Bidirectional charging, where your EV can send power back to your home or the grid, has been promised for years. Now it’s actually here in the UK, with compatible chargers from Ohme and Wallbox available, and cars like the MG ZS EV Long Range and Hyundai Ioniq 6 supporting the tech. The pitch is compelling: use your car as a giant battery to slash your electricity bills. But does it actually work out financially?
I’ve run the numbers based on real tariffs and current hardware costs, and the answer is more complicated than the marketing suggests.
What You’ll Actually Pay Upfront
Let’s start with the painful bit. A bidirectional charger will set you back considerably more than a standard wallbox. The Wallbox Quasar 2 costs around £3,500 to £4,000 installed, whilst Ohme’s V2X charger is in a similar bracket. Compare that to £800 to £1,200 for a decent non-bidirectional unit, and you’re looking at an extra £2,500 to £3,000 just to get the capability.
You’ll also need a compatible EV, which currently means specific models. The MG ZS EV Long Range is probably the most affordable V2G-capable option at around £32,000, though the Hyundai Ioniq 5 and 6 also support it. Most EVs on UK roads right now can’t do bidirectional charging at all, which means if you’re buying specifically for this feature, factor that into your calculations too.
The Best Case Scenario: Agile Tariffs
Where bidirectional charging makes the most sense is pairing it with Octopus Agile, which has half-hourly pricing that fluctuates based on wholesale electricity costs. On a typical day, you might pay 7p per kWh at 3am and 35p at 6pm.
Here’s a realistic example. Let’s say you have a 65kWh usable battery (typical for something like an Ioniq 6) and you use 25kWh per day for driving. That leaves 40kWh you could theoretically cycle through your home.
If you charge at cheap rates (averaging 10p per kWh during the night) and discharge during expensive evening periods (averaging 30p per kWh), you’re making 20p per kWh cycled. Discharge 20kWh per day and that’s £4. Do that every weekday and you’re looking at around £80 per month, or roughly £960 per year.
Sounds good, right? But there are several catches.
The Real World Gets in the Way
First, you need to actually be home during peak price periods to use that stored electricity. If you’re driving during the evening rush, you can’t power your home with your car. That £960 annual saving assumes you’re home most evenings and your driving patterns are predictable.
Second, battery degradation is real. Cycling an extra 20kWh through your battery daily adds wear. Most manufacturers warrant batteries for eight years or 100,000 miles, whichever comes first, but adding significant charge cycles could theoretically accelerate degradation. The industry argues this is minimal with modern thermal management, but we don’t yet have a decade of real-world data to prove it.
Third, round-trip efficiency isn’t 100%. You’ll lose around 10% to 15% of energy in the charging and discharging process. That eats into your theoretical savings, reducing that £960 to closer to £800 once you account for the energy that disappears as heat.
What About Vehicle-to-Grid Payments?
Some V2G schemes will actually pay you for providing grid services, where your car helps balance supply and demand. Octopus offers its Intelligent Octopus Flux customers potential payments, though the terms vary.
Realistically, you might earn an additional £100 to £200 per year from these services if you’re enrolled and your car is plugged in at the right times. It’s not nothing, but it’s also not transformative.
There’s also the Smart Export Guarantee (SEG) to consider if you have solar panels. You could store solar energy in your car during the day and export it in the evening when SEG rates are higher on some tariffs. Octopus Outgoing Agile, for instance, pays wholesale rates for exports. This adds complexity but could boost savings by another £100 to £150 annually if you’ve got the full setup.
So What’s the Payback Period?
Taking our optimistic scenario of £800 annual savings from price arbitrage plus £150 from grid services and SEG, that’s £950 per year. Against an extra £2,500 upfront cost for the bidirectional charger, you’re looking at roughly 2.5 to 3 years to break even.
That’s actually not terrible, assuming energy price volatility continues and you’re genuinely able to optimise your usage most days. But if you’re out during peak hours several days a week, or energy prices stabilise, or you’re on a simpler tariff like Octopus Go where the arbitrage opportunity is smaller, that payback period stretches to five years or more.
Who Should Actually Consider This?
Bidirectional charging makes most sense if you’re home during peak price periods, you’re comfortable with dynamic tariffs and automation, and you’ve got predictable driving patterns that leave plenty of battery capacity spare. If you work from home or have evening routines that keep you plugged in, the numbers can work.
It’s also genuinely useful for backup power during outages, though that’s a harder benefit to quantify financially unless you live somewhere with unreliable supply.
For everyone else, honestly, a cheaper wallbox and a simple time-of-use tariff will get you 80% of the savings with none of the complexity. The tech is brilliant and I’m excited about where it’s heading, but right now it’s for early adopters who enjoy optimising systems, not for people who just want to plug in and forget about it.