Adding battery to existing solar PV system - any thoughts/advice please.

Screwdriva

JKenH said:

Thanks @Screwdiva. Yes, that does make sense. I was just concerned that with the faulty panels being on 2 elevations of a two storey roof the scaffolding cost would be quite high for the extra generation I would be gaining. I will see what the contractors say when they investigate.

Just out of interest why do DNOs opt for a 11.04 kW limit. I worked out it is 3 x 3.68 so it would make sense if I had a 3 phase supply but my house is only single phase.

In my experience, if you insist on this before they arrive, they will likely include this while on the roof.

It's actually the PW3's limit (peak generation) that the DNO's approve. A dual PW3 application would yield a ~22kWh allowance.

Oscarmax

At present we have a 4.4 kWh solar system and an AC Solax triple 5.8 battery my battery is now  2 years old rather than adding solax slave battery , my question can I add another battery system Victron inverter Fogstar 15/30 kWh battery.

QrizB

Oscarmax said:

At present we have a 4.4 kWh solar system and an AC Solax triple 5.8 battery my battery is now  2 years old rather than adding solax slave battery , my question can I add another battery system Victron inverter Fogstar 15/30 kWh battery.

Yes, with DNO approval.

Will need some care with the installation and configuration to make sure the two systems don't parasitise one another.

nakie999

I added a 10 kWh battery to my system last year and noticed a clear drop in grid use. I went with a Huawei Luna model, with a separate inverter, and everything worked fine. Final cost was around £4,900, so yeah, your quote seems a bit above average.

JKenH

Installation completed today. It was a tight squeeze on the roof but 5kWp added. Now all I need is some sunshine to test them out. PW3 installed as well but currently awaiting permission to charge from the grid and export

Screwdriva

You should already have permission (MCS G99 approval) so feel free to enable this on the Tesla app. The app does auto generate tax and export permission warnings but these can be disregarded, as you are installing on your residence. Same for grid charging, which will need programming in the app. 

The image shared looks really nice.. though I do see space for one more panel in the 2nd row to the left. Did they manage to relocate panels and fit more on your West aspect? 

JKenH

I did try to enable it but clicking yes just comes up with this message. Clicking yes in this screen clears the screen but doesn’t confirm that I have authorised export. I will have to wait until tomorrow to see if it works.





Of more immediate concern is this screen.

Clicking yes just takes me back to the previous screen so I can’t charge the battery from the grid at the moment. I assume the installer has set this up in this way and I have requested charging be allowed.  I have opted for time based control setting a peak period of 1600 to 1900 and the PW3 has just taken over the house load (having been delivered with 21% charge). I just don’t know how it will charge up again.

Yes, it does look like there would be room for another panel but it would overhang the valley. 

The installer did test all the old panels on the suspect strings and found 3 defective on the east roof and one on the west. A good one was swapped from the East roof to the west roof so I should now have 3 good strings and I not so good. It was dreadfully dull today (only getting 0.1 amp) so I won’t really know how effective that has been until we get some sunshine. 

We started off with string voltages of 231 and 183 on the west roof (7 panels per string) and 200 and 145 on the east roof (6 panels per string). After juggling around ended up with 240 and 245v on the west roof and 209 and 102v on the east roof. So both the untouched good strings increased by 9v. The revised west string went up by 62v and the poor (now worse) east string went down by 43v. 

It seems we have 4 defective panels out of 26 so we decided (at least for now and bearing in mind the old panels were a FiT installation) to leave things as they are. The installer will see if he can find any matching panels but we are not sure if it will be cost effective to switch. I was very appreciative of the testing they did which involved lifting 13 panels and shuffling them about at no extra cost.

JKenH

In case anyone is concerned that expanding their system with a battery and more panels would cause complications in relation to SEG or FiT , these responses from my SEG and FiT will hopefully set minds at rest. The response I received from Octopus (with whom I have  my export contract) following my notification of changes was as follows.

Hi Ken,

Thank you for letting us know about your new Tesla Powerwall and additional solar panels, and for sending over the MCS certificate and DNO documentation.

I can confirm that you already have an export tariff set up for account A-********, and we are currently crediting you for your exported energy.

If you’re interested in exploring other export tariff options that might better suit your new setup, you can find more information and sign up for different tariffs here: https://octopus.energy/export-tariffs/

If you have any questions or need further assistance, please don’t hesitate to get in touch.

Best regards,
Ellen

Octopus Energy

I also notified my FiT provider, Good Energy, that I had added a battery and more panels which bypassed the FiT generation meter. Given the problems with existing panels I also asked them to confirm my understanding that if I replaced the original  panels with larger panels any additional capacity connected to the generation meter would result in a pro rata adjustment to FiT payments. This was the response.

Hello Ken,

Thank you for your message and for letting us know about the recent additions of your Tesla Powerwall and extra solar panels. It’s helpful to understand that these are wired independently of your FiT generation meter and won’t affect the readings you submit.

Regarding your question about replacing some of the existing solar panels under the FiT scheme: your understanding is correct. If the overall capacity of the panels registered under the FiT increases beyond the original capacity, the payments you receive will be pro rata based on the original capacity. So, if your original capacity was 7.8kW and the new total capacity is 10kW, you would receive payments equivalent to 78% of the generation recorded by your FiT meter.

It’s good to hear you’re considering your options carefully, especially given the orientation of your roofs and the inverter capacity. If you decide to proceed with any changes or need further assistance, please don’t hesitate to get in touch.

Thank you for supporting a cleaner, greener future.

Kind regards,
Juliana

It really couldn’t have been more straightforward.

JKenH

It snowed last night and my new panels are still covered. I am however generating 0.2kW. Is this because the panels are bi facial or is a bit of sunshine bleeding through the snow? The snow does let me see that there is some shading from a neighbours trees that I had not previously noticed.

EricMears

JKenH said:

It snowed last night and my new panels are still covered. I am however generating 0.2kW. Is this because the panels are bi facial or is a bit of sunshine bleeding through the snow? The snow does let me see that there is some shading from a neighbours trees that I had not previously noticed.

From the picture, there doesn't seem to be much of a covering on the panels so almost certainly some light is getting through to generate a little power.   Good news is that process will produce some heat to melt the little bit of snow already there and give better generation.

Fortunately we've had very little snow this week but from past experience when there's an inch or more snow on the panels generation will be zero and there'll be no melting effect.