Generation costs for solar photovoltaics and wind energy have decreased at an impressive pace in recent years. Due to falling costs, wind power and solar photovoltaics are the fastest-growing sources of electricity globally, and they are expected to make up a considerable share of the electricity mix in the near future.
Wind energy and solar energy are weather dependent. As the share of variable renewable energy sources (vRES) increases, fundamental changes to grid operation become necessary. Many researchers and policymakers are therefore looking at countries in which variable renewables already make up a considerable share of the electricity supply. Integrating high shares of vRES can be a challenge for system operators. Yet countries with high shares of vRES appear to fare quite well, and the reliability of electricity supply continues to be very high. For example, key indicators such as the System Average Interruption Duration Index (SAIDI) and the loss of load expectation (LOLE) show that the power system in Germany is among the most stable in the world, despite its rising share of vRES and decreasing level of baseload production: High grid reliability and the integration of increasing shares of renewables need not be incompatible.
This paper provides an overview of some of the lessons learned from integrating vRES into the grid of countries that, like Germany and Denmark, have high shares of variable power. Current practices in the context of their regulatory framework will be presented, as well as changes that have been adopted in order to cope with challenges that grid operators have faced along the way. Section 1 describes future trends and challenges for grids in power systems with rising levels of vRES generation. Section 2 focuses on the building of new power lines and transformer stations. Section 3 focuses on system operation and ancillary services.