Help with calculating best Octopus tariff option, adding EV charger to solar/battery setup?

gardenharrison

Hi all, I'm getting myself confused so would welcome some direct advice, or suggestions on where to go for it

We have a Growatt system, which is not ‘intelligent’. I can manually set it for timings (eg push export out during peak evening period).
I am about to purchase an electric car, and install an EV charger. I am most likely to install a Zappi charger.
I have so far been on Flux for our solar/battery. Our solar panels are SW facing and so we benefit from the export period during the summer. Our battery is about 7kWh (wish it was bigger, that's another story)
Octopus says our import over a year is approx. 1300kwh. Our export was about 2400kwh over the same period. (Solar Assistant says our "load" for the year is about 2100kwh. I'm not smart enough to fully understand what those three numbers mean in relation to each other)
Being on Flux has seemed to work fairly well so far.

I have struggled to work out whether adding the EV charger changes which tariff would be most appropriate. Our EV use will likely be limited. I anticipate us driving less than 6000 miles/year (perhaps as little as 3000 miles).
 The automated advice on the Octopus website suggests Go for import + Outgoing for export. I can see that through the winter this may be preferable over Flux. But in the summer I’m not sure the calculation holds. Can anyone advise, is there a way to work out the calculations involved?

Note 1: If I had my time again, I would definitely have gone for a better solar/battery setup than Growatt, that'd be my advice to anyone else. It's a pain to control, I've had to sort a DIY Solar Assistant control setup. That works great, but feels liable to fall over and then I'll be stuck

Note 2: I'm going with Zappi in part because apparently it can use a wireless CT clamp, which means I can use an existing electric cable we have out to the drive. Any other charger apparently can't do this and would require installing of new EV cable. (Also Zappi make a big thing about being able to have the control actively to draw on our solar surplus(?) Which would seem a slight benefit for the sunny half of the year where we have surplus most early afternoons that gets maybe 10p/kWh)

Note 3: I've so far stayed on Flux all year round. I know there's debate about switching for winter, but I've taken the view that the benefits of the summer export outweighs other tariffs maybe being a bit better for winter. Especially as it seems it's much harder (impossible?) to be confident to be able to switch tariff at a whim given current volatility (?)

QrizB

Some initial thoughts:

Octopus says our import over a year is approx. 1300kwh. Our export was about 2400kwh over the same period. (Solar Assistant says our "load" for the year is about 2100kwh. I'm not smart enough to fully understand what those three numbers mean in relation to each other)

I would interpret that as being that your house used 2100kWh. 1300 of those were imported, so your self-consumption from PV was 800. Together with your export of 2400 that suggests your total annual generation was in the region of 3200kWh.

Does your inverter agree with that?

Our EV use will likely be limited. I anticipate us driving less than 6000 miles/year (perhaps as little as 3000 miles).

At 3 miles per kWh that would mean adding 1000-2000kWh to your annual consumption. That in turn would make you a net importer over the year, and that's important because Flux is fairly good for net exporters but (because the export rates are lower than the import rates) is less optimal for net importers.

If you don't want to switch tariffs whenever an equinox comes around, I suspect you'll be better off with Octopus Intelligent Go for import and Outgoing for export. Whether you choose Outgoing Fixed or Agile Outgoing is entirely up to you.

NedS

I would strongly recommend you check out Tim and Kat's excellent solar tariff optimisation tool here:

https://timandkatsgreenwalk.co.uk/

If you know your monthly solar generation and usage, and you can estimate your new additional usage from charging your EV (maybe assume 3-4 miles per kWh, split evenly over the year), the tool above will tell you which tariff would be cheaper over a whole year and which tariff is cheaper in each individual month if you want to switch tariffs seasonally for the best overall outcome.

As with any modelling tool, the results depend on the quality of the data you give it, so the more accurate you are with your usage data, the more accurate the result. I use the tool, and have back tested it with my last 12 months of data, and it proved very accurate.

