Ronski's Solar & battery DIY build with whole house backup
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I expect so, we'll see next winter.
November through to February we used £368 of gas and around £36 worth of SC, that buys a lot of 7p electric, even if we run out of battery I think we'll still be better off.
November through to February we used £368 of gas and around £36 worth of SC, that buys a lot of 7p electric, even if we run out of battery I think we'll still be better off.
The way I looked at it was that our gas bill for last year alone was £583. At the very worst, we could use 2328kWh of peak rate electricity over the year and it'd be break even. Bearing in mind the water heating and legionella cycle would be overnight at the cheap rate (6p/kWh) and we usually have at least 6kWh left in the battery each day to export and also export some solar too. It should be much less.
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I’m usually at least 40% off peak with my heat pump before we consider battery power. It only drops into the 30’s when it doesn’t get above ~3C all day. I can be up in the 50’s some days e.g. when it’s above 10C most of the day.
I’m running at 30C flow temp at 12C outside, it’s just on tick over at 350w at that temperature.
I’m running at 30C flow temp at 12C outside, it’s just on tick over at 350w at that temperature.
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I always fully charge the house batteries overnight from midnight, they are not charged at the full rate, the system constantly alters the charge so they are full at 05:00, then until the end off the off peak period at 05:30 the house loads are covered by the grid, this allows the cells to balance.
In the evening from 19:30 until 23:25 the system exports the house batteries down to 15% SOC, again, this is calculated on the fly to reach 15% at 23:25. If it wasn't for the saving sessions I'd probably start the export earlier.
Using the auto adjusted import and export rates means I'm not pulling or exporting at high power, this is good for the grid and good for my equipment.
As I'm on Intelligent Octopus Go we get car charging slots outside the normal off peak hours, when this happens my house batteries will charge at 4kW, once they are full, just the house load is pulled from the grid, this stop my batteries discharging into the car, as car charging is seen as house load.
I only charge the car once a week, I don't game the car charging like some do, I just can't be bothered.
We've been in profit for the last two years, in fact it's even covered the gas bill, gas is going in April and we'll be totally electric.
Our electric bill for the last week is -£20 roughly.
The Victron system is highly flexible, the main limitation being my brains power and programing skills, or lack of. A lot of what I do can be achieved using Home Assistant to control inverters, I see a lot of people doing similar on other forums with lots of different inverters.
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That's a really well thought out strategy. I guess part of the joy of building your system with the end in mind.
I don't quite have that level of autonomy, though I'm sure I could make it do something with HA. I like the idea of increasing the longevity of your batteries by reducing power to more "trickle" changing.
I'm still very much manually intervening based on season. As it's now getting lighter I've reduced the overnight charge. But I probably should look into synchronising it with solar forecast.
You still rely on the grid a fair bit, would you want to be less grid dependent or are you happy to game it? I suppose you're supporting the grid too by exporting during the evening reducing the grid's need for fossil fuels?
I don't quite have that level of autonomy, though I'm sure I could make it do something with HA. I like the idea of increasing the longevity of your batteries by reducing power to more "trickle" changing.
I'm still very much manually intervening based on season. As it's now getting lighter I've reduced the overnight charge. But I probably should look into synchronising it with solar forecast.
You still rely on the grid a fair bit, would you want to be less grid dependent or are you happy to game it? I suppose you're supporting the grid too by exporting during the evening reducing the grid's need for fossil fuels?
Being grid more independent just costs you more money.
The grid has pricing signals which are loosely based on ‘scarcity’ and carbon emissions. The higher the price, the more carbon Intensive the grid is and the less capacity there is.
Buy low, sell high is the best way you can support the grid and cost you the least amount of money.
Think of it as a big energy trading scheme.
The grid has pricing signals which are loosely based on ‘scarcity’ and carbon emissions. The higher the price, the more carbon Intensive the grid is and the less capacity there is.
Buy low, sell high is the best way you can support the grid and cost you the least amount of money.
Think of it as a big energy trading scheme.
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But when you're on tariffs like flux there's little fluctuation in the price it's fairly fixed so I guess you'd need to go onto a more "agile" sort of tariff to really do that buy low sell high strategy?
I guess I've just become complacent with my solar and battery after a few years of having it. Ronski's strategy has just made me think/consider changing things.
Perhaps I should look at HA to do some more intelligent exporting/importing.
I do pretty much the same as Ronski but on good days have to make sure the batteries are depleted as much as possible to balance the generation, storage and export for the that particular day.
All the time its cheaper per kWh compared to what you get for export, then financially you're better off fully charging the batteries overnight.
I charge at 7p and export at 15p on IOG, yes there is some efficiency losses, and there is wear and tear on the system, but I'm not concerned about that.
