How simple would it be to use electricity from renewable resources rather than coal or nuclear? The answer may lie partly in the dispatch characteristics of the generating facilities. Because electricity cannot be economically stored on a system-wide basis, electricity supply must match demand at all times during the day. So, when demand is low much of the electric generating capacity on the system is turned off. As demand increases throughout the day, capacity is added to meet the demand. In general, electric plants can be categorized by when they are turned on or “dispatched” to meet demand. Some plants are baseload, i.e, they run all of the time – 24/7; some plants are intermediate, i.e., they run mostly during the day during significant demand hours; and some plants are peaking, i.e., they run only in the hours when they are needed the most. The order in which generating plants are dispatched is largely a function of price – cheapest first.
However, the ability of a plant to turn on and turn off in response to changes in electricity demand can vary with the fuel used to generate the electricity. For example, nuclear power plants take a long time to turn on and provide electricity to the grid, and the use of nuclear fuel is highly regulated. Consequently, once a nuclear unit is on, it generally stays on until it has to be refueled or be brought down for maintenance. So, nuclear plants are almost exclusively baseload plants. Coal plants also have long ramp up times. They are generally baseload or intermediate plants. On the other hand, natural gas-fired generators have fairly short ramp up times and are often used as peaking plants.
Based on these dispatch characteristics, I doubt that renewable resources would end up displacing nuclear generation – not necessarily an undesirable outcome from a carbon standpoint. However, intermittent renewable resources such as wind or solar may have a hard time displacing coal-fired generation unless they can show themselves to be good baseload or intermediate resources. It may be the case that renewables will displace gas-fired generation because gas plants can more easily turn on and off in response to changes in the amount of electricity capable of being generated from wind or solar – a potentially undesirable outcome from a carbon standpoint.