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Western Wind and Solar Integration Study

The Western Wind and Solar Integration Study, one of the largest regional solar and wind integration studies to date, explores the question: Can we integrate large amounts of wind and solar energy into the electric power system of the West?

Released September 2013—Phase 2 Research

NREL Calculates Emissions and Costs of Power Plant Cycling Necessary for Increased Wind and Solar in the West
Study finds that cycling fossil-fueled power plants has little impact on avoided emissions but modestly increases wear-and-tear costs.

Phase 3 Research

All the large-scale regional integration studies performed by NREL and others to date have identified the lack of traditional transmission planning analysis as a significant research gap.

There is also general concern regarding the degradation of frequency response in North America over the past two decades. The decline is due to various factors, such as the withdrawal of primary or governor response shortly after an event, the lack of in-service governors on conventional generation, and the unknown and changing nature of load frequency characteristics. Large penetrations of inverter-based technologies further complicate this issue. Without special operation or controls, wind and solar plants do not inherently participate in the regulation of grid frequency. By contrast, synchronous machines always contribute to system inertia, and a fraction of the synchronous generation in operation at any point has governor controls enabled. When wind and solar generation displaces conventional synchronous generation, the mix of the remaining synchronous generators changes and has the potential to adversely impact overall frequency response.

The impact of significant renewable penetration on large-scale system stability is also an open question. The transient stability of the Western Interconnection is critical to system operations, as many major interface constraints are dictated by transient stability limitations. While transient stability can be both systemic and local, Phase 3 of the Western Wind and Solar Integration Study (WWSIS-3) focuses on large-scale events that affect the security of the entire interconnection. Large penetrations of inverter-based wind and solar generation increase stability concerns as a result of (a) changes in angle/speed swing behavior due to reduced inertia, different power flow patterns, and displacement of synchronous generation at key locations, and (b) changes in voltage swing behavior due to different voltage control systems, flow patterns. and generation location differences.

The primary objectives of WWSIS-3 are to examine the Western Interconnection large-scale stability and frequency response with high wind and solar penetration, and identify means to mitigate any adverse performance impacts via transmission reinforcements, storage, advanced control capabilities or other alternative means. A Technical Review Committee from Western Interconnection power system operators/planners, national reliability experts, and the research community was convened to vet the assumptions, models, data, results, and conclusions to ensure a technically rigorous study.

WWSIS-3 will be complete in late 2014.

Phase 2 Research

Phase 2 of the Western Wind and Solar Integration Study (WWSIS-2) was initiated to determine the wear-and-tear costs and emissions impacts of cycling and to simulate grid operations to investigate the detailed impacts of wind and solar power on the fossil-fueled fleet in the West.

Key Findings

  • The negative impact of cycling on overall plant emissions is relatively small. The increase in plant emissions from cycling to accommodate variable renewables are more than offset by the overall reduction in CO2, NOx, and SO2. In the high wind and solar scenario, net carbon emissions were reduced by one third.

    Table comparing emission reductions due to renewables with emissions due to cycling impact

    The increase in plant emissions from cycling to accomodate variable renewables are more than offset by the overall reduction in CO2, NOx, and SO2.

  • Operating costs increase by 2–5% on average for fossil fueled plants when high penetrations of variable renewables are added to the electric grid.

    Graph illustrating that operating costs increase from .50 $/MWh to approximately 3.30 $MWh at fossil fueled plants when renewables are added to the mix.

    From a fossil fuel generator perspective, cycling costs increase with increased wind and solar penetration.

  • From a system perspective, these increased costs are relatively small compared to the fuel savings associated with wind and solar generation.

    Graph illustrating that from a system perspective, operating costs decrease when renewables are added to the mix.
  • Cycling costs vary based on penetration level and wind/solar mix.

    Table showing cycling cost data for each study scenario.

Phase 1 Research

The first phase of the Western Wind and Solar Integration Study investigated the benefits and challenges of integrating up to 35% wind and solar energy in the WestConnect subregion and, more broadly, the Western Interconnection, in 2017. The study showed it is operationally possible to accommodate 30% wind and 5% solar energy if utilities substantially increase their coordination of operations over wider geographic areas and schedule their generation and interchanges on an intra-hour basis.

Key Findings

  • The integration of 35% wind and solar energy into the electric power system will not require extensive infrastructure if changes are made to operational practices.

  • Wind and solar energy displace fossil fuels. A 35% penetration of solar and wind power would reduce fuel costs by 40% and carbon emissions by 25%–45%—the rough equivalent of taking 22–36 million cars off the road—compared to today's system.

  • Increasing the size of the geographic area over which the wind and solar resources are drawn substantially reduces variability.

  • Scheduling generation and interchanges subhourly reduces the need for fast reserves.

  • Using wind and solar forecasts in utility operations reduces operating costs by up to 14%.

  • Existing transmission capacity can be better used. This will reduce new transmission needs.

  • Demand response programs can provide flexibility that enables the electric power system to more easily integrate wind and solar—and may be cheaper than alternatives.

For More Information

For more information about the Western Wind and Solar Integration Study, see the following resources. Additional publications can be found in the NREL Publications Database.

Phase 2 Publications

Phase 1 Publications

Wind Data

Solar Data

  • Solar Power Data for Integration Studies
    The Solar Power Data for Integration Studies consist of one year (2006) of 5-minute solar power and hourly day-ahead forecasts for approximately 6,000 simulated PV plants.


Kara Clark