Small home battery advice please

[Jinx]

Hi all,
I have a small solar system I DIY’d, consisting of 6x 455w panels feeding a 2KW Growatt inverter. This is working perfectly but I’d now like to add batteries in a cost effective matter.

On average I’m drawing 5kWh/day from the grid so I’d like to aim for a battery around that size at first with ability to double later on.
I’m thinking that a stand alone solution will be easiest solution and it looks like Pylontech batteries are popular on here, can anyone advise on a charger/inverter that would suit.

The battery will be remote to the house so I would need a remote (15m but no easy cable route) CT to detect import or export.

Just to be clear I’m looking to cover majority of use rather than eliminate grid draw. I realise fully discharging batteries every night will hammer them so will add capacity when funds allow.

I’d be happy with sub 1.6kW of output if it causes DNO issues but obviously more is better.

The other choice I guess is swapping the growatt for a hybrid so any advice there please however I do prefer the idea of a separate independent system.

[AGT]

Reading with thread with interest.

Also wondering if there is a wireless CT unit that works with these units like the harvi/Eddie unit but asssume that only works within their brand equipment?

[Oldgreybeard]

Long cable runs for a CT aren't an issue. The grid CT for our Sofar ME3000SP has a cable run of about 19m. I extended the CT cable using a bit of spare outdoor Ethernet cable I had, the gel-filled stuff with a very tough outer sheath. That cable runs around the base of a wall, with a short length( about 2m) buried across a gravel path and running through a bit of left over electrical conduit.

To try and provide a low impedance connection, plus to allow the twisted pair structure of the Ethernet cable to help a bit with screening (not that I think it's really needed) I paralleled up the Ethernet cable conductors, using the four solid colours for one side of the CT, the four striped colours for the other side. Been working fine now for a long time. Hardest bit was dealing with the sticky mess from the gel inside the outdoor Ethernet cable, horribly tenacious stuff.

AFAIK, the smallest battery inverter/charger systems around are about 3kW inverter output, so dealing with the DNO is inevitable if you already have a system that can export. I don't think there is an easy way out of that.

The Sofar ME3000SP and Pylontech combination we have works fine, no real complaints about it and it was pretty good value at the time I bought it (less so now that prices have gone up). Few minor niggles with the detail of the way some of the settings work, but it's a flexible enough unit that I think it would handle the needs of the majority of users OK.

The app that works with it (Solarman) is a bit basic, and relies on the inverter data logger stick being programmed to connect to a Chinese server, via your home WiFi network. I don't use this now, but when I did I took the precaution of only giving it access to our guest WiFi network (our router, like quite a few, offers the option to run two independent WiFi networks). Not sure if this was really necessary, but I do get a bit concerned about just giving stuff open access to our main WiFi network, and I hate to sound prejudiced, but I really do not trust any server in China in terms of it possibly being used for some nefarious purpose.

[Stinsy]

I'd be tempted to swap your current inverter for a 3.6kW hybrid. That way there is no need to ask permission from the DNO. Your old one will get good money on eBay or wherever. You could then attach as many Pylontechs as you like. There is problem cycling LiFePO4 batteries from 100% to 10% every day. The latest ones are certified for 6000 cycles from 100-5%, although you will see some capacity deg over the 10-15 years.

Starting out with 4.8kWh is perfectly sensible, however this will only allow 2.4kW of charging/discharging.

There are a wide range of inverters that are suitable. Solax, SoFar, Solis, LuxPower, and others are all good. This is mature tech, they're all reliable, and you need a sense of humour reading the translated-from-Chinese manual/menus. Just get what you can find in stock for a reasonable price.

[MoSTiE]

or you could use this

https://www.pluginsolar.co.uk/?product= ... ry-charger

[nowty]

A) Stinsy is suggesting replacing your existing inverter for a hybrid which takes your existing panels and batteries into a single inverter.

B) To expand on MoSTiE's offering, that is to keep the existing solar PV system as is and add a separate AC coupled battery inverter with batteries only.

Option A does not require DNO notification assuming you already did a notification on the original install, I note you did it DIY.

Option B officially requires a pre install Fast Track G99 application to the DNO and if a DNO notification was not previously done, then you would officially have to apply as if your doing both at the same time, still a Fast Track G99 application. Oldgreybeard is talking about option B with his system.

As you have a small system and relatively small needs, I personally would opt for option A with a view of adding some more PV if you can. The batteries being housed 30m away, may cause some issue as you really need the battery inverter to be as close to the batteries as possible with as short a battery cable as possible. So if that's difficult to do with option A, then option B may become physically easier. As Oldgreybeard says, a long distance for a CT cable is no big deal and can be overcome with paralleled up the Ethernet cable conductors.

[Jinx]

Great replies guys, some food for thought there.