If you don't have an EV you can get on Octopus Go, yes you're supposed to have an EV, but no one asks for proof, and if you're charging a battery every night it looks like an EV. Thats 8.5p cheap rate, and 15p export.
I think Agile is just too much hassle, there are people that automate it, but its a lot of work, and if you don't have a powerful inverter then I should think it could be quite problematic. It can also get very expensive, its been a £1 a kWh recently, and not many cheap slots either.
I was on Flux, and I used to charge every night, but even with my 8kW inverter I couldn't fully charge my batteries, the peak export slot was also only three hours, and I needed to make sure I kept enough back to last until the cheap slot which I think was 1am, so I would stop exporting at 45% SOC.
When I looked at the sums in December, Go would cost me far less, well, make me more profit, I should have switched ages ago.
I do consider I'm helping the grid, during the day I export all excess, and through out the evening I export, I do feel a little guilty that I don't export in the peak period (thats down to saving sessions), but now summer is coming I'm still exporting excess solar after 4pm.
These systems cost a lot of money, so maximising what they save is key.
At the end of the day, I'm doing just the same as lot of people on here, and other forums do, my main difference is I spread it out, so I'm not exporting at 8kW at 23:00 for example.
If you want to maximise your ROI then you do need to make the system work, but it does depend a lot on the system and size of battery.
Is that because you are DNO export limited?
I charge at 7p and export at 15p on IOG, yes there is some efficiency losses, and there is wear and tear on the system, but I'm not concerned about that.
If you don't have an EV you can get on Octopus Go, yes you're supposed to have an EV, but no one asks for proof, and if you're charging a battery every night it looks like an EV. Thats 8.5p cheap rate, and 15p export.
I think Agile is just too much hassle, there are people that automate it, but its a lot of work, and if you don't have a powerful inverter then I should think it could be quite problematic. It can also get very expensive, its been a £1 a kWh recently, and not many cheap slots either.
I was on Flux, and I used to charge every night, but even with my 8kW inverter I couldn't fully charge my batteries, the peak export slot was also only three hours, and I needed to make sure I kept enough back to last until the cheap slot which I think was 1am, so I would stop exporting at 45% SOC.
When I looked at the sums in December, Go would cost me far less, well, make me more profit, I should have switched ages ago.
I do consider I'm helping the grid, during the day I export all excess, and through out the evening I export, I do feel a little guilty that I don't export in the peak period (thats down to saving sessions), but now summer is coming I'm still exporting excess solar after 4pm.
These systems cost a lot of money, so maximising what they save is key.
At the end of the day, I'm doing just the same as lot of people on here, and other forums do, my main difference is I spread it out, so I'm not exporting at 8kW at 23:00 for example.
If you want to maximise your ROI then you do need to make the system work, but it does depend a lot on the system and size of battery.
Is that because you are DNO export limited?
Limited with the ability export no more than 5 kW per inverter ( 10 kW) subject to house load. But I can charge 3.3 kW to each set of batteries at the same time (hybrid inverters) giving me a max potential usable of 16.6 kW.
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I tell you what seems to be a bit of an issue now though. Octopus' systems seem to recognise when you're exporting and the car is plugged in. Without fail now, if I'm exporting in an evening it'll start charging the car if it's plugged in despite there being no prior notice of an earlier slot. It happened again yesterday: I plugged in and was given a charge period of 23:00 to 05:30. I started exporting at 20:30 as normal and Octopus started the car charging from 21:00 to 22:30 with no notice at all, essentially stealing the export in that time.
I've set the export margin in the Zappi to >8kW, so it's not that and can confirm it doesn't do this in the daytime. Very sneaky. If it keeps doing this as it gets lighter I will not be plugging in until after the export is finished. I can't automate it as the inverter cannot see the car load.
@reef I'm pretty sure I had that happen last night, when I plugged it I was given slots from 23:00. I looked at what was happening about 22:40 and noticed I was exporting at 8kW, so investigated further. I'd been given a charge slot at 22:00, in my case that means the batteries also charge, so come 22:30 when it went back to exporting, the system was now trying to reach 15% SOC by 23:35 and exporting at maximum.
So if Octopus are being sneaky, its going to back fire on them with regards to my system, and many others that charge their house batteries when they get a cheap slot via automation.
If you use HA you can automate your system providing HA can control it, you have two options.
So if Octopus are being sneaky, its going to back fire on them with regards to my system, and many others that charge their house batteries when they get a cheap slot via automation.
If you use HA you can automate your system providing HA can control it, you have two options.
- You could fit a CT clamp on the supply to the EV charger, HA could then control the inverter/batteries accordingly.
- Use BottleCapDave's Octopus plugin, you can then use the dispatching flag, this is what I do.