FoxESS Community - Owners & Installers Forum

Hi all,

I currently have a KH9 and 20KWh ECS2900 Battery system with 12kw solar and been running for nearly 2 years now absolutely perfectly and covers all the house demand easily.

However, This year I had a heat pump installed and during these winter months with little solar im finding that i could do with an additional 10kwh of storage to cover this extra load.

On the face of it I can see i have 2 options (let me know if I have got this right):

1) Replace the ECS2900 (20kwh) batteries with newer EQ4800 (30kwh) circa £8k
2) Buy 2nd KH Inverter and run in parallel with EQ4800 (14kwh) circa £5k

Obviously the easiest is replace batteries but this is costly and I'm not aware of a way to resell batteries (unless anyone can advise or partx service with a supplier?)

Second option more cost effective and provide more MPPTs and larger inverter capacity but these are not really advantageous to me and also takes up double the space.

Also, I was wondering if there is another solution such as buy another smaller fox system or AIO that can link with HK9, possibly to be turned on only for the winter months when needed, or any other system that I can roll in for the winter months when the extra capacity is needed? Does anyone else have this issue and overcome it? Or even a third party system that can be rolled in during the winter months?

Thanks all

Yes those are your 2 options and you have covered the cost/benefit analysis very well.

On your existing batteries, there is a relatively healthy resale market using eBay or similar and there is a Facebook community page linked to this site https://www.facebook.com/groups/foxessownersgroup, if you join there and mention your ebay advert they won’t hang around very long - difficult to predict the resale value but i’d be surprised if you don’t get at least 50% of what you paid for them, probably a lot more.

The EQ4800 is an excellent battery and gives you ample scope to expand the stack later.

You could also consider the EP12 which can have up to 4 batteries linked together, these are slightly better value at around £7k for 3 of them including the junction box with ~ 34.5kWh - but they are heavy and need to be wall mounted and work well in a garage or similar where you have a long wall that they can be spread along.

On the parallel KH, yes agree with all of those points but as you say if you have no need of the extra MPPT’s or the extra power there is zero advantage in having them running in parallel and the second would consume it’s own standby power as well as the master so you’ll have double the losses to think about.

There is no easy way to add a smaller AC battery system to your existing unless you can re-wire the house with split consumer units and have the second inverter running in series powering that second consumer - but same point about losses, although a bit smaller for a smaller inverter (you’d be better leaving the wiring and going with 2 KH’s in parallel).

If you have a heavy user that comes off a single 13A plug - such as a large aquarium, you could consider buying something like an ECOFLOW DELTA Pro3 (~£2k) which is a standalone battery(LFP)/inverter, it would sit in line with that appliance and could be set to charge in your low tariff and run the appliance for the rest of the day on it’s internal battery. I’ve been thinking about doing the same for my aquarium which at this time of year takes upto 3kW a day but the maths don’t really add up.

All of that said, the bigger battery stack would likely be your most effective option, assuming you re-sell your current stack.

Thanks Dave very useful information. I did think about the 2nd inverter consumption as mine currently uses up to 500w on its own (does that seem a little high?) and wouldn't want to extra consumption as you say. Saying that I suppose I could only turn it on 4 months of the year when needed.

I will deffinately look into advertising on eBay, I did check previousoy but didn't see much on there but it's probably because they dont hang around long like you say.

Its shame there is no magic box you can hook mutilple batteries up to