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Minimal Impacts Could Mean More Deployment for Wind and Solar

March 22, 2013

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The Western Wind and Solar Integration Study (WWSIS) is one of the largest regional wind and solar integration studies to date. Phase 1 (WWSIS-1), published in 2010 by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL), was a landmark analysis of the operational impacts of high penetrations of wind and solar power on the Western Interconnection power system of the United States. It found no technical barriers to the integration of high penetrations of wind and solar power (up to 35%) if certain operational changes could be made. The two most important changes are increased balancing authority coordination and subhourly scheduling between balancing authority areas. However, one of the barriers to increasing the deployment of wind energy to this level of penetration has been the utilities' concern that wind-induced cycling will 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 Phase 2 (WWSIS-2) to examine new data and 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-1 was conducted, there was little available information on wear-and-tear costs because this information was considered proprietary by plant owners. For WWSIS-2, researchers worked with industry partners to analyze wear-and-tear cost data collected from cost studies on 400 fossil-fueled plants over several decades. By disaggregating the study results, the researchers were able to extract generic, nonproprietary data that could be used in production simulation modeling.

The simulations and analysis conducted for WWSIS-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 further validated the study results and will help boost industry acceptance going forward.