Most people will charge their electric vehicles (EVs) from the grid and as the grid is fueled mostly by fossil fuels (approx 70%) there will be emissions created at the power stations. This much is pretty much universally accepted. A figure of about 500g CO2/kWh is often quoted but this figure is not a fixed value. The amount of CO2 varies from hour to hour, in fact from minute to minute, as the load on the grid varies and as power stations need to ramp up generation to meet demand.
Wouldn’t it be good if you could know when the least amount of CO2 is being produced by the grid? You could then charge your EV at those times of reduced emissions? Well actually… you can!
There are several places you can get this information both in real time and historically. The real time information is useful because you can look at the CO2 being produced right now and that can help you decide if now is a good time to plug in. The place I go to get this real time information is the Ecotricity web site.
This web site is updated about ever 15 minutes. It is clear and easy to see what CO2 is currently being produced by the grid and also the current mix of renewables, fossil fuels and nuclear. There is a simple traffic light graphic to guide you… green means emissions are currently low so now is a good time to plug in, orange means more emissions so you might want to hold off and red is high emissions so don’t plug in now unless you have to. Very useful if you want a snapshot of the currect state of the grid.
However, most of us charge our EVs overnight. We are not going to get up in the middle of the night and get on the internet to decide whether to charge or not! Well we don’t have to. The daily cycle of demand is such that the patterns of high and low demand, and hence high and low CO2 emissions, is fairly predictable. At the moment the period of lowest demand is 11pm through to 5am. You can be pretty sure that if you charge your car between these times you will create the lowest levels CO2 as a result.
You can see the hourly breakdown of the previous day here:
But surely it doesn’t matter that much does it? Don’t power stations run regardless? Well yes it does matter – a lot! Typically, fossil fuel power stations are powered up and down to meet the demand. At night, during that period of low demand coal and gas power stations are simply shut down or put into a standby mode. Shutting down a power station in this way allows it to cool down and must then be brought back up to working temperature in the morning when demand increases. This stopping and restarting the power station wastes a huge amount of energy… and for wasted energy read unnecessary CO2! By charging our car at night we are increasing demand on the grid during that quiet period reducing the need to shut down power stations and evening out the demand over the 24hr period. This saves huge amounts of CO2.
There is another aspect… CO2 generated during the day is affected by the sun resulting in more harm to the atmosphere. If we have to produce any CO2 at all then producing it at night is much less harmful to the environment.
CO2 emissions vary throughout the day from about 350g/kWh to about 550g/kWh. Charging your EV during the low demand periods saves huge amounts of CO2 and is well worth it.
So, if you have a Nissan Leaf why not set your charging timer to charge between 12pm and 5am? If you don’t need a full charge everyday it won’t affect you at all and you will be ensuring that you create the least possible CO2. If you need a boost or need to ensure that you have charged to 100% then just press the charge button on the dash. The car will then start charging immediately and also charge to 100%. Easy.
There is a caveat that is worth mentioning here and I have yet to find a satisfactory solution to this… what if you have solar PV? Isn’t it better to charge when the sun is shining and so not taking power from the grid at all? Possibly. If you have a large solar PV system, say over 3.5kWp and the sun is shining then charging your car will not use power from the grid, you will not be loading up demand and you will not be paying for that electricity. However, if the sun isn’t shining, or if like me you have a smaller PV system (mine is 2.4kWp) then things are less clear. Charging during the day then does take some power from the grid because the solar PV system will not be generating sufficient power to fully satify the 3.6kW needed for the car. What then? Am I better off charging during the day, using all the solar power I can but still needing to take power from the grid during peak times? Or am I better off allowing that solar power to go out to the grid where someone else can use it, reducing the overall demand on the grid, and then me charging my car at night?
I think it depends on my priorities. If it is more important to me that I reduce the CO2 emissions then charging overnight is the way to go. I then reduce the grid load at peak demand times (during the day) and load up the grid at night when I charge. This has the best effect on the grid and on emissions. However, it will cost me a bit more because I then have to buy all my car power from the grid at your normal rate (13p/kWh for me) but I can only sell my solar power at 3p/kWh. If money is my priority then I will be better off using my solar power myself by charging the car during the day.
So, from now on I will be charging at night between 12pm and 5am whenever possible. It will cost me a little more (for me probably about £100pa) but as the car is costing so little to run anyway I am happy to pay that little bit extra to significantly reduce my CO2 emissions. Or why not subscribe to dual-tariff electricity? There are Economy 7 or special EV tariffs now. Price is a little more in the day but very much cheaper at night. Worth a thought I would imagine.