Moving Beyond Marginal Carbon Intensity: A Poor Metric for Both Carbon Accounting and Grid Flexibility

TL;DR

This paper critiques the use of Marginal Carbon Intensity as a metric for carbon-aware computing and grid flexibility, highlighting its limitations and proposing the development of more actionable alternatives.

Contribution

It provides a critical analysis of MCI's shortcomings and advocates for new metrics that better support carbon accounting and grid management.

Findings

MCI is unreliable for carbon accounting and grid optimization.

MCI relies on opaque predictive models and lacks verifiability.

Alternative metrics like direct excess power reporting are recommended.

Abstract

Marginal Carbon Intensity (MCI) has been promoted as an effective metric for carbon-aware computing. Although it is already considered as impractical for carbon accounting purposes, many still view it as valuable when optimizing for grid flexibility by incentivizing electricity usage during curtailment periods. In this statement paper, we argue that MCI is neither reliable nor actionable for either purpose. We outline its fundamental limitations, including non-observability, reliance on opaque predictive models, and the lack of verifiability. Moreover, MCI fails to reflect curtailment caused by high-carbon sources and offers no insight into the quantity of available excess power. We advocate moving beyond MCI and instead call for research on more actionable metrics, such as direct reporting of excess power, explicit modeling of energy storage and grid stability, and integration with emerging granular renewable energy certificate markets.