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Renewable Electricity Futures Study Summary

Core Content

The Renewable Electricity Futures Study (RE Futures) is a comprehensive analysis of the potential for a U.S. electricity system to achieve high penetration of renewable energy sources. The study is not focused on market or policy assessments but rather on the technical feasibility, challenges, and implications of integrating large amounts of renewable electricity into the grid.

The primary goal of the study is to assess whether a U.S. electricity system powered largely by renewable energy is possible, and to explore the characteristics, technologies, and system adaptations required to achieve this.

Main Findings

• High Renewable Penetration is Feasible: The study concludes that renewable electricity generation from commercially available technologies, combined with a more flexible electric system, is more than adequate to supply 80% of total U.S. electricity generation by 2050 while meeting hourly demand in all regions.
• Renewable Technologies: The study explores a diverse set of renewable technologies, including wind, solar photovoltaic (PV), hydropower, biomass, and geothermal. It also considers nuclear, efficient natural gas, and energy efficiency as complementary clean energy solutions.
• Scenario Analysis: The study evaluates several scenarios with varying levels of renewable penetration (from 30% to 90%) and focuses on the 80% by 2050 scenario, which includes nearly 50% variable wind and solar generation.
• System Flexibility: To accommodate high levels of renewable energy, the U.S. electricity system must become more flexible. This flexibility can be achieved through a combination of flexible conventional generation, grid storage, new transmission, responsive loads, and changes in power system operations.
• Transmission Needs: The study identifies that significant new transmission infrastructure will be required to support the deployment of renewable energy, especially in regions with high renewable potential.
• Curtailment and Storage: An estimated 8%–10% of wind, solar, and hydropower generation would be curtailed in an 80% renewable electricity future due to intermittency and grid constraints. However, the study suggests that storage and grid management can help mitigate these issues.
• Cost Implications: The incremental cost of high renewable generation is comparable to other clean energy scenarios. Improvements in the cost and performance of renewable technologies are identified as the most impactful lever for reducing these costs.
• Environmental and Social Impacts: The study finds that high renewable penetration can lead to significant reductions in greenhouse gas emissions and water use. It also highlights the importance of considering the full life cycle impacts of renewable technologies.
• Limitations and Uncertainties: The study acknowledges several limitations, including:
  • It focuses on renewable-specific technology pathways and does not explore the full portfolio of clean technologies.
  • It does not include a full reliability analysis, particularly addressing sub-hourly and distribution system requirements.
  • It does not examine institutional, market, or regulatory changes needed for a renewable-dominated grid.
  • A comprehensive cost-benefit analysis was not conducted.
  • The study was based on assumptions and data from 2009–2010, and recent market changes (e.g., natural gas price declines and solar cost reductions) were not reflected in the analysis.

Key Technologies and Models

• ReEDS (Regional Energy Deployment System): A primary modeling tool used to simulate the deployment of renewable and other energy technologies across the U.S.
• GridView: A complementary model that provides detailed hourly analysis of the power system.
• Renewable Technologies: Wind, solar PV, hydropower, biomass, and geothermal are the main technologies considered.
• Storage Technologies: Grid storage, including pumped-storage hydropower (PSH) and compressed air energy storage (CAES), are evaluated for their role in managing variability.
• Demand-Side Technologies: Responsive loads and energy efficiency measures are considered as part of a flexible system.

Key Implications

• Electricity Demand Management: A more flexible system is essential to balance supply and demand when renewable generation is high.
• Regional Variations: Each region of the U.S. would require different mixes of renewable technologies based on resource availability and system conditions.
• Water Use Reduction: High renewable penetration can significantly reduce water use in the electricity sector, which is a critical environmental benefit.
• Economic Considerations: While the study does not provide a full cost-benefit analysis, it notes that the economic impact is manageable and comparable to other clean energy scenarios.

Study Structure

The study is divided into four volumes, with Volume 1 focusing on:

• Analysis methods and assumptions
• Scenario framework
• Key results and insights
• Technical and operational challenges

Other volumes cover:

• Volume 2: Renewable generation and storage technologies
• Volume 3: End-use demand and energy efficiency assumptions
• Volume 4: Operational and institutional challenges

Acknowledgments

The study was conducted by a team of experts from:

• National Renewable Energy Laboratory (NREL)
• Massachusetts Institute of Technology (MIT)
• U.S. Department of Energy (DOE) national laboratories
• Industry, utility, and academic partners

Special thanks are given to Walter Short for his leadership in developing the ReEDS model and to Sam Baldwin for his support and vision in the study.

Conclusion

The Renewable Electricity Futures Study is a foundational analysis that provides insights into the technical and operational feasibility of achieving an 80% renewable electricity future in the U.S. It highlights the need for flexible systems, new transmission infrastructure, and improved renewable technologies, while also acknowledging the need for further research into policy, market, and institutional changes required for such a transformation.