1 Feb 2020

Carbon-free electricity

The race is on to produce zero carbon electricity, which is the most straightforward way of slowing/stopping climate change. But how realistic is this goal, and how long will it take? Here's a summary of the situation in the UK.

When we say 'zero carbon electricity' we are referring to how electricity is made, not what's in it. Using fossil fuels to make electricity (the traditional method, if you like) burns lots of carbon which releases loads of carbon dioxide (CO2) into the atmosphere. Renewable technologies, hydro power and nuclear power produce electricity without burning any carbon and are therefore said to be zero carbon. The electricity we now use is from a mix of sources and therefore can be said to have a carbon intensity factor, depending on how much is derived from fossil fuels (carbon) and how much from zero carbon sources. The higher the proportion from fossil fuels, the greater the carbon intensity is said to be.

The standard measurement (or metric) used to express the carbon intensity of electricity is grams of CO2 equivalent per kWh (kilowatt hour) of power, written XXXgCO2ee/kWh. The word "equivalent" is in here because other climate changing gases (notably methane) are also released during the production processes and these have to be taken into account when considering the global warming effect of the different gases. It's a complex field and the maths is not quite as straighforward as we might hope for. Methane has a large global warming footprint, but only stays in the atmosphere for a few years, unlike CO2 which hangs around for centuries before slowly being absorbed by the oceans.

When we first started making electricity on a commercial scale, the preferred method of production was to use coal-fired power stations to drive huge turbines. Coal-fired electricity has a very high carbon intensity factor, as it releases masses of CO2: anywhere from 750 to 1,000g/kWh, depending on the type of coal and the efficiency of the plant. Coal also happens to be a dirty, toxic fuel which poisons a lot of people, but that is not what concerns us here. Using gas to make electricity is a much better option than coal (and it's cleaner) but it still produces a lot of CO2 —  it scores between 380 and 480g CO2ee/kWh/kWh.

In contrast, with the notable exception of biomass, all the non-fossil fuel production methods are zero-carbon. That doesn't mean there aren't other issues surrounding their use: nuclear power maybe zero-carbon but it is not zero-problem (Chernobyl, Fukashima etc). But from a carbon intensity point of view, they all score zero. Or 0g CO2ee/kWh. To be pedantic, there are carbon costs with renewables but they are solely to do with the construction or manufacture of the equipment — known as embodied carbon.

The carbon intensity of fuel table can be summarised thus (all in g CO2ee/kWh):
Lignite: 850 - 1100
Coal: 750 - 1000
Oil: 550 - 700
Natural gas: 380 - 480
Biomass: 50 upwards
Nuclear: 0
Wind, solar: 0
Hydroelectric: 0

More details via Google or Wikipedia but a good source is here.


The history of UK electricity production shows the carbon intensity was high, at around 700g CO2ee/kWh in the 1970s when it was almost all produced by coal-fired power stations. As the switch to gas took place over the following decades, the intensity falls to around 450g CO2ee/kWh. Here is a useful summary of the situation up till 2015.  However, since 2015, the rate of change has accelerated dramatically, as you can follow here. The principle reason for this is the switch to offshore wind farms, which have had a massive effect. Maybe because it is happening out at sea, we are only barely aware of this major infrastructural change. Other factors include decreasing demand for electricity overall (which makes it easier to drop coal from the energy sources), an uptake in solar PV and a switch from coal to biomass as the huge Drax power station in Yorkshire which alone accounts for around 8% of the UK electricity demand. Currently UK electricity averages around 230g CO2ee/kWh


What it means is that electricity has gone from being a much higher carbon intensity than gas to becoming much the lowest carbon intensity power source, all in the past five years. And it is due to head lower still over the next 15 years, as we move to decarbonise the grid. Electricity is, however, over three times the price of natural gas, so a switch to electric heating is still unlikely any time soon, especially as the cost of heat pumps, the obvious technology to employ here is way more than a standard gas boiler.

I for one hadn't realised quite how quickly this change would take place and as a result fitted a gas condensing boiler in our new home - a decision made in 2017 - on the basis that we had done everything possible to minimise the heat load and that, as electricity released rather more CO than gas, it made sense to go with the cheaper power source.

The government has recently published the Future Homes Standard which is a mixed bag of proposals outlining measures to decarbonise our housing over the coming decade. It's received a very lukewarm review from almost every commentator, but the headline move contained in the proposals is that ‘new homes should not be connected to the gas grid from 2025’. 


Given the huge change in the mix of energy sources we are using to make electricity, this single proposal will rank as the most significant decarbonising measure we have ever taken.

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