Bear in mind that the amount you can export will be determined by the discharge capacity of your inverter; some can discharge more than others. Ours is limited to 4000W for example. So if yours was the same you could export 4000W from the battery (less what the house consumes) for the three peak Flux hours of 4pm to 7pm. That would be 12kWh. How much that makes depends on the difference between export and import rates. If they are 30p and 15p the ‘profit’ is 15p times 12, so £1.80. That’s more than three times the daily standing charge. If you are using gas for heating and hot water you probably don’t need anything like 22kWh of storage.
Thanks HH.
Proposed is 6kW inverter. If I read Octopus’s details correctly they won’t take batt below 20% so 22 kWh battery effectively has only 17.6KWh available. If we use, say, 1kW ourselves during peak period, probably less on average, that would allow 5kw exportable, over 3 hours = 15kWh. My thinking is that the bigger battery seems justified as it would allow this, while providing greater buffer for solar in winter, but as this is new to me I may be missing something?
We are with British gas, they have moved us from 7.9p overnight to 9p recently, but export anytime at 15.1p. I like the certainty, for the moment, rather than knee jerk changes by other suppliers.
While we have a 6kW inverter - ie it can turn 6kW of DC into 6kW of AC, the battery charge / discharge limit is only 4kW, so that’s the evening maximum export, as the power is coming from the battery. It’s slightly frustrating as the manufacturer of our inverter upgraded the charge /discharge lining to 6kW very soon after we bought it.
The other thing to be aware of is whether your DNO (distribution network operator) will permit a G99 approval for your property. That depends on whether the local network has capacity. If not, you will get a G98, which limits export to 3.68kW.
We have 19.2kWh of storage. In the summer the battery is still full by 7pm, so we discharge and export for three hours. In the winter we don’t discharge as we need all the power to run the house until the cheap hours start at 11.30pm. We have ordered another 9.6kWh battery to reduce the risk of running out on cold winter days. But that’s with a heat pump and no gas, if we didn’t have the pump we’d not consider more storage and it would not be necessary or useful.
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@MrFixit @james_n Now that we are back from our holiday in Cornwall, which we did in our ICE car, I’m home again and looking to sort out the EV charging which I mentioned here three or so weeks ago.
The issue I had is that my Zappi charger, BMW i3 and Intelligent Octopus Go wouldn’t play together. @MrFixit had a number of suggestions. I also discussed it with our system designer and his basic answer was “don’t use IOG”.
Having read around the issue before we went on holiday (I gave myself a break from the subject while we were actually on holiday), I decided that I needed to give IOG a proper go at detecting the car was plugged in and sending it a charge plan.
So I set the Zappi to eco mode, set the i3 to charge immediately and stood back. The car started to charge immediately, using a mixture of solar and grid power. Then, just as Octopus said would happen, the car stopped charging and I was notified that Octopus had created a charge plan. (One insight I now had from Octopus was that you set the target charge level and departure time in the BMW app rather than the Octopus app for all BMWs.)
Now I could see that the Octopus IOG charge plan included a slot from 1550 to 1630 (ie outside the normal cheap window). I had anticipated this and downloaded the Netzero app which includes specific IOG functionality. This sets the PW3 to 100% so the car charge comes from solar and the grid (which Octopus charge at the off-peak tariff) and not the PW3. This worked perfectly and I could see the grid was topping up what the solar was providing. By setting the Zappi to Fast mode, the charger was giving me 7.6 kW and at the end of the IOG additional slot, the charging stopped and everything went back to normal, with the Zappi showing a blue light.
Before I went to bed, I set the PW3 minimum level of charge to 50% (it was at about 91%). Then I resisted the temptation to get up during the night and see what was happening.
When I did get up, at 6 am, I found the car fully charged, but the PW3 was now at 50%. So the Netzero app hadn’t stopped it discharging into the car during the subsequent slots in the IOG charging plan. Sadly today is a low solar day, so the PW3 may or may not recover to 100% before solar generation stops today,
From a deep dive into the Netzero documentation, I discovered that Netzero doesn’t change the reserve level on the PW3 to 100% while in charging slots that are entirely within the cheap rate window. They advise that if the system doesn’t already protect the PW3 during off peak charging sessions then I might want to set up an automation within Netzero to do that.
Before I do that though, I will try ensuring that the Zappi is set to Eco rather than Fast for charging inside the cheap period. It will be a couple of days before I need to charge the car again, so I have time to think more about this….
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There are a number of tools I have mentioned already that would allow you to evaluate which tariff will work best for your specific circumstances.
As I have said previously, get your Zappi wired via Henley Blocks to avoid it being seen as a load
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Yes of course I did see you said that. But this is quite tricky because I don’t have any spare wall space for an EV consumer unit.
Also it would be good to be able to charge the car with excess solar, especially as I can’t export it yet.
My additional CU is about 4 inches square, so not big.
I can still charge with excess solar if I want to.
This was my upthread solution too. Switch to Octopus Go - and all the hassle of IOG just melts away.
But IOG is better and cheaper!
Yes I remember you saying that. IOG is better tariffs right now and I’d rather try to get IOG working properly before I give up.
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I’d be somewhat concerned if my installer said don’t use IOG.
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Yes well he still thinks that EON or Utility Warehouse economy 7 tariffs are the ones to go for. But I don’t think he has looked at the rates recently. He uses IOG himself, but he has a way to not trigger a charging plan when he charges his car, so the I bit of IOG doesn’t arise.
Well we are generating quite a bit of solar now the sun is here. We had over 9kw per hour being generated from the panels the other day.
But i now have the new kia PV5 van to charge as well as the tesla, house, batteries and hot tube.
So not really sending anything back, certainly nothing to be bothered about.
But my electrician is going MCS, so will get the correct documentation soon to export if i want.
But a quick question, on the cheapest night traffif,is there a limit to how much you can inport? As ideally i would want to have a vehicle plugged in, charge my house battery and could also heat the hot tube. This would pull about 12 kw per house, so about 60 kw per night, but probably not every night.
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I don’t think there is any limitation of the amount you can import during the off peak period, except that imposed by the size of the DNO fuse (which is probably 100A for a single phase supply). 12 kW per hour for 5 or 6 hours or whatever your tariff gives you should be ok.
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But Octopus Go just works ! Every time ! And the price difference is small enough to be an irrelevance for most of us lucky to own a newish EV. What are you paying for IOG ?
A big benefit to us of IOG is the extra hour of cheap power. With our heat pump it means the batteries can start charging and the heat pump run off the mains at 11.30 and not have to start depleting batteries until 5.30am. We control everything via the car, delaying charge until 11.30pm and requiring it to be ready by 5.30. The extra hour of cheap power is useful if you need to do a big charge.
We are currently paying 8p overnight on the 12 month fixed tariff.
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Unless your DNO applies an import restriction (unusual ) I think your main fuse will be the limit. I’ve imported over 60 kWh overnight recently (Octopus). My main fuse is 100 A, but yours might be 80 or even 60, so worth checking. If you ask nicely your DNO might upgrade it.
I’m on 3.49p on IOG, fixed for 12 months. It works every time for me with an Ohme Pro charge point. The integration is very good and the main reason I chose the Ohme.