE-penetration and low load.High transits of renewable overproduction from the north to the south will be necessary at nearly every day per year.Therefore,a tremendous change is needed within the German power grid.This paper will give a first overview followed by several others,describing possible solutions on how to overcome this critical situation.