Solar panels and battery - any real world reccomendations?

b0rn2sk8 said:
Are you using GivTCP?

You have to use the charge start and end times for controlling the battery charge.
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Awesome. Yes I'm using givtcp.
Which octopus integration are you using?

I was wondering actually if you could just set "force charge" on?

select.givtcp_xxxxxxxxxxx_force_charge
Options are
Normal
Running
Cancel
Then a series of run times
 
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I’m using the Octopus integration called ‘Octopus Energy’ that’s the full integration that has all your energy data in it.

I wouldn’t use the force charge setting as you’ll not know for sure how long the dispatching flag will be set for by Octopus. Using the charge timers is a simpler option.
 
I use that setup and it works really well. You set the solar threshold really high on the zappi to avoid it charging from your export.
The only behavior change I have had to make is to not plug the car in during the day on a sunny day as the car often gets given extra 7.5p off peak slots during the day when I would rather be exporting. In winter those extra slots are a perk. You only get them when you plug in and the zappi then requests them. If you leave the car plugged it doesn’t request new ones until the evening so it’s just when you re-plug.
 
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Hoping to tap into the OcUK hive mind to confirm/deny some solar maths.

I have a system on the way to being installed - 18x 440w panels, 6kW inverter, 15kWh of battery storage. My roof faces roughly South East, about 130* ish, 40* pitch. My roof is an L shape with the long side facing SE. Every company we spoke to suggested that putting panels on the NW-facing part of the roof wouldn't likely get an ROI on the cost of the panels and installation etc. By my rough calcs, I could get another 6 or 7 panels on the NW-facing part of the roof...

cgRawz7.jpeg


My question is: Are they all correct? I've seen plenty of people have split E-W systems but far fewer SE/NW systems.

I suppose at a later point I could add the NW-facing panels and a second inverter if I wanted to, just wondering if the time to do it was now while the main system is going in.
 
DRZ said:
My question is: Are they all correct? I've seen plenty of people have split E-W systems but far fewer SE/NW systems.
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They are not correct, and your 6kW inverter is too small for the system you are having put in IMHO. What output can it do, bear in mind we are moving to a fully electric future so peak demand now isn't peak demand in the 15-25 year life span of the system. :)

Also - yes do it all at once. How much you paying thus far?
 
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Journey said:
They are not correct, and your 6kW inverter is too small for the system you are having put in IMHO. What output can it do, bear in mind we are moving to a fully electric future so peak demand now isn't peak demand in the 15-25 year life span of the system. :)

Also - yes do it all at once. How much you paying thus far?
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Do you have the maths to back that up? It seemed that none of the 5 serious proposals would even entertain the idea of any ROI from the NW side of the roof, even after survey.

The inverter is an SAJ H1-6K-S2-15 (https://img.saj-electric.com/file/H1-3~6K-S2-15-- EN-2023081005385455.pdf), it can do 6000VA indefinitely from what I can see when on-grid, that drops to 6000VA for 10s and then 5000VA for the back-up power option (which I am feeding to my server stuff to replace a UPS). The 18 panels can only generate a peak of 7.9kW so yes in absolutely peak ideal STC conditions there will be clipping but from my calcs and experience of where I live that is going to be basically never. That ratio of solar power to inverter power is well within the spec.

The cost all-in which includes a new DB for the backup power in the loft, bird protection stuff and some other (not straightforward/difficult) labour bits and pieces is £14k.
 
DRZ said:
Hoping to tap into the OcUK hive mind to confirm/deny some solar maths.

I have a system on the way to being installed - 18x 440w panels, 6kW inverter, 15kWh of battery storage. My roof faces roughly South East, about 130* ish, 40* pitch. My roof is an L shape with the long side facing SE. Every company we spoke to suggested that putting panels on the NW-facing part of the roof wouldn't likely get an ROI on the cost of the panels and installation etc. By my rough calcs, I could get another 6 or 7 panels on the NW-facing part of the roof...

cgRawz7.jpeg


My question is: Are they all correct? I've seen plenty of people have split E-W systems but far fewer SE/NW systems.

I suppose at a later point I could add the NW-facing panels and a second inverter if I wanted to, just wondering if the time to do it was now while the main system is going in.
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I have a SE-NW system and it makes a huge difference. You would find the NW system makes around 65% of the SE system annually (for the same kWp), but that generation is mostly in the second half of the day so very useful.

I would get it done now as you'll essentially just be paying for the scaffolding and panels etc. It would not be worth it doing it separately later if it's only 6 or 7 panels.

As mentioned above, that inverter is too small, I would be looking for an 8kW inverter for that system, especially if you do get the NW panels too.
 
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DRZ said:
Do you have the maths to back that up? It seemed that none of the 5 serious proposals would even entertain the idea of any ROI from the NW side of the roof, even after survey.
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Plug the numbers into PVGIS and see how much they will generate:

JRC Photovoltaic Geographical Information System (PVGIS) - European Commission

Photovoltaic Geographical Information System (PVGIS)
re.jrc.ec.europa.eu re.jrc.ec.europa.eu

EDIT: I also agree, the inverter is slightly too small, the cost between a 6kw and 8kw inverter is negligible.

Edit2: I just plugged in 6 430w NW panels (130 Azimuth* @ 40 slope) and they would generate 1550kwh/year which is not to be sniffed at given it will be mostly be in the afternoon/evening.

Call it 0.15p export, that's a minimum of £232/year, I'd think it would add £1500 into your install cost.

*south is 0 east is -90, west is 90.
 
