Total Carbon Accounting: A Framework to Deliver Localized Carbon Intensity Data

Published on November 4th, 2021, in partnership with National Grid, Exelon, and ComEd, this white paper proposes a methodology for measuring carbon intensity on the electric grid, which we call Total Carbon Accounting (TCA). TCA integrates locational carbon intensity with modern carbon accounting methods to more precisely determine how much carbon emissions are associated with a load in a specific location at a given time.
Presented at COP26

Executive Summary

Climate change is the greatest existential threat of our time. The purpose of this white paper is to provide a framework to measure locational carbon intensity which will be important in determining where to best prioritize our climate change mitigation efforts. The co-authors are currently testing these framework methods and invite others to join in this collaboration to ensure that the best possible approaches are used to evaluate, prioritize and measure decarbonization activities.

Globally, the decarbonization of the electricity sector is a fundamental requirement to combating climate change. Much progress has been made on the deployment of sustainable, renewable energy technologies in recent decades, to the extent that solar and wind are the fastest growing and most economical forms of new electricity generation in many countries. Also increasing are residential and behind-the-meter deployments, with and without battery storage. This trend has been accompanied by an increasing focus on the electrification of “everything,” meaning moving buildings, heating, and transportation from fossil fuels to clean, decarbonized electricity. The race to net zero, or ensuring the balance between the amount of greenhouse gas (GHG) emissions produced and removed from the atmosphere, has gained speed, and such goals are now prominent in policy and legislation in most of the world’s leading economies. There is an urgent need to pick up the pace on our efforts to decarbonize, moving toward the elimination of GHG emissions. If our goal is to remove carbon from the electricity system, we require a more informed assessment of the locational carbon intensity of the grid. 

Current efforts to measure the carbon intensity of electricity to inform decision making use averages across long time horizons and/or large market areas. These existing approaches have enabled voluntary emissions reporting and investment decisions related to decarbonization. While these efforts have moved the industry forward, an approach that neglects to consider the actual power flows on the grid and how they change over time is not sufficient for decarbonizing the global economy. It is now essential that new, transparent, accurate, and well-understood metrics for the locational carbon intensity of the grid are defined as a matter of priority. These issues are being considered by governments, regulators, large corporations and industry. The need for improvement in this area is becoming increasingly urgent.

In this paper we posit that the solution lies in the ability to compute the carbon intensity of the electricity supplied by the grid with a high degree of geographic and temporal granularity. This solution is achieved by leveraging information about the topography of the grid and the magnitude and direction of flows in light of the variability of both supply and demand. Using an illustrative example, we lay out the framework for calculating these values in a transparent and scientifically defensible way and call this method “Total Carbon Accounting” (TCA).

Total Carbon Accounting (TCA) identifies where the consumed power is generated for any location on the grid. For any given point in time, TCA provides a basis for quantifying the carbon intensity of all energy consumption. TCA focuses on the physical flows of electricity and supports improved reporting of carbon emissions, and in so doing, also enables better planning and operations of infrastructure, rates design, and programs. This goal is achieved by quantifying the carbon associated with all generation sources, including those embedded in the distribution system, customer premises, as well as the delivery paths taken by the power from these generators to supply load.

TCA represents a new approach to solving an increasingly important problem. The co-authors, including leading energy companies operating in the US and UK, and a data and analytics company, are currently testing these methods in the field across multiple geographies and invite others to join in this collaboration to ensure that the best possible approaches are used to evaluate, prioritize, and measure decarbonization activities.

TCA, delivered through specific locational and temporal carbon intensity calculations, provides a much more accurate basis for examining the carbon associated with electricity consumption at a location. The averaging methods currently used can introduce significant error, which we discuss in detail.

Additionally, TCA will support a more accurate matching of renewable energy to demand for large loads and corporations. Recent developments in locational marginal emissions (LMEs) will also be enhanced by the TCA framework, providing a basis for considering the actual electricity consumed at a location rather than the marginal generator meeting the market-wide marginal need.

By focusing on discrete analysis of all components in the balance of supply and demand on the grid, TCA serves as a long-term foundation for evolving carbon awareness efforts. TCA provides distinct advantages over current methods that average carbon intensity over large geographic areas, or focus on the emissions of marginal units. These outdated practices can lead to unintended changes in the formulation of carbon intensity in energy markets. TCA supports climate action policies, program and rate designs, and procurement strategies for policymakers, utilities, and energy consumers, and can underpin carbon reporting efforts.

In this white paper, we consider an illustrative example of a market area, with three generators and two load locations (X and Y) of interest from a carbon intensity perspective. As illustrated in Figure 1, relying on averages at the market area or regional level, result in significantly different carbon intensity estimates for a given location. Through a more granular approach, TCA leads to improved insight into where carbon intensity is higher or lower within a particular market or region.

Having a clear understanding of the carbon content of the electricity at any location and time is a key component of enabling and facilitating decarbonization. The TCA framework presented in this white paper is a step forward for industry in the pursuit of a common framework for greater clarity on the carbon emissions associated with delivered power.


Figure 1: Illustration of different carbon calculation approaches and benefit of TCA


Presented at COP26