FoxESS Community - Owners & Installers Forum

Hi I have just set up a pair of 5kW AC chargers for a customer who already has an existing PV array. Double checked through all settings with Tech support and all looked good when we left site. This morning the system hasn't force charged over night as it was set up to do and now were seeing export to the grid while the batteries are at 10%. just wondered if there's something in the advanced settings that we've missed that is causing this?

Thanks

Joe

Are you using the charge periods, or scheduler to charge the batteries ?

Often exporting unexpectedly, particularly on a new install suggests the CT clamp is in the wrong place or facing the wrong direction

Hi

My current 2kW PV Fox ESS grid tied system currently has no battery backup.
The system has been installed for a year now and has managed to produce 17kwh, thankfully my usage is 14kwh annually, so installing batteries to eliminate this bill altogether might be a good idea!

I am interested AC charger, backup with EPS for off grid use, in an emergency, would also want an option to charge a portable generator or power station. I want to stick with a lithium battery option, maybe minimum batter size would be best, I am not sure. Should I get a larger battery and switch to an agility product and purchase energy at lower costs when available? Open to suggestions/recommendations .

Cheers.

Solar PV 2KW
Fox ESS series 2.0

Can I just check your metrics, I would expect a 2kW system to generate something in the region of 1700 kWh over a year, and i'm guessing that makes your home usage 1400 kWh per year ? (which is very low ~ 4kw per day).

If you have an EV the ability to charge at very low rates (typically 7p / kWh) and export at a higher rate (Octopus 15p / kWh) would mean with a big enough battery to cover you daily usage you should never pay much more than the lowest rate for your electricity.
Last year was different as Octopus only paid 4.1p, and this could always change in the future

If you don't have the EV, there are tariffs such as Octopus Flux or Economy 7 where you can buy the energy cheaper during the night and then use the stored energy during the day so that you export all your solar at a higher rate - again having enough battery storage to cover your daily needs is a pre-requisite for that.

It would be helpful if you could confirm your annual / daily usage and what tariffs you are on (or considering), but on the basis of those maths you then need to consider what your peak power usage is, for example if you do a lot of cooking and the oven takes 4 kW, having a 3.7kW inverter even with batteries would see you take some power from the grid (admittedly only 300 watts but if you had a 5kW inverter it would all come from your batteries).

On the basis of what you have said you probably don't need a lot more than 4kW per day from the batteries, so an ECS2900-H2 (5.76kwh) would provide that but of the 5.76kWh 10% is unusable as they have a max depth of discharge of 90% which reduces it to 5.1kWh which is still just enough. Obviously if you are thinking of also charging other things such as powerbanks your might need to take that into account.
But I would always say get more battery power than you think you will need, not least as they age their depth of discharge will reduce so after 10 years of constant operation they may only provide 75% of what they do when they are new.

EPS is quite the subject on it's own and you need to consider if you want just a few critical circuits to be supported (lights, downstairs sockets perhaps) or whether you want the whole house to be supported as that would have a major impact on the design, wiring and cost.
The easiest (cheapest) option is to fit a double socket on the EPS and simply plug in an extension lead to support a few appliances, lights etc.. - after that it will get more complicated so make sure the installer you choose understands your requirements.

There is no single answer to this as it will depend on your personal requirements so best to look at all the possible solutions and give it some time to weigh up all the options.

Thank you Dave
Yes Solar produced this year is 1700. Estimated usage for current year 1000KW taking into consideration offset cost to house load needs..

Thanks for clarifying my considerations.. I am on Octopus 12mths Fixed Outgoing 15p KwH. I think it's worth getting a bigger batter if only to purchase /store cheaper energy and offset the depreciation in battery efficiency.

Have I understood correctly, my AC charger inverter must match battery size? The AC charger would be independent? How will it work seamlessly with my existing solar PV system?

Thank you
Judy

Judy01 wrote: ↑Mon Sep 30, 2024 2:16 pm Have I understood correctly, my AC charger inverter must match battery size? The AC charger would be independent? How will it work seamlessly with my existing solar PV system?

No sorry what I was trying to say is you should get an AC charger that is powerful enough to cover the majority of your house loads - for example a 3.7kW inverter can supply a maximum of 3.7kW from battery, so if you put the cooker hob on (~2kw) and boiled a kettle (~3kw) the inverter would provide 3.7kW and the rest (1.3kW) would be topped up from the grid for the couple of minutes it takes to boil. Whereas if your AC charger was a 5kW version it would all be supplied by the AC charger from battery.

The AC charger will work fine with your existing solar inverter, you can set it to use excess solar to charge the batteries (called self use), or simply charge the batteries on a low tariff and export everything you generate (called feed-in first).

Thanks Dave

LOL I see what you mean - consider likely house load peak ! That is a very good point..
The price difference between 3 and 5kW isn't much anyway..
Really appreciated...

Judy

Hi

I checked my analysed data, my peak usage does not exceed 3KW but given the price difference between 3 - 5 KW, i get the advantages of servicing a higher demand when needed.

I have now talked with an installer. He explained that the new AC Charger and existing Grid tied Inverter will both need to be on its on 'board' in order for the CT clamps required for both devices to communicate properly.

I would like to achieve independence from the grid in an emergency I was advised adding an AC Charger was the only (or most cost effective) way to do this with an existing solar PV system. Would I also need EPS?

What are your thoughts?

Any idea what the likely installation costs should be

Thanks


Solar PV 2KW
Fox ESS series 2.0

If your installer thinks a separate CU is required i'd take his advice, it will certainly make the install much tidier.

If you want grid independence you will need an AC charger which has the EPS output. You will then need to decide which of your house circuits that you want to continue should the grid fail as you won't be able to run your entire house on an inverter (in particular the cooker, shower or very heavy loads).

The installer can split your consumer unit and transfer those circuits to that and wire that up as an EPS solution for you but it is quite complex so make sure your installer understands what it is you want - it's quite a bit of work and costs will depend on your specific install so very difficult to offer prices, but it will be much easier and cheaper to do when you are installing the AC charger than retro-fitting later.

The cheapest option for EPS is where the installer simply adds a double socket near the inverter and you plug your trailing leads into that.

There is a whole section on EPS in the forum, this might help a bit to understand the options viewtopic.php?t=52