Scope 2 Renewable Procurement Calculator (REC / PPA / VPPA / Onsite)

Renewable Procurement Under Scope 2 — The Market-Based Method

Scope 2 covers the indirect emissions from electricity an organisation purchases and consumes. The GHG Protocol Scope 2 Guidance (2015) requires every reporting entity to compute that figure two ways and disclose both: the location-based method applies a grid-average emission factor to grid-supplied consumption, and the market-based method reflects the emissions of the specific electricity products the entity has contractually chosen. Renewable procurement is the lever that moves the market-based number — and only the market-based number.

Why Both Numbers Are Mandatory

Dual reporting exists because each method answers a different question. Location-based answers “what does the grid your meters draw from emit on average?” Market-based answers “what have you contracted to buy?” A company on a high-carbon grid that signs a large power purchase agreement will show a low market-based figure and a high location-based figure — and both are true. Reporting only the market-based number hides grid exposure; reporting only location-based hides procurement effort. The location-based vs market-based comparison sets out where the two diverge in practice.

The Order of Operations in the Market-Based Method

The market-based method is a waterfall. Renewable volume backed by a quality-passing instrument is counted first, at zero on the matched megawatt-hours. Whatever consumption remains unmatched is then priced — not at the grid average, but at the residual mix, the factor that remains once every claimed certificate has been stripped out of the grid pool. Getting this order wrong, or pricing the remainder at the grid average instead of the residual mix, is the most common market-based error and is covered in the audit checklist below.

The Procurement Instruments — REC, PPA, VPPA, Green Tariff, Onsite

Five instrument families move the market-based number, and they do not all convey an emission-rate attribute the same way. The distinction that matters for the calculation is whether the instrument inherently carries the generation’s attribute, or only carries it when a certificate is tracked and retired on your behalf.

The critical asymmetry: a REC, GO, or physical PPA conveys the attribute inherently, but a VPPA or green tariff conveys nothing on its own. A virtual PPA is a price hedge; it only delivers a zero-carbon claim when the associated certificate is separately tracked and retired. The calculator enforces this — a VPPA with the “Tracked & retired” box unchecked fails the quality gate and its volume reverts to the residual mix.

The Five Scope 2 Quality Criteria a Claim Must Meet

The GHG Protocol Scope 2 Guidance §6 sets five quality criteria that a contractual instrument must satisfy before its volume can be counted at zero in the market-based method. This calculator tests every instrument against all five and labels the result. Three are hard gates — failing one reverts the volume to the residual factor and removes it from renewable coverage. Two are soft — failing one marks the volume Partial: still counted, but flagged for review.

How the Scorecard Reads the Result

The calculator’s confidence verdict — shown as a chip on each instrument in the quality scorecard — follows three tiers:

• High — all three hard criteria (C1, C3, C5) pass and both soft criteria (C2, C4) pass. The volume counts at zero with no flags.
• Partial — all hard criteria pass, but C2 or C4 soft-fails. The volume still counts toward coverage, but is flagged for review (typically a vintage mismatch or an unconfirmed exclusivity attestation).
• Weak — any of C1, C3, or C5 fails. The volume reverts to the residual factor, is excluded from renewable coverage, and the scorecard names the failing criterion.

The Residual Mix — What Your Unmatched Load Actually Emits

The residual mix is the emission factor of the grid after every certificate claimed by every renewable purchaser has been removed from the pool. It is the correct factor for your unmatched load in the market-based method, and it is almost always higher than the grid average — because the renewable generation has been stripped out and sold, leaving a more carbon-intensive remainder behind.

Why This Calculator Does Not Publish a Residual-Mix Factor

There is no residual-mix factor in the GreenCalculus MasterBrain. Residual mixes are published annually by national and regional bodies — the AIB European Residual Mixes for European markets, Green-e for the United States — and they are not currently surfaced as a live data feed in this engine. The calculator resolves the residual factor in this order:

• User-supplied. You enter the published residual-mix factor for your market directly into the optional residual-mix field. This is the correct, audit-grade input — obtain it from the AIB (Europe) or Green-e (US) annual publication.
• Conservative proxy. If you leave the field blank, the calculator falls back to the location-based grid factor (GB: 0.177 kg CO₂e/kWh) as a stated conservative proxy, shown with an amber warning. This understates the residual mix slightly — the true residual is higher — but it never fabricates an uplift multiplier, and it errs toward the defensible side.

The deliberate design choice is transparency over false precision: the engine will not invent a residual-mix number it cannot source. If your market’s published residual mix matters to your disclosure — and for RE100 or CSRD it does — supply it.

