The Western Wind and Solar Integration Study (WWSIS) Phase 1 published by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) in 2010 showed that up to 35% wind and solar energy penetration could be accommodated by the utility system in the western United States. One of the barriers to increasing the deployment of wind energy to this level of penetration has been concern from utilities that wind-induced cycling of fossil-fueled generation may have a negative impact on the emissions and cost benefits of wind power. Cycling refers to the operation of electric generating units at varying load levels, including on/off, load following, and minimum load operation, in response to changes in system load requirements. In 2012, NREL completed a reanalysis of the WWSIS and examined new data to address these concerns.
Past regional integration studies have shown that variable generation plants such as wind may cause fossil-fueled generators to cycle more frequently and potentially more rapidly. Increased frequency in starting and stopping and the need to increase or decrease the power output to manage changing power demands may result in wear and tear impacts on fossil-fueled generators that lead to higher capital and maintenance costs and degraded performance over time. In addition, heat rates and emissions from fossil-fueled generators may be higher during cycling than during steady-state operation. In 2011, NREL launched Phase 2 of the WWSIS to determine the level of these impacts.
At the time that WWSIS Phase 1 was conducted, there was little available information on wear and tear costs as this information was considered proprietary by plant owners. For Phase 2, researchers worked with industry partners to analyze wear and tear cost data collected from cost studies on 400 fossil-fuel plants over several decades. By disaggregating the study results, the researchers were able to extract generic, nonproprietary data that they could use in production simulation modeling.
The simulations and analysis conducted for WWSIS Phase 2 determined that the impacts of wind-induced cycling are minimal. The study capped the wear-and-tear costs at 2% of the value of wind and the emissions impacts at +/- 3%. Although there are wear and tear and emissions impacts from generator cycling, these impacts are modest compared to the overall benefits of replacing fossil-fueled generation with variable renewable generation.
The results of the WWSIS will help reduce barriers to wind energy development and increase deployment of both wind and solar technologies. The inclusion of input from industry partners through a technical review committee further validated the study results and will help boost industry acceptance going forward.
To read more about the methods and results of the WWSIS Phase 2 study, see: