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

[babba]

Another Sticky thread.

 

[juniperz]

Another Sticky thread.

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.

 

[babba]

Is it verbar or on a contract ?

 

[juniperz]

Is it verbar or on a contract ?

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

 

[FB.]

.

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):

.

 

[Eco Deal]

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

 

[juniperz]

.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).

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.

 

[FB.]

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.

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.

 

[juniperz]

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:

House 30 degrees to the horizontal (12 x 245w panels)
Garage 35 degrees to the horizontal (4 x 245w panels)​

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.

 

[poheZ]

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.

 

[juniperz]

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.

Oh I am following advice - I have an email drafted that clearly tells them to stop - though how I stop the roofer from leaving home on Monday morning at 5:30am to travel 100 miles to us I don't know! Not my problem.
In my email I have to ask them to do something.
I can either ask for my 20% deposit back and for them to remove all their equipment (and try and find someone else to do a good job before the FIT rate change on 1st August - I live in Bristol by the way ).
OR
I can ask them to stop what they are doing and come up with a design involving 2 inverters (if that is the best way to cope with differing roof pitches) with mounting on fire retardant materials. I would probably put the proposed design here for comments.

Obviously the second option causes less disruption, but I am not sure how I am going to re-establish trust. In the mean time we have a house covered in scaffolding and I am working away 5 days this week - leaving any on-site problems with my wife (who works 3 days a week!).
At the moment, my draft email is asking for option 2.

I don't know how MCS accreditation works. Could I ask them to audit / check that work is to MIS 3002 standards post commissioning and pre final payment?

PS - To answer questions - Yes, recommendation and yes, price - payback in 6 years seemed attractive, though with different roof pitch and 12+4 wiring that is seriously in question I am now assuming.

 

[Noshocks]

There is no way that four Suntech panels will operate the MPPT channel, even if you did mange to get an output now, or managed to reduce input voltage parameters, in 10 years time after degredation it would stop operating anyway, five is almost always the minimum from experience. I know many people rate the Samil inverters as a budget alternative to the German ones but although the Growatt is also a chineese inverter it just looks, feels and seems when you touch and compare them a much better product, I would stop any more work being done. I suspect you may end up not having the four panel array and use a smaller inverter on the remaining 12 modules, at least this setup will do what it says on the tin.

As said the labeling is another red flag, if you hadent been reccomended by them I would have assumed they were very inexperienced with all the things stated.

I'm not far from you, if you need advice and it cant be resolved.

 

[sedgy34]

Hmmmm....If I was quoted for a BMW and was delivered an Audi I would at least expect an explination

Let them finish it and then ask why???

At least you have working kit and have only paid 25%

your system is not going to work!! correctly if it works at all

 

[Noshocks]

your system is not going to work!! correctly if it works at all

I have seen the Samil Factory, and they dont make Audi's, Proton is a better comparison..

 

[juniperz]

... I suspect you may end up not having the four panel array and use a smaller inverter on the remaining 12 modules, at least this setup will do what it says on the tin.

I'm not far from you, if you need advice and it cant be resolved.

I sent a very detailed email and a follow-up text to the sales person and she called me in 5 minutes. They will try to stop the roofer travelling if they can and know that I am er, unhappy, to say the least.
I asked them to propose a new way forward.
Edit - just got an email - the Ops Director has been contacted and they will stop people travelling and investigate.

If I am going to do this, coming as close to 4kW seems the way to do it, so I would prefer not to go for 12 x 245W as you suggest. Nearly 4kW was being achieved by the use of 16 x 245W panels = 3.92kW.
Do 325W panels exist (in the same size)? 12 x 325w = 3.90kW.
Thanks for the offer.

 

[FB.]

There is no way that four Suntech panels will operate the MPPT channel, even if you did mange to get an output now, or managed to reduce input voltage parameters, in 10 years time after degredation it would stop operating anyway, five is almost always the minimum from experience. .............. I suspect you may end up not having the four panel array and use a smaller inverter on the remaining 12 modules, at least this setup will do what it says on the tin.

I agree.
I suspect that the system will end up being revised to 12x250W = 3kWp on the main roof with a 3kW inverter.

