U.S. Department of Energy

Transmission Grid Integration

The levels of solar energy penetration envisioned by the DOE SunShot Initiative must be interconnected effectively onto the transmission grid. This interconnection requires an in-depth understanding of the impact on the grid at various spatial and temporal scales, quantifying and analyzing the variability in solar generation, and developing real-world solutions that can be implemented economically and efficiently.

DOE's transmission grid integration research and development (R&D) focuses on the bulk system integration issues that face utilities, such as the ability to ensure adequate transmission system capacity and power system flexibility for accommodating variable generation. These efforts help develop and validate models, provide support for enhancing utility operations, engage in transmission planning forums, and model generator output. More information on transmission grid integration is available in the Transmission section of the High Penetration Solar Portal.

Within the SunShot Systems Integration activities, transmission grid integration R&D is being funded through DOE national laboratories.

National Laboratory R&D

The National Renewable Energy Laboratory (NREL) and Sandia National Laboratories, with funding from DOE, are working to address the technical, operational, market, and regulatory challenges associated with integrating high penetration levels of utility-scale solar energy into the bulk transmission system. The solar technologies addressed include both photovoltaics (PV) and concentrating solar power (CSP).


NREL and Sandia transmission grid integration activities are organized within the following seven categories.

  • Measured and Synthesized Data: High-quality data are needed to support all the other transmission grid integration activities. These data may include weather, solar resource, solar forecast, plant generation output, and grid performance measurements. This work includes data collection and dissemination as well as development and validation of synthesized solar plant outputs and forecasts. A critical goal is to better understand how plant characteristics (e.g., size, technology, tracking, and location) affect plant output under various weather conditions.
  • Power System Models and Tools: Improved modeling and simulation of both PV and CSP plants in utility-standard simulation platforms for transmission planning and interconnection studies are critical to increasing the solar grid integration. Better power flow models, small- and large-signal dynamic models, short-circuit models, and transient stability models are needed to properly study the impact of solar systems on the grid. In addition to these electrical models, there are also numerous utility operations and planning models and tools for scheduling, dispatch, and integration studies (e.g., production cost simulation tools, solar plant production models). Model validation and documentation is an integral part of this effort.
  • Operational Analysis and Optimization: Determining the most cost-effective way to integrate large quantities of solar energy into the bulk power system is key to increasing the penetration of solar electricity on the grid. To accomplish this, a variety of technical and institutional mechanisms are analyzed to determine which combination of factors is best suited to complement solar energy integration using the models and tools described above. Effective integration encompasses all facets of grid operation and planning over all relevant time scales of utility operation, spanning seconds to minutes to years.
  • Codes and Standards: An improved national and regional electrical infrastructure is required, including more effective codes, standards, and regulatory practices. This improvement will be accomplished by working with standards organizations to create and update documents applicable to the transmission and bulk generation side of the grid that will include the impact of renewable penetration.
  • Transmission Utilization and Expansion: This work will identify and determine how to mitigate impacts on transmission system reliability, frequency, and stability; improve transmission system utilization; optimize transmission system development sequencing; enhance transmission system expansion planning policies; provide essential generation fleet flexibility characteristics (e.g., start-up time and cycling); and develop improved transmission system models.
  • Technology Development and Optimization: Improving the grid integration technologies of large-scale PV and CSP plants by working in partnership with industry will accelerate the adoption of cost-effective technical options for meeting interconnection requirements and enhancing the value of solar systems to the grid. These efforts include enabling solar plants to provide a wider range of ancillary services. Several options for industry engagement are being explored, including technical collaboration with the national laboratories, industry solicitations for technology development, and field deployment of advanced technologies.
  • Stakeholder Engagement: DOE will address barriers associated with high solar penetration levels by providing a direct interface among industry groups, regulatory agencies, utilities, reliability entities, codes and standards developers, universities, manufacturers, and solar project operators and developers.


NREL and Sandia's activities focus on:

  • Acquiring field data to support and validate solar data synthesis (including forecasting), solar plant modeling, and analytical results
  • Developing and validating solar plant models, power system simulation tools, and analytical techniques to support integration analysis
  • Performing analyses to identify, understand, and cost-effectively mitigate the impact of high solar penetration on power system operation and performance
  • Developing and updating interconnection and performance standards to enable reliable integration
  • Developing market and regulatory approaches to increase transmission utilization and enable expansion
  • Developing improved inverter technology to enable reliable integration at high penetration levels
  • Collaborating with industry and other stakeholders to inform and receive feedback on issues involving high penetrations of solar on the grid.