I will add that your charging strategies will change depending on your tariff. If you are on Flux, then excess solar during summer is your cheapest form of electricity so you would want an EV charger that is capable of charging from excess solar, great if your car is home all day and you do low mileage as you can constantly trickle in that excess solar rather than exporting it to the grid. However, if you are on a cheap rate EV tariff, you will want to charge the car (and house battery) overnight when your electricity is cheapest and then export all your solar during the day as the export price will be higher. The tool above will help you determine which is best for you based on your usage.

Whether Intelligent Octopus Go for import and Fixed Outgoing for export as @QrizB suggests above or Flux is likely to be best should become apparent if you are able to feed your usage and generation data into the tool above.

EricMears

gardenharrison : "which means I can use an existing electric cable we have out to the drive"

That of course depends on the rating of that existing cable; EV charger would need to support a steady 32A for long periods so probably require a 6 sq mms cable. Unless specified as an EV supply, the existing cable might be a much lighter one intended only for plugging in a lawn mower or vacuum cleaner.

gardenharrison : "Our EV use will likely be limited" That really doesn't matter. For installing e.g. Octopus Intelligent Go you'd just need to prove you had an EV and to keep it you'd have to have an 'intelligent' charge at least once a month. We're on OIG and relatively low mileage EV users but the main advantage of that tariff is that we can charge our house batteries overnight at 6.9ppu and avoid almost any imports at 28ppu.

gardenharrison : "I would definitely have gone for a better solar/battery setup than Growatt," You could of course add extra batteries to your existing battery management system or even install a separate independent system (though ensuring the two systems don't cause problems for each other can be tricky).

Afraid I can't advise on export tariffs. As an early solar adopter, I'm still on deemed export and try very hard actually to export as little as possible.

Reed_Richards

I know little about Octopus tariffs but at the moment you can find better rates for EV charging with other companies. What I do know if that when I got an EV it completely changed the way I used my solar + battery system. Now I charge my battery overnight for long enough that for at least half the year it keeps me going until the battery recharges via solar. Even in the middle of winter I can effectively extend the cheap EV hours by charging the battery then and using it until it runs down.

gardenharrison

Thanks @NedS , I'll give that tool a try! And yes @EricMears you're right about the cable requirements. I currently have my fingers crossed… (got it put in as part of a renovation - was pleased to be thinking ahead, but left the electrician to it…) And thanks @Reed_Richards , yes I guess that's what feels hard to know for sure in advance, how our usage of the existing system may change given the addition of the EV. We'll see!

born_again

"which means I can use an existing electric cable we have out to the drive"

Make sure that the socket complies with.

The IET Wiring Regulations (722.55.101.0.201.1i) specify that 13A UK sockets which are installed to charge an EV must comply with BS 1363-2 and be marked ‘EV’ on the back of the plate. 

QrizB

Make sure that the socket complies with.

You're correct inasfar as that's the present requirement for a socket used with a plug-in "granny charger" but the OP is looking to install a Zappi which needs a 32A supply and is generally hard-wired.

EricMears

gardenharrison : "was pleased to be thinking ahead, but left the electrician to it"

Providing you told the electrician you intended to put an EV charger, there you should be fine. If you just said "it would be good to have a power outlet there" you probably got a low power supply.

gardenharrison

https://forums.moneysavingexpert.com/discussion/comment/82143607#Comment_82143607

Thanks, yes I think it's all in order. The electrician definitely knew it was for EV.

(I've found that almost all companies don't want to actually visit the property these days. They want you to send lots of photos etc. Which is a pain when something isn't particularly clear, but could be resolved by an electrician actually being there in a few minutes. Thankfully I've got one coming round later this week)

gardenharrison

And thanks again @NedS for suggesting the Tim and Kate's tool. It seems fantastic!

(And really helps with the mindset-change that can be needed when changing situation. If I'm likely to be using all of what I produce, I realise that really is quite a different way of approaching the existing PV/battery setup, and how different tariffs relate to that)