Market-based vs location-based electricity

Electricity has two factors because the GHG Protocol Scope 2 Guidance asks you to report it twice. The location-based figure uses the average emissions of the grid where you consume the power. The market-based figure uses what you bought: your supplier's contract, a certified green tariff, or the residual mix when you hold no such contract.

Two methods, reported side by side#

• Location-based. It reflects the physical grid. Every consumer in the same country gets the same number, whatever tariff they signed.
• Market-based. It reflects your purchasing choices. A contract backed by guarantees of origin can bring the number close to zero, and whoever buys no such contract picks up what is left over.

You report both totals, next to each other. They answer different questions, so you never add them and never swap one for the other inside a total.

Watch out. The two methods can differ by a factor of two or more for the same country and year. A location-based factor in a market-based inventory is not a small approximation, it is a different answer.

The grid mixes#

The data records the method in calculation_approach and the precise mix in grid_mix. Each mix belongs to exactly one method, and the pair is enforced, so a row can never claim a residual mix under the location-based method.

In factor search, filter on the method with approach and on the mix with grid_mix, for example all residual mixes.

The residual mix#

A residual mix exists to prevent double counting. When a wind farm sells a guarantee of origin to one buyer, that buyer claims the low-carbon power. The same kilowatt-hours must then leave the pool shared by everyone else. The residual mix is that remaining pool, so it is usually higher than the grid average.

Which library publishes which mix#

Counts are default top-level factors. These are the libraries these docs use for examples; other libraries in factor search publish grid mixes too, and the grid_mix filter shows them all.

A worked example: the UK#

Both factors below cover only the power generation stage (system_boundary = generation), so they compare like for like.

The market-based residual mix is more than twice the grid average. A UK company with no green contract reports 0.28064 in its market-based total and 0.13096 in its location-based total, for the same meter reading.

Spain shows the other end of the range. MITECO's residual mix is 0.258 kg CO2e per kWh, and its renewable guarantee-of-origin factor is 0.0. The zero applies only to power covered by those guarantees. AIB publishes its own Spanish residual mix too, at 0.23828: two publishers, two methods of building the residual, two numbers. Pick one and say which.

For France, see the AIB residual mix factor page.

What the grid factor leaves out#

A generation row covers the power plants only. Losses in the transmission and distribution network, and the upstream emissions of the fuels the plants burn, are separate rows with their own system_boundary (transmission_distribution, upstream_fuel). DESNZ publishes all of them for the UK. Where a publisher prints generation only (AIB, EPA and eGRID among the public libraries), open-climate.ai adds the two legs and a total as marked estimates; Estimated electricity legs gives the rule, the numbers and how to leave them out. Check the boundary before you add an upstream or losses factor, and read System boundaries for how the parts relate to the total.

Related#

• Choose a supplier-specific electricity factor
• Glossary: grid mix and calculation approach
• Choosing between similar factors
• System boundaries
• Estimated electricity legs