I am directly quoting from this very informative article:
"Renewables now provide close to 30% of Germany’s power on an average basis. And on some peak days in 2014, solar and wind supplied close to 80% of peak power demand at specific times of the day. In the future, Germany is targeting a 35% average share by 2020 and a 50% average share by 2030. Because of the feed-in tariff law (EEG), renewables have dispatch priority, meaning they are always used first, sometimes leaving very little power demand left to be supplied by coal, nuclear, and natural gas plants. So how is Germany integrating and balancing renewable energy today? What has Germany needed to do so far?
The answer is that Germany has so far managed to integrate and balance high shares of renewable energy with very modest changes to its power system. Bigger changes will be necessary in the future, certainly, including new market frameworks that are currently under active discussion. But today, Germany has managed quite well to reach close to a 30% share, for seven main reasons, which are discussed below.
The two most important reasons are: (1) the existing strength of its power grids; and (2) flexible operation of coal and nuclear plants (and to a lesser extent gas and pumped hydro). In addition, Germany has managed quite well because of: (3) better design of the balancing (ancillary) power markets, to make them more effective, faster, and open; (4) better system control software and day-ahead weather forecasting; (5) modest technical improvements to local-level distribution systems; (6) exports of power to neighboring countries; and (7) solving the “50.2 hertz” inverter problem."
For more details see http://www.martinot.info/renewables2050/how-is-germany-integrating-and-b...