US Monthly Power Generation Capacity Factors

Subtitle:  EIA Shows Actual Capacity Factors

A part of the ongoing debate over renewable energy vs coal, nuclear, and natural gas-based energy has to do with capacity factors.   The wind, and solar detractors (one is tempted to call them ignorant, but one refrains) constantly complain that wind has a capacity factor of only 20 percent, and solar is even worse at 25 percent.   The math behind those observations is just staggering.  

Despite having actual data from reputable, objective sources that show the true state of

Source: http://www.eia.gov/todayinenergy/detail.cfm?id=14611#

affairs, the anti-renewable crowd continue to push the false figures.   The chart shows actual monthly capacity factors for several forms of electric power generation in the US over a recent few years 2011-2013.  Data is from the US Energy Information Agency, EIA.   see link    The EIA writes that capacity factor is "the ratio of a fleet's actual generation to its maximum potential generation."  Here, "fleet" is the combined set of power generation plants that have identical fuel. 

Several things are apparent from the chart.   First, in direct contradiction to the nuclear cheerleaders who constantly claim that nuclear "runs at 100 percent baseload," it is quite clear that the top line, the nuclear power capacity factors, never reaches 100 percent but oscillates between 79 percent and the mid-90s.  

Second, coal-powered plants also do not run "at 100 percent baseload" as their cheerleaders insist, but oscillate between approximately 50 to 70 percent.  Both coal and natural gas combined-cycle plants increase output in each summer due to the greater electric loads from air conditioning.  

Third, the blue line for hydroelectric averages about 40 percent with peaks in the Spring, corresponding to snowmelt and rainfall.  

Fourth, and quite importantly, the green line for wind shows maximum capacity factor of 40 percent (April of 2011 and 2013) and 39 percent three times in late 2011 and early 2012.   Wind capacity factor is at a minimum of 21 percent in the summer for each year.   As I have stated before, the wind energy capacity factors are approximately the same as for hydroelectric in many months.   What is not shown here is the actual electricity delivered in MWh.  In recent months (end of 2015), wind power produced the same MWh as did hydroelectric power.   The average capacity factor for wind in the US is 34 percent. 

Fifth and last, the bottom (gold color) line for combustion turbines is for those plants that are used for peaking power.  As expected, such turbines run most often in the hottest months of July and August.  Their capacity factors average approximately 3 to 4 percent, with peaks of 10 to 11 percent.   

None of this is surprising to those of us who are knowledgeable in matters of power grids, generation technologies, and the relative merits of renewables and legacy power plants.   This is entirely consistent with what we have known for decades.   What is surprising to me is the lack of knowledge of those who write such strong opinions, those who apparently dream up their facts without any basis in reality.  

Roger E. Sowell, Esq.
Marina del Rey, California

copyright (c) 2016 by Roger Sowell, all rights reserved