At the end of July, S&P Global ran a curious article, “Xcel Energy temporarily stops load following at Prairie Island after NRC inspection.” Xcel Energy stopped load-following operations at the Prairie Island nuclear plant in Minnesota after the NRC determined that plant procedures should have had further analysis of such operations due to possible long-term effects on safety.
This was not a big deal. Xcel had changed the positions of the control rods something like thirty times between September, 2019 and June, 2020 to follow grid demand. The problem the NRC had was that safety analysis should have been done as the plant was used in an unusual way. The NRC said the plant failed to follow allowed procedures, but it was of “very low safety significance.”
All told, there was not much thrill in the article. Nearly all of the conventional media seem to have ignored the matter altogether, but it struck me that broader implications are being overlooked.
By its nature, a nuclear power plant is built to supply baseload power. Baseload power is the quantity of power needed to cover the minimum demand that can be expected to appear over a period of time. For the purpose of designing a power plant, the period would be a year.
The reason for this is that if you are certain grid demand will not fall below a certain level, you can design a plant without any concessions to flexibility. That plant is designed to run at 100% of its nameplate capacity, as close to 100% of the time as possible. By giving up flexibility, efficiencies can be built into the plant that would otherwise not be there. For example, such a plant can have a huge, highly efficient boiler that takes days to get up to full pressure. In the days these plants were designed, they delivered electricity at what was considered a very low price. They typically use coal, natural gas, or nuclear power.
Because of the nature of baseload power plants, only supplying enough to cover the base load, other plants have to be put online to cover any demand above the base load. These include load-following plants, which are more costly to run. In the old days, many of these ran on oil. Nowadays, the fuel of choice is natural gas, though the design of the plant is a different from that of a gas-fired baseload plant.
In addition to baseload and load-following plants, there are peaker plants, which often deliver electricity at wholesale prices exceeding what utilities can charge for retail power; they only run when absolutely needed.
The thing that set me to thinking on the S&P Global article was that a baseload power plant, in fact a nuclear plant, was being used for a purpose that it was not designed for at all. And in fact, the article indicates that Xcel is using other nuclear plants to follow loads also.
What we are seeing here, I believe, is a change in the nature of the base load. When wind power was first put on the grid, the turbines could not just turn through nights, because grid operators will not allow power on the grid unless there is demand to cover it. Their energy was more expensive than what a coal-burning or nuclear plant could provide, so if the supply exceeded the demand, wind power was curtailed.
Today, however, wind turbines can supply energy at lower prices than baseload power, even taking subsidies into account. If the grid operators are to buy the least expensive energy, they will buy from wind farms rather than baseload power plants. And the baseload demand that baseload power plants can meet is disappearing.
Another thing to note about wind power is that the old saw, “the wind doesn’t always blow,” is just wrong. While it is true that the wind might not be sufficient to spin a specific turbine at a specific time, over the expanse of the greater grid, the wind is always blowing – always.
When sufficient wind power is available, the most economical solution today may be to curtail the baseload plants, because their energy is more expensive. One little problem with this is that some of these plants ramp up and down excruciatingly slowly.
Reading between the lines of the S&P Global, what I saw was that the Prairie Island nuclear plant is running in a way different from what was intended. I see no reason to do this except that its owners are not willing to let go of an asset they consider valuable – the nuclear plant is “worth a lot of money,” and they do not want to lose that. Running it as a load-following plant speaks to inefficiencies, however, and a potential for very much reduced profits.
This put me in mind of an article by Tina Casey that appeared in June at CleanTechnica, “Air-Powered Energy Storage Knocks Out Coal & Gas – Wait, What?” It included this quote from Highview Power about its CRYOBattery™: “At giga-scale, CRYOBatteries paired with renewables are equivalent in performance to – and could replace – thermal and nuclear baseload power in addition to supporting electricity transmission and distribution systems while providing additional security of supply.”
The use of a nuclear power plant for load-following looks to me like yet another symptom of an inexorable move away from baseload power toward a new paradigm built around combinations of renewable technologies with storage. This is happening partly because renewables and storage are cheaper than fossil fuels or nuclear. But increasingly, they are more reliable, more secure, and far more flexible, as Highview Power pointed out.
Photo: Prairie Island nuclear plant under construction in 1970 (US DOE image – public domain)
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