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ROI depends how much they are charging really but it will be longer than the south facing panels for sure. Keep in mind NW panels really only produce anything outside of the winter months when you really need the extra production so a lot of the extra generation will end up being exported so ROI will be dependent on export rates staying good over the long term. That said panels are so cheap now I think it's a no brainer to max all roofspace out regardless.
 
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So the OcUK wisdom would be to up the inverter to ~8kW and pack as many extra panels as I can on the NW side of the roof? I'll see what the installers think - I know the DNO application paperwork has gone in already so they might not be too keen to change things at this stage but it is worth an ask.
 
DRZ said:
My question is: Are they all correct? I've seen plenty of people have split E-W systems but far fewer SE/NW systems.
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I've had 4 kWp solar panels on my main house roof facing SE and SW since 2015, generates very nicely, early last year I added another 12 panels (4.74 kWp) to my garage facing NW and SE, these are at a pitch of 10 degrees, they also generate very nicely, but not so well in the winter due to shading and the shallow angle.

I'm now planning to add another 12 panels (5.22 kWp) to my NW roof (its about 120° actually, so not quite NW). These 12 panels at 30 degrees will add 3950 kWh over the course of the year. I'm doing the bulk of the work myself, and I know a scaffolder, so that will keep costs down, but I will be paying VAT on the panels etc.

I'm also doing three panels (1.575 kWp) on my SW facing rear wall, these three panels will generate more in December and January than the 12 panels on the NW roof.

Is that a flat roofed garage to the left? If so get panels on there as well, the more the better :D

As above, ROI will really depend on how much you are being charged to have the additional panels installed. A bigger inverter would also be better, not only for peak solar but for charging the battery in the winter. One thing to think about, panels pointing in multiple directions ideally need to be on different strings.
 
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Ron-ski said:
I've had 4 kWp solar panels on my main house roof facing SE and SW since 2015, generates very nicely, early last year I added another 12 panels (4.74 kWp) to my garage facing NW and SE, these are at a pitch of 10 degrees, they also generate very nicely, but not so well in the winter due to shading and the shallow angle.

I'm now planning to add another 12 panels (5.22 kWp) to my NW roof (its about 120° actually, so not quite NW). These 12 panels at 30 degrees will add 3950 kWh over the course of the year. I'm doing the bulk of the work myself, and I know a scaffolder, so that will keep costs down, but I will be paying VAT on the panels etc.

I'm also doing three panels (1.575 kWp) on my SW facing rear wall, these three panels will generate more in December and January than the 12 panels on the NW roof.

Is that a flat roofed garage to the left? If so get panels on there as well, the more the better :D

As above, ROI will really depend on how much you are being charged to have the additional panels installed. A bigger inverter would also be better, not only for peak solar but for charging the battery in the winter. One thing to think about, panels pointing in multiple directions ideally need to be on different strings.
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Thanks Ron-ski!

I think with the as-spec'd inverter I couldn't have all 18 SE panels on one string as it'd exceed the capacity for one string so the plan was 2x9 panel strings, which maxes out the inverter's DC inputs. Needs some thinking about if I do decide to go down this path... The garage roof almost never gets full sun. In the morning it is shaded by the house and in the afternoon it is shaded by the enormous house next door. There's a period for about 2 hours in the day when some meaningful light gets on it but that's about it. I have an experimental 60w panel there and it barely generates anything.

BTW, I've got optimisers (at my request) as I have a few tall trees in my garden (each well in excess of 25m tall) and 2x chimneys on the roof that will all partially shade the panels to some degree. The trees actually very significantly reduce production in the winter. At the lowest peak height the Sun won't appear above the trees. Not a problem for the oak which won't have leaves come winter but the pine, conifer and eucalyptus definitely will cause shading pretty much throughout the day.
 
DRZ said:
The cost all-in which includes a new DB for the backup power in the loft, bird protection stuff and some other (not straightforward/difficult) labour bits and pieces is £14k.
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So currently that is ~£1800 per kWp installed solar, adding the £600 worth of panels to the NW, mounting equipment, cabling and bird protection (optimizers if you really think they are worth it) maybe £1,200-1,500 all in, and the uplift to a 8kWp inverter, maybe another £200. That puts you at ~£1450 per kWp installed, and probably decreases the total return time of the whole system rather than increasing it. For me personally money return was the lowest priority on my list, just like when replacing the old double glazed windows I didn't think how long will these take to pay back.

DRZ said:
The inverter is an SAJ H1-6K-S2-15 (https://img.saj-electric.com/file/H1-3~6K-S2-15-- EN-2023081005385455.pdf), it can do 6000VA indefinitely from what I can see when on-grid, that drops to 6000VA for 10s and then 5000VA for the back-up power option (which I am feeding to my server stuff to replace a UPS). The 18 panels can only generate a peak of 7.9kW so yes in absolutely peak ideal STC conditions there will be clipping but from my calcs and experience of where I live that is going to be basically never. That ratio of solar power to inverter power is well within the spec.
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Inverters are, for the most part, the thing that will most likely break in a solar PV setup, and over specifying isn't a bad thing if is less stressed, but still running at almost optimal input/output. I've had no personal experience of SAJ, but I have read quite a few things about how poor there app is and the monitoring tools you have, if you care about that, and issue surrounding warranty claims. GivEnergy have a 10kW single phase inverter due out in September and you can get put on a tester/early adopter list if you contact them, of you could look at the Sunsynk option at 8kW which is pretty solid and I know quite a few people with Sunsynk and various battery setups, e.g. Pylon, Sunsynk, and Fogstar. the latter offering the best price to kWh ratio and expandability, with 30kWh per racked costing only £4.75k ex VAT.
 
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