The Calculation Chain — Two Heroes and a Counterfactual

The calculator surfaces two headline numbers and a coverage percentage, plus an abatement panel built on a third number that is not a hero. Understanding which is which is the single most important thing on this page, because the intuitive expectation — “location-based equals total load times the grid factor” — is wrong, and a reader who expects it will read the correct figure as a bug.

The Three Numbers

Why Location-Based Is Not Total Load × Grid Factor

Onsite self-consumed renewable generation is behind-the-meter — it never enters the purchased-electricity boundary because it is not bought from the grid. Location-based Scope 2 therefore applies the grid factor to grid-supplied electricity only: total consumption minus onsite self-consumption. In the worked example below, a site consuming 10,000 MWh with 1,000 MWh of onsite self-consumption has a location-based figure built on 9,000 MWh, not 10,000.

The all-grid baseline — total load × grid factor — is the counterfactual “what your emissions would be if you bought all of it from the grid.” It exists solely to measure avoided emissions, and is never reported as a hero figure. The abatement panel splits the gap between that baseline and your market-based figure into onsite displacement and contractual benefit.

Worked Example — Mixed Procurement Portfolio, Dual Reporting

This is the calculator’s default scenario, computed client-side from the live GB grid factor (0.177 kg CO₂e/kWh, DEFRA 2025). A site consuming 10,000 MWh annually meets it from three sources: 1,000 MWh onsite self-consumed solar, 7,000 MWh of quality-passing contractual instruments, and 2,000 MWh of unmatched grid purchase.

Inputs

• Total consumption: 10,000 MWh/yr
• Onsite self-consumed renewable: 1,000 MWh (behind-the-meter — excluded from grid-supplied load)
• Contractual instruments (passing C1–C5): 7,000 MWh, counted at 0 kg CO₂e/kWh
• Unmatched grid purchase: 2,000 MWh, priced at the residual mix (proxy 0.177)
• Grid factor: 0.177 kg CO₂e/kWh (GB, DEFRA 2025, AR5 GWP-100)

The Two Heroes

Market-based Scope 2 = 2,000 MWh unmatched × 0.177 = 354 tCO₂e. The 1,000 MWh onsite and 7,000 MWh contractual both count at zero; only the 2,000 MWh remainder carries emissions.

Location-based Scope 2 = 9,000 MWh grid-supplied × 0.177 = 1,593 tCO₂e. The 9,000 MWh is total consumption (10,000) minus onsite self-consumption (1,000), because onsite never enters the purchased-electricity boundary. This is not 10,000 × 0.177.

Renewable Coverage

Coverage = (1,000 onsite + 7,000 contractual) ÷ 10,000 total = 80% — 10% onsite plus 70% contractual.

The Counterfactual and Abatement

The all-grid baseline — the hypothetical where all 10,000 MWh comes from the grid — is 10,000 × 0.177 = 1,770 tCO₂e. This is not a reported figure; it is the reference point for avoided emissions:

The identity reconciles: 177 + 1,239 = 1,416, and 1,770 − 354 = 1,416. The onsite displacement and contractual benefit together account for the entire gap between the all-grid counterfactual and the reported market-based figure.

The Green-Tariff Trap — Why “100% Renewable” Is Not Zero-Carbon

A supplier’s “100% renewable” green tariff is the most common source of an over-stated market-based claim, because the marketing implies a zero-carbon outcome the accounting does not deliver. In this calculator, a green tariff’s “Tracked & retired” (C3) and “Exclusive claim” (C2) flags default to off. A fresh, un-attested green tariff therefore fails C3 — a hard criterion — and its entire volume reverts to the residual factor. It never auto-zeroes.

The tariff volume only reaches zero when you explicitly attest that the backing certificates were retired and exclusively claimed, and that the instrument market matches your consumption market. This is the audit-trap guard: a “100% renewable” tariff is not zero-carbon unless it is backed by retired, additional certificates that no one else is counting. The default-off behaviour forces the attestation to be deliberate rather than assumed.

RE100, SBTi, and CSRD — How Procurement Claims Are Scrutinised

Renewable procurement claims do not exist in a vacuum — three frameworks examine the market-based number and the certificates behind it, each with its own emphasis.

RE100

The RE100 Technical Criteria define what counts as a credible renewable electricity claim for members committed to 100% renewable power. They set requirements on certificate type, vintage, market boundary, and the credibility of bundled versus unbundled sourcing — closely mirroring the Scope 2 quality criteria this calculator enforces. A volume that fails C1–C5 here would not be RE100-creditable either.

