The flexibility challenge

In many parts of Europe, wind and solar energy will be the backbone of the future sustainable power system. They are weather dependent and not fully predictable. When they are not available, back-up generation is necessary. As their shares in the power mix grow, a paradigm shift towards more flexibility in the power system is needed.


The chart above shows the extent of this chal lenge, using the example of two weeks in 2022 in Germany.(1)

The red line represents demand: high during the day, low at night and weekends. The colours below the red line show the generation mix. On the very bottom, biomass (green) and hydropower (light blue) play small roles in Germany. In the August week on the left, renewables cover a very high share of consumption – even 100% or more at peak production hours. In the November week, their contribution is still low.

The grey area represents the residual demand, i.e. the share of demand not covered by domestic renewable generation. It can be covered by nuclear, coal, gas, and imported electricity. Many weeks of the year have a similar profile as the August week. Therefore, during the next decades the growth of renewables will increasingly push the traditional baseload business model of inflexible power stations out of the market. Thus, coal and nuclear will suffer, while the demand for flexible back-up generation will increase dramatically.


  • The transition to renewables requires power system flexibility.
  • Within the next decade, Germany will cover 80 to 100% of its consumption with domestic renewables during many hours of the year.
  • At other times, Germany and other countries will need large amounts of back-up generation to balance their wind and solar capacities.
  • In the long term, the German Energiewende destroys the business case for inflexible baseload power plants (nuclear, coal). Back-up generation capacities will need to be flexible (hydropower, gas, biomass).

There are four sources of power system flexibility:

Flexible generation, namely power plants that can rapidly adapt their production. Flexible gas plants will benefit from the transition to renewables in the medium term. Because fossil sources damage the climate, flexible generation should come as much as possible from renewables, mainly hydropower and to a certain extent biomass. Norway and Scandinavia have the best resources in Europe.

Flexible or responsive demand is a clean and often cheap solution. There is a considerable potential to shift demand by minutes or hours, but much less can be shifted over days or weeks.

Storage capacityInterconnection and market integration provide flexibility and economic benefits. With its highly flexible hydropower, Norway is complementary with countries developing wind and solar energy, like Germany.

Storage. Thanks to its natural endowments and previous investments, Norway holds about half of Europe’s power storage capacity.


(1) The charts represent an hour-by-hour simulation. The demand curve and the weather assumptions are based on real 2011 data. The generation mix is based on the main scenario of the regulator. During the last 15 years, the growth of renewables regularly exceeded the official forecasts. All 52 weeks can be downloaded for free. Source: Agora Energiewende (2012).