Category: Electric Vehicles

House with frost on the solar panels.

I recently read Kate de Selincourt's excellent article in Passive House Plus about Zero Bills homes, and was curious how our bills, on Octopus's "Intelligent Go" tariff (very cheap rate for six hours overnight, and a considerably higher one the rest of the time), would compare. We've now got a full twelve months of PV-generation data for our EnerPHit retrofit near Fort William, so I was able to check it properly against Octopus Energy's Zero Bills tariff, which guarantees that residents pay nothing for electricity for five to ten years. To qualify, a house needs to be off the gas grid, heated by a heat pump, and kitted out with solar PV and a battery, on fabric that only has to be "at least as good as current new-build regulations."

 

We got close. Not quite there, but close enough to be interesting. Over the twelve months from March 2025 to February 2026 we bought around 6,050 kWh of grid electricity and generated about 4,320 kWh of our own. Between the roughly £900 we spent on imports and the £510 we got back for exports, our net spend was about £390 — covering everything, including EV charging. The Zero Bills tariff covers everything except EV charging, so subtracting the roughly £310 I estimate our charging cost brings our net spend down to about £80 for the year. £80 against Octopus's £0.

 

Kate's article cites Octopus's own guidance for developers, which puts a typical Zero Bills installation at around 13 kWp of solar (25-30 panels) and a 13.5 kWh battery. We have 6.4 kWp and no battery at all: roughly half the panels, and none of the storage. How did we get so close with so much less kit?

 

The first answer is the house. More than half of our electricity use for space heating, and almost all of the electricity use for water heating takes place on the cheap overnight tariff. Our heat demand is low, and, importantly, it can be significantly shifted onto cheap overnight electricity even without a battery. That only works because the house needs very little heat and loses heat slowly: we boost the temperature of the downstairs rooms, which we aren't in, during the cheap window overnight and let the fabric coast through the rest of the day needing much less heating.

 

The second answer is the heat pump itself. Low heat demand only translates into low electricity use if whatever's delivering the heat is efficient, and our air-to-air minisplit is doing that well. I estimate a SCOP somewhere in the region of 4 to 5. Heating and hot water together have consistently cost under £200 a year, across two full years of monitoring.

 

Third: our appliances are efficient. Everything had the top efficiency rating when we bought it, but all of it is ten to fifteen years old now, and none of it is smart. What it can do is run on a timer, so it goes on during the cheap overnight window, or over the middle of the day if we need a second load of clothes or dish-washing and want to use the solar directly instead.

 

This combination of low and shiftable demand means that 81% of all the electricity we bought this year was bought off-peak, EV charging included. Stripping out heating, hot water and EV charging, the rest of the household's electricity use came to around 2,100 kWh for the year. For a family of five, that's well below typical: four-to-five person, four-plus-bed UK homes average around 4,100 kWh a year for non-heating electricity use.

 

None of this involves being obsessional about it, either. There's no dashboard, no home energy management system, nothing clever running in the background. The heating, hot water, dishwasher and washing machine are on timers, everything else just happens when it happens.

 

Fourth: we're taking on the risk that Octopus takes on for Zero Bills customers, our bill could go up or down. Their guarantee is zero regardless of what happens to electricity prices.

 

Octopus's own figures on how much a Passivhaus would reduce the PV and battery requirement to qualify for the tariff make for an interesting comparison: their technical director, Nigel Banks, has said that building to Passivhaus standard instead of current regs would cut the solar PV requirement by 25-35% — but leaves the battery requirement unchanged. We're able to nearly match the Zero Bills tariff, with half the solar and no battery, by being more engaged, and taking the risk ourselves.

 

Would a battery get us to zero? By the Zero Bills definition (everything except car charging), it would actually take us significantly below zero. The smallest home batteries on the market look to be 5 kWh units. Having one would have saved about £209 over the monitored year, simply by charging during the night-time off-peak rate and reducing our use of on-peak electricity even further. Knock that off our £80 net spend and we'd be £129 in credit. Without a battery, 81% of our electricity use was off-peak. A 5 kWh battery, without any other changes, would increase that to more than 97%. The economics of this don't look great for a case like ours where we're already able to shift such a high proportion of our use to off-peak — even the cheapest 5 kWh option runs to £2,500-4,000 installed, more than the saving would pay back within a typical warranty period.

 

I've not considered the possibility of using a battery to buy and sell power (including our own solar power). I don't know how mature this technology is yet, but this could well change the economics of a battery dramatically. I'd be interested to hear from folk that know more than I do on this.

 

Perhaps even better for our use case, where our car is on the drive most of the time, would be if we could use the (already paid for and much larger) car battery to do all this. It'd be interesting to know whether that long-promised tech is likely to arrive any time soon.

 

I’ve owned an electric car since July 2016 and I’m generally pretty enthusiastic about EVs. I’m excited by the idea that we might be able to make enormous reductions in transport energy use through switching from fossil fuels to electricity, and that we can simultaneously decarbonise electricity generation in order to have truly zero-carbon transport.

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An extended version of this article appeared on UKclimbing in March 2017.

 

This summer we made a big move from Brussels to near Fort William on the west coast of Scotland. Moving away from the good transport links of a big city had us looking to buy our first family car to make the most of life in the highlands.