I would prefer not to combine two different tilts (e.g. 30 and 35 degrees) on one string, as I can imagine in certain situations (especially when the sun is relatively low in the sky) the angle of the sun to the panels may cause very different output from those on a different roof pitch, which, over time, might push the bypass diodes a bit too much leading to premature failure of the bypass diodes, which subsequently vents-off as overheating of the panels (degrading performance) due to lack of a bypass for differing amounts of power.
Five degrees difference might be OK, but personally I wouldn't be happy to have them on the same string.
So unless by some miracle the inverter MPPT can cope with a single string of four panels, or unless a 1kW and a 3kW inverter is used in a twin-inverter system, then I see the system being downsized.

I think that the best course of action is not to cancel or to start gobbing-off, but to try to work amicably on an agreeable solution.

I would want:

1.
An inverter "capped" at 16Amps in order to be G83 compliant and not risk the DNO ordering the system to be disconnected from the grid until a current-restricted inverter is fitted.

2.
Proof that adding the four extra panels into one MPPT will actually add to performance.


In regards to #2, since since increasing from 15 to 16 panels contributes 7% more power, but only adds 3.5% to the cost of the system, it can be cost-effective to have panels running at as little as 50% efficiency. Perhaps the installers know that the garage panels will not be as efficient due to small string size, but perhaps they also know that the garage panels will still generate enough to justify their fitting.

Someone I know has a back-to-back array on a 30-degree roof with 2kWp SSW plus 2kWp NNE. The near-North panels will only generate about 50-60% as much as the SSW panels over the course of a year, but it actually worked out slightly more profitable in percentage and absolute terms than having 3kWp South due to the cheapness of panels and all the fixed costs.

 

[juniperz]

...
So unless by some miracle the inverter MPPT can cope with a single string of four panels, or unless a 1kW and a 3kW inverter is used in a twin-inverter system, then I see the system being downsized.

I think that the best course of action is not to cancel or to start gobbing-off, but to try to work amicably on an agreeable solution.

Thanks FB. This is pretty much where I have got to. My email was civil and factual. I am asking them to come up with a spec for 4 panels into 1 inverter and 12 panels into another inverter. This will cost them more but I expect them to swallow it. It will cost me more since I understand inverters need replacing after 10 years, and I will have to replace 2. I am hoping that prices come down with economies of scale!
One problem I can forsee is that they quoted Growatt 3.6kW and fitted Sunil 4.4kW. If I ask them to spec for a 1kW and a 3kW inverter, they can chose whatever they like, and if I am expecting them to pay, they are going to go as cheap as they can. So I might post a spec here tomorrow morning, if they get their act together, and you good people will all be out earning a living!

 

[MorganPVI]

What is the voltage of Suntech panels? If they are high voltage like some 12 x 50v = 600v, this will be a problem when the panels get cold as the voltage will spike and possibly blow some models of inverter.

Also the DTI guide has specific requirements for RCD protection, it is unlikely that you can connect it to a spare way in an existing box also you run the risk of having no RCD protection in the event of electrocution, some inverters can take .4s to discharge /power down.

I think you legally need to allow the present installer to rectify the issues to a satisfactory standard, I suggest you hire a local installer (billing the present installer for their time) to oversee the works and ensure the rectifications are completed to at least a minimum standard.

 

[juniperz]

What is the voltage of Suntech panels? If they are high voltage like some 12 x 50v = 600v, this will be a problem when the panels get cold as the voltage will spike and possibly blow some models of inverter.

Also the DTI guide has specific requirements for RCD protection, it is unlikely that you can connect it to a spare way in an existing box also you run the risk of having no RCD protection in the event of electrocution, some inverters can take .4s to discharge /power down.

I think you legally need to allow the present installer to rectify the issues to a satisfactory standard, I suggest you hire a local installer (billing the present installer for their time) to oversee the works and ensure the rectifications are completed to at least a minimum standard.

There is a tech spec PDF on this page - their quote had said they were using STP245S-20/Wd 245 W (and I have 16 of them in my garage!)
Suntech STP 245S 20/Wd + Solar PV Module | Suntech Solar PV Modules / Panels | Solar PV Modules | Urban Energy
Optimum Operating Voltage (Vmp) 30.5 V
Open - Circuit Voltage (Voc) 37.3 V

On RCDs and existing ways - the quote had said "Additional: Installation of MCB required £150.00" but the electrician had said he would use a spare way. I guess this should also worry me...

 

[sedgy34]

If its aspare way on the rcd side you will have lots of inconvenience with tripping etc
if not just tell this company you will deduct the £150 as you don't require a new distribution board

Im concerned you should be using this company at all after all your concerns