Our editor at large has discovered a quick and easy way to double an EV’s energy storage – not that it’ll do much for its range. By Alex Grant.

Alex Grant, Fleet World editor at large

What is a kilowatt-hour? It’s a term that might need less introduction than it used to – having been thrust into the headlines by the recent energy crisis and momentum behind EVs – but it’s still abstract in isolation.

You can’t spill a couple of kWh of electricity on your shoes while charging, for example – but what if I told you that was entirely possible if that energy was in liquid form?

The Grant household is home to a couple of very different long-term residents alongside the visiting press cars. We’re straddling a couple of sometimes vocally opposed groups, with a three-year-old Peugeot e-Rifter on the drive and 33-year-old Volkswagen Polo G40 in the garage. They’re a useful case study for an otherwise abstract concept.

Every 30,000 miles or so, the Polo’s intricate supercharger requires a full rebuild – replacing the seals, belts and bearings that, at best, sap horsepower and, at worst, could lead to catastrophic failure.

It’s a specialist job, requiring a few weeks of downtime and complex logistics, so I treated the car to some fresh fuel before recommissioning it. For perhaps the only time in its life, the Corsa Electric I was driving at the time visited a fuel station and left with some petrol on board – a jerry can of super unleaded. This got me thinking.

Figures vary a little, but a litre of petrol contains roughly 9kWh of energy, which means my five-litre jerry can stores 45kWh of energy. That’s almost identical to the usable battery capacity of our e-Rifter – except, in energy-dense liquid form, I can carry it with one hand and it fitted into the Corsa’s boot. I’d need a roof rack, an intensive gym course and some extra air in the tyres to move the Peugeot’s battery around like that.

Five litres of super unleaded set me back £7.50, which is actually quite cheap. My posh petrol costs around 16p/kWh, whereas the e-Rifter is charging at 22p/kWh when it’s plugged in at home. Yes, I know, we should be using a dual-rate tariff and charging overnight, but we haven’t got there yet.

However, EV efficiency more than closes the gap. Our aerodynamically compromised, seven-seat e-Rifter can travel between 130 and 140 miles on 45kWh of electricity – whereas the smaller, lighter Polo consumes as much energy (in liquid form) within 45-50 miles, if it’s driven gently. On a ‘tank’ to wheel basis, the e- Rifter comes in between 7.0 and 7.6p per mile, compared with about 15p for a motorway trip in the Polo.

Calculating carbon emissions is tricky, as neither vehicle gives the full picture. National Grid ESO (Electricity System Operator) publishes accurate carbon intensity, from source to plug, for the UK’s electrical grid, but an EV’s trip computer doesn’t include energy lost while charging (WLTP data does). Petrol cars have the opposite problem – no leaks while refuelling, but published CO2 figures don’t include extracting, refining or transporting the fuel.

However, with a lifetime average of 3.2MPkWh, the e-Rifter comes in at 29g/km CO2 on a tank-to-wheel basis (using last year’s 149g/kWh average from National Grid ESO). The Polo doesn’t have a trip computer but, at 35-40mpg, it’s emitting between 164 and 187g/km CO2 on the same basis. Sure, two-minute refuelling times sound appealing, but I can’t fill up with super unleaded on my driveway.

Of course, Polo miles are fun miles and our driveway’s permanent residents have very different talents – neither of which I’m in a hurry to give up. But as a dweller of the grey area between unusual old combustion engines and battery power, it’s hard to question the void in jerry can range between them.