Deep decarbonisation is still a huge challenge

In 2019 I wrote a blogpost called The challenge of deep decarbonisation, stressing the scale of the economic and technological transition implied by a transition to net zero by 2050. I think the piece bears re-reading, but I wanted to update the numbers to see how much progress we had made in 4 years (the piece used the statistics for 2018; the most up-to-date current figures are for 2022). Of course, in the intervening four years we have had a pandemic and global energy price spike.

The headline figure is that the fossil fuel share of our primary consumption has fallen, but not by much. In 2018, 79.8% of our energy came from oil, gas and coal. In 2022, this share was 77.8%.

There is good news – if we look solely at electrical power generation, generation from hydro, wind and solar was up 32% 2018-2022, from 75 TWh to 99 TWh. Now 30.5% of our electricity production comes from renewables (excluding biomass, which I will come to later).

The less good news is that electrical power generation from nuclear is down 27%, from 65 TWh to 48 TWh, and this now represents just 14.7% of our electricity production. The increase in wind & solar is a real achievement – but it is largely offset by the decline in nuclear power production. This is the entirely predictable result of the AGR fleet reaching the end of its life, and the slow-motion debacle of the new nuclear build program.

The UK had 5.9 GW of nominal nuclear generation capacity in 2022. Of this, all but Sizewell B (1.2 GW) will close by 2030. In the early 2010’s, 17 GW of new nuclear capacity was planned – with the potential to produce more than 140 TWh per year. But, of these ambitious plans, the only project that is currently proceeding is Hinkley Point, late and over budget. The best we can hope for is that in 2030 we’ll have Hinkley’s 3.2 GW, which together with Sizewell B’s continuing operation could produce at best 38 TWh a year.

In 2022, another 36 TWh of electrical power – 11% – came from thermal renewables – largely burning imported wood chips. This supports a claim that more than half (56%) of our electricity is currently low carbon. It’s not clear, though, that imported biomass is truly sustainable or scaleable.

It’s easy to focus on electrical power generation. But – and this can’t be stressed too much – most of the energy we use is in the form of directly burnt gas (to heat our homes) and oil (to propel our cars and lorries).

The total primary energy we used in 2022 was 2055 TWh; and of this 1600 TWh was oil, gas and coal. 280 TWh (mostly gas) was converted into electricity (to produce 133 TWh of electricity), and 60 TWh’s worth of fossil fuel (mostly oil) was diverted into non-energy uses – mostly feedstocks for the petrochemical industry – leaving 1260 TWh to be directly burnt.

To achieve our net-zero target, we need to stop burning gas and oil, and instead use electricity. This implies a considerable increase in the amount of electricity we generate – and this increase all needs to come from low-carbon sources. There is good news, though – thanks to the second law of thermodynamics, we can convert electricity more efficiently into useful work than we can by burning fuels. So the increase in electrical generation capacity in principle can be a lot less than this 1260 TWh per year.

Projecting energy demand into the future is uncertain. On the one hand, we can rely on continuing improvements in energy efficiency from incremental technological advances; on the other, new demands on electrical power are likely to emerge (the huge energy hunger of the data centres needed to implement artificial intelligence being one example). To illustrate the scale of the problem, let’s consider the orders of magnitude involved in converting the current major uses of directly burnt fossil fuels to electrical power.

In 2022, 554 TWh of oil were used, in the form of petrol and diesel, to propel our cars and lorries. We do use some electricity directly for transport – currently just 8.4 TWh. A little of this is for trains (and, of course, we should long ago have electrified all intercity and suburban lines), but the biggest growth is for battery electrical vehicles. Internal combustion engines are heat engines, whose efficiency is limited by Carnot, whereas electric motors can in principle convert all inputted electrical energy into useful work. Very roughly, to replace the energy demands of current cars and lorries with electric vehicles would need another 165 TWh/year of electrical power.

The other major application of directly burnt fossil fuels is for heating houses and offices. This used 334 TWh/year in 2022, mostly in the form of natural gas. It’s increasingly clear that the most effective way of decarbonising this sector is through the installation of heat pumps. A heat pump is essentially a refrigerator run backwards, cooling the outside air or ground, and heating up the interior. Here the second law of thermodynamics is on our side; one ends up with more heat out than energy put in, because rather than directly converting electricity into heat, one is using it to move heat from one place to another.

Using a reasonable guess for the attainable, seasonally adjusted “coefficient of performance” for heat pumps, one might be able to achieve the same heating effect as we currently get from gas boilers with another 100 TWh of low carbon electricity. This figure could be substantially reduced if we had a serious programme of insulating old houses and commercial buildings, and were serious about imposing modern energy efficiency standards for new ones.

So, as an order of magnitude, we probably need to roughly double our current electricity generation capacity from its current value of 320 TWh/year, to more than 600 TWh/year. This will take big increases in generation from wind and solar, currently running around 100 TWh/year. In addition to intermittent renewables, we need a significant fraction of firm power, which can always be relied on, whatever the state of wind and sunshine. Nuclear would be my favoured source for this, so that would need a big increase from the 40 TWh/year we’ll have in place by 2030. The alternative would be to continue to generate electricity from gas, but to capture and store the carbon dioxide produce. For why I think this is less desirable for power generation (though possibly necessary for some industrial processes), see my earlier piece: Carbon Capture and Storage: technically possible, but politically and economically a bad idea.

Industrial uses of energy, which currently amount to 266 TWh, are a mix of gas, electricity and some oil. Some of these applications (e.g. making cement and fertiliser) are going to be rather hard to electrify, so, in addition to requiring carbon capture and storage, this may provide a demand for hydrogen, produced from renewable electricity, or conceivably process heat from high temperature nuclear reactors.

It’s also important to remember that a true reckoning of our national contribution to climate change would include taking account of the carbon dioxide produced in the goods and commodities we import, and our share of air travel. This is very significant, though hard to quantify – in my 2019 piece, I estimated that this could add as much as 60% to our personal carbon budget.

To conclude, we know what we have to do:

  • Electrify everything we can (heat pumps for houses, electric cars), and reduce demand where possible (especially by insulating houses and offices);
  • Use green hydrogen for energy intensive industry & hard to electrify sectors;
  • Hugely increase zero carbon electrical generation, through a mix of wind, solar and nuclear.

In each case, we’re going to need innovation, focused on reducing cost and increasing scale.

There’s a long way to go!

All figures are taken from the UK Government’s Digest of UK Energy Statistics, with some simplification and rounding.