Panel Outputs. A newbie needs some advice please.

[Rincewindwiz]

Hi All
I got a solar panel installation nearly a year ago. (Nov 2015)
12 panels (Sunmodule Plus SW250) on the roof and 4 on the garage roof (same direction nearly the same tilt)
Faces S; minimal shade; I'd guess about 40 degree tilt.
12 panels are tied to 1 inverter (Afore HNS3000TL-1) and the 4 panels to another inverter
(Afore HNS3000TL-1)

Since it started, the generating meter reports 2926 (Kw I presume?)
The two inverters report 2512Kw and 611Kw

So:
- Is 2926 a reasonable output for this system over the last 9 months?
- If the panels are the ratio 3 to 1 (12 to 4), why is the inverter output in the ratio 4:1 (2512 to 611)?
Does this suggest I have a non-working panel in the 4 panel array or is it just a measurement error or what?

I did ask the inverter company but they simply said the inverter meters are not calibrated so you cant tell anything but said they come and look for £250!

Seemed a load of b*l*o*k* to me. If the meters are that inaccurate what is the point of having them?

 

[Gary K]

I'm sure someone with more practical knowledge than me will put you right but I suspect that 4x 250w panels are not enough to get an inverter of that size to fire up most of the time.

 

[SibertSolar]

I think those Sunmodule Plus panels have a Voc of around 38vdc, and an MPP voltage of around 32vdc. The 3kW Afore inverter needs 140vdc to start up. You may just about be providing enough DC voltage first thing in the morning when the panels are cold, but it's borderline....you've obviously seen some yield from it though.

Bit of a strange design decision by the installer though tbh, you may have been ok to have all 16 modules on one inverter, either 1*MPPT or 2*MPPT. You could have also had a 1kW Afore unit fitted for the garage array - 60vdc start up/MPPT minimum.

Inverter logs showing kWh values are typically innacurate, most (not all) inverters don't have certified and calibration metering hardware in them. Your generation meter is the most accurate energy measurement device on your system.

 

[Gavin A]

as sibert indicates the 4 panels are way undersized for the 3kW inverter, and you're losing a significant portion of that generation as a result.

I'd put that in as a formal complaint to the company and ask them to rectify it under warranty, which is going to mean that they need to put in a smaller inverter with a lower start up voltage as a replacement.

It's a bit odd really as the extra 3kW inverter would have cost them more than the correctly sized inverter, so either they were just running down stock or the installer made a mistake and picked the wrong inverter up. Either way you shouldn't suffer as a result.

 

[Rincewindwiz]

000 Apologies - typo. The 4 panels are tied to HNS1000TL-1 - which seems sensible

I understand inverter meters are inaccurate but I am surprised at the degree of inaccuracy (25% or so) implied by the expectation that 12 panls woudl generate 3 times more power than 4 panels

 

[Gavin A]

inverters tend to measure the DC ampage and multiply that by voltage and some allowance for average inverter efficiency to produce their KWh figure.

The level of inaccuracy is therefore dictated by the difference between the actual inverter efficiency and the assumed efficiency in the calculation.

There's no way this level of difference could possibly be down to that sort of inaccuracy in the inverter.

if this is a 1kW inverter that changes things, can you switch the inverter off and back on and see what the string voltage reading is before the inverter cuts in fully? It should be around 130-140V in full sunlight, or more like 110-120V if the inverter has cut in and power is being produced.

IF it's something like 30V below those readings then it'd look like you've got either a faulty panel or a panel that's been missed from being wired in to the circuit, which would explain the 25% lost generation.

 

[Gavin A]

but this really is something the installation company should be checking under warranty, 25% underperformance relative to another almost identical system on the same site with no shading should merit a warranty visit... as long as you're sure that the garage system isn't subject to shading.

 

[Rincewindwiz]

Thanks for this - confirms my suspicions.
Installers have closed down. I spoke to the warranty company and they said (as above) £250 to come and check.
I can switch the 1K inverter off so I'll do the check tomorrow (weather supposed to be good) and report back.

 

[Sunshine777]

You say minimal shading - can you quantify how much shading and for how long on each of the 2 sets of panels?

 

[Rincewindwiz]

I can try:
The roof faces due S (about 170 degrees). There are trees down the East side (12 panel array) side.
For about 9 months of the year (March through November), the morning sun is high enough so the trees have no impact. Before then, the 12 panel array is in some degree of shade maxing out (when the sun is at its lowest) at around 60% shade until about 11 am.
The 4 panel array is on the West side and I've never noticed it in shade.

In the evenings the sun disappears round the West side of the house around 7pm when both sets of panels go into shade.

I''d guess, allowing for more/better sun in summer than winter this amounts to maybe 5% shade on average throughout the year - hence 'minimal' with the garage array in much less shade than the 12 panel array

 

[whinmoor]

A small side-point...

Shouldn't this inverter arrangement involve a G59 application? I haven't studied the datasheets but I reckon there's a fair chance that when combined they exceed 16A per phase.

 

[Rincewindwiz]

So here are the readings. Decent sunshine for all readings
Ipv, Vpv Idc Vdc are the text on the display next to the values. Different for the 1Kw and 3Kw inverters!

Running - before switching off
.........1Kw.........3KW
Ipv......5.0........ Idc 6.3
Vpv ......93........ Vdc 240

Inverter Off
........ 1Kw........ 3KW
Ipv........0........ Idc ........ 0
Vpv......140........ Vdc ........ 410

Inverter On. After 1 approx 1 Min
........ 1Kw........ 3Kw
Ipv......2.1 Idc....... 1.4
Vpv......111 Vdc....... 310

Inverter On After 1 approx 2 Min
........ 1Kw........ 3Kw
Ipv....... 5........ Idc........ 1.0
Vpv.......93........ Vdc........ 305

Inverter On After 1 approx 3 Min and onwards
........1Kw........ 3Kw
Ipv......5.7........ Idc........ 6.7
Vpv...... 92........ Vdc........ 240

Hope that helps

 

[Sunshine777]

You've got me well confused. In your original post you state that both sets of panels face the same direction (almost south) but then you state that the panels on the garage face west?? Which post is correct?

 

[Rincewindwiz]

Ahha I see the confusion. I was trying to describe the relationship of the 12 and 4 panel arrays both of which face South. The 12 panel array is on the East side of the property closest to the trees (but faces S!) and therefore suffers some shade in the early morning. The 4 panel array is on the West side of the property (also facing S!) and therefore gets no interference from the trees and does not suffer from shade until around 7 or 8 pm

 

[Rincewindwiz]

And these readings sem much more sensible.After switching back on the power (V*I) from the 3kw is pretty much 3 time the power from the 1Kw

And yet the original numbers giving cause for concern (2512Kw and 611Kw) show a 4 to 1 ratio

Today (overcast and rain) the inverters report (average of 3 readings over a 1 hour period)
........1Kw........ 3Kw
Ipv...... 0.6........ Idc........ 0.8
Vpv...... 117........ Vdc........ 320
so the 3 KW array is producing more power than the 1kw array. Can it be that one array is more efficient in overcast conditions? Unlikely since they are identical panels. I remain confused!!