Fitting Battery to Solar

tamste

I have 11.04 kWh of solar panels with a 10kWh Growatt MOD 10KTL3-XH (BP) inverter, fitted in November last year. Its on a a 3 phase domestic system and export agreed under G98.

I am considering fitting a battery, mainly to reduce the impact of peak rate in winter. As I understand it, the inverter is battery ready, so its mainly the question on size, manufacturer and cost of a battery system, then its time for me to run the numbers!

Max peak rate used in one day over winter was ~30kW, though most days its ~25kW. Heating is via HHR/SSH storage heaters with hot water through immersion, so I am a high user.

Anyone able to give a rough outline of what I need with recommendations and rough costings please?

Screwdriva

If it was my home, I would sell the Growatt inverter on and get a PW3 battery inverter for around £7.3K installed. Nothing I know comes close on performance or capability. And you benefit from the Intelligent Flux tariff too! 

QrizB

Screwdriva said:

If it was my home, I would sell the Growatt inverter on and get a PW3 battery inverter for around £7.3K installed.

Does a PW3 do three-phase? Or will the OP need £22k for three separate ones, one person phase?

OP if you keep your Growatt, the spec says it uses APX high-voltage batteries. Here's the datasheet:

https://cdn.shopify.com/s/files/1/0706/5105/2300/files/Growatt_APX_5.0P-B1_5kWh_HV_Battery_D.pdf?v=1724923006

It appears to be made up of a battery management system plus one to six 5kWh modules, for a total of 5-30 kWh of storage. The modules seem to be about £1200 each, plus any fitting costs.

Screwdriva

I missed the 3 phase bit and focused on G98 for some reason - oops! Tesla is months away from launching their 3phase solution but it will not address your requirement today!

tamste

So only option is the Growatt APX if I keep the inverter? The Growatt inverter is a hybrid model designed for the 3 phase system.
If I change the inverter also, are there any 3 phase systems available that are better and more cost effective?

In my system:
L1 does all non storage heater power
L2 1st bank of storage heaters (on 24hr supply, controlled through the SH)
L3 2nd bank of storage heaters (on 24hr supply, controlled through the SH)

Thanks

QrizB

tamste said:

So only option is the Growatt APX if I keep the inverter? The Growatt inverter is a hybrid model designed for the 3 phase system.

Your Growatt inverter is designed for high voltage batteries, probably due to its high power capacity. I don't think there are any non-Growatt battery options.

That's unlike many smaller inverters, which are designed for 48v batteries which are available from a variety of sources (Pylon, Fogstar etc.). However 10kW at 48v would be about 200 amps, rather than the 30 amps that Growatt's high voltage batteries would demand.

The spec sheet for your inverter only mentions APX batteries as being compatible.

https://en.growatt.com/upload/file/MOD_3000~10000TL3-XH-Backup+APX_HV_Battery.pdf

tamste said:

If I change the inverter also, are there any 3 phase systems available that are better and more cost effective?
In my system:
L1 does all non storage heater power
L2 1st bank of storage heaters (on 24hr supply, controlled through the SH)
L3 2nd bank of storage heaters (on 24hr supply, controlled through the SH)

If only L1 serves 24h loads, with L2 and L3 being used solely for storage heaters, you could add a battery to L1 only? You could even keep your current inverter and use an AC-coupled battery on L1.

Adding any sort of battery will take you out of scope of G98 and will need permission from your DNO in advance. You might be allowed to export 10kW on L1, in which case replacing the three-phase inverter with a PW3 on L1 would be an option.

Martyn1981

Screwdriva said:

I missed the 3 phase bit and focused on G98 for some reason - oops! Tesla is months away from launching their 3phase solution but it will not address your requirement today!

That's interesting as my sister is on 3phase and interested in batts maybe in a year or two. I did look into the idea of 3x PW3, but a bit of overkill and expense. But what I'd really be interested in (for her) is the DC side PV inputs, allowing for additional PV in the future, without any DNO red tape.

Screwdriva

Martyn1981 said:!

That's interesting as my sister is on 3phase and interested in batts maybe in a year or two. I did look into the idea of 3x PW3, but a bit of overkill and expense. But what I'd really be interested in (for her) is the DC side PV inputs, allowing for additional PV in the future, without any DNO red tape.

My last conversation with Tesla UK (May ‘25) indicated that 3phase compatibility would come via the new “Gateway” solution & that it was due later this year. No date provided despite some pushing for this on my part. 

They did share that they were aware and surprised by the demand for this and were working on it ahead of all other customer requests (extended warranty, optimizer compatibility etc)

tamste

L2 and L3 though purely for storage heaters are set up on a 24hr circuit, with charging period controlled by the SH's. They also need a little boost energy (i.e. peak rate) at the coldest times .. average ~25kWh in the coldest months, but can go up to 35kWh on the coldest days within those months. Taking this into consideration, I feel I need a 3-phase solution.

As I buy electricity on E7 at ~10.5p/kWh and export at 16.5p/kWh, my main thought is to offset the peak rate usage to E7 in the colder months and gain more in export during the summer by running the house from the battery charged at E7 rates. Does this make sense?
At ~ £1200 per 5kWh for the APX batteries, I seem to be looking at ~ 6 years to break even on the investment presuming the SEG rate doesn't reduce.

As above, I feel I need 25kWh of storage. Is there an alternate inverter and battery setup that comes in cheaper than the APX's - note its a 3 phase system

QrizB

Hypothetically, you could do it with an 8kW Sunsynk inverter:

https://www.bimblesolar.com/ongrid/hybrid-inverters/g99-hyrbid-inverters/Sunsynk8kW-3Phase

And a 32kWh Fogstar battery:

https://www.bimblesolar.com/fogstar-house/fogstar-48v-32kwh

That's about £6k in parts, before any cabling/installation costs.

I've not checked the specs in detail to confirm compatibility, but they're both 48v on the DC side.

There are a few members of the forum with Sunsynk inverters, and a coutof threads from the past year or two if you have a search.

tamste

Just looking at the prices .. I thought batteries were 0 rated for VAT but everybody seems to be pricing them with 20% VAT?