When a company buys renewable energy certificates and reports zero Scope 2 emissions, a skeptical auditor might ask: zero according to which method? The GHG Protocol Corporate Standard requires companies reporting Scope 2 to disclose figures under both the market-based method and the location-based method, and to explain any difference. That gap can easily reach 30 to 60 percent of your total Scope 2 footprint. If you are filing under CSRD's ESRS E1 or the SEC climate rule, or simply reporting to CDP, getting both methods right and documented is non-negotiable.
What the GHG Protocol Actually Requires
The GHG Protocol Scope 2 Guidance, published in 2015 and incorporated by reference into the Corporate Standard, introduced dual reporting as mandatory for companies that want to claim market-based Scope 2 emissions. The two methods are not alternatives you get to choose between. You report both, and you disclose the methodology you use for primary inventory purposes.
Location-based Scope 2 uses an average emission factor for the electrical grid in the geography where your facilities draw power. In the United States, that means US EPA eGRID subregion factors. In the EU, it means the residual mix factors published by the Association of Issuing Bodies or national grid average factors. You multiply your electricity consumption (kWh) by the relevant factor and get tCO2e. No certificates involved. The number reflects what the grid actually delivered to everyone connected to it, averaged across all generation sources including coal, gas, nuclear, and renewables.
Market-based Scope 2 uses contractual instruments to assign the emissions attribute of specific electricity generation to the purchaser. The hierarchy of instruments the GHG Protocol recognizes runs: supplier-specific emission rates, then energy attribute certificates (EACs, which in the US context are renewable energy certificates or RECs, and in Europe are Guarantees of Origin), then residual mix factors for power you did not attribute via contract, and finally grid averages as a last resort.
Why the Two Numbers Can Differ Substantially
Consider a mid-size manufacturer in the US Southeast operating in an eGRID subregion where the grid mix includes roughly 40 percent coal. Their location-based Scope 2 factor might be 0.52 kg CO2e per kWh. If they buy bundled RECs sourced from a wind farm in the same region, their market-based factor for that portion becomes close to zero. A facility consuming 8 GWh annually would report approximately 4,160 tCO2e location-based and near-zero market-based. That is a 4,000 tonne swing from a single procurement decision, not a change in actual physical electricity use.
This is where auditors and disclosure reviewers focus scrutiny. The GHG Protocol's Scope 2 Quality Criteria require that EACs used for market-based accounting be issued in the same market as consumption, not retired on behalf of another entity, and from generation within the same contract year. A company buying RECs sourced from a different country's grid does not meet the criteria for market-based retirement against that facility's consumption under the GHG Protocol framework.
The Residual Mix Problem Most Companies Miss
Here is where we see the most errors in practice. Companies that cover, say, 70 percent of their electricity consumption with RECs often assume the remaining 30 percent can default to the grid average factor. Under market-based accounting, it cannot. The correct factor for unattributed consumption is the residual mix factor for the relevant grid. Residual mix factors reflect what is left on the grid after all EAC-attributed generation has been removed. In markets with high EAC issuance, the residual mix factor can be significantly higher than the simple grid average, because all the renewable generation has been "claimed" by buyers and subtracted from the mix.
In practice, for EU markets the Association of Issuing Bodies publishes national residual mix factors annually. For US markets, the calculation is more complex because the REC registry and grid accounting systems are not as tightly coupled. Many US companies default to eGRID averages for their unattributed consumption, which is technically defensible under GHG Protocol guidance if supplier-specific and residual mix data are genuinely unavailable, but it understates the market-based footprint.
We built Emitpulse's Scope 2 calculation module to track both methods as parallel ledger entries rather than sequential calculations. Each facility gets a location-based row and a market-based row, both sourced from the same consumption input. When RECs or Guarantees of Origin are entered, the system applies them to the market-based row only, and flags any unattributed residual consumption for factor assignment. That separation prevents the common mistake of accidentally applying market-based numbers to the location-based calculation.
Which Method to Report for Primary Inventory
Both methods must be disclosed, but companies often ask which one drives their target-setting and public commitments. Science-based targets set through SBTi, for instance, are evaluated against market-based figures if the company is using EACs as part of its reduction strategy. CDP scoring considers both methods but focuses on market-based when assessing procurement-related reduction claims.
We are not saying location-based emissions are irrelevant. They matter for understanding physical grid dependency and for stakeholders who question whether purchased certificates represent genuine additionality. There is a legitimate ongoing policy debate about whether 20-year-old wind farms generate RECs that mean anything from a climate impact standpoint versus new-build renewable capacity. That debate is outside the scope of accounting, but it is worth flagging in your disclosure methodology notes.
CSRD's ESRS E1 requires disclosure of both methods under disclosure requirement E1-4 (climate-related targets) and E1-5 (energy consumption and mix). If you are filing under ESRS E1, you cannot simply report market-based and call it done. The European Sustainability Reporting Standards are explicit that both figures appear in your disclosure with methodology notes explaining the difference.
Common Data Problems in Scope 2 Reporting
In working through Scope 2 data with early users, we have seen a few recurring issues. First, REC vintage mismatches: certificates from generation in year T applied to consumption in year T+1. The GHG Protocol requires same-year vintage matching. If your certificates are from the prior year, they do not satisfy the quality criteria for market-based accounting in the current reporting year.
Second, geographic mismatch: RECs from a different grid region than the consumption facility. A California office cannot use RECs from a Texas wind farm to claim market-based zero emissions in the WECC grid region. The GHG Protocol says the certificate must be issued in the same market as the electricity consumption.
Third, double-counting across entities: parent companies sometimes apply RECs to facilities whose consumption has already been attributed at the subsidiary level. The certificate retirement records need to clearly identify which facility and which reporting year.
Fourth, missing factor versioning: the eGRID factors update every one to two years. Using the 2020 eGRID factor for 2024 consumption is an error that an auditor will catch. Your emissions ledger needs to record which factor version was applied to each calculation, not just the resulting number.
Practical Setup for Dual-Method Reporting
The cleanest approach we have found is to treat Scope 2 as four inputs: electricity consumption by facility, applicable grid emission factor (location-based), any contractual instruments with their respective emission rates, and the residual mix factor for unattributed consumption. With those four inputs per facility per reporting period, both method calculations follow mechanically.
The documentation burden is as important as the calculation. When a sustainability manager or finance controller submits to an external verifier, the verifier needs to see the REC retirement certificates with dates and registry record numbers, the mapping of each certificate to the facility it covers, and the factor sources with publication dates. Without that chain of custody, the market-based number is an assertion without evidence.
If you are starting Scope 2 reporting for the first time, report both methods even if your market-based and location-based numbers are identical (which they will be if you have no EACs). Establishing the dual-method baseline in year one makes the comparison meaningful in future years when you do purchase certificates. It also avoids the awkward situation of introducing the location-based figure for the first time in a later disclosure year, which can look like you are hiding an unflattering comparison.