Replacing your car with an EV

How much can you reduce your greenhouse gas emissions (GHG) by switching from your diesel car to an EV and how much will this cost?
Introduction This tool is based ona simple model and the results are only an estimate. All the assumptions used are listed and you can modify them for your situation - apart from the GHG emissions of the fuels.
Vehicles and mileage
  • Current vehicle   
  • Your EV replacement   
  • Enter year 0 for now, enter 100 for never

Results summary
  • Your EV will use   kWh each year.
  • Of this you get  % from your solar panels.
  • Over   years you save   tonnes carbon.
  • Your initial cost is £  and overall net   of £ 

For comparison, the average UK resident emissions is 8-12 tonnes/year depending on how you measure it.

GHG emissions graph
GHG emissions table (tonnes)
When Current EV Difference
Initial/replacement Diesel C EV C  
Annual Diesel 1 EV  
Total emissions ( ) Diesel EV Difference
Cost graph
Costs table (£)
When Current EV Difference
Diesel £ EV £  
Annual Diesel 1 EV  
Total cost ( ) Diesel EV Difference

Additional assumptions

  • If you know it in miles per litre, multiply by 4.5

  • If you know it in miles per litre, multiply by 4.5

Fuel/electricity prices
  • If you charge at home you should get a suitable tariff with cheap off-peak electricity. If you charge in different locations, give the average price you wll pay.

Other costs
  • Cost to buy your new (or second hand) EV and charging equipment. The RAC lists EVs from £17,000 but mid-range is £30-40,000

  • Cost to buy your new (or second hand) replacement car

  • Cost to buy your new (or second hand) replacement car

  • Proceeds from selling your current car

  • Yearly cost for insurance, maintenance etc. excluding lease.

  • Yearly cost for insurance, tax, maintenance etc

Upfront emissions
  • For a new car, specify the emissions here: 5 tonnes is typical for a mid range car. Enter 0 for a second hand car.

  • For a new car, enter the emissions here. 10 tonnes is typical for a mid range electric car . Enter zero for a second hand car .

Solar PV panels
  • Enter your parameters to estimate how much of your EV charging energy could come from your solar PV panels. It assumes that you can charge up during the day directly from your panels, using power that you would have exported.

  • Estimation method

    If you know your typical monthly export by month then we can use that. Otherwise we can estimate it less accurately

  • If you do not know, multiple your array size in kWp by 800. So if you have a 4 kWp array try 3200.

  • This is the usable kWh, which may be less than the nominal capacity.

  • If you have a solar array at home with an export meter and you get paid for your measured export, enter the export tariff here. This is the cost to you of using your own electricity.

  • More solar assumptions
    • You do not have any solar panels

    • This is the average over the year and it includes everything that you do not export to the grid. So if you have a battery, this includes losses in the battery.

    • Many homes use more electricity in winter than in summer - for example you use the tumble dryer more in the winter

    • Using your own solar power or taking it from the grid makes no difference to overall carbon emissions, because your solar panels are effectively part of the grid and they generate whether you need power or not. If you prefer you can treat your solar power as zero emissions.

  • Solar chart

The GHG emissions factors are xxkg/kWh for electricity, xxkg/litre for petrol and xxkg/litre for diesel. These factors include upstream emissions for fuel and and transmission losses for electricity. Carbon emissions from electricity reduce by xx% each year. Inflation has not been taken into account.

See Assumptions and data sources for background on these default values.


A small car could be as little as half the average, a larger car two or three times as much. For EVs, the size of the battery is an inportant part of the embodied emissions.


You can also consider the new car emissions over the lifetime over the car. For example, if you are likely to get a car with 30,000 miles on the clock and you consider 100,000 miles is a reasonable lifetime, you could allocate 30% of the emissions to the previous owner and 70% to you - so adjust the emissions down by 30% from new. Or if you intend to sell it after 30,000 miles, adjust the emissions to just your 30%.

  • The yield from your solar panels varies over the year according to the season and weather. We have used figures for the East of England.
  • If you do not know your export we estimate your self consumption based on monthly electricity use, solar power yield and battery size according to the standard method used in SAP 10 - an update of the method currently used to calculate the Energy Performance Rating of your house. From this we calculate your monthly export.
  • For charging a car, or for use of stored heat, we assume that all this exported energy is available for charging, on a day to day basis. I.e. the amount used for charging is either the daily requirement or the daily export, whichever is the smaller.
  • For other applications we assume that only a proportion of this energy is available for use and a proportion of the demand can be met, because of misalignment between the demand and the available power. For example, space heating is needed mainly in the mornings and evenings when there is little if any sun, and the power generated during the day may be more than is required at that time. This is less of a problem if you are using a battery but it still applies as the battery is of limited size. The estimate is rather crude and not as reliable as a professional estimate with more information to work on.

For more detail see References