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Solar panels concern


Ballar
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Hi guys,

 

Wish I found this platform before I installed the system I have at home. But anyways...

 

Quick background on my system:

- I have 2 5kvA MS inverters running in parallel mode

- 16 300w Solar panels (4800w capacity in total)

- 8 180A/h batteries

and all necessary accessories pulling these together.

 

My issue is that my Solar panels are not generating half the power I expect them to generate

 

At midday in full sunlight the max input to my inverters is 2.5Kw from my panels. This is about 50% of the Solar panels' capacity.

 

Is this expected or may I have faulty equipment.

 

Look forward to some expert advice :D

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I suppose it will depend where you are, but 50% certainly doesn't sound right. I rarely get the rated output of my array (I doubt anybody does), because the rated output is at ideal conditions (1000W/square meter), but... I do get at least 85% of the rated power (Somerset West). 50% doesn't sound right.

 

You don't state battery voltage, but I will assume that's 48V. So at peak you're looking at 85A-100A current? 8 batteries, 4 per string, so that's 360Ah at 48V? You want no more than 15% of capacity in charge current (please correct me if I am wrong), so 50A is about the max charge current for your battery bank. This might actually be by design... ???

 

Also, what Edmundp said. Some of these inverters have a PWM controller instead of an MPPT. They will be 30% down.

 

Still, your solar array appears to be oversized relative to the batteries.

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So correct me if I am wrong but from what plonkster is saying the inverters will also calculate max charge current based on the batteries installed?

 

The plan was to eventually install 8 more batteries after a while, so could this increase charge current from panels once installed?

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Hi Ballar

 

The points made is valid , however i think one of your strings on your solar panels must have a dry joint(loose) even a PWM controller's output wont be this low. There is an easy way to find out if one of your strings have loose joint if you can get to the panels easily. You will have to put load on your inverter during the day in good sunlight so the output from your panels is maxed. You must then shade each string of panels (just one panel in a string will do)  with a piece of cardboard for example. The string that is not making a difference on the output is the one that got the loose joint.

 

But lets not jump the gun, check all your connections in your combiner box firstly. Just two weeks ago i had a problem with one of my mobile solar units and one of the strings had a faulty connection in the combiner box.

 

Hope this helps.

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Just want to address the question about the battery size. When you design a system, you're supposed to consider the maximum charging current, obviously for the sake of the batteries, but also for safety. The rule says to try and keep your peak charge current to 15% of the Ah capacity of the battery. Nothing stops you from breaking the rule, but it's generally not a good idea.

 

There is however something you can do: You can tell your MPPT charger to restrict the max current to some percentage of its capability. This allows you to set a safe limit even though the solar array is oversized. There is also a good reason to oversize a solar array: It means a flatter power curve, you make more power earlier in the morning, do peak for a greater part of the day, get more power on cloudy days, etc. But usually it makes little financial sense to oversize by more than 10%-20%.

 

Anyway, so the reason I brought it up: It is possible your installer oversized the array (for whatever reason), but set the MPPT controller (assuming you have one) to a safe limit. And that's why you only see about half the power, because it's limiting to 50 amps. It's a wild guess... but it's a possibility.

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  • 9 months later...

i have the some problem. 

same inverter with MPPT charge controller. 

i have 1 string.    2 x 150W + 4 x 180W  = 1020W 

I only get about 550W max from PV input.   115V +- 5A

I dont believe there is a bad connection because the power is fairly constant and available. 

my panels face north at about 15 degree angle , full sun.

cables = 4mm2   , 5m length

any help?

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47 minutes ago, Fritz said:

i have the some problem. 

same inverter with MPPT charge controller. 

i have 1 string.    2 x 150W + 4 x 180W  = 1020W 

I only get about 550W max from PV input.   115V +- 5A

I dont believe there is a bad connection because the power is fairly constant and available. 

my panels face north at about 15 degree angle , full sun.

cables = 4mm2   , 5m length

any help?

Hi Fritz

2 things here...

If your panels are fixed, in other words the tilt angle is not adjusted seasonally etc., then it should be tilted at more than 15° to get the most from them - 19° for Mussina, which is the most northern place in SA and almost 30° if you are in the most southern place in SA. solarpaneltilt.com

The one serial string consisting of different panel types worries me a bit. If all your panels have the same (or very close) voltage at maximum power point, the total current flowing through them will be limited to the current flowing through the 150W panels and effectively you will lose at least 120W or more at MPP on a good day (4 x (180-150) = > 4 x 30W => 120W).

