How well renewables are working, and what gets wasted

Britain's windiest places and its biggest demand are at opposite ends of the country. Scotland generates far more wind power than it uses, and the transmission lines running south can only carry so much. When more is produced than the network can move, something has to give.

What gives is the generator. The system operator accepts a bid from it to produce less, and pays it to stop. The energy is not stored or redirected anywhere - it simply never gets produced, and the wind passes through the turbines unused. Gas plants nearer the demand are then paid to make up the shortfall, so consumers pay twice.

This is a network problem rather than a wind problem. New transmission links and grid-scale storage are being built to relieve it, but they take years, while wind capacity has grown quickly. Curtailment is the visible cost of that mismatch.

Forecast error matters for a related reason. Wind being variable is manageable; wind being unpredictable is expensive, because the system operator has to hold other plant in reserve to cover whatever the forecast gets wrong. A smaller error means less standby generation burning fuel for nothing.

Solar curtailment cannot be reported from this data, and it would be misleading to show a zero. Almost all of Britain's solar is connected to local distribution networks rather than the transmission system, so it never enters the Balancing Mechanism - the market through which generators are instructed and paid to change output.

There is no solar fuel type in the Balancing Mechanism unit register at all. A handful of very large solar farms are registered under a general category, but they are a small fraction of installed solar and are not identifiable as solar with any confidence.

Wind, hydro and biomass are all shown above, because those do appear in the register and are all curtailed in practice. Solar is the one renewable this data cannot speak to.