ELECTRIC vehicles are only as "green" as the electricity they draw from the grid. The National Grid draws on low-carbon generation in preference to high-carbon. When the wind blows strongly, gas generation is shut down. When the wind doesn’t blow, gas is ramped up to compensate. Worst of all for climate change, coal is brought on line.
On a fairly benign November day (Monday 6th, 9:45 a.m.) 12 per cent of Great Britain’s electricity is coming from burning coal. Just over half is from gas, and under one-third from low-carbon generation such as nuclear, wind, solar and hydro.
Compared with my Euro-6 diesel emitting 96g/km of CO2, an electric car being charged from the grid at this time would appear to emit only one-third of the CO2 per km. But that’s not how the grid works.
The appropriate comparison is not the average grid emissions but the marginal grid emissions caused by increased demand. As demand increases, so increasingly higher-carbon generators are brought on line. Initially that’s gas, then coal.
If electric car charging requires more gas generation to be added to the grid, the CO2 emissions per km increase to over half those of my diesel car. If it requires coal generation to be added, the emissions are 15 per cent higher than my diesel.
If demand for electricity was reduced we could cut out coal completely, but electric vehicles are adding to demand and helping to keep coal going.
(Dr) Dave Gordon,
60 Bonhard Road, Scone.
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