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Hi all,

Like many others, I'm currently researching and planning to buy our first EV. We currently have a 4kWp solar array on our roof with a device to divert unused electricity to the immersion heater (both came with the house!). The car we buy will largely only do shorter runs - school, shops etc and will spend a lot of time on the drive during the day.

When considering what home charger to have fitted, I see that some chargers (like the Zappi) can charge from solar. My question is, is this worth doing? Thinking it through, if you don't use solar and get a smart charger such as the Ohme, you would just have to make sure the car's plugged in in the evening and unplug in the morning. If you want to use solar, then clearly, the car would need to be plugged in every time you park it on the drive (and unplugged for every trip out!).

At this time of year (OK, December) we often barely generate 1kWh a day - so even if we could capture that, it's very little distance added to the car. In June, the daily average seems to be around 12kWh but can be as high as 24kWh and as low as 3kWh. So 24kWh is a fair chunk of energy but still less than half a Zoe or e-Niro battery.

Using (what look like) reasonable assumptions from the Octopus Energy website below, 8,000 miles a year could cost as little as £100, it feels like I may be able to save 50% on electricity costs over a year. If we do around 8,000 miles a year, that's a saving of just £50 a year and no hot water!

On average it takes 1 kWh of energy to travel 4 miles. 8000 miles is therefore 2000 kWh of energy. On Octopus Go it's 5p per kWh during off-peak charge time, hence it's £100 to use 2000 kWh of energy.
So does anyone have experience of this? Does plugging and unplugging the car become habit or have you set up charge from solar and now never bother plugging in during the day? Or have I made a catastrophic mistake with my understanding?

As we're thinking of something with a large battery, if we discount solar, I'd envisage plugging in only every few nights or so, or as and when required. I've not researched the best way to look after an EV battery yet though wrt charging.

I hope all this makes sense and that I've posted in the right place.

Matt
 

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If you are already using most of the solar power at home then you will only 'save' the bit you don't currently use.
So the cost of capturing that amount to the car over a period of time, typically 10 years, needs to be less than the 'saving'.
Then, as you say, there's the extra inconvenience and wear of having to plug the car in when you normally wouldn't bother.

Trying to get the numbers and crunch them is the correct thing to do - but my gut feeling is that it's probably not worth the bother and expense. Some would call that heresy, but I always expect the inquisition :)
 

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Hi all,

Like many others, I'm currently researching and planning to buy our first EV. We currently have a 4kWp solar array on our roof with a device to divert unused electricity to the immersion heater (both came with the house!). The car we buy will largely only do shorter runs - school, shops etc and will spend a lot of time on the drive during the day.

When considering what home charger to have fitted, I see that some chargers (like the Zappi) can charge from solar. My question is, is this worth doing? Thinking it through, if you don't use solar and get a smart charger such as the Ohme, you would just have to make sure the car's plugged in in the evening and unplug in the morning. If you want to use solar, then clearly, the car would need to be plugged in every time you park it on the drive (and unplugged for every trip out!).

At this time of year (OK, December) we often barely generate 1kWh a day - so even if we could capture that, it's very little distance added to the car. In June, the daily average seems to be around 12kWh but can be as high as 24kWh and as low as 3kWh. So 24kWh is a fair chunk of energy but still less than half a Zoe or e-Niro battery.

Using (what look like) reasonable assumptions from the Octopus Energy website below, 8,000 miles a year could cost as little as £100, it feels like I may be able to save 50% on electricity costs over a year. If we do around 8,000 miles a year, that's a saving of just £50 a year and no hot water!



So does anyone have experience of this? Does plugging and unplugging the car become habit or have you set up charge from solar and now never bother plugging in during the day? Or have I made a catastrophic mistake with my understanding?

As we're thinking of something with a large battery, if we discount solar, I'd envisage plugging in only every few nights or so, or as and when required. I've not researched the best way to look after an EV battery yet though wrt charging.

I hope all this makes sense and that I've posted in the right place.

Matt
Welcome!

The short answer is that, from a financial point of view, it's probably not worth purchasing an expensive chargepoint (like a Zappi) to charge from PV. It would take years of electricity savings to recover the extra cost of the Zappi against a cheaper chargepoint like the OHME. Plus the car obviously needs to be on the driveway during the day! On the flipside it feels great driving using power you produced yourself!

