The wild tide of the mix

Much is said of the energy transition, in particular the task of generating power (electricity). The UK in particular has made great strides in reducing its national carbon emissions, through largely phasing out the use of coal power stations and greatly increasing the installation of wind turbines out at sea. 

The sometimes flipside of this transition, for all of its benefits to the climate and local air quality, is that the carbon reductions aren't evenly spread. Many consumers have been lulled into a false sense of security, by spending a few minutes signing up to a 'green energy supplier' and thinking that it's all it takes to reduce their household's impact on the climate. (The UK government is so concerned that consumers are being mislead by 'green tariffs' that it has launched an official probe.)

Leaving aside for a moment that the majority of the energy consumed in most UK homes is natural gas (a fossil fuel), it's not even always the case that the electricity that you use is consistently 'green'.

I can illustrate this inconsistency over the course of two recent contiguous days, by showing you the 'carbon intensity' of the power carried on the 'South England' zone of the UK power grid, which supplies my home (and many millions of others).

Here is Sunday 3 October 2021. The picture is a screenshot of the free Android app 'GreenTime' (also available for Apple iOS devices). It uses public data from the UK power grid to show the actual and forecast carbon intensity of your power supply, using forecasts of wind and solar potential, planned outages at power stations, and so on. 

You can see that on Sunday it's a fairly green state of affairs. Pretty much whenever I turned on my appliances or plug in my devices, it would be relatively low impact from a carbon emissions perspective. The bottom half of the screen shows why. At around 9pm, the most carbon-intense time, roughly half of the power generation being supplied came from low carbon sources: wind, nuclear, biomass (ok, that one's hotly debated) and imports from France (most nuclear powered). If this were a typical summer day, we'd also expect to see solar power performing strongly, especially in the early afternoon, making the daily variation more pronounced. I used this graph to work out when to set the timer on my washing machine, and when to bake some bread in my electric oven (i.e. between midday and 1pm, when carbon emissions were around 130 grams per kWh).

Now let's look at the next day. You'll see from the chart that Monday has a very different perspective.

And here we can see that it doesn't really matter whether or not I had chosen a 'green' tariff (which I happen to have). Whatever is in the grid is what powers our homes, for if the wind resource is lower, Britain has little alternative but to rely more heavily on power stations powered by natural gas, especially on cloudy or winter days. Here we can see that, again at 9pm, natural gas is likely producing over three quarters of the electrons powering my house. (At best, gas was around two thirds of the source, and carbon intensity was still over 200 grams per kWh).

Wind was a low 7% contributor. It didn't help on either day that the main France to UK power interconnector cable had recently suffered a fire, putting the 2GW cable out of action until at least spring 2022. Despite gas prices quadrupling in the space of four months, gas power stations have had to fill a lot of the gap of record lower wind resource over the past year.

My point is that it makes a difference when to charge your electric car, put on a heavy load of washing or cook that roast, regardless of your choice of tariff or energy supplier. Looking at the GreenTime app, I might see that I should do my washing on Saturday, not Sunday, or that charging my car for the week ahead is best on Sunday morning, not Sunday night. Sometimes we are lucky that wind power (which Britain leads the world in harnessing) is plentiful, and the sun shines, but this isn't always the case. Much of the gap is still powered today, despite what many of us think, by fossil fuel.