Electric fuel costs per mile
Looking back to this post, small family cars, Renault Megane, Ford Focus, VW Golf, etc, do about 4 miles per kWh.
Electricity costs about 18p per kWh if you charge in the day, 10p per kWh for charging at night and quite a lot more if you charge away from home. I am going to use 12p per kWh for the average charging cost. If a car will travel 4 miles per kWh, that’s 3p per mile in electricity costs.
But when the weather is cold, the car uses much more, perhaps even twice as much because the battery has to heat the car as well as propel it through the air. That means that the electricity cost per mile is 6p.
I am going to use 5p per mile as a reasonable average figure for electricity cost.
How large does an electric car batter need to be
Here are the specifications of the current Tesla Model 3.
The useable battery capacity of a Tesla is 70 kWh. Bearing in mind the above figure, that a medium family car will do 4 miles per kWh, that 70 kWh will take the car
4 miles/kWh x 70 kWh = 280 miles. That is broadly comparable with the quoted figures, which show the range to be 215-415 miles.
Lifetime mileages
Lifetime mileage for diesel cars is 130,000 miles (208,000 km). For petrol cars it is 100,000 miles (160,000 km). Let’s use a figure of 120,000 miles for a desired lifetime mileage of an electric car.
That’s 10,000 miles per year for 12 years, an average of 200 miles per week.
Number of charging cycles
Let’s suppose that we charge the car twice a week, ie every 120 miles. That means we need to charge the car 1200 times in its life. That’s a reasonable figure. Elon Musk stated that the Tesla Model 3 battery has a minimum lifespan of 1,500 charge cycles. So it looks as though electric cars might broadly go far enough and the batteries last long enough.
Problems with electric batteries
1500 cycles seems fine. The problem is that the number of cycles depends on the extent to which you charge and discharge the battery. Batteries last longest if they are charged to 75% charge maximum and not discharged below 25%. It’s like saying that your car fuel tank will wear out rapidly if you fill it completely or let it get near empty. Effectively we only have 50% capacity with an electric car so this battery that might take you 400 miles in ideal conditions on a mild day really needs to be used in such a way that it will only take you 200 miles – and in non-ideal conditions on a cold day only 100 miles. That ain’t great.
Aging batteries
If that isn’t enough, batteries age. A battery might last 1500 charge cycles but by that many cycles, the capacity and therefore range will typically be down to 70% of the initial range anyway. This means that an old battery, used in a way that will preserve its life, will only travel 70 miles. Fine for pootling around town but not great for visiting the family living 200 miles away.
The battery capacity we want
If electric cars are to compete with petrol and diesel cars, they need capacities of four or five times as much. That’s quite a long way away.
The cost of replacing a car battery
Battery manufacturers are coy about stating a price for a replacement battery. It’s a sign that the prices are horrendously high. The manufacturers shrug off questions about the cost of replacements, giving guarantees that batteries will serve for 80-100,000 miles, but only 8 years, saying that owners won’t need to replacement. One’s guess is that by the time the car is 8 years old it might be with the second or third owner, who won’t remember the original promises from the manufacturer.
The lower power batter of the Nissan Leaf is 40 kWh. Nissan apparently quotes £5000 for a replacement battery, plus fitting costs. The general feeling is that it will be regarded as uneconomic to fit a replacement battery to an 8-year-old car. After all, for less than £4000 you can get a whole replacement 8-year old car.
This Renault Megane is 8 years old with 72,000 miles on the clock has 5 or 6 years of life left in it. It has a range of over 450 miles and fuel costs of about 12p per mile. But the great thing is that there will be no sudden surprises of £5000 or more for a replacement battery.
In practice the 8-year guarantee of the battery means that Electric cars won’t last as long as internal combustion cars.
Fuel taxes on electric and petrol cars
I’ve used the figure of 12p/kWh for the average charging cost of an electric car. If most of that charging is done at home, tax will have been levied on that at 5%. So the actual fuel cost is about 11.5 p per kWh, which is 3.8p/mile.
Fuel duty is 58p/litre on petrol or diesel. On top of that VAT is levied at 20%. With petrol at £1.20/litre (above its current price) that’s £1/litre before VAT. Since there is 58p fuel duty, the actual cost per litre is £1 – 58p = 42p/litre. If tax were the same for both electric and internal combustion cars, the fuel costs for this petrol Megane would be 4.5p/mile.
Depreciation, the capital costs of owning a car
Here is a new Megane estate. Relatively cheap but a substantial and comfortable medium family car.
£18,000 brand new.
Suppose it lasts about the average 100,000 miles.
That’s £18,000/100,000 which is 18p per mile in depreciation.
Compare it with an electrical rival.
The leaf, a smaller car with half the range, costs £23,000. It’s only as cheap as that because there is a government grant of £3000. The battery is only guaranteed for 80,000 miles. Will it need a replacement battery after 8 years at 10,000 miles a year? I’m going to guess that it will only last for 90,000 miles. I think that’s generous.
Depreciation = £23,000/90,000 = 25.5p/mile (29p/mile without the subsidy).
Servicing costs
A typical petrol car costs £400 per year to maintain.
That’s £400/10000 = 4p/mile
Electric car cost can be expected to be 2/3 of that of a petrol car, say 2.5 p/mile
Overall running costs
Type of car Electric Petrol
Fuel costs 5p/mile 12p/mile
Depreciation 25.5p/mile 18p/mile
Servicing 2.5p/mile 4p/mile
Totals 33p/mile 34p/mile
There really is very little difference in the running costs because petrol and diesel cars are taxed so heavily.
Running costs if both petrol and electric cars were taxed in the same way
Type of car Electric Petrol
Fuel costs 5p/mile 3.8p/mile
Depreciation 29p/mile 18p/mile
Servicing 2.5p/mile 4p/mile
Totals 36.5p/mile 25.8p/mile
So with identical tax treatment, petrol cars cost about 2/3 of that of electric cars to run.