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High-Penetration Variable Generation

Operating experience and detailed integration studies have yet to find an absolute limit to the penetration of variable generation, such as wind and solar power, that can be accommodated on the electric power system. Some countries already receive a significant amount of their electricity from solar and wind power. For example, Ireland has achieved 50% instantaneous wind penetration with no energy storage. Denmark receives about 20% of its electricity from wind power, and Germany has reached 7% wind-energy penetration. Solar penetration is also increasing dramatically. Germany has produced as much as 22 MW of solar power to serve about one-third of energy demand during peak hours.

There is no technical limit to variable generation penetration, but there might be an economic limit—a point at which it is deemed too expensive to accommodate more variable generation in relation to the value that it adds to the system.

Chart showing wind penetration as a percent of overall electricity in Ireland for four days. On May 7, wind penetration reached a maximum of approximately 33%. On May 8, it reached approximately 41%, and on May 9 it reached approximately 23%. On May 10, it reached only 7% at its maximum.

Hourly wind penetration in Ireland May 7–10, 2009

Bar chart of energy production by hour and source (solar, wind, and conventional generation) on May 25, 2012. Solar energy begins to serve demand around 5 a.m. and peaks around noon before declining again until the 9 p.m. hour. At its maximum, the solar power provides approximately one-third of all generation.

Hourly energy production in Germany on May 25, 2012

Increasing amounts of variable generation cannot necessarily be incorporated into electric power system planning and operations using current approaches. Achieving high levels of penetration will require investments in infrastructure such as transmission, changes to market rules, and incentives and requirements to encourage generation owners and transmission operators to make better use of available technology and assets.

NREL is addressing variable generation penetration issues on the transmission system through its work on:

For additional information, see the Renewable Electricity Futures Study.