Battery installation conundrum ac or dc coupled

rangor gubbins

rangor gubbins

rangor gubbins

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Kent, UK
Hi all,
I'm trying to figure out what route makes the most sense for installing a battery to our existing PV system.
We have a 4.1 kW PV array, with solaredge HD Wave inverter (3.68 kW).
It will cost approximately £4.5k (maybe £5k) to add a solaredge 10 kW battery, which would dc coupled. It will charge from the existing inverter. This seems the most efficient and neatest solution but is quite a bit more expensive.

Alternatively, I can get a 9.7 kW battery and inverter installed (AC coupled) for £3.4k, or a 14kw system for £3.9k. These would use Fox ESS H1 (G2) or AC1(G2) inverter plus fox ESS EP5 batteries.

Additional considerations:
- I'd like to have whole house back now or in the future,
- we might want an EV charging point at some point.
- We have an ASHP and I plan to switch our tariff to the octopus Cosy which has 3 low price periods per day, and one peak price, so battery needs to cover our usage from 16:00 to 19:00.

Anyone get experience with Fox ESS? Any hardware or software issues?
What do people who have dc or AC coupled batteries think would work best for us?
 
Solar edge isn't worth £5k for a 10kw battery.

With AC you may need a G99 as you can export from it independently of the solar panels. I'm sure someone else will comment on that though.
 
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200sols said:
Solar edge isn't worth £5k for a 10kw battery.

With AC you may need a G99 as you can export from it independently of the solar panels. I'm sure someone else will comment on that though.
Click to expand...
I've not had the quote for the solar edge system yet, but I'm estimating based on price of the parts.
 
How old is the solar edge inverter and is it linked to FIT (if its FIT linked probably best left well alone)

Considering what your talking about it may be better to ditch that inverter, get a hybrid that can take the PV and new batteries so moving to DC as opposed to AC.
The prices of inverters are hardly any more for larger ones, or going hybrid vs string.

Just another dimension.
 
We've got the tale end of the FIT, so we only get something like 5.8 p/kW generation plus similar for 50% deemed export.

Our inverter got replaced in 2021 due to a fault, so isn't that old.
 
Does anyone have experience with Fox ESS inverters and battery charging?
Is it possible to set specific time periods for battery charging and discharging?
We will likely switch tariff to octopus cosy, which has low price periods from 4:00 to 7:00, 13:00 to 16:00, and22:00 to 00:00. And a peak period 16:00 to 19:00. So I want to be able to set it up so that the battery charges during low price periods and from solar, and discharges during the peak price period.
 
rangor gubbins said:
Does anyone have experience with Fox ESS inverters and battery charging?
Is it possible to set specific time periods for battery charging and discharging?
We will likely switch tariff to octopus cosy, which has low price periods from 4:00 to 7:00, 13:00 to 16:00, and22:00 to 00:00. And a peak period 16:00 to 19:00. So I want to be able to set it up so that the battery charges during low price periods and from solar, and discharges during the peak price period.
Click to expand...
Yes, this can be done.

Don't spend £5k on a 10kWh solaredge battery. Ridiculous pricing.
 
rangor gubbins said:
One more question, if I change our solar edge inverter for a hybrid fox ESS inverter, will we lose the FIT payments, or can it be transferred to the new inverter?
Click to expand...

@ronski is probably the only one round here with enough FIT knowledge to answer.

I think the main issue is the panels and any changes to them as opposed to eg the inverter but thats based on very limited knowledge so best to check it out.

You can make some changes now, like more panels but the output gets scaled so eg if you double generative capacity you only get half the amount generated as qualifying for FIT.

Edit a quick google threw this up, which sounds like adding a hybrid with battery to replace the string FIT inverter is a no go
"You should still receive FIT payments after fitting battery storage as long as the configuration conforms to the rules (essentially if the batteries are after the generation meter you should be okay)."

So you would need to add batteries between the generation meter and the grid itself.
 
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Mercenary Keyboard Warrior said:
@ronski is probably the only one round here with enough FIT knowledge to answer.

I think the main issue is the panels and any changes to them as opposed to eg the inverter but thats based on very limited knowledge so best to check it out.

You can make some changes now, like more panels but the output gets scaled so eg if you double generative capacity you only get half the amount generated as qualifying for FIT.

Edit a quick google threw this up, which sounds like adding a hybrid with battery to replace the string FIT inverter is a no go
"You should still receive FIT payments after fitting battery storage as long as the configuration conforms to the rules (essentially if the batteries are after the generation meter you should be okay)."

So you would need to add batteries between the generation meter and the grid itself.
Click to expand...
Great, thanks.
My understanding is that we'd need to change the meter on the solar so that any mains import for charging the battery doesn't get included in solar generation when it comes back from battery to the house. Bi-directional meter is what (I think) we need.
 
We won't change the panels. But if we get a new hybrid inverter it will be with higher wattage output (5kw), so generation from the panels should be slightly higher as they won't get trimmed as they do now with our existing 3.6kw inverter.
 
rangor gubbins said:
Does anyone have experience with Fox ESS inverters and battery charging?
Is it possible to set specific time periods for battery charging and discharging?
We will likely switch tariff to octopus cosy, which has low price periods from 4:00 to 7:00, 13:00 to 16:00, and22:00 to 00:00. And a peak period 16:00 to 19:00. So I want to be able to set it up so that the battery charges during low price periods and from solar, and discharges during the peak price period.
Click to expand...
I have this. As others have said don't pay £5k for 10kw of storage.

Without VAT, my 5.2kwh Fox was about £1k. Kinda wish I'd got the two, but never mind. You can force charge/discharge but the app isn't the greatest if I'm honest. You can set it to self use, feed in priority, backup or peak shaving. I have self use to minimise draw from the grid. At the moment I'm basically getting paid (which I will offset with my high electric use in winter - storage heaters).

At the moment my battery is back to 100% pretty early in the morning and I'm not bothering with charging it. I should really be forcing discharge overnight and then top it up again to repeat. I've exported 280.8 so far this month. May was far better unless a mircale happens I did 712kwh.
 
rangor gubbins said:
@SeatIbiza thanks.
Can you set the batteries to charge and supply the house during specific periods?
Click to expand...

Yes you can charge overnight (if you have a cheap dual rate for example) and then the house will use the solar/battery over the grid. For example, my biggest use this week was saturday (wasn't too sunny) and I use a massive 2.34kwh from the grid. 90%+ of my cost over the past few months has been the standing charge which is 42p a day. My live meter monitor isn't usually above 70p by day end, but tit doesn't factor in power sold back to the grid which varies. Last weeek (excluding yesterday as the data isn't complete) I exported 116kwh, 31 of which was on Friday!
 
It looks like Fox ESS inverters can not work with Solar Edge optimisers. So I'm assuming that swapping our solaredge inverter over to a Fox ESS won't work. If i go with Fox ESS I'll have to have an AC coupled inverter.
 
Finally got a proper quote for a solaredge battery installation. It is almost £6K! for a 10KW battery, doesn't include some minor ground works to dig a 10 m trench for ducting. Its madness. It would use the solar edge inverter we already have, so its just for the battery, some extra components for comms and monitoring, and installation.
So I've opted for the Fox ESS system, which will have to be AC coupled. It's £3.9K for a 14KW battery, inverter, and installation.
 
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