Calculating a Residual Mix

Credible residual mix information is important for accurate clean energy and GHG accounting and disclosure. This CEAP initiative will develop consensus guidance for the calculation of annual residual mixes and residual mix emissions factors for use in different voluntary and compliance disclosures.

Residual mixes are the attributes of unallocated or unclaimed energy delivered to customers on the electricity grid and are a critical tool that prevents the double counting of clean energy and supports accurate calculations of greenhouse gas emissions resulting from electricity use. To date, there has been no consensus on what data is needed and how it should be used. This guidance was created by CRS’s Clean Energy Accounting Project (CEAP) through a consensus-based process, and provides a long-needed roadmap on the appropriate residual mix methodologies and geographic boundaries for a variety of use cases.

This guidance addresses a variety of residual mixes and data challenges and provides standardized approaches that enable organizations to accurately calculate residual mixes. It can be used by electricity users for scope 2 reporting and utilities mandated to transparently report emissions to customers and regulators. The guidance aids regulators, policymakers, and wholesale market operators in utilizing residual mixes for regulatory policy and publishing credible residual mix data. Furthermore, it emphasizes the significance of renewable energy certificate registries and nationwide tracking systems encompassing all generation types, facilitating accurate data collection, allocation, and utilization for grid-connected fossil and clean electricity generation resources.

This document, released by CRS’s Clean Energy Accounting Project (CEAP), is intended to provide background on how residual mixes (electricity delivered as part of system mix and untracked or unclaimed energy) and associated emissions should be defined and calculated in the U.S. for different uses. Residual mix calculations are often used for greenhouse gas emissions calculations and reporting by either electricity providers or customers, and is currently produced by both governmental agencies and NGOs. Even when residual mixes are developed for the same application, they can vary in terms of data sources, treatment of clean generation resources used for compliance and voluntary purposes, and geographic and temporal boundaries. This backgrounder is intended to provide a baseline of available information, but is not comprehensive list of applications, residual mix emission factors, or considerations.