Q: Bidirectional charging into a home is being referenced consistently in the media post Storm Éowyn. How difficult is this to set up for a home in a residential estate, and does the ESB allow it? Also limited cars allow it, but will doing it void any warranties? – Reader, Co Dublin
Q: What about EVs in places where the power has been out for several days? – B Ní Shuilleabhain, Co Kerry
A: We have partly covered these questions in a feature separate to our regular Your EV Questions Answered strand, but it bears a revisit, not least because bidirectional charging is so often touted as being a major benefit of electric cars.
In fact, as far back as 2010, bidirectional charging was being highlighted as a major boon to electric car owners, and this was when the only EVs on sale were the original Nissan Leaf and the Mitsubishi i-MIEV.
At that point, it wasn’t so much the prospect of powering your house from your EV, but more about making some handy cash on the side. The idea being that you could plug your bidirectional electric car into your home charger at 5pm or 6pm presumably with some amount of charge still left in the battery.
That being peak electricity use time, your electricity provider could then, in theory, draw on the excess juice in your battery to help balance the grid demand as everyone came home and started putting on kettles, ovens, PlayStations etc.
You would, in theory, be paid the peak electricity rate price for that power usage.
Later on, when the demand had dropped, the power company could sell you back the electricity again, charging up your car at the cheap rate.
The idea being that you could at least alleviate some of your charging cost, and potentially break-even given the disparity between peak and offpeak pricing.
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To do that, you need two things – an electric car that has vehicle-to-grid charging (V2G) or at least vehicle-to-load (V2L) charging, and a smart home electricity meter.
The mechanisms for selling power to the grid as a private user are already in place, as some people already do this with their home solar panels or their home windmills.
The downside, of course, is that although you’ve plugged your car in when you come home, it won’t be actually charging until later in the night, and indeed may actually lose some charge in the meantime – not great if you have to dash back out at short notice.
However, what’s become a more pertinent benefit of late is the idea of actually powering your house directly from your car in the event of a power cut.
As we all saw with Storm Éowyn, if the power goes out, especially in a remote area, it can take a few days to come back on again. So can your EV really keep you going in the meantime?
In theory, yes, although it does help if you’ve come home with a full or nearly-full battery, which perhaps isn’t that likely. With the right car and the right meter, you could potentially keep your home running for two to three days from your car’s battery.
According to the Commission for Regulation of Utilities, the average household in Ireland uses approximately 4,200 kilowatt-hours (kWh) of electricity annually, so divide that by 365 and you get daily energy usage of 11.5kWh. The average electric car battery, in the European market, holds between 75kWh-80kWh, so that could be enough to keep you going for almost a full week.
Indeed, one reader – P Fitzgerald from Co Limerick – recently told us: “I had my heating system running off the car this weekend when we had not power for three days. The only problem was that I didn’t think to plug in my freezer and fridge as well…”
It is also worth remembering that the power output of some EV batteries and on-board chargers may not be enough to run all the high-power systems in your house at once.
For instance, if you’re running your oven and an electric shower at the same time, that’s getting close to the peak power demand for your house, and not all EVs will have the capacity to do that, so a certain amount of power rationing might be needed. However, you will be able to at least keep the basics going – fridge, heating, lights, and crucially sockets for keeping mobile phones and wifi alive.
Then of course, there’s a problem – as our reader from Co Kerry points out above: what to do if the power stays out for several days, something that most definitely happened for many people in the wake of Storm Éowyn.
Assuming that you haven’t plugged your car into your home charger with a full battery, it’s likely that you’ll only be able to get a couple of days, at most, out of the car before it too will need to be charged. At which point, you do… what, exactly?
Here, you’ll need to do some planning. As an EV driver you’ll probably know where all the local public chargers are nearby, so start monitoring the battery level in your car, and when it reaches a point at which you can safely, with some in reserve, reach one of those chargers, it’s time to disconnect and get going.
Power restoration after a storm is difficult business, but in theory power will come back on first in the major population areas, so it’s probably best to plan to head to the nearest town which has a fast charging point, and top up there. You’re effectively at this point using your car as a kind of electric bucket, carrying electricity back home. It’s not especially straightforward, and not foolproof, but hopefully it will keep you going.
There is a better way, however – which is to use an EV battery that’s no longer in an EV. Another of the potential benefits of electric cars is that when the batteries do eventually wear out, they’re not entirely dead.
In an EV the battery is put under the kinds of stresses and strains that are entirely alien to other use cases, so most electric car batteries are considered to need replacement once they reach about 70 per cent of their original power storage capacity – something that is taking way, way longer in almost all cases, than we ever initially thought.
However, at 70 per cent capacity, those batteries are still usable in other scenarios, and one of those is as a home power wall. Irish company Range Therapy is already taking batteries out of older, tired EVs, and indeed those that have become damaged in a write-off incident, and turning those valuable power cells into home energy storage.
With one of these, your home has a useful buffer in the event of a power cut and at peak electricity use times as a power wall battery that can work on the same basis as your EV – using the energy in it at times of high electricity cost, and then charging it back up again at night on the cheap rate.
Eventually, as EVs become more and more prevalent, and older cars age into the arms of the recyclers, hopefully this will become a more common fitment for Irish houses, and we can worry less about losing power in the event of a big storm.