SBTi

The SBTi Corporate Net-Zero Standard validates emission-reduction targets against the market-based Scope 2 figure. SBTi requires the market-based method for tracking progress on electricity targets, which makes the integrity of your certificate portfolio a target-validation issue, not just a reporting one. A coverage percentage built on Partial or Weak instruments is a target-tracking risk.

CSRD / ESRS E1

Under the EU Corporate Sustainability Reporting Directive, ESRS E1 requires disclosure of both location-based and market-based Scope 2 consistent with the GHG Protocol. The dual-reporting output of this calculator maps directly onto that requirement. ESRS E1 also expects transparency on the contractual instruments underpinning the market-based figure — which is where the quality scorecard’s audit trail supports the disclosure.

Audit Checklist — Common Market-Based Reporting Errors

The errors below are the recurring sources of restated Scope 2 figures and qualified verification opinions in market-based reporting. The calculator guards against each; spreadsheet-based inventories rarely do.

• Pricing the unmatched remainder at the grid average instead of the residual mix. The remainder must carry the residual factor — grid average with claimed renewables removed. Using the grid average double-counts renewable generation someone else has already claimed, and understates the market-based figure.
• Treating a VPPA as automatically zero. A virtual PPA is a financial contract. It conveys no attribute unless the associated certificate is separately tracked and retired (C1 + C3). A bare contract-for-difference with no certificate retirement counts at the residual mix, not zero.
• Accepting a green tariff at face value. “100% renewable” supplier tariffs fail C3 by default. Without attested certificate retirement and exclusivity, the volume reverts to residual. See the green-tariff trap above.
• Including onsite self-consumed generation in location-based load. Behind-the-meter self-consumption is outside the purchased-electricity boundary. Counting it in grid-supplied load over-states location-based Scope 2.
• Double-claiming exported onsite generation. Once onsite generation is exported and its certificate sold, the attribute is gone. You can only claim self-consumed volume plus any exported volume whose certificates you retained.
• Vintage drift. Certificates redeemed more than a year from the consumption period soft-fail C4 and should be flagged. Persistent vintage mismatch undermines the credibility of the whole portfolio.
• Cross-market certificate use. An instrument sourced outside the consumption market fails C5 — a hard criterion. A North American REC does not back European consumption.
• Reporting only one figure. Location-based and market-based are both mandatory. Disclosing only the market-based number hides grid exposure and breaches the dual-reporting requirement.

Data Sources, Factor Provenance, and Uncertainty

Factor Provenance

GWP Basis

The calculator reports each grid factor at its published GWP basis and performs no reweighting — GB at AR5 GWP-100 (the AR6 alternate is identical at 0.177), US at AR4 GWP-100 as published by eGRID. Where an inventory blends markets, the basis difference is disclosed rather than harmonised, consistent with reporting the factor as its source body publishes it.

Uncertainty and Matching Basis

Grid-average factors are national annual averages and carry the uncertainty of the underlying generation-mix accounting. The residual mix carries additional uncertainty because it depends on total certificate claims across the market, which are reconciled with a reporting lag. The matching basis is annual volumetric — a coverage figure reflects annual MWh balance, not hour-by-hour supply-demand matching. Organisations pursuing 24/7 carbon-free energy claims need time-matched certificate data beyond the scope of this tool.

Frequently Asked Questions

Methodology Notes and Limitations

Dual reporting is invariant. The calculator always outputs both a market-based and a location-based figure. Neither substitutes for the other, and both are disclosed under the GHG Protocol Scope 2 Guidance and CSRD ESRS E1.

Residual mix is user-supplied or proxied. No residual-mix factor is published in the MasterBrain. You enter your market’s published residual mix (AIB for Europe, Green-e for the US), or the calculator falls back to the location-based grid factor as a stated conservative proxy with an amber warning. No uplift multiplier is fabricated.

Onsite self-consumption sits outside both figures. Behind-the-meter self-consumed generation is not grid-supplied electricity and is excluded from both the location-based and market-based totals. Only exported onsite volume with retained certificates can be claimed contractually.

Quality criteria are decisive. A contractual volume counts at zero only when it passes C1–C5. A hard-criterion failure reverts the volume to the residual factor and removes it from coverage; the scorecard names the failing criterion. Verify the coverage percentage against procured volume to catch silent reversions.

Annual volumetric matching. Coverage reflects annual MWh balance, not hourly supply-demand matching. Organisations pursuing 24/7 carbon-free energy claims require time-matched certificate data beyond the scope of this tool.

No GWP reweighting. Grid factors are reported at their published basis (GB AR5 GWP-100; US AR4 GWP-100 via eGRID). The calculator does not harmonise across GWP versions.