 

Electrifying transport is a big part of every strategy I’ve seen to move to a sustainable and zero CO2 economy, so I was keen to avoid internal combustion engine, (ICE) car if I could. Initially I thought an electric car in such a remote place would be a non-starter. Surely the range would be inadequate? What about the hills? But the more I looked into it the more I thought it could maybe work. I checked maps of charging points and realised that, in every possible direction from our new house there was a rapid charger at least every 60 miles, comfortably within the range of the cars in our budget. But even experienced owners of electric cars were dubious of the idea, the message seemed to be these cars were great for urban commuting or as a second car, but as your only car in the wilds of Scotland? Forget it.

 

Finally we decided to take the plunge and see what happened. Jonathan Porterfield of eco-cars.net was an extremely helpful font of information and found us a pre-registered 30 kWh (that’s the battery capacity) Nissan LEAF Acenta with a dozen miles on the clock for £16k, £10k less than the retail price. It was even red, our son’s favourite colour.

 

The car’s stated range is 155 miles under the European testing method and considerably less under the US testing method (107 miles). Of course the range you actually get will depend very heavily on weather conditions, terrain and how you drive it, especially how fast you go (just as it does in an ICE car).

 

I’m going to focus on the practicalities rather than the costs except to note that a recent study from MIT concluded that electric cars had the cheapest lifetime costs of all cars; the very low running costs more than pay back the small additional purchase cost.

 

Here are some quick thoughts about how it’s been for the first 4 months of highland life. We’ve driven 4700 miles in it so far, a mix of short, medium and long journeys.

 

  • I thought the range/efficiency would get really hammered by all the hills around here. It doesn’t. I’m sure there is a difference in efficiency, but it’s small enough that I don’t notice it compared to flat driving. Of course it uses loads more energy going up hill than on the flat, but much of that extra energy is won back by the regenerative braking recharging the batteries on the way back down.
  • Because of the hills and the remoteness I thought the highlands would be a really difficult place to make life with an electric car work. So far I’d say the opposite. Because the hills don’t make much difference to your efficiency (see above) and because speeds are generally much lower than elsewhere in the country, the range is actually better here than elsewhere.
  • Although I don’t have a lot of experience driving nice cars (this is the second car I’ve owned but I’ve driven quite a few smart hire cars) I’d say this is by far the nicest I’ve driven. It accelerates really quickly, it’s extremely quiet, corners really well, has a really useful speed limiter for everyday driving and cruise control for the motorways.
  • Because of the regenerative braking you hardly have to use the brakes at all, you just take your foot off the accelerator and that’s enough to slow you for corners etc. I pretty much only use the brake pedal (which is part regenerative, part friction) for stopping at lights/junctions/roundabouts. This is pleasant to drive and I’m hoping it, along with a vastly simpler transmission compared to an ICE car, will translate into very low maintenance costs.
  • We’ve found that we get around the advertised EU range of 155 miles for pootling around into town to do the shopping (30 and 40mph max speeds), but for more general use around the highlands we typically get between 120 and 130 miles on a charge. For the energy geeks amongst you 120 miles of range from a 30kWh battery equates to 15kWh per 100km, which is what Mackay used as his assumption for electric cars in ‘Without Hot Air’. For faster driving on motorways and dual carriageways we seem to get about 90 miles of range on a full charge.
  • For any journey up to ~100 miles round trip I’d say it’s more convenient than an ICE car. For most people journeys longer than that are rare (they certainly are for us). So on a day to day basis you just charge it overnight and never have to worry about stopping to charge. This is a big improvement on an ICE car even before you start thinking about the cost savings.
  • Anything up to a 200 mile journey I’d say it’s as convenient, for me, as an ICE car. Sure, for that distance you have to stop once or twice, for 20 or 30 minutes each time, but I’d want to do that anyway to give my body and mind a break from driving.
  • For longer distances it’s certainly less convenient than an ICE car, but in reasonable weather it’s not that bad (see below). For these journeys hiring an ICE car is an option, or getting the train. In fact Nissan offer 2 weeks of ICE car use per year if you buy a LEAF, although that doesn’t really work for us as it is from the dealer you bought from and our’s was in Darlington!
  • For long journeys the fact that rapid charging is free (if you’re an Ecotricity customer) goes a long way to making up for the extra inconvenience of more frequent stopping…

 

Having said that the experience has on the whole been very good, we have had two minor epics. The first in the very early days, leaving the house for a trip to the beach at Arisaig with only 65% charge (before we had the home charger installed) thinking it would probably be OK and if it wasn’t I could nip to Mallaig where there is a fast charger. It wasn’t enough and when we got to Mallaig the charger wasn’t working (this is the only time I’ve had a charger not work, so in general they are very reliable). I found a friendly man at the harbour who let me plug in to his wall socket for two hours before I drove very slowly home. Now we’ve got a home charger and never leave for a long journey without a fully charged battery.

 

The second was driving to Derbyshire (400 miles from here) to see family in stormy weather with gale-force southerly winds. The range was considerably reduced and we had to stop 7 or 8 times to charge. Grim grim grim. On the way back the weather was calmer and the whole journey was really nice, we stopped 5 times, the last one just a 10 minute top up. I reckon it took about an hour longer than it would have done in an ICE car, although more than that if you normally share driving and don’t actually stop for breaks. I think in future if the weather forecast was as bad as it was I would either change my plans or split such a long journey halfway.

 

I thought having an electric car would be one of those things, like rarely flying and heating my house to only 19 degrees, that I do because I’m concerned about climate change, but that I’d rather not do. On the contrary I’d say for our lifestyle it’s a nicer, more convenient car to have. The experience so far has been really positive and it gives me hope that electric cars can very rapidly take over from ICE cars in the years to come, especially as cars with double the range of ours for a similar price are on the horizon in the next 2 or 3 years.