I am a new PV householder - advice please. Unbalanced strings and wrong inverter

Thanks whinmoor - I decided to get to 6 posts! The post above shows the connections and the front of the inverter

FB. said:

Although I would reject the system on the basis of the inverter, is it not possible that the installer has wired four of the roof panels with the four garage panels on one string, then the other eight roof panels on a second string?

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I guess that is possible, but if that is the case, then his annotation on the junction boxes is misleading.

I can trace the wires actually - 1 set goes straight out through the house roof, and the other finds its way to the garage roof, so it must be 12 + 4.

Oh dear, this does not look good, apart from what you have mentioned, If an inverter is mounted on a board, it has to be fire retardant, not just plywood..

It should also be correctly labeled, sorry, but a marker pen does not conform.
Post some more pics of the rest of the install, panel mounting also would be good.

We are seeing far too much of this type of work....

I was wondering if they could write on the inverter about dual supply etc.....

Another Sticky thread.

babba said:

Another Sticky thread.

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I guess I should be flattered!
Can anybody point me at the rules that say that under MCS accreditation, the installer should have issued a variation notice from the different inverted. A quick google didn't find it.

Is it verbar or on a contract ?

babba said:

Is it verbar or on a contract ?

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Contract, but my wife has put it somewhere and I can't find right now (and she's out). One for tomorrow.

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The inverter and isolators should be clearly labelled, including warning stickers and ideally with schematics provided nearby - here's mine (wall-mounted in a cool downstairs utility room). edit: there is also a "warning: dual supply" yellow sticker on the CU (fusebox).
The inverter is a PowerOne Aurora PVI-3600-UK (output limited to 16A to comply with DNO requirements). As per the schematic to the left of the inverter: it has a string of 7x250W and a string of 8x250W (total 3750W nominal panel output in standard test conditions)- this inverter works best with two strings of 7 or 8 panels and would not be very efficient if running with a string of four panels, while it would exceed the string limit into one MPPT of 2000W if it had more than eight panels into either input (although theoretically a single string of 16 panels could have its power split across the two trackers by connecting the two inside the inverter):

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yes looks like the four panels might as well not be there as they not going to start up the MPPT! as stated above .

Tricky one they should of either used a Mastervolt 600 for the four panels then a single tracker inverter for the other 12.

or gone for solar edge the dip sticks !!!

Makes me laugh really does

FB. said:

.The inverter and isolators should be clearly labelled, including warning stickers and ideally with schematics provided nearby - here's mine (wall-mounted in a cool downstairs utility room). edit: there is also a "warning: dual supply" yellow sticker on the CU (fusebox).

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Thanks FB - a couple of points. You specifically emphasise your "cool downstairs utility room". Is loft mounting a problem? It does get pretty hot there in the summer... (Standard red/brown concrete tiles).
The electrician said that he would not need to replace the consumer unit because he would be able to use one of the "ways". As yet, there is no apparent change to the CU, certainly no new labels on the 3 free ways or anything else. It is possible that this happens with the final connection - certainly the power didn't go down yesterday.

juniperz said:

Thanks FB - a couple of points. You specifically emphasise your "cool downstairs utility room". Is loft mounting a problem? It does get pretty hot there in the summer... (Standard red/brown concrete tiles).
The electrician said that he would not need to replace the consumer unit because he would be able to use one of the "ways". As yet, there is no apparent change to the CU, certainly no new labels on the 3 free ways or anything else. It is possible that this happens with the final connection - certainly the power didn't go down yesterday.

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Some inverters cope better than others with heat. I reckon that 40-45 degrees is possible in a loft peak summer (if we ever see a summer again in our lifetimes!).
Check the manual which comes with your inverter to see at which ambient temperature it starts to lose power. Mine is expected to lose power at ambient 40'C although its internal temperature gets to 45-50'C (according to its stored-data logs) with ambient 20-25'C without power derating - this being on sunny days when the inverter is running at or slightly above maximum power (3.75kW+ coming in from the panels and 3.6kW+ going out; yes, a system can occasionally slightly exceed its nominal performance, such as my 250W panels which, occasionally, have reached 270W output per panel in exceptionally good conditions).

The inverter which I have is not ideal for a loft (although I was offered the OUTD version if the inverter was going int the loft).

It seems as if most inverters are fitted in lofts, but I wanted mine downstairs to make it easy to see what it's doing, and easily accessible; no need to clamber around the loft. The North-facing utility room also remains much cooler and more stable temperature than the loft. Electronics prefer cool, stable-temperature locations.

If you have an inverter and isolators in the loft, you ought to also have a smoke detector in the unlikely (but theoretically possible) event of a malfunction starting a small fire which woudl spread to the junk which people inevitably hoard in the loft. There have been one or two reports of loft fires which were thought to have been started by a malfunction of the isolator switches or inverter.

Thanks again FB - a smoke detector sounds like good advice.

And I have an update on Roof Pitch - I have just braved the strong sunshine and rain (what IS going on?) to go on both roofs and measured the pitch:Does the collective wisdom of this forum think that this renders a single inverter of whichever brand, with one or 2 MPPTs, completely unworkable?
Does it reduce efficiency for one or both strings by a significant amount? Cause damage? Mean that 2 MPPTs is essential?

And THANK YOU. I must say I have been truly impressed by the amount of support that you have all shown to me. It is appreciated that nobody is criticising me for barely knowing what I am talking about - you are helping me learn fast.

You must follow advice and stop the works, it would be futile to carry on as lots of errors have already been made. Did you choose the contractor because of price or were they recommended?

You must think long term on this decision.