The short answer
RECs (renewable energy certificates) are tradeable green attestations.
A "100% renewable" electricity supply contract does not mean the electrons flowing to your meter were generated by wind and solar — that is impossible to track on a shared grid. What it means is that for every kWh you consume, a corresponding kWh of certified-renewable generation has been generated and the renewable attestation (a Renewable Energy Certificate, or REC) has been retired on your behalf. This guide walks through how RECs actually work, the difference between voluntary and certified-renewable, and what Green-e Energy adds.
How RECs work — the 1-MWh attestation
A Renewable Energy Certificate (REC) is a tradeable certificate that represents 1 MWh of certified-renewable generation. Wind farms, solar farms, and hydro generators issue RECs as part of the same generation event that puts kWh onto the grid.
Suppliers buy RECs in bulk and retire them on behalf of customers who choose a renewable supply contract. When the supplier retires a REC for you, the renewable attestation flows through to your bill as "100% renewable" (or "30% renewable" if you chose a partial-renewable tier).
The electrons themselves are physically indistinguishable from non-renewable electrons on the grid. The REC is the accounting layer that makes "100% renewable" verifiable.
Voluntary RECs vs Green-e certified — the quality tier
Voluntary RECs are the standard product. They cover renewable generation but do not require third-party verification of the supply chain. The premium over standard supply is typically 0.3–0.6¢/kWh.
Green-e Energy is the strictest US third-party certification. It requires independent verification that the RECs come from generation built within the last 15 years, that they are not double-counted, and that they meet additional sustainability criteria. The premium is typically 0.6–1.2¢/kWh.
For commercial accounts with sustainability reporting requirements (CDP, GRI, SBTi), Green-e certification is usually the relevant tier. For households, voluntary is usually sufficient.
Infographic
Green electricity premium by certification tier
Direct power-purchase agreements (PPAs) — the next tier up
A Direct PPA is a contract directly with a specific renewable generator (a specific wind farm, a specific solar farm) for a specific volume of generation over a long term — typically 10–15 years. Direct PPAs are the strongest renewable supply structure but also the most operationally complex.
Direct PPAs are usually only economical at scale — 10+ MW of contracted load — and require a long-term commitment that most commercial buyers cannot justify. For most commercial accounts, Green-e certified RECs deliver 90% of the same sustainability outcome at 10% of the operational complexity.
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