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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?
 
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.
 
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.
 
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.
 
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
 
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.
 
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.
 
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.
 
You say minimal shading - can you quantify how much shading and for how long on each of the 2 sets of panels?
 
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
 
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.
 
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
 
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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?
 
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
 
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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!!
 
it looks like you have shading of some nature (maybe bird droppings) on the smaller array, sufficient to knock out 2-3 strings of cells in bright sunlight but not in cloudy weather.

Or one of the panels on the smaller array has particularly bad cells in it / is actually a much lower rated panel.

All panels are connected in the strings though.
 
Your 1kW inverter has an MPPT range of 50 - 320V. It will operate right down to 47v. So the panels, with a nominal Vmp (operating voltage) @ STC of 30.5V x 4 will operate the inverter ... but ... the inverter would much prefer to see higher voltages. In fact, your little 1kW inverter can take up to 450VDC from the panels, and would very much prefer the voltage to be around 300V (that's why 300V is the recommended and rated voltage for this inverter), if it could choose for itself!

The panels are not the issue, they are working fine - it's the inverter that is the issue. While there are several smaller inverters that will run at lower voltages it's quite common to find they will lose a lot of power at sub-200V or lower. The boost/buck circuits can use a lot just converting the lower voltages to a usable AC 230/240V level. The inverter can be a lot more inefficient at low voltages due to what is called "Voltage derating". Almost all manufacturers (even the ones I'd recommend like SMA or Fronius) really don't like to talk about this or publicise it. But here's an example from one manual: (fig. 21, page 84) http://www.energymatters.com.au/wp-content/uploads/2014/09/aurora-2000-au.pdf

You can see that once DC input voltage for the above ABB inverter drops much below what the inverter is trying to output, the losses get progressively worse as DC voltage works. This inverter is often used for short strings as installers know it will operate down to 90v. Handy! But ... at a price! At 200V DC in, it's fine - but if you used say 4 of your panels, (meaning 120V operating voltage, right?), then that's always going to be more than the published 90V that that inverter can go down to - so it's all good, yes? Well, no. If you tried that, the lower voltage than the inverter likes means that at 120V you will lose maybe 30% or so of the expected output. But most people, even many installers, don't know that. And most manuals won't tell them! :p :)

I have no idea how much your inverter might lose at low string voltages, but this is a very common thing for inverters, and I doubt very much whether yours is any different - it generally is an issue that historically has shown most in smaller cheaper Chinese inverters - so maybe food for thought. :)

What small inverters really need in these situations is higher-voltage panels - the older 5" celled ones were very handy for that, nowadays there are only a couple panels like Sunpowers (not Sunmodules!) that have that high voltage.
 
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I've just noticed that there seem to be 2 different sets of specs for this inverter.

One spec has the MPPT range as 120V-350V, the other has it at 50-400V.

That may have been a typo, but it also ended up in the manual.

odd.

I see what you're saying kaju and that's going to be having an impact on the annual generation figures, but aren't the readings just posted taken on the DC side, so before the inverter losses?

In which case the inverter losses wouldn't explain the lower ampage readings shown in those posts for the smaller inverter.`

Though I did make a bit of a mistake as I thought the per panel voltage on the smaller string was lower than on the bigger string, but it isn't in the 3 minute readings once the MPPT has settled down.
 
Annoying when the manuals are different! :) Looks like the (MPPT Range starting from) 120V version was for an earlier model, dated July 09, and the 50V version is more current. Having said that I have known for there to be mistakes in spec sheets before now too. So it appears there were two versions of this model inverter.

All the indications are that the older version really was designed to go with higher voltage 5" celled panels - these were around 180-200w in size, with an average operating current of about 5A. Back at this time there weren't really any 250w panels (like your Solarworlds) - these use bigger 6" cells and have higher current, generally 8-9A, and lower voltages, perhaps 30v compared to 36-37V from an average 200w panel. This is confirmed on the older manual where it shows a max DC current of 6A, while the newer model is 10A.

Your inverter should be reporting the string current that it sees before it does anything with the power - if everything else is the same on both strings (dirt/shade/direction/tilt, etc) you should _overall_ be seeing very similar current from both strings - but they will still very often be different at times too! :)

If you have the older model, your inverter may well be losing some power as it may be clipping the panels' current a little - a good inverter's MPPT can try and juggle the voltage and current to some extent to minimise the effect on output, but not all can do this, and in any case, the 8+A at STC for Imp (operating current) that your panels are capable of may be a little high for that anyway, for this inverter. Never mind the fact that the old inverter's MPPT range starts at 120v and sometimes the four panel string's voltage will be bumping around at or below that level. :)

Panel current is related to insolation - how much sun is getting through to the panel - voltage stays comparatively stable throughout the day, but current can fluctuate much more dramatically with the light hitting the panels, even when you may not notice the difference visually much, if at all. Your four panels have been making close to 120V, which indicates that they are all functioning. Remember each panel you add adds voltage to the string, not current. You've _apparently_ been getting a bit less current on the 4 panel string and overall, it should have the same current as the other string if both have identical directions and tilt - the number of panels in a string doesn't affect the current. It may be you have something wrong with a few cells (I'd think this unlikely, but it is possible), or a panel may be in very slight partial shade (even along the edge of one panel, etc), or perhaps the 4 panel string simply needs a bit of a clean!

Different strings will have different current, even with the same panels - of course they should be closer than you have been seeing - but 20% difference on a momentary basis is not unheard of. You are apparently not getting this difference consistently - one of your figures showed that at one point the 4 panel string was making 50% more current than the bigger string, so you can see that current on separate strings really can bounce around a lot. I'd want to be looking at both strings current in the middle of the day on a clear day over several intervals, probably on a couple of different days, checking that both strings actually do have the same direction and tilt, are genuinely unshaded and clean.

Even so, I would still expect losses from the 1kW inverter given the 4 panel string is bumping along at the bottom of its MPPT range, and that the 4 panel string's nominal current is a little higher than the inverter was apparently designed for. But I'd suspect that the low string voltage of about 120v is in any case going to cause substantial losses as the inverter tries to convert it to higher voltage usable AC power. :)

Unfortunately, you have a couple of variables here that are going to make it hard to diagnose what is causing the lower generation from the 4 panel string. Yes, it's making less power than you expect, but whether that is due to a loss of current from the panels (I'm not entirely convinced) or a loss due to voltage derating (which I'd suspect has at least some part here), it's going to be hard to apportion these losses without measuring each of the 4 panels individually. Even if you did find something, I'd still expect voltage derating losses, so it's highly unlikely that any testing would be cost-effective.

You're pretty much stuck with what you have - getting a new inverter more suited to your panels current and with perhaps less voltage derating too, _might_ help a little - but given the cost vs generation gain, that too is unlikely to be cost-effective.
 

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