As increasing levels of renewable energy enter the U.S. electrical system in decades to come, conventional baseload power suppliers will have to become more flexible, with plants ramping up and down to compensate for the inherent gaps in wind and solar power production.
Power “cycling,” however, comes with its own set of complications. Plants that run only part of the time have more difficulty recovering costs than those that can perpetually send out power. Likewise, frequent cycling can lead to greater wear and tear on generation equipment, not unlike the effects of inner-city driving on a car’s engine. And like a car, just turning on a power plant comes with its own energy cost.
In the second phase of its Western Wind and Solar Integration Study (WWSIS-2), the Department of Energy’s National Renewable Energy Laboratory (NREL) attempts to forecast some of the costs and consequences of power plant cycling in a future where renewables have been scaled up to 33 percent of Western energy supplies.
They find that, while wear-and-tear costs and added greenhouse gas emissions would be low, ramping up renewable output would primarily displace natural gas plants, leaving coal, nuclear and hydro to produce a steadier output.
This is not entirely surprising, considering that many new combined-cycle natural gas plants are designed specifically to cycle up and down efficiently, as a complement to renewables (ClimateWire, Nov. 12).
“Combined cycle natural gas can handle the flexibility. They also tend to be more expensive” than conventional coal power plants, said Greg Brinkman, a member of the Energy Forecasting and Modeling Group for NREL’s Strategic Energy Analysis Center. “That being the case, they’re the ones that get turned down first.”
For thermal power plant operators, the study found that the added annual cost of cycling would fall between 47 cents and $1.28 per megawatt-hour, compared to a total cost of $27 to $28 per MWh that plants pay today for fuel and maintenance.
Meanwhile, operators of conventional power plants would see big savings from the deferred cost of unused fuel, estimated in the report at $7 billion per year.
Added energy costs from ramping power output up and down would likewise be low and would be marginal to inconsequential in conjunction with the larger emissions reductions associated with bringing 33 percent renewable energy online.
Levels of cycling would be highly seasonal, Brinkman noted. “The spring is the most challenging time for operators in the high [wind] penetration scenario because of what existing units are asked to do,” he said. Lots of wind power, fluctuating over the course of the day, would require all other power sources save nuclear to cycle to some extent to compensate, he said.
However, despite these challenges, the study found no technical barriers to 35 percent penetration of wind and solar on the Western Interconnection. Such a scenario would require improvements to the transmission system, however, as well as accompanying operational changes.