Utility-scale energy storage is becoming essential to a cleaner and more reliable grid. Batteries and other storage resources can absorb electricity when renewable generation is abundant and discharge it later when demand is higher or renewable output is lower. This flexibility can help integrate more wind and solar, reduce curtailment, support grid reliability, and give voluntary buyers new tools to better align clean electricity supply with demand.
But storage also creates an accounting challenge: how should renewable electricity and its associated attributes be counted when electricity is stored before it is used?
The answer matters. If storage is not accounted for correctly, it can multiply renewable energy claims, obscure storage losses, or create conflicting claims across certificate tracking systems, emissions reporting frameworks, and wholesale market tools. As storage deployment grows and resources are increasingly operated across energy, capacity, and ancillary service markets, accounting rules must be clear enough to preserve the credibility of renewable electricity and emissions claims.
CRS’s Clean Energy Accounting Project (CEAP) is currently convening an expert working group on Accounting for Utility-scale Clean Energy Storage to provide stakeholder-driven guidance on this issue. While official guidance is still being developed, the working group found that three possible accounting approaches help clarify the choices facing voluntary markets.
Under a “storage-as-load” approach, storage is treated as the endpoint of electricity consumption. Renewable attributes are assigned when electricity is used to charge the storage asset (e.g., battery), and storage discharge does not independently support a subsequent renewable electricity use or delivery claim. This approach is conservative and reduces double-counting risk, but it does not allow for storage output to be characterized or fully recognize storage’s ability to shift renewable electricity across time.
Under a “storage-as-generation” approach, storage output may be credited as clean generation, but only within a specific compliance program or policy framework. This can work for bounded programs designed to achieve specific system outcomes, such as peak-period emissions reductions. But it is not well suited for voluntary renewable electricity claims, because storage does not itself generate renewable energy.
For voluntary markets, the strongest approach is likely “storage-as-transmission.” This treats storage as a mechanism for conveying renewable attributes through time, much like transmission conveys electricity across a geographic area. Under this model, renewable attributes associated with input electricity may be carried forward to discharged electricity—but only if the accounting system demonstrates continuity, exclusivity, mass balance, and comprehensive treatment of storage losses.
A credible storage-as-transmission framework should include several safeguards:
- Renewable attributes must derive from eligible renewable generation and qualifying contractual instruments. Storage output should not be treated as renewable merely because it comes from a battery.
- The framework must define the conditions under which renewable attributes may be assigned to electricity entering storage, including the role of contractual instruments and relevant physical or operational factors.
- Upstream certificates or attributes must be retired, cancelled, or otherwise linked to stored output so they cannot be claimed elsewhere.
- Claimable output must be limited to metered discharge net of storage losses, including conversion losses, auxiliary consumption, and other losses within the accounting boundary.
- Where storage is charged with a mix of renewable-backed and unspecified electricity, output attributes must be allocated using a transparent method, such as proportional allocation or first-in, first-out accounting.
- Storage accounting must be reconciled with existing REC and energy attribute certificate systems. Administrative emissions allocation systems can provide useful information, but they should not be treated as evidence of renewable attribute ownership unless linked to certificate retirement or equivalent controls.
Adopting a storage-as-transmission approach supports broader voluntary market goals because it works with existing markets for RECs and other contractual instruments, which remain essential for credible renewable electricity use claims. REC revenues generated through voluntary markets can support renewable deployment, expand access, and help finance new projects.
Storage should strengthen existing markets, not confuse them. A well-designed storage-as-transmission approach can help voluntary buyers support clean energy storage and procure clean electricity to match their consumption with greater temporal precision, while preserving the core principles that make voluntary markets credible: exclusive ownership, no double counting, and claims grounded in auditable instruments.
CEAP’s initiative is expected to publish accounting guidance in time for the Renewable Energy Markets™ (REM™) conference, September 1–3, 2026. Come join us in Washington, DC to learn more.
CEAP periodically has openings for Advisory Committee and working group members to help shape the program’s work and advance credible clean energy accounting. If you would like to propose an accounting question, learn more about CEAP, or are interested in joining the Advisory Committee or a working group, contact us to get involved.