I have 4kWp of PV on the roof, and both a Zappi and Eddi but (as you've guessed) the winter PV generation is so poor I use the Zappi's timer to charge overnight from the grid using the Octopus 'GO' tariff. Your house will need to have a minimum of 1.4kW of PV generation spare for hours on end to charge completely from solar. Anything less than 1.4kW spare and the extra power will be pulled from the grid (at a much more expensive rate if you have cheap off-peak)

I would expect the most cost-effective thing method of getting a chargepoint installed is to switch to Octopus using my referral code below to earn yourself £50 credit. Once you have an Octopus account number order a OHME chargepoint (32A Commando version) for just £150 currently (RRP £400 for non-Octopus customers) using the link below...


Then get it installed by a qualified electrician that understands the rules around EV chargepoints. The Commando socket will probably need an earth rod installing, or a PEN fault detection device like a MATT:E if an earth rod is not practical.

Once the switch to Octopus is complete and you have had the compatible smart meters installed move to the 'Agile' tariff, and set the OHME to charge at the cheapest times. However if you find you use a lot of electricity between 4pm and 7pm you might find scheduled charging using the 'GO' tariff more cost effective (5p/kWh between 00:30 and 00:30).

I think that pretty much covers it!

Edit: The the OHME wasn't around when I purchased the Zappi. If it had been I would have gone with the OHME.
 

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I have a similar panel setup, Solic immersion-heater diverter, max ever is 30 kWh on perfect summer day. Am retired so car is on drive most days. Now I have 58 kWh to fill, I'm going to adapt my cheapo dumb Rolec to become solar-aware, as follows:
1) change the controller inside to a Viridian one, easy swap, £80. Viridian takes external resistor to set the current. This bit's done & dusted.
2) code an Arduino + digipot (software-settable variable resistor) to alter the current acc to solar export etc. Tested on bare-bones breadboard, needs proper tidying up, psu sorting inside Rolec etc.
3) Integrate this to talk to home-monitoring Arduino my son built that updates & displays export/import current every 20 seconds. Monitor bit's done dusted, need to get son to explain/supply his internet stuff or better still code it himself!

So it's possible to get some, at least, EVSEs to become smart. Aim is to trickle-charge the car for free over the week, and burn it on outings at the w/e. And do all this cheaply in £££, if not in hours.
 

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Now I have 58 kWh to fill, I'm going to adapt my cheapo dumb Rolec to become solar-aware, as follows:
How possible is it to build a mains lead charger complete with an arduino controller? Could an iBoost sensor be the sensing device. Getting solar PV fitted on Arran but we only travel a few miles so no benefit from a Zappi, just need someone to bring out an iBoost type 3 pin mains charge point.
 

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I have 4kWp on the roof too. I bought a 6 amp (1.4kW) EVSE lead, in the days before Zappi, and quickly came to the conclusion that it would never pay for itself.

At the end of the day, when the sun is shining you want to be driving the car, not faffing about charging it. Charging overnight is far more sensible - at least that way you have a fully charged car sat in the drive, if you need to go anywhere. Economy 7 (or one of the newer tariffs) may make sense - it does for me, as many other appliances can be set for overnight use.

I still use the 6 amp lead on days when it is completely clear sun all day, but frequently I end up charging with cloud overhead if I forget, and I can't be bothered with the hassle.
 

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I bought a 6 amp (1.4kW) EVSE lead, in the days before Zappi, and quickly came to the conclusion that it would never pay for itself.
Do cars ever pay for themselves? We all use our cars so differently that each has their own answer. Mine sits for days at home, charging on the Zappi, then does longer drives and returns to charge. A Zappi is not a lot different to many installed 7kW charge points in cost.
 

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I have a 3.4kw setup so not the biggest, but went through the same deliberation and came to the conclusion that using a zappi would save me nothing.

If I were charging during the day from solar, I would be saving 5p per kwh that I would have otherwise put in overnight on Octopus Go. But if I don't charge during the day using the solar, the excess is fed back to the grid and Bulb pay me 5.5p per kwh for it.

So, even if were at home during the day, which in normal times I wouldn't be half the time during the week, all it does it move the timing of when I do the charge.

So i got an Ohme.
 

