Why you report Scope 2 two ways
The GHG Protocol Scope 2 Guidance asks companies to report the same purchased-electricity emissions using two methods at once. They answer different questions, and reporting both prevents cherry-picking.
| Location-based | Market-based | |
|---|---|---|
| Question it answers | What the local grid emits on average | What you actually chose to buy or generate |
| Inputs | Consumption × regional grid factor | Contracts, green tariffs, RECs/I-RECs, on-site generation |
| Does solar reduce it? | Barely — it reflects the grid, not you | Yes — self-generation and renewables lower it directly |
| Evidence needed | Metered consumption + published grid factor | Per-MWh proof of the clean energy generated or procured |
The market-based method is where solar counts — if you can prove it
Because the market-based method reflects your actual electricity choices, it is the one that credits your on-site solar and any renewable procurement. That is the good news. The catch is the evidence bar: the market-based method requires contractual instruments and per-MWh generation data, and dual reporting under the GHG Protocol, CSRD/ESRS E1, and California’s SB 253 all expect it.
In other words, the market-based number is only as strong as your ability to show, per megawatt-hour, the clean energy behind it. An annual estimate from an inverter app does not meet that bar.
- RECs / I-RECs each represent 1 MWh and must be backed by auditable generation data.
- On-site generation must be evidenced per-MWh, not estimated once a year.
- The weakest link is almost always the generation proof, not the contract.
Where Wattey Energy fits — the per-MWh evidence layer
This is precisely the gap Solar Performance Cloud (SPC) fills. SPC keeps an independent, per-string, auditable record of what each system generated across every major inverter brand — the per-MWh generation evidence a market-based Scope 2 claim (and any REC issued against that generation) is built on.
As always: SPC is the measurement/source layer — it supplies the evidence; it does not compute your carbon number or issue certificates, and its records are “aligned to” monitoring standards, not a certification of your report.
