02What's flowing through the wires?

Why the price is what it is: the fuel on the margin

Which fuel decides what everyone pays for electricity, hour by hour?

When gas sets the electricity price, the wholesale price tracks the cost of running a gas plant. Comparing each day's German price to the modelled running cost of a gas-fired plant over the 12 months to September 2026, the model has gas setting the price on about 64% of the 351 days classified, and renewables on about 4%.

A model: it infers when gas sets the price, which nobody observes directly.

This is a model: it infers when gas sets the price from a gas plant's running cost and the day-ahead price. Its assumptions are listed under "How the model works"; change them and the picture changes.
Wholesale price and the running cost of a gas plant
Wholesale price (ENTSO-E, measured) Gas plant running cost (modelled) Gas price (TTF, World Bank)
What sets the price
modelled, over the classified days
How the model works
  • The gas series is the TTF benchmark (the Dutch gas trading hub, Title Transfer Facility) from the World Bank's monthly commodity price table, the “Pink Sheet”, published under CC BY 4.0 and converted from USD/mmbtu to €/MWh with ECB reference rates. It is a monthly benchmark; a plant pays the day-ahead spot.
  • The carbon price is the price of an EU permit to emit a tonne of CO2 (an EUA), from EEX primary auctions, set by hand and dated on the page. It moves slowly.
  • The marginal fuel is the fuel of the most expensive plant still needed, which sets the price for everyone. Wattlas compares each day's wholesale price to the modelled running cost of a gas plant and attributes the day to gas, renewables or "other". The split carries assumptions about plant efficiency, fuel cost and bidding that Wattlas cannot check.

For what Wattlas measures directly from ENTSO-E, Generation Mix shows generation by fuel, and Carbon Intensity shows the grams of CO₂ in each kilowatt-hour, counted where the power is generated.

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Questions

How often does gas set the German electricity price?

On about 64% of the 351 days classified over the 12 months to September 2026, according to a model that compares each day's German price with the running cost of a gas-fired plant; renewables set it on about 4%. This is a model: it infers when gas sets the price, which nobody observes directly.

What is the marginal fuel?

The fuel of the most expensive plant still needed in an hour, which sets the price for everyone. When gas is marginal, the wholesale price tracks the cost of running a gas plant. Over the 12 months to September 2026, the model has gas setting the German price on about 64% of the days it classified.

How these numbers are made: The marginal-fuel model.

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More in “What's on the Grid”
Midday Ramp-downWhen solar peaks at midday, how far the plants that can turn down do turn down, in six bidding zones, fuel by fuel, and at what price.Generation MixGeneration by fuel for any bidding zone: France's steady nuclear beside Germany's changeable wind and solar.Carbon IntensityHow many grams of CO₂ each kilowatt-hour carries, computed from the generation mix.Residual LoadDemand minus wind and solar: what other plants and batteries must still cover.