Q4 2017: Carbon emissions down 12%

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by Dr Iain Staffell – Imperial College London 

2017 was once again the cleanest year for electricity production in Britain. 

Carbon emissions (including those from imported electricity) were 72 million tonnes over the year, down 12% on 2016 due to lower coal and gas production. This amounts to 150 kg of CO2 saved per person – equivalent to taking one in seven cars off the road (4.7 million in total).1 Yet this saving comes without requiring any active change in people’s lifestyles.

The average carbon content of electricity has fallen to 237 g/kWh over 2017. The average during Quarter 4 was 272 g/kWh, greater than the year-round number as more fossil fuels are used when demand is higher. The range2 last quarter was 140–360 g/kWh, compared to 400–510 g/kWh just four years ago (see chart bottom left). The instantaneous carbon intensity hit a record low of 56 g/kWh just after midnight on the 2nd of October (20% below the previous minimum in June). At the time, just 12% of electricity came from gas, the rest was low carbon. Q4 saw 41 hours with a carbon intensity under the important threshold of 100 g/kWh, bringing the total for the year to 139 hours (up from just 4 hours in 2016).

What does a low-carbon grid mix look like? The chart below-right shows Britain’s average grid mix for different levels of carbon intensity. The cleanest mixes are only seen during times of low demand (e.g. overnight in Summer). Reaching below 100 g/kWh generally requires 50% renewable energy and demand below 30 GW. An absence of coal is generally needed to stay below 200 g/kWh. As all of these features are becoming more common, we expect more time under 100 or 200 g/kWh in the future.

Daily average carbon intensity of electricity in 2017 and previous years (left). The average generation mix for different levels of carbon intensity (right). The cleanest mixes on the left are mostly seen in recent years, and the dirtiest mixes on the right were mostly seen before 2013 

1: Based on there being 31.7 million cars in the UK which emit 68.5 MTCO2 per year
2: 5th to 95th percentile of daily averages – meaning 90% of days in the quarter lie within this range.

Authors: Dr Iain StaffellProfessor Richard GreenDr Rob Gross and Professor Tim Green.

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