I had a solar array installed in October 2024. I went with 13 panels and 15kWh of battery storage. It’s going great: I have practically free electricity and free motoring. I had thought I was covered for power cuts, but no, that’s not how it’s configured. It was explained to me that you couldn’t have a situation where people working on repairing the grid were exposed to a surprise surge in electric current coming from a source they were not in control of. – Paul O from Co Dublin
Please stop saying that a solar and battery system provides backup power in the event of a blackout. This requires further major investment and is not generally installed. – Deane McE from Co Dublin
So, we thought we’d dig a little deeper into the ins and outs of using your electric car’s battery as a backup power supply for your house, or even to send power back to the grid at peak times. Our guide for this maze is Joe Tugwell, technical director of Irish charging solutions provider ePower.
First off, Deane, you’re quite right. Yes, you can use solar, a backup battery, and an electric car as an emergency power supply in the event of a blackout, but as you point out, it’s not an automatic given that this will work for you in your particular house.
RM Block
As with anything to do with electricity supply in general, and EV charging in particular, much is going to depend on both the wiring that’s in your house (how old it is, how capable it is at dealing with higher power outputs, and what kind of condition it’s all in) and the power supply to your house (how much, how reliable, how distant from the nearest transformer). Hands up on our side: we often tend to be a bit blasé when it comes to assuming that if you choose to go electric, that you can just chuck a wallbox charger up and off you go – it’s not always quite that simple, and you may need to upgrade the wiring in your house if you want to switch to electric motoring.
When it comes to actually using your EV’s battery as an emergency power source, though? It certainly can be done, but as Tugwell told The Irish Times, there are certain minimum standards you need to have in place before doing this.
First, you need to know the difference between Vehicle-to-Load (V2L), Vehicle-to-Grid (V2G), and Vehicle-to-House (V2H). V2G, the idea that excess power can be drawn from your battery at peak power demand times, earning you a little extra cash from your electricity supplier, you can forget about for the moment – it simply doesn’t exist in Ireland.
When we asked Tugwell if such a thing were possible right now, he replied: “No – there is still work to be done on hardware, software and the regulatory side for this to be a reality. Aspirations of V2G are excellent, but it is very much tied into the brands that are doing the pilot work together and their own commercial arrangements.
“More open protocols, so it’s scalable and accessible, are required. The cost and speed of this for our country will sit with how the regulator deals with it. An innovative, collaborative approach could make V2G a foundation of Ireland’s energy security. It needs the vision to make it an accessible reality.”
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On this point, Paul, we have to ask – who told you that you can’t send solar energy back to the grid? Unlike drawing on car battery power, this absolutely exists right now, and it’s done on a demand basis, controlled by your energy supplier, so anyone working on a line should be under no specific danger. We suggest you check with your energy supplier.
V2H though? Using your car’s battery locally, to power your house in the event of a power cut? Yup, that’s totally doable, although Deane is absolutely right to say that you need to invest a bit up front to make sure all the equipment is in place.
According to Tugwell, the minimum you will need to achieve V2H is “a bidirectional-ready EV, a certified charger, preferably ISO 15118-compatible and supporting OCPP 2.x, and suitable islanding/changeover infrastructure along with a backup-loads board. Electrical wiring, protection and grounding should be tailored for operation in island mode, and compliance with ESB Networks generator standards is necessary even if there’s no routine export”.
Of course, there’s a potentially simpler solution – use Vehicle-to-Load (V2L). This is a function increasingly common in electric cars. Indeed, most new EVs already have it, and instead of having your electric car plugged into the house, and sending power “backwards” up through your charging point and electricity meter, V2L simply involves plugging an accessory connector directly into the car’s charging port, at which point you can simply attach a conventional three-pin plug to power whatever you need.
We’ve seen this demonstrated many times, using spare power in an EV’s battery to boil a kettle, fire up an espresso maker, or charge an e-bike, but you can conceivably use it at home too, assuming that your driveway allows you to park the car close enough to run an extension cable (use a heavy-duty one that’s designed for high-amp applications) in from the car.
Doing so can, according to Tugwell, allow you to power your essentials, such as lights, fridge/freezer, router, phones, laptop or TV. “Even the gas boiler, so that central heating still works if gas is available, and the occasional kettle or microwave use – but not alongside everything else at full whack.”
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Going down the proper V2H route – using a two-way smart-meter with all of the correct wiring solutions outlined above – gives you more options. Basic V2G usually yields only 3.6kW of energy, but going down the properly wired V2H route, depending on your choice of electric car, can give you as much as 7.4kW of power. Now, says Tugwell, you can run “your essentials, plus the oven, plus a few sockets at the same time. Short electric shower use might be possible depending on wiring and main fuse, but simultaneous oven and shower is pushing it”.
Having said all that, Tugwell’s advice is that rather than relying on your EV’s battery for backup power in the event of a power cut, you’d be better off investing in a dedicated storage battery for the house, even though there are limitations with that too.
“Technically your EV has the storage capacity and ability to deliver enough power to act as a whole-house backup for up to five days if you are careful with your usage,” Tugwell says. “Conversely, as it stands now, a home storage battery will only have enough energy for 1-2 days and the current power output limitations because of regulatory limitations mean that you would struggle to power a shower.
“However, that being said, there are a lot of things that need to happen before your EV will be able to perform all these tasks, and a home storage battery is a very well-proven solution, so for now and the next three to five years, I suggest the home battery to be the best solution.”