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Is your solar on the FIT scheme? if not, you can earn more in SEG export payments selling excess solar back to the grid (5.4-5.5p) and then charging on Go for 5p, or you might be able to get on Go Faster, 3 hours at 4.5p, then graze charge each night to top up. This is what we do with our 6.2kW system. Not bothered with a solar hot water diverter for the same reason. Export is worth more than the gas costs.
 

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Is your solar on the FIT scheme? if not, you can earn more in SEG export payments selling excess solar back to the grid (5.4-5.5p) and then charging on Go for 5p, or you might be able to get on Go Faster, 3 hours at 4.5p, then graze charge each night to top up. This is what we do with our 6.2kW system. Not bothered with a solar hot water diverter for the same reason. Export is worth more than the gas costs.
Yep, that's me. Things would look different on FIT scheme because, as I understand, you get paid for half of what you generate whether you feed it to the grid or not. So you can eat all your generated electricity on a zappi and still get paid as well for half of it. But if, like me, you missed the FIT boat, and are using a SEG sign up, then feeding it in is worth at least as much as consuming it, if the alternative was to then consume on an overnight tariff like GO.
 

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Yep, that's me. Things would look different on FIT scheme because, as I understand, you get paid for half of what you generate whether you feed it to the grid or not. So you can eat all your generated electricity on a zappi and still get paid as well for half of it. But if, like me, you missed the FIT boat, and are using a SEG sign up, then feeding it in is worth at least as much as consuming it, if the alternative was to then consume on an overnight tariff like GO.
Yep, exactly the same for us. Your right, it used to be deemed 50/50 for export under FIT. We had a 4kW system on our last house with the FIT. It was good for £1500 a year in payments! Now at the next house even with 6.2kW I think the saving is less than half that much (SEG payments and leccy saved).

We are on Go Faster, but take 4 hours at the usual 5p. I only really charge for 2.5 hours with the Soul every couple of days. Might see if I can change to 4.5p for 3 hours. Still leaves long enough to run the dishwasher and things before bed (5p starts at 8.30 pm)
 

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Discussion Starter · #12 ·
Thanks all for the replies and discussion on this. Our solar is on the FIT scheme and we get regular payments for generated electricity even though the actual amount exported isn't monitored. I think it's probably worth more to us to have the hot water heated than try to charge an EV.
 

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How possible is it to build a mains lead charger complete with an arduino controller?
Not hard at all. See OpenEVSE.org for a real kit approach to it. Or you can buy a Viridian Controller module that's current-controllable via resistor, an RCBO, a Contactor, Type 2 socket, add in an arduino/whatever CPU of your choice, & do whatever code you like. Basically, get a Viridian or Rolec, broken's cheaper, or broken Podpoint to supply you a case, socket & some of the bits, replace what's missing/broken yourself and add smarts yourself.

Could an iBoost sensor be the sensing device?
Absolutely not. This thing is an immersion-heater diverter, just like my Solic 2000 is. The bit sensing import/export is fine, problem is the way it puts the diverted power into the imemrsion tank. It does this at a variable current, anything from 0 to 13A, and the control is by chopping the mains on & off at a very high frequency. This kind of control is only suitable for resistive loads. It is absolutely NOT suitable for EVs, EVSEs, televisions, radios, routers, computers, etc. Fine for electric heating elements, and could be used to boil your 13A kettle at perhaps a very slow rate, and that's it. Will also work on old fashioned filament bulbs, could be one way to monitor easily if you wired up a very low-wattage filament bulb like a cooker bulb.

EVSE work by telling the EV down a signal line what current they may take as a maximum. It's then up to the car to not exceed this maximum amount. Under no circumstances should anyone, ever, be feeding a chopped mains waveform into EVs.
 

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I managed to get a Zappi installed for £215 cost to me (£500 grant, new installer, contribution from the company). I used it to divert roughly 1,000kWh to the car from February to November, saving roughly £125. It has been sitting unused for over a year but we are getting our MG5 on Tuesday.

If we can save £100 per year then it's been a great investment. Obviously the numbers are very different if you have to pay £700+ for the Zappi. It's really not much effort to plug the car in when we get home, and it's really satisfying knowing that it's charging from the sun.

There is another side to using Octopus Go which is that you do pay significantly more for the standing charges and increased unit costs for your daytime usage. It would cost us around £80 more per year for our regular usage, which would more than offset the cheaper car charging.
 

