Wind Energy FAQs: Generation By Renewables
This chart shows how much of U.S. electricity comes from each type of renewable generator: hydro, wind, solar, wood, other biomass and geothermal. Most notable is the rapid expansion of wind energy which started in 2008 and which was followed by the equally rapid expansion of solar around 2013/2014.
By breaking out the hydro data, it is possible to see more clearly how much hydro output varies from year-to-year. The following chart shows the degree of variability and, surprisingly for some, demonstrates that – at least on an annual basis – hydro output is significantly more variable than that of wind (or solar).
The chart shows that although no new hydro capacity was added in 2011, that year saw annualized hydro output increase 23% from 261 terawatt hours (TWh) in January to 322 TWh in December before declining back to 265 TWh in January 2014. By comparison: the U.S. experienced a low wind year in 2015. That year was admittedly one in which there was a rapid build out of new wind capacity: nonetheless annualized wind output declined by only 2% from a peak of 179 TWh in January to a low of 175 TWh in June before rising by 8.3% to 190.5 TWh at the end of 2015.
The point is not that one form of generator is inherently better than the other. It is not. The point is rather that both forms are complimentary. Wind (and solar) play a useful role in balancing out the considerable annual variability in output of hydro electric power stations. Hydro also plays a key role in balancing the considerable monthly and daily variability of wind and solar.
It is also interesting to note that the seasonal output of wind and solar is inversely correlated: wind output peaks in the winter and solar in the summer. Yet another illustration of the important role multiple generators play in reducing overall system variability.