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Illustration of the U.S. states that are part of the Eastern Interconnection.

The Eastern Interconnection provides power to more than 70% of the U.S, population (study area shown in color, but not including pink/IESO area.)
Map provided by NREL

Integrating Wind and Solar on the Grid—NREL Analysis Leads the Way

NREL studies confirm big wind, solar potential for grid integration

To fully harvest the nation's bountiful wind and solar resources, it is critical to know how much electrical power from these renewable resources can be integrated reliably into the grid. To better inform the debate about the potential of such resources, over the past NREL has released four regional grid integration studies.

Taken together, these studies represent a major step forward in understanding the integration of large amounts of wind and solar resources into our electrical grid.

NREL is a leading expert in grid integration analysis of renewables, and collaborates closely with the power industry to share such transformative information. NREL has helped educate the power industry about the viability of significant penetration of renewable energy on the grid, while helping overcome and better understand operational, reliability, and economic concerns.

Eastern Wind Integration and Transmission

The Eastern Wind Integration and Transmission Study is one of the largest regional wind integration studies to date. Initiated in 2008, the study examines the operational impact of a significant energy penetration of wind on the power system in the Eastern Interconnection of the United States. The Eastern Interconnection is one of the two major alternating current (AC) power grids in North America. The other major interconnection is the Western Interconnection.

According to the study, 20%-30% wind power is technically achievable, although transmission infrastructure upgrades and investment are necessary. In addition, drawing wind energy from a larger geographic area makes it both a less expensive and more reliable energy source, and wind power displaces substantial amounts of fossil fuels, resulting in emissions reductions. The study also pointed to the need for additional analysis to further examine the issues, including reliability impact.

Western Wind and Solar Integration Study

The Western Wind and Solar Integration Study examines the benefits and challenges of integrating up to 35% wind and solar energy penetration into the grid by 2017. The study finds that these targets are technically feasible and do not necessitate extensive additional infrastructure, but do require key changes to current operational practice.

Though wind and solar output vary over time and cannot be perfectly forecast, the technical analysis performed in this study shows that it is operationally possible to accommodate 30% wind and 5% solar energy penetration. The study also finds that a 27% wind and solar energy penetration across the Western Interconnection decreases fuel and emissions costs by 40% and carbon emissions by 25%–45%, depending on the future price of natural gas.

Nebraska Statewide Wind Integration Study

NREL worked with the Nebraska Power Association to conduct a state-wide wind integration study. The study looked at what it would cost to integrate wind-powered resources into the state's existing generation mix at much higher levels than exists today. The specific levels evaluated included new wind-powered generation, as a percent of total Nebraska electricity needs, at 10%, 20%, and 40% levels for the base year 2018.

Major carbon emission reductions were found in all scenarios, with CO2 emissions dropping by more than 25 million tons per year in moving from the 10% wind scenario to the 40% wind scenario. The study also found that the cost of operating the power system differently to accommodate wind energy was modest, although exact integration costs varied depending on the methodology used to account for the costs.

Oahu Wind Integration and Transmission Study

NREL led in the Oahu Wind Integration and Transmission Study to examine grid and transmission integration of renewables as part of the Hawaii Clean Energy Initiative's Energy Agreement.

The Hawaii Clean Energy Initiative includes an aggressive mandate for the State of Hawaii to generate 40% of its energy from renewable resources by 2030. The Energy Agreement includes a commitment to integrate up to 400 megawatts of wind energy from Molokai or Lanai and transmit it to Oahu via undersea cable systems (the "Big Wind" projects).

The Oahu study is an important application of integrating wind power onto a smaller electrical grid system than other grid integration studies have typically encountered. In addition, the undersea cable is state-of-the-art technology and really pushes the envelope of an undersea island-grid interconnection. Such technology and attaining a better understanding of its capabilities should prove quite helpful for domestic offshore wind development.

Findings Support Utility Scale

These four geographically and operationally diverse studies uncovered a handful of common, general findings:

  • 20% to 30% wind and solar energy penetration can be managed, but the role of wind forecasting is important to meet this objective, and additional work is needed to study the reliability impacts.

  • Larger balancing areas (i.e., the designated authority responsible for system balancing of loads and generation) provide greater flexibility and easier accommodation of variable renewable energy sources such as wind and solar.

  • Additional transmission will be needed to deliver wind power to market, and storage appears to be unnecessary to achieve this penetration.

  • Results for the 30% case appear to be more challenging, and as the studies move forward, we anticipate more analysis will be done to achieve a better understanding of the operational challenges and potential solutions.

  • High penetrations of wind reduce spot energy prices and production costs.

  • Carbon emissions are reduced, but the level of reduction is a function of the displaced generation. The higher wind penetration cases tend to offset more coal than the lower penetration rates, consistent with an economically rational dispatch process.

Learn more about NREL's analysis capability.

The Utility-Scale Future

Spring 2011 / Issue 1

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