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I managed to get a Zappi installed for £215 cost to me (£500 grant, new installer, contribution from the company). I used it to divert roughly 1,000kWh to the car from February to November, saving roughly £125. It has been sitting unused for over a year but we are getting our MG5 on Tuesday.

If we can save £100 per year then it's been a great investment. Obviously the numbers are very different if you have to pay £700+ for the Zappi. It's really not much effort to plug the car in when we get home, and it's really satisfying knowing that it's charging from the sun.

There is another side to using Octopus Go which is that you do pay significantly more for the standing charges and increased unit costs for your daytime usage. It would cost us around £80 more per year for our regular usage, which would more than offset the cheaper car charging.
1,000kWh on Octopus GO would have only cost you £50 (or £45 on GO faster). Offset as you said by the higher standing charge and higher day rate. However in our region the GO day rate is cheaper than pretty much every other supplier, and that's important in the winter when the PV isn't doing much and our 'leccy usage is much higher during the day. A Powerwall would sort that out, but that starts a whole new discussion of cost-effectiveness.

I guess my point is that you do need to do the sums very carefully, as you obviously have.

I'd definitely agree that a cheap Zappi is the best of both worlds, especially as they can now link to the Agile tariff (if that is your preferred tariff). However as the grant has been reduced to £350 they probably won't ever be as cheap again, which goes back to original suggestion of an OHME being the most cost-effective option, especially as they are currently on sale at less than half price.
 

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To add my tuppence to the conversation, like many have said this is very much user dependant and I have also found that it is dependant on your home setup.

This year has been odd and now working from home the car spent a lot of the summer being used at zero cost. I probably had a couple of months of totally free motoring, but I am on the very early FIT payments so make out like a bandit from solar. Previous years I have not used solar anywhere near enough as the car was at work during the day.

FYI The old FIT system pays out for ALL of the generation at one (higher) rate and also 50% at a feed in rate for your assumed feed in to the grid irrespective of consumption. Not helpful for the OP but just making sure people know the full story.

If your house has a hot water tank (I took mine out to get a combi boiler years back) then pushing the extra generation to hot water is a lot easier than charging the car as it can use every spare watt and not need the 1.4kW (might be 1.1kW not sure) that the car needs to start charging. Having a Zappi and Harvi would still be a decent call though. The Zappi is pretty good, I can't recommend them enough. Hopefully everyone who has solar and a water tank already something like that though.

Just to beat @Petriix I managed to get my Zappi installed for nothing Mwhahahahahahah. The installer was supposed to come back and sort a minor issue, they never came back and never asked for any money. :p
 

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With 3.5kWp of solar panels, and Economy 7 heating, I decided it was not worth the hassle of trying to charge using surplus daytime solar; I just charge at night on the E7 cheap rate (would be better if I could get paid for all the surplus solar I export, rather than assuming it is 50% of what my panels generate).
 
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With 3.5kWp of solar panels, and Economy 7 heating, I decided it was not worth the hassle of trying to charge using surplus daytime solar; I just charge at night on the E7 cheap rate (would be better if I could get paid for all the surplus solar I export, rather than assuming it is 50% of what my panels generate).
If you have a smart meter you can come off FIT and sign up to SEG instead. But whilst the measurement of what you export would then be accurate, I am assuming that the rates wouldn't be anywhere near as good as FIT.
 

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If you are on an FIT rate, there is the FIT generation payment for all the units that you generate (in my case 17.61p/kWh), plus an FIT Export payment of 5.5p/kWh for all the units that I export. Because my main electricity meter does not register the export kWh, this is deemed to be 50% of what I generate. If I had a smart meter installed (and there seems to be a dearth of 3-phase smart meters) which would register my export kWh, as far as I understand it I would still get my FIT generation payment, but my Export payment would then be based on an actual export reading rather than assuming it is 50% of my generation. With E7 night units at 7.6p/kWh (7.2p + VAT) the possible 2.1p/kWh saving by trying to charge from the solar surplus is not worth the hassle.
 

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You don't have to give up the FIT to get paid for metered exports; you can opt out of the deemed export payments and receive SEG payments from a different supplier if you like. You just need a qualifying export meter.
 
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