Reports on renewable energy often inflate their contribution to our energy supply. An example recently appeared in The Connecticut Mirror. In “Plans for offshore wind power blow back into New England” by Jan Ellen Spiegel, 6.8 GW of offshore wind (OSW) is claimed to be equivalent to more than three Millstones. This is misleading.
One reason is 6.8 GW of installed off-shore wind power does not consistently provide 6.8 GW. Typical of just about all reports on renewable energy, the nameplate capacity is used to describe the generation capacity. While technically correct, nameplate capacities indicate the maximum output under ideal conditions. Real life is seldom ideal, and the power supplied over time is a percent of the nameplate capacity.
Capacity factors account for this and are applied to describe power output more accurately. For OSW worldwide the capacity factor is around 42%. Since winds off New England are said to be more reliable, we’ll use 50%. Applying that, OSW rated at 6.8 GW can be expected to supply an average of 3.4 GW over the course of a year. Sometimes it will crank out 6.8 GW (or close to it) — great! Other times that will shrink to near zero — not so great.
Getting back to the Millstone comparison, units 1 and 2 have a nameplate capacity of 2.1 GW and a capacity factor around 90%. A reasonable estimate for Millstone’s average output is 1.9 GW. Therefore, a 6.8 nameplate capacity OSW installation will supply on average the same amount of electricity as 1.8 Millstones, not more than 3. The 5.6 GW being bid can supply 2.8 GW on average — or 1.5 Millstones.
However, comparing power output from OSW to nuclear plants should also be qualified because of differences in reliability. Reliability is a critical aspect of the grid and provides value that is often overlooked. Sources of electricity with different levels of reliability are not the same. To be part of a reliable grid OSW requires dispatchable backup/storage and additional transmission. The requirement for these is at a much smaller scale for nuclear. Comparing the variable OSW to baseload nuclear is comparing apples to oranges.
Another misleading characterization of renewables is the often-seen claim that a renewable source will power “x” number of houses. For example, the article “State launches effort to keep Connecticut at forefront of the wind industry” (The New London Day, Jan. 31, 2024, by Lee Howard) states “Revolution Wind … will power more than 350,000 homes.” The problem with this statement is it implies 350,000 households will be powered by Revolution Wind alone. Some days Revolution Wind could power many more homes, on other days very few. The same applies to solar. In the case of Revolution Wind, over the course of a year it will produce energy equivalent to the energy needed for 350,000 homes, but it won’t supply the power all the time to do that. To reliably power those homes it needs to be paired with storage to capture excess energy and provide that when turbine output drops.
This is not an argument against renewables. Offshore wind in particular will become a significant part of electricity generation. However, as decisions are made regarding the mix of technologies to deploy, it’s important to have an accurate and objective understanding of the options. Reporters need to start getting the basic facts right. Examples such as the above can lead to expecting more from renewables than they can deliver and not appreciate the added costs and environmental impact involved in maintaining a reliable grid.
Fred Behringer lives in Old Lyme.