Critics of renewable energy often point to coal, gas, and nuclear plants and assert that they operate whenever power systems are at peaks. They suggest that renewable plants are "intermittent" and not reliable, but coal, gas, and nuclear plants are fully dispatchable and, therefore, are reliable.
No power plant operates all the time. They are shutdown for planned maintenance often for weeks every year. And power plants also breakdown, like a car not starting, when you need it to run.
In the vicious cold of the last few weeks, winter demand soared to a record within PJM to more than 138,000 megawatts. That demand was high but fortunately much less than the system's total capacity.
An incredible 36,600 megawatts of supposedly fully dispatchable capacity--nearly all coal, nuclear and gas--broke down in the cold. Some gas plants could not run, because they had no gas to burn.
PJM's cold weather experience reminds that no generation technology can absolutely guarantee that it will be able to run at periods of daily, monthly, annual or historic peak demands. In truth, all power plants, not just wind and solar capacity, are "intermittent."