John Palsgrave, a linguist and tutor in Henry VIII’s court, illustrated a point by writing, “He cracked afore we came hyther that he wolde do marvaylles, but nowe he is shronke asyde no man can tell whyther.” The word “cracked” was often used in the Middle Ages to mean “boast,” as in “he cracked on about his battlefield achievements.” 

That archaic meaning gave us the modern expression “not all it’s cracked up to be,” used when something or someone fails to meet high expectations. Davy Crockett once said, “Martin Van Buren is not the man he is cracked up to be.”

The expression is now being used in reference to renewable energy, but not for the reasons you might think. It isn’t that public support has waned or policymakers have weakened. On the contrary, it’s that wind and solar generation is nowhere near the capacity people were promised. Promises like, “We’ve just added 1,000 megawatts of solar capacity.” The actual generation, especially during high demand, is often a small fraction of the announced capacity.

I have studied energy policy much of my life but have never run across any analysis of why “capacity” is measured differently for wind and solar installations than for coal or gas power plants. A brilliant new assessment by my friend Alex Epstein, popular author and speaker and founder of EnergyTalkingPoints.com, explains it. His article “Solar and wind aren’t real power sources, they’re intermittent fuel-savers” is transformational. 

You see, every power generator is rated for the maximum electrical output it is designed to produce under ideal, standardized conditions. The number (in kilowatts or megawatts) is stamped on the equipment’s factory nameplate and is thus called “nameplate capacity.” But it’s apples and oranges for different types of power plants.

For solar installations, that “nameplate capacity” assumes sunny skies, a specific sun angle, standard 75-degree temperatures and clean panels. In other words, a 100-megawatt-rated solar farm can produce 100 megawatts, but only around midday on a perfect day. Output is lower during mornings, evenings, winter, and cloudy days – and zero when it’s dark. 

For wind turbines, “nameplate capacity” assumes wind blowing at an ideal wind speed of 35 mph. So, a 3-megawatt-rated turbine provides 3 megawatts when the wind is in that range. Below that, the system produces less power, and above that it shuts down for safety.

By contrast, gas and coal plants are designed to run 24 hours a day – and can do so because the fuel supply is not intermittent like the sun or wind. So, the nameplate capacity is the actual capacity most of the time. Such plants run less than 100 percent only when cheaper power is available from a different generator. They can reduce power when demand is low and ramp up when demand rises, to supply all the power the grid demands. 

That is the only “capacity” that matters, the ability to generate all the electricity needed at a given time – 24/7/365. And that has always been the primary issue with wind and solar power. The sun doesn’t always shine and the wind doesn’t always blow, so there is always a need for dependable fossil fuel plants, too. That does not make solar and wind useless. In fact, they are sometimes the source of cheaper power that allows the traditional plants to power down, as mentioned above. In that sense, they save fuel during those times, with the resulting emission reductions. 

The cost of those reductions is controversial, compared to generally cheaper fossil fuels, though many Americans concerned about climate change think the higher energy cost is worth it. That is a debate for another column another day. The point of this one is that wind and solar save fuel but can never satisfy the need for energy that is always available.

That became obvious during the January storm that blanketed a third of North America. As Epstein notes, wind provided very little electricity during much of that storm. In one six-hour midday period in the Mid-Atlantic grid, wind provided barely 2 percent of its “capacity.” Solar power was essentially unavailable during times of highest demand, morning and evening. Even in Florida, the Sunshine State, solar installations provided nothing during the peak demand for three days. In New England, solar systems that were installed with great fanfare produced almost nothing for a week. 

Wind and solar can supplement, save fuel and reduce emissions. But if the promise is to replace fossil fuels, then they are not all they’re cracked up to be. 

Greg Walcher is an author and columnist, a fellow at the Common Sense Institute, former head of the Colorado Department of Natural Resources and former president of Club 20.