How much energy does your car use?

As part of our Energy Descent Plan we’re trying to progressively reduce our energy consumption – fuel for the car, electricity and gas in the house. This’ll save us significant money but also will reduce our carbon footprint and dependance on Fossil Fuels.

The first thing is to work out how much energy we’re using, and to that end we’ve started measuring it monthly. We’ve just finished the second month of monitoring our car usage, although they have been two crazy months (due to moving in to the eco-house) so the results may not be typical of our normal lifestyle. We’re converting all our energy use to kWh/day so that we can compare fuel/electricity/gas on an equal basis:

Month Miles MPG Litres Used kWh kWh/day
June 429 46 42.4 454 15.12
July 423 47.2 40.74 436 14.06

So we’ve already seen a significant drop in our daily energy consumption from the car 😀

I’d have to say that is a bit of a fluke – we haven’t tried particularly hard to reduce our consumption yet. It’ll be interesting to see how our consumption changes as we settle into our new routines here.

As it’s the first of the month I’ve just taken the first Gas and Electric readings in the eco-house so we can work out our standard consumption for those next month too – it’ll be interesting reading and will give us a base to measure our changes.

One of the first learning  points from this is that if we had a plug-in electric car we’d have to have at least 15 kWp of solar panels installed – that is a LOT of solar panels. It makes you realise how big an impact the car has on our energy consumption.


5 responses to this post.

  1. Browsing on a mobile, so u may already have a similar comment. Have you read Mike Berners-Lee’s new “How Bad are Bananas: The Carbon Footprint of Everything”?
    He is rightly a bit disparaging of home Solar PV installations as a v v expensive way to cut CO2. The CO2 emissions of a congested 5mile commute can equal those for the gas CH of the entire house.


    • Posted by lepotager on August 15, 2010 at 6:58 pm

      It is a very good point, and I just have two thoughts in return.
      – they are an expensive way to reduce CO2, but they are far better than doing nothing at all which seems to be the likely international governmental outcome (IMHO).
      – we are using them not only to reduce our CO2 emissions, but to increase our resilience to future power interruptions and price hikes.


      • Plus money spent on PV is not spent elsewhere, where it would cause CO2 emissions….

      • Posted by lepotager on August 17, 2010 at 6:29 am

        Very true – much better to have big shiny panels that generate power, rather than big shiny panels that broadcast Big Brother while consuming huge amounts of Electricity.

  2. Electric cars use much fewer kWh of electricity to travel 100 km than the kWh-equivalent of the petrol a conventional car would use to travel the same distance. A small electric car uses about 12 kWh to travel 100 km. A larger car might use 20 kWh.

    In your July figures, you’re travelling about 22 km/day, which would only use 4.4 kWh even in a 20 kWh/100km electric car. So you’d only need about 1 kW of solar panels to keep the car charged (assuming you get 4-5 peak sun-hours equivalent per day).

    I did some calculations on the CO2 comparisons between electric and petrol cars on my blog, and even assuming electricity from a coal-fired power station the electric cars come out ahead:

    Oh, and I agree with Nick on the solar panel thing. You could just sign up for “green electricity” for a fraction of the price and completely negate the CO2 output. Also, most grid-tied home solar systems won’t give you resilience to power interruptions, since they normally don’t have any battery storage system. They have safety cutouts so they stop producing if the grid goes down.


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