Solar PV split array advice please!

pigglypots

Hi everybody...need a bit of advice.
I have two roofs ESE with shading issues (chimney, winter trees) and WNW no shading at all. I wanted to put a split on the 2 roofs , 10 on the back which would allow a bit of space from chimney, then plus panels on the front. Will be using SolarEdge optimizers (either embedded modules or separate).
The problem comes with differing advice about if I had only 4 panels on the front whether they would be able to function when the ESE is in complete shade? I want to split the array to try and generate for longer in the evenings.
I have had conflicting advice..one installer said minimum 6, the other said that 4 would still be OK as the 10 panels would still be generating enough voltage even when in shade.
Grateful for anybody's input from experience?

loskie

it sounds as if your roof may not make solar worthwhile at all

Martyn1981

Hiya pigglypots.

I'm a little confused about the 6 panels minimum thing. I understand that for a normal string inverter, you have to reach the minimum required voltage for each string, and all panels on a string must match exactly. That usually means 5 or 6 panels, but you can find some inverters with lower string voltages, such as 100V, which would work with 4 panels, but less choice. But ......

if the 10+4 was with Solaredge, then that is irrelevant. My understanding is that the panels all act independently, so they can be combined in any way to suit the inverter. So you could have every panel at a different orientation and pitch, but just select as many as you want for the string.

Perhaps I'm misunderstanding, or perhaps the installer doesn't want to connect 4 panels from one side to 2 panels from the other roof, as that would cause problems running the cable ...... that might be it, but I'm not sure. Looking at the spec sheet for the 4kW 16A Solaredge inverter it says that the max DC input is 500V. Most panels run at about 30V, but can have a start up open voltage of 40V, which for 14 panels would exceed 500, hence the need for two strings then ...... I think. The BenQ 285's are 30V and 40V as described. So a max of 12 on a string, hence the need for two strings.

Is this the blind leading the blind?

Does anyone else know if the normal string rules apply to a Solaredge system?

However, a 2.5kWp ESE + 1.5kWp WNW system would be very nice. I appreciate it shifts slightly more Wp's to the WNW (1,500 v's 1,140 (4x285Wp)), but that won't make a huge difference to total annual generation, and you will enjoy having more generation around teatime for cooking etc. In fact, if the ESE has slightly more shading than the WNW, then there may be very little difference in performance.

Don't worry about an E/W split system, whilst it won't generate as much kWh's or £'s as a due south system, it will still work well, and give you a nice return, so long as it's under £6k.

Mart.

pigglypots

Hi Martyn
Thanks for the useful comment
My quotes are £5700 for the 10+4 split with 285W panels+addon optimisers, and £5400 for the 10+6 250W with SolarEdge embedded in modules.
Appreciate any directions...must admit leaning toward the lower price (obviously)
Thanks in advance from all you experienced Solar geeks!!

Martyn1981

Hi. Split roof and SolarEdge for £5,400 is actually a very good price.

Hopefully, if only for curiosity, someone might know about the minimum panel issue as it pertains to Solaredge ...... anyone?

Anymore quotes to come? Are you closing in, or sensibly taking some nice quiet time to ponder?

Mart.

theboylard

I've just thrown this up as a fyi excercise - it's not set in stone and I know that Liverpool is not in Cheshire - I'm tired ok!!





If you want me to play with figures, move stuff around, different panels, inverter, optimisers etc, let me know.

FYI, SolarEdge installs as a single string - might be mutiple arrays, but it's all on one string. THere does appear to be a minimum string length - config tool would not do anything with less than 6 panels - dunno why.

Martyn1981

pigglypots wrote: »

My quotes are £5700 for the 10+4 split with 285W panels+addon optimisers, and £5400 for the 10+6 250W with SolarEdge embedded in modules.

I just tried PVGIS for a 2.5ESE + 1.5WNW system in Chester, and the total was 3,070kWh almost identical to TBL's figure of 3,050kWh. Let's call it 3,000.

So that would earn approx:
FiT 3,000 @ 12.92p = £388
Export 1,500 @ 4.85p = £73
Leccy savings (guess) = £120
Total = £581pa

So, you're looking at an approx 10 year payback. For peace of mind, might be worth extending the inverter warranty from 12 years to 20 years. Costs about £200.

Mart.

Martyn1981

theboylard wrote: »

FYI, SolarEdge installs as a single string - might be mutiple arrays, but it's all on one string. THere does appear to be a minimum string length - config tool would not do anything with less than 6 panels - dunno why.

Hiya TBL. That was my understanding, until I read piggly's post. I checked the inverter specs and spotted a difference between the 3500 and 4000 models which threw me:-

Under DC input the 4000 model says "2 MC4 pairs". Does that suggest to you that it can take two strings? I'm a little confused by this, as I thought they were single string inverters.

Still doesn't explain the problem of a 10+4 split since the installer can connect up any panels onto a string as orientation and pitch are irrelevant (in this instance). I wonder if it was just poor advice, or miscommunication, either way, I'd prefer the 10+6 layout for some extra teatime generation.

Mart.

pigglypots

Martyn1981 wrote: »

Hiya TBL. That was my understanding, until I read piggly's post. I checked the inverter specs and spotted a difference between the 3500 and 4000 models which threw me:-

Under DC input the 4000 model says "2 MC4 pairs". Does that suggest to you that it can take two strings? I'm a little confused by this, as I thought they were single string inverters.


Still doesn't explain the problem of a 10+4 split since the installer can connect up any panels onto a string as orientation and pitch are irrelevant (in this instance). I wonder if it was just poor advice, or miscommunication, either way, I'd prefer the 10+6 layout for some extra teatime generation.



Mart.

Hi Martyn
From all installers I don't think there is an issue that it won't kind of work with 10+4 as you say they are all on one string...but my certified SolarEdge installer guide said, and I quote...
"The SolarEdge system isn't a minimum of six panels in the string - there would only be one string anyway, as you have learned. It is a minimum of six panels per module area. 10+4 would never work properly because the voltages on the 4 panels would never be sufficient for the fixed 380V that the inverter requires"
So that's what I am going on...anyway hoping to chat face to face at the weekend. I don't understand it really myself. Thats why I was asking on here, maybe others experiences?
But as you say 10+6 is perhaps a good split anyway.
Must admit not sure if I am glad I ever started looking into this solar lark!!

Martyn1981

pigglypots wrote: »

Hi Martyn
It is a minimum of six panels per module area. 10+4 would never work properly because the voltages on the 4 panels would never be sufficient for the fixed 380V that the inverter requires"

Must admit not sure if I am glad I ever started looking into this solar lark!!

Cheers, that's quite interesting. Looking at the inverter specs they give a max, and a nominal 350V but not a minimum. Most specs state a max and a minimum, which is generally in the 100V to 200V range.

So, as you say, things are a little different with the Solaredge technology.

Don't worry about this solar lark, you don't need to know everything, and it can be interesting to keep learning, for instance I've just learnt something new from you. Well done and thanks.

Mart.

MEVW62

I've got a split arrangement with embedded SolarEdge, 14 on the SW-facing back and 2 on the SE-facing front for 4kWp total and it seems to be working well since installation 2 months ago. The 2 SE facing panels do make some morning juice at this time of year at least, before the sun gets round to the main array on the back - assuming it's allowed to shine at all,it's been quite a crap summer here since the installation

ISTR there was some kind of an issue with how to hook it all up to the inverter, it was the first one the installer had done since some kind of revision had been made to the spec. Can't remember the details, I'm afraid but it definitely works.