DNO notification was done by myself, I was surprised how easy that was. I’m tempted to apply for more but will need to look into what that involves.

I have room for loads more solar but not quite the right time yet, house will be getting a re-roof in next few years. Ground array will be an option but I’m not ready to commit to the location until some other things are sorted. It’s certainly in the future and hopefully this supply/demand issue will ease and prices drop again.

Batteries can be adjacent to inverter, it will all be located in the garage but it is detached from house (current panels are on garage). It’s just the main consumer unit, smart meter and tails are all in the house, CT will be 15m away wireless, a cable run is awkward and likely be over 20m due to route.

I do prefer the idea of a separate system but the DNO notification looks like it will decide that then.

The Sofar looks good, I see it can also do lead acid, I know these are rubbish but I have free access to some of these and associated cabling. Might be a way to get up and running cheaply. The Chinese app server bit is rubbish, I’ve got the growatt one already and that’s a similar issue. Do victron do an equivalent? Not seen much mention of them on here?

[Stinsy]

Great replies guys, some food for thought there.

DNO notification was done by myself, I was surprised how easy that was. I’m tempted to apply for more but will need to look into what that involves.

I have room for loads more solar but not quite the right time yet, house will be getting a re-roof in next few years. Ground array will be an option but I’m not ready to commit to the location until some other things are sorted. It’s certainly in the future and hopefully this supply/demand issue will ease and prices drop again.

Batteries can be adjacent to inverter, it will all be located in the garage but it is detached from house (current panels are on garage). It’s just the main consumer unit, smart meter and tails are all in the house, CT will be 15m away wireless, a cable run is awkward and likely be over 20m due to route.

I do prefer the idea of a separate system but the DNO notification looks like it will decide that then.

The Sofar looks good, I see it can also do lead acid, I know these are rubbish but I have free access to some of these and associated cabling. Might be a way to get up and running cheaply. The Chinese app server bit is rubbish, I’ve got the growatt one already and that’s a similar issue. Do victron do an equivalent? Not seen much mention of them on here?

The batteries pretty much have to be adjacent to the inverter. It is silly to do anything else!

Be aware when running cables that you'll probably have to oversize the mains cable because voltage drop works in reverse with an inverter! Think of it like a pipe pushing water to your house your house is already at one pressure (Voltage) so to move water (current) from the garage to the house you need higher pressure (Voltage) in the garage than the house. How much higher the pressure has to be depends on the thickenss of the pipe (wire). If your grid voltage is already a bit high the extra needed for your inverter to export can push it out of spec an it'll turn off. (Sorry if this is patronising, even if you're all over this already it might benefit someone else).

A 16A circuit would normally be wired in 1.5mm², but I went 2 sizes bigger to 4mm² for my 3.6kW inverter which is in the attic 2 stories above the CU. You might want to go bigger still depending on distances, inverter power, and your own grid voltage.

You can get armoured Cat5e cable any lay that with the power cable. This gives 4 pairs, you only need one pair for the CT, in future you can use 2-pairs for 100mbps network connection and still have a spare pair.

[sharpener]

I'd be tempted to swap your current inverter for a 3.6kW hybrid. That way there is no need to ask permission from the DNO.

Don't think that is right, AFAIK a new battery system requires a new DNO application. But if the existing panels are behind the new inverter then the export capability will be limited by that so they have no grounds to refuse.

Great replies guys, some food for thought there.
Batteries can be adjacent to inverter, it will all be located in the garage but it is detached from house (current panels are on garage). It’s just the main consumer unit, smart meter and tails are all in the house, CT will be 15m away wireless, a cable run is awkward and likely be over 20m due to route.

I do prefer the idea of a separate system but the DNO notification looks like it will decide that then.

Do victron do an equivalent? Not seen much mention of them on here?

Yes, the Victron Multiplus II-GX 3kVA is probably the one you want, works well with Pylontechs. Will accept 2kW PV on the AC-Out (which will keep the DNO happy) and keep generating in a blackout. Would give you a UPS capabilty too but you would need a new cable from the garage for that. You could also add more panels later with an MPPT charge controller on the battery side with no need for a further DNO application.

PM me for details of my very helpful dealer.

[Stinsy]

I'd be tempted to swap your current inverter for a 3.6kW hybrid. That way there is no need to ask permission from the DNO.

Don't think that is right, AFAIK a new battery system requires a new DNO application. But if the existing panels are behind the new inverter then the export capability will be limited by that so they have no grounds to refuse.

We get into semantics here. But basically you can swap out the inverter for a 3.6kW hybrid and "notify" the DNO afterwards. Whereas a 2nd inverter would require "asking permission" which they could refuse. Some people have found their DNO easy to deal with, others notsomuch.