Electric vehicles: How much will our EV cost to charge annually versus the fuel costs of an equivalent petrol car?

Our EV is an MG4. Can you tell me how much it should cost to run in comparison to a similar car run on petrol? We have 13 Solar panels and we charge it mostly at home for 8 cents per kilowatt hour with Energia between 2am and 6am.
There’s a bit of maths to do here, so excuse me while I try to think back to my Junior Cert, which was probably the last time I actually did any maths.
You haven’t specified the precise model of MG4 you own, but I’m going to assume for argument’s sake that it’s the 64kWh model, with a range of 450km on one charge. If it’s the smaller-battery model, with a 310km range, then the figures will be slightly more favourable; if it’s the powerful MG4 X-Power, then they will be somewhat worse.
Charging at home is of course the most cost-efficient way to run an electric car, and from what you’ve told me above you’re getting some exceptionally cheap electricity for part of the night.
That burst of power between 2am and 6am will get you 28kWh of energy at 8c per kWh, which works out at €2.24. With the MG’s net usable battery capacity of 61.7kWh, that’s just shy of half a charge, which going by the WLTP range figure will be about 200km. On that basis, you’re spending just €1.12 to travel each 100km, give or take.
Of course, that’s only if you’re charging up those 28kWh and using only those. For longer journeys, you’ll need a little more. There’s another 33.7kWh to fill up. Assuming you’re paying the discounted Energia night rate of 15.03c per kWh for the rest of the charge, that’s €5.06 for the other 33.7kWh, giving you a full charge cost of €7.30, which will – in theory – allow you to cover 450km.
That means you could cover the annual average Irish mileage of just over 14,000km with 32 full charges, leaving you with a potential annual “fuel” cost of €234. Of course, you won’t always get a full 450km out of each full charge, as driving on motorways and in colder weather will reduce your average range. Let’s assume that on average you manage to squeeze 400km out of each full charge. Now you will need to fully charge the car 35 times, leaving you with an annual “fuel” cost of €255.
Let’s further assume that you occasionally need to fast-charge your MG 4 from 20 to 80 per cent charge at a DC rapid charging point. Using the worst-case scenario, ESB e-cars charges 59c per kWh for a DC high-power charger. You’ll need to buy 37kWh each time, and let’s assume that you need to do this once a month. So that’s an extra €261 per year (I’ve given you these extra-long journeys over and above the annual average mileage, just for the sake of wiggle room and less complicated maths).
So that’s a total annual “fuel” cost of €516 per year to cover the average annual Irish mileage in your MG4.
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By comparison, an equivalent petrol-powered hatchback would be a Volkswagen Golf 1.5 TSI 150hp, which has official WLTP average fuel economy of 5.5 litres per 100km. Which means you’ll need 770-litres of petrol to cover the average Irish annual mileage, which at the average price per litre of petrol right now (€1.73) is going to be €1,332 in petrol costs every year.
Of course, just as the MG won’t get 450km out of every full charge, so neither will the Golf get 100km out of every 5.5 litres of fuel. So let’s assume that the Golf gets a more realistic 6 litres per 100km average fuel consumption. Now, you’ll need 840 litres of petrol each year, which will cost you €1,453.
So, assuming that all my Junior Cert maths haven’t run out of my brain in the years since, and assuming that these figures represent a reasonably accurate ballpark, you will save on average each year €937 by running the MG4 instead of a comparable petrol-engine car.
Of course, there are other bonuses. The MG4 won’t need oil filters nor oil at its annual service, and while electric cars tend to get through tyres slightly more quickly than a petrol-engine car, they equally tend to be much gentler on their brakes, so there are more potential savings when it comes to servicing and maintenance.
The only potential financial downside is depreciation – obviously, if you’ve bought your MG4 on a PCP finance package, then your car’s future value is guaranteed, but what’s not guaranteed is the value above that level – the equity – which is what you use to roll over to a new deal on a new car. That amount, given current fragile EV second-hand values, is less easy to predict, although it is starting to look as if electric car used values have bottomed out in some markets, so fingers crossed they’re starting to come back up again when you come to trade-in time.