What role do battery energy storage systems play in reducing greenhouse gas emissions

Battery energy storage systems (BESS) play a complex but increasingly important role in reducing greenhouse gas (GHG) emissions, primarily by enabling higher integration of renewable energy and optimizing grid emissions through smart charging and discharging strategies.

How BESS Reduce Greenhouse Gas Emissions

• Integration with Renewable Energy: BESS co-located with variable renewable energy sources (like solar or wind) can store excess renewable generation that would otherwise be curtailed and release it during times of low renewable output or high demand. This shifting helps reduce reliance on fossil fuel-based generation during peak periods, thus lowering carbon emissions from the grid.
• Load Shifting Based on Carbon Intensity: By charging batteries during periods of low carbon intensity on the grid (e.g., overnight when renewable generation like wind might be high or demand is low) and discharging during peak demand when carbon intensity is high (typically when fossil fuel plants are running), BESS can reduce the carbon emissions associated with electricity use. For example, a 1MW BESS charging overnight can save approximately 10,000 kg of CO₂ annually compared to charging during high-demand periods.
• Grid Reliability and Support for Renewable Expansion: BESS provide grid reliability and flexibility services, such as frequency regulation and peak shaving, which support the integration of more intermittent renewable energy, indirectly contributing to emissions reductions over time.

Challenges and Conditions for Emissions Reduction

• Operational Strategy and Market Signals are Crucial: Batteries do not inherently reduce emissions. If BESS operate based solely on economic price signals without considering the carbon intensity of the electricity being stored and discharged, they can inadvertently increase emissions. For instance, batteries charging when the grid is coal-heavy and discharging when marginal generation is cleaner can lead to a net increase in emissions.
• Geographic and Market Variance: The impact of BESS on emissions varies by region and market structure. In California, strong policies and control algorithms that incorporate carbon signals have flipped battery impact from increasing emissions to significantly reducing emissions. Conversely, in Texas (ERCOT market), about 92% of batteries increased emissions in 2023 due to lack of carbon-aware operational incentives.
• Potential for Market Distortions: A study in the PJM grid found that using batteries for grid reliability can shift generation from natural gas to coal because storage frees up coal plants to provide other services, potentially increasing overall emissions. Thus, battery deployment must be coupled with policies discouraging coal reliance to achieve emission reductions effectively.
• Roundtrip Efficiency Losses: Battery inefficiencies (usually 65%-90% roundtrip efficiency) mean some energy is lost during storage cycles, which can also affect net emissions benefits, especially if charged with carbon-intensive electricity.

Summary

Battery energy storage systems can significantly enable greenhouse gas emissions reductions by:

• Enhancing renewable energy utilization by storing excess generation and reducing curtailment.
• Reducing carbon intensity of electricity usage through smart charge/discharge aligned with grid carbon emissions signals.
• Supporting grid reliability and flexibility to facilitate deeper decarbonization of the power sector.

However, to realize these benefits, BESS must be operated with control algorithms and market incentives that incorporate real-time carbon emissions data. Without such integration, batteries risk increasing emissions by charging during dirty energy periods and discharging when cleaner generation is available. Policymakers and grid operators need to ensure proper emissions-aware frameworks are in place to maximize the climate benefits of battery storage.