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?

The charts below show cumulative emissions and cost. All the assumptions used are listed and you can modify them for your situation - apart from the GHG emissions of the fuels. If you expect to charge from your own solar PV panels, use the Solar estimator below to see how much difference this will make.


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

Your overall GHG savings and costs over the period.

When Carbon (t CO2e) Cost (£)
  Current EV Difference Current EV Difference
Diesel C EV C   Diesel £ EV £  
Annual Diesel 1 EV   Diesel 1 EV  
Total Diesel EV Difference Diesel EV Difference

Edit these assumptions for your situation


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

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

Yearly cost for insurance, tax, maintenance etc

Enter year 0 for now, enter 100 for never

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

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

Your EV replacement

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.

If you have a solar PV array, estimate the proportion of charging electricity you will be able to use for this here.

Yearly cost for insurance, maintenance etc. excluding lease.

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

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 .

The GHG emissions factors ar 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.

Solar Estimator

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.

You do not have any solar panels

Estimated current import and export:
0 kWh import from the grid (your electricity bill)
0 kWh export to the grid

Charging direct from your panels during the day (with a smart charger so it only runs when you have power to spare), you could obtain 0% of your EV charging from your PV array.

To use the estimated value, enter 0 below. If you think this is too high, enter your value here.

Solar power assumptions

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

Please enter your typical export in kWh/month

Ok - we will estimate from your array size and your own use

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.

We need to estimate how much of your solar power you are already using but this is not measured directly. If you know your bill, please adjust these values until the estimated import (right) is reasonably close to your bill. Within 10% is about as good as you can expect.

This includes your self consumption from your solar PV. As a first guess, try your annual bill kWh (what you draw from the grid) plus a third of your annual generation.

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

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.

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.

Assumptions behind the solar calculations

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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