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Summary of Charging Up: The State of Utility-Scale Electricity Storage in the United States

Core Content

This report by Molly Robertson, Omid Mirzapour, and Karen Palmer from Resources for the Future (RFF) provides a comprehensive overview of the role, deployment, and market dynamics of utility-scale electricity storage in the United States. It examines how energy storage supports grid reliability, the economic and policy factors influencing its adoption, and the future potential of long-duration storage in a high-renewables energy system.

Main Points

1. Current Roles of Energy Storage

• Arbitrage: Storage, especially batteries, can arbitrage energy prices by buying low and selling high. This role becomes more valuable with higher renewable penetration and greater price volatility.

  • Qin et al. (2023): Storage participation in real-time markets lowers prices the most, while day-ahead participation reduces emissions the most.
  • Profitability: As storage capacity increases, arbitrage profits diminish due to competition and saturation in the market.
  • Saturation: Markets like CAISO and ERCOT are nearing saturation in ancillary service markets, leading to declining prices and revenues.

• Ancillary Services: Storage provides grid stability through services like frequency regulation, which are short-term and require fast response.

  • Mansfield and Konet (2023): Storage may need to charge during high-price periods to meet state-of-charge requirements, potentially increasing emissions if fossil generators adjust to meet these needs.
  • Ancillary Services Revenue: They form a significant part of the current revenue stream for storage.

• Capacity and Resource Adequacy: Storage supports system capacity by providing backup power during high-demand or low-supply periods.

  • Capacity Markets: Storage providers are compensated for future availability, with longer-duration storage typically receiving higher payments.
  • Variable Generation Support: Storage can enhance the capacity value of renewables by extending their availability.

• Transmission-Only Assets (SATOAs): Storage can act as a transmission asset, helping to relieve congestion by shifting demand.

  • FERC Policy: FERC has provided guidelines for cost-based regulated pricing of SATOAs, but only a few ISOs and RTOs have implemented them.
  • Challenges: Integration into transmission planning and defining ownership and operational responsibilities remain key hurdles.

• Vertically Integrated Utilities: These utilities may have advantages in deploying storage due to control over grid and generation infrastructure.

  • Lack of Price Signals: Absence of hourly price signals in some markets may hinder storage adoption.
  • Ownership Data: Investor-owned utilities (IOUs) own a smaller share of storage capacity compared to renewables like wind and solar.

2. Role in a High-Renewables Future

• Value of Storage: The value of storage is expected to grow as renewable penetration increases and price volatility rises.
• Carbon Constraints: Tighter carbon regulations could lead to a greater share of variable generation, energy storage, and carbon capture in the generation mix by 2050.
• Price Variability: Under stringent carbon constraints, the share of hours with very low and very high prices increases, with moderate prices becoming less frequent.
• Long-Duration Storage: May be needed to support long periods of low renewable generation, but current market structures are not well-suited to incentivize such technologies.

3. Policies Supporting Storage

• Reduction of Fossil Fuel Generation: Policies such as renewable portfolio standards (RPS), carbon cap-and-trade, and emissions standards reduce the attractiveness of fossil generators, indirectly supporting storage.
• Clean Energy Deployment: Policies promoting renewable energy, such as the Inflation Reduction Act (IRA), can also benefit storage through tax credits.
• Clean Firm Generation Incentives: Future policies may directly support clean firm generation technologies, such as advanced nuclear, hydrogen, and long-duration storage, to ensure grid reliability.
• Storage Procurement Requirements: Some policies may mandate the procurement of storage, directly driving its deployment.

4. Market Rules for Storage

• Interconnection: Efficient interconnection is crucial for storage deployment.
• Compensation for Resource Adequacy: Storage is increasingly being compensated for its role in ensuring system reliability.
• Bidding Rules: These influence how storage participates in markets and its profitability.
• State of Charge Requirements: These can affect storage operations and lead to unintended consequences, such as increased reliance on fossil fuels.

5. Evidence on Storage Deployment

• Regional Variation: Storage growth varies by region, with some areas seeing faster adoption.
• Interaction with Variable Generation: Storage complements renewable sources by managing intermittency and price fluctuations.
• Capacity by Product Class: Lithium-ion batteries dominate current storage capacity, while long-duration storage remains underdeveloped.
• Drivers of Adoption: Market opportunities, policy support, and price volatility are key drivers of storage deployment.

6. Conclusions

• Storage plays a vital role in enhancing grid reliability and supporting the integration of renewables.
• Current market structures and policies are not fully aligned with the needs of long-duration storage.
• Future storage development will depend on evolving market rules, policy incentives, and the expansion of renewable energy.
• The transition to a net-zero grid will likely require a mix of storage technologies and new market mechanisms to ensure affordability and reliability.

Key Information

• Market Potential: Storage can provide arbitrage, ancillary services, capacity support, and transmission relief.
• Current Trends: Lithium-ion batteries are the dominant storage technology, while long-duration storage is still underdeveloped.
• Policy Impact: Renewable standards, carbon pricing, and direct storage incentives are shaping the storage landscape.
• Market Challenges: Price volatility, interconnection, and state-of-charge requirements are critical factors in storage deployment.
• Future Outlook: Long-duration storage may become more economically viable as renewable penetration increases and carbon constraints tighten.

References

• Qin et al. (2023): Impact of short-duration battery storage on electricity markets.
• Mallapragada et al. (2023): Carbon constraints and generation mix in 2050.
• Denholm et al. (2023): Economics of short-duration storage in current markets.
• Scott (2023): Requirements for long-duration storage deployment.
• Staadecker et al. (2024): Modeling the role of long-duration storage in a net-zero future.
• DOE GDO (2023, 2024): Transmission planning and storage penetration.
• CAISO (2024): Ancillary service market saturation.
• EIA (2023b, 2018, 2024): Data on storage and renewable ownership.
• FERC (2017): Dual-use of storage as a transmission and generation asset.
• Ascend Analytics (2023): Ancillary service market analysis.
• Vermillion (2023b): Market saturation and price trends.

This report underscores the importance of aligning market rules and policy frameworks to support the growth and integration of utility-scale storage, especially as the U.S. electricity sector transitions toward a low-carbon future.