solar panel output/production questions 6 June 2012 at 7:53PM edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving 28 replies 3.7K views

[Deleted User]

Just for ref we were 1126 over these months with wet weather in Scotland. SW 3.92kWp system.

Cheers

bris

Can you isolate the strings individually? I tested all three of my strings by turning off two and made sure I was generating on each string. I have a Sunnyboy sb4000 though so this was possible. If you can, turn off the 10 string group and see if the 5 string is generating on its own.

emjayjee

Hi

I heard back from the company and I quote "your system is working fine. Your estimated annual reading is 3115.3 so that’s 259.6 per month so for 3 months would be 778.8 which isn’t a lot more than you have produced. Weather hasn’t been great so that’s pretty good going really."

Any comments/suggestions?

Bris - how do I go about doing that?

Martyn1981

emjayjee wrote: »

Hi

I heard back from the company and I quote "your system is working fine. Your estimated annual reading is 3115.3 so that’s 259.6 per month so for 3 months would be 778.8 which isn’t a lot more than you have produced. Weather hasn’t been great so that’s pretty good going really."

Any comments/suggestions?

Bris - how do I go about doing that?

Total horse 'stuff'.

They can't average out the months, unless you were looking at 3 average months. The only average(ish) months per year are Mch and Sept, which running 3.67, south facing in Birmingham at 30deg (what is your roof pitch by the way) gives Mch 282 and Sept 291

Since Apr and May are above average, they are talking ...... (PM me to fill in the bits I daren't post on here!) .......

Here are the rough PVGIS figs I just ran, sorry but the formatting will go astray.

Fixed system: inclination=30°, orientation=0°
Month Ed Em Hd Hm
Jan 3.55 110 1.21 37.4
Feb 5.45 153 1.88 52.7
Mar 9.11 282 3.26 101
Apr 12.20 365 4.53 136
May 13.40 414 5.06 157
Jun 13.60 409 5.24 157
Jul 13.00 402 5.02 156
Aug 11.40 352 4.38 136
Sep 9.70 291 3.63 109
Oct 6.75 209 2.43 75.2
Nov 4.37 131 1.51 45.2
Dec 3.18 98.7 1.08 33.4
Yearly average 8.82 268 3.27 99.6
Total for year 3220 1200

It's the Em column you're interested in.

Can you try the solargis site, I appreciate it's a bit odd looking, but it's actually quite easy to use. That gives a very good estimate of generation for each day.

PM me if you want me to direct you to some technical sites for more professional advice.

Mart.

PS This kind of nonsense really annoys me!

grahamc2003

The way to tell whether both strings are connected is to look at the output around midday on a sunny day, if we ever get another one. If you get around 3.5/3.8kW, then both strings are connected, if you only get around 2.6/2.8kW, then something is very wrong.

Judging by my output, yours definitely looks low - and I get pretty bad shading with my system, and it points SW.

Just some possible pointers - all panels for a system should be matched (i.e. have the same characteristics as to voltage vs radiation etc.). They are matched during testing after manufacture, and they all vary of course. But they are grouped with similar characteristics, and this helps overall system performance (i.e. the mppt gets the max power). The more the panels vary in individual performance, the less effectively the tracker works. (All that applies to Suntek panels - I assume other manufacturers do the same, but I'm not sure). So if one of your panels broke and was replaced with one from a different batch, you may have a performance penalty due to that.

A second point - are both strings on the same roof (i.e. the same inclination as well as direction? With a single mppt they have to be (else it won't get the max power from the panels).

Also - are you certain you get no shading at all? Even a little really knocks the generation a lot, and any around 11 to 3pm would really have a large effect.

albyota

emjayjee, your system is wrong, this set-up will not work to its maximum as you have already found, tell the installation company to come and take out the Eversolar TL4000 and replace with the Evershine TL4000 this has twin MPPT inputs

http://www.ever-solar.com/product_details.php?id=63

alternatively one SMA SB2500 for the 10 panel string and one SMA1200 for the 5 panel string.

give us a shout if you need an independent PV designer to write up a report so you can put pressure on them.

Martyn1981

I was hoping you'd turn up Albyota, as I was after a quick free lesson on MPPT's. Please.

Am I right in thinking that the MPPT will 'lock' onto the strongest generation it finds, and 'ignore' the lower one?

My reasoning on the 2/3 generation, was that even if the 5 string is fully functional, the inverter, given the choice of two voltages, will only be processing the 10 string. Or is it more complex than that?

Thanks.

Mart.

emjayjee

Hi Martyn - I used http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php# and it definitely shows I should be producing more, and consistent with what you have said. I couldn't work out how to use your link.

I know they are talking rubbish, but I am stuck. How do I pursuade them/convince someone if they don't want to believe? I checked with my credit card company and they will help put pressure on them if I go down that line but need something objective too.

Graham - I understand the panel maybe from a different batch - but I am trusting them on that. Feel very let down. There is definitely no shading - completely clear. South facing roof, and all panels on same roof.

The max we have ever got at one time is less than 3KW, and 17 over the course of the whole day.

I need something objective to show them as they not believing the data card readings.

Need help/advice!!

Martyn1981

emjayjee wrote: »

I need something objective to show them as they not believing the data card readings.

Need help/advice!!

Albyota is probably your man, but you could give REAl or MCS a bell. I'm 99.9% certain if you mention single MPPT with unmatched strings they should listen very hard from there on, to you.

Mart.

emjayjee

Hi albyota - thanks for that. I might need to take you up on that if they still failing to believe me.

I have sent them an email stating they cannot work on a monthly average to tell me there is correct production during the higher production months.

Secondly I asked if someone from the company could come and check or if they can tell me how to check that all strings are working and that the inverter can handle the 2 uneven strings.

Really annoying that they trying to get out of this (but I did think they would have tried as they probably know they are in the wrong).

Are you based/travel around the West Mids?

Thanks in advance