Please post specific model numbers or datasheets for all the panel types you are using, maybe we can suggest a different configuration which might have better results.

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5 hours ago, Fritz said:

i have the some problem. 

same inverter with MPPT charge controller. 

i have 1 string.    2 x 150W + 4 x 180W  = 1020W 

I only get about 550W max from PV input.   115V +- 5A

I dont believe there is a bad connection because the power is fairly constant and available. 

my panels face north at about 15 degree angle , full sun.

cables = 4mm2   , 5m length

any help?

You effectively have 900W worth of PV array. Without going into too much technical detail, the lower denominator always wins. Take off 20% (average) and you're left with 720W. What you're getting now sounds about right to me. In summer you might get upto 700W

Let me explain:

These smaller / cheaper solar panels are generally between 14% and 17% efficient, depending on which make & model panels you have. Cheaper, and also smaller panels, are generally less efficient for their size. The record is 24%, but this is on a  i.e. if the solar rays in a given square meter is 1Kw, you'll only get about 14% - 17% of that. Larger panels tend to be more efficient. In simple laymen terms: The more Watt the panel produce, for a given size (for example 265W on 60 cells, 315W on 70 cells), the more efficient it is. And then some manufacturers have been able to produce more efficient panels than others due to the components and assembly process they use. 

This gets worse since your panels are not 100% aligned for your are. 15% is a bit low for South Africa. A simple rule of thumb is to use your latitude as angle, i.e. 28degrees, 30 degrees, etc. To get 100% possible solar energy from your setup, you would need a solar tracker, but that would cost an arm and a leg. And a kidney. Many people adjust their panels two or three times per year for optimized energy harvesting. This is if you are physically able to adjust them. 

As matter of interest, an installation we did two weeks ago, was done flat on a tin roof due to many factors. 8x 250w panels. We only got 1400W out of the PV that day. It was cold. And the panels are mounted at about 4 degrees (normal angle of carport?). The structure it's mounted on didn't allow to mount the panels pointed to 0 degree north, cost effectively, so this was a compromise the client was willing to take. The system suffered 30% loss due to this arrangement. The manufacturer says the panels are 15.06% efficient. So we should get 150.6W/square meter, on a perfect solar day - which doesn't happen often, and generally not for very long either. The panels are 1665mm x 999m, thus 1.6sqm per panel, which means it could product 250W on 1.6sqm area, or 156.25w/sqm. 

 

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Thank you for the all the responses.  :)

@superdiy My specs:    6 panels all in series. 

2 x amerisolar  150W  ,      12V   ,  18Vp max  and 21.4V open circuit. Imax = 8.33A

+

4 x omega 180W,   12V , 18Vp max and 21.4V open circuit,  Imax = 10A

* just a note these panels looks almost exactly the same , i think the amerisolar just got a stronger alu frame. 

So my inverter input PV show,   +-115V and +-6A

The MPPT controller will look for the max power point which should be at  18 x 6 = 108V but it runs at 115V

so surely it must get max power?

I wish the answer will be that i bought shit panels and thats it..... ?!! yes ? no ? maybe?

 

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54 minutes ago, Fritz said:

Thank you for the all the responses.  :)

@superdiy My specs:    6 panels all in series. 

2 x amerisolar  150W  ,      12V   ,  18Vp max  and 21.4V open circuit. Imax = 8.33A

+

4 x omega 180W,   12V , 18Vp max and 21.4V open circuit,  Imax = 10A

* just a note these panels looks almost exactly the same , i think the amerisolar just got a stronger alu frame. 

So my inverter input PV show,   +-115V and +-6A

The MPPT controller will look for the max power point which should be at  18 x 6 = 108V but it runs at 115V

so surely it must get max power?

I wish the answer will be that i bought shit panels and thats it..... ?!! yes ? no ? maybe?

 

OK, I was afraid that this would be your problem. The voltages of the panels are similar, that means that they will perform much better in parallel, but all connected in parallel would be way to low for the MPPT to work properly - you need between 60V and 115V. You have not mentioned the MPP current, only max current, the MPP current will just be a bit lower for both panel types, but with 1 serial string you will be limited to the current through the smaller panels which would be 8.33A under short circuit condition and a bit lower at MPP - the +- 6A you see looks in line if you keep in mind that your tilt angle is way too low, especially for winter.

I don't think you really have any other option than to tilt the panels more or to add more panels and configure them differently. Any serial / parallel combination of the current panels will leave you with either the same amount of losses or a too low total pv voltage, which would be too low for the MPPT to work effectively.

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