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Forum Index : Solar : solar performances

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muso1
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Joined: 13/01/2020
Location: Australia
Posts: 2
Posted: 12:20am 14 Jan 2020
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muso1    I have 2 solar systems one is 7 years old  and is 3kw no 2 is 2 years old and is 5.4kw
on a cloudy day the 3kw  gives out abut 200w more than the 5kw
so this means that in the morning the 3kw system has a better output until the sun is fairly high   the same happens in the afternoon the 3kw starts to produce more after about 3pm in the afternoon the 5.4 system works brilliantly from 10am till3 pm
on a cloudy day I get more out off the small system I have asked the supplier for a reason and they say it is because of the higher voltage  anyone got any clues without getting to technical   muso1
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 3371
Posted: 01:27am 14 Jan 2020
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Hi Musso1, welcome to the Forum.

A lot can depend on the type of panels and the angle and direction they are pointing.

Monocrystaline panels give a slightly higher output in direct sun and a clear blue sky. Polycrystaline panels less output in full sun, but usually better in heavy cloud.

If you have an MPPT (maximum peak power tracking) type of solar controller, the panel voltage hardly matters, because the controller will automatically load the panels up to their most efficient working voltage.

Other effects such as partial shading or built up dust/dirt/bird crap should be obvious.
Cheers,  Tony.
 
Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 540
Posted: 09:11pm 16 Jan 2020
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Sounds likely your smaller system is at a more ideal orientation and flatter angle than the larger system. I would assume that the original system was installed in the best position and the newer one was installed where they could fit it, Ie, with the best positions already taken.

Sometimes it's just the nature of the beast as to outputs. I have several systems and it's common for a smaller setup to out do a larger one under certain conditions and at various times of the year.
I have an array on the south side of my garage. It's fairly flat  so in summer it puts out good power. In winter, would barely run a light bulb.  Same for the north and west arrays. The west one is over clocked far more than the north setup so produces well on smoke heavy ( we don't have clouds here any more unless it's smoke clouds) days and of course late afternoon.

I know it can be frustrating to see a smaller system out do a larger one but just the way it works. The only thing really to worry about is the total you get. Under some conditions and at different times of the year smaller systems can produce more power but the comparison really comes at Midday in summer on a clear day.

Your larger system should always win in that scenario but again, if the original small system was installed in the choice spot and the  newer one where there was space to put it, that alone would  explain a lot to me.
 
muso1
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Joined: 13/01/2020
Location: Australia
Posts: 2
Posted: 06:08am 18 Jan 2020
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Thank you Warpspeed and Davo99 for your help suggestions.
The panels are all at the same angle and facing the same direction. I have no tracking devices. Davo99, you are right. It must have something to do with the type of panels because that is the only variable. There is no shade. We live on the coast near Sydney Australia and mostly the days are sunny apart from all the smoke over the last few weeks.  If you want to have a look at my panels go to Google Earth at 166 Booker Bay Road, Booker Bay NSW Australia  you can distinctly see the two sets of panels. Was my supplier trying to fob me of by talking about higher voltages ?
 
Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 540
Posted: 09:30am 18 Jan 2020
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Let me get this Right:

Old system is 3KW
New system is 5.4 KW
Both on same angle and orientation and neither array have any shading.

3 Kw System makes more power than 5.4  system in cloudy weather and early/ mid morning and later afternoon.

If this is correct, I'd say your 5.4 system has a problem. A substantial one.

Differences in cell type are NOT going to account for a system nearly half the size with 5 years more degradation to make more power at any time than the other larger, newer system on the same roof. Nothing else I can think of is going to come near it either.
Yes, I would say your supplier is talking complete and utter sh*t.

I assumed that the 2 systems would have to be on different roofs for the 3 Kw to outdo the 5.4 but given they are on the same roof, something isn't right at all.

Maybe your inverter on the 5.4 has dropped a tracker if it's a dual version or you may have some panels that have fallen over ( unusual) or the wiring has issues but There is no way in hell the 3 Kw system should outdo the 5.4 in this scenario.
Quite the opposite as one would expect.

What is the max sort of output you see from the 5.4 System?
Wondering if you actualy have a 5.4 System at all so interested to know what you see as the max power it puts out? It would be rare for any system to output it's rated capacity but I have seen mine do more on occasions due to cloud edge effect  but the majority of the time in clear blue sky you'd be lucky to see 5 Kw and I'd expect less.

What size is your inverter? I'm guessing if the system is rated at 5.4 the actual inverter may only be a 4 kw or it may be a 5. Either way, should still outdo the 3Kw under any conditions.

I'd be getting the guy back, telling him to stop playing you for an idiot and fix whatever is wrong which he clearly doesn't want to do under warranty.
People like this Chit me to tears. Probably told you what an honest and reputable installer he was when he wanted your money but them when things are going to cost him money.....

Tell him you have spoken to other installers and they say something is wrong and it's NOTHING to do with voltage differences and is he going to fix it or do you need to seek remedy in other ways?

The voltage has nothing to do with the difference. The inputs are basically balanced between Volts and watts and a larger system with this difference should come in sooner and certainly not be outdone by something nearly half the size.
Cloudy weather should definitely be in favour of the larger system because there is simply no substitute for sq inches of panels.  The efficiency between the older panels and the newer ones would be bugger all and certainly no where near enough to account for what you are seeing.

The ONLY way you can have this situation ( if I have it correct) is the 5.4 System has a Fault or was not installed correctly or you were short cut somewhere along the line and didn't get what you were told.
Edited 2020-01-18 19:34 by Davo99
 
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