Germany's climate goal is to reduce greenhouse gas emissions by 55% by 2030 and to be climate neutral by 2050 (compared with 1990 levels). In 1990, renewable energy accounted for only 3% of electricity consumption, but by the first half of 2019, this proportion has risen to 44%. By 2030, renewable energy will account for 65% of total electricity consumption. The increasing proportion of renewable energy presents new challenges to the German power system. Today, about 75% of Germany's renewable electricity comes from wind and solar photovoltaic, or fluctuating intermittent sources. Therefore, the flexibility of power system plays an important role in the increasing consumption ratio of volatile renewable energy power.