Are my solar panels working correctly?

Nostrodamus

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I have some new solar panels fitted and I believe they may not be giving out the amps they are supposed to.
They are 4 x 95w fixed panels (Total 380w) and we are in the cloudless Greek waters.
The panels are fitted in Parallel.
When the sun is strait above and the batteries are not full I tend to get about 11 to 12 amps going in which seems a bit low to me.
Do I need to check my wiring and what sort of amps would you expect individually and collectively.
There are no shadows over them and the are fixed to point strait up.
Thank you for any advice
 

RobbieW

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It may depend on how you're measuring the current. If you're measuring that at the output of the solar controller it should be an accurate measure of the panel output. If you're using a 'normally' installed ammeter what you're measuring is the net current flowing in the system, ie difference between load and supply. With the second, try turning off all the loads, fridge, computers, instruments etc etc and see if the current reading goes up
 

Nostrodamus

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The set up I have has the panels going to a MPPT box which can be read directly. The box also has a lead going directly to the batteries so the measurement can be taken directly from them.
At the moment the batteries are reading 12.9v, the watts in is 138w and the amps is 10.7
 

Mistroma

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The set up I have has the panels going to a MPPT box which can be read directly. The box also has a lead going directly to the batteries so the measurement can be taken directly from them.
At the moment the batteries are reading 12.9v, the watts in is 138w and the amps is 10.7

These readings are fairly similar to those on my setup on a good day. I get a readout of Amps from panel and to batteries and panels are all rigid type. However, I only have 145W of panels and so would expect more like 24A if I had 380W.

Amps going to battery will of course be much lower if batteries are well charged. In fact, I have to set charge V limit to 15.0V to avoid the regulator throwing away useful Amps. Otherwise it tends to dump most of the input when at 80% if left at default setting and I only see a few Amps going to the domestic bank. Battery V never gets anywhere near 15V though (often only 14.6V if lucky and Trojan would prefer 14.8V).
 
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.....When the sun is strait above and the batteries are not full I tend to get about 11 to 12 amps going in which seems a bit low to me......
In this situation the MPPT controller may well have been in Absorption mode for its maximum period, maybe 2-3 hours, and has now switched to Float mode at maybe 13.2 v, even though the batteries are nowhere near charged. The MPTT controller should tell you what mode it us in!

You may have to force the MPPT controller back into Absorption mode by turning it off - pull out the fuse that you should have going to the batteries - and it will come back in to Absorption mode for 2-3 hours again. This should take the voltage to 14.4 v and force more amps into the batteries.

If this is not the problem simple disconnect all the panels and reconnect one at a time to see if each us giving the same voltage and current.

It could also be the cables from the panels are much too small and you are getting a big volt drop along the cables with all 4 connected. Measure the voltage from the panels ALONG the cable to the input to the MPPT controller. This should be very small, less than 0.1 volts. Do the same from the controller to the batteries.
 

Caladh

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These readings are fairly similar to those on my setup on a good day. I get a readout of Amps from panel and to batteries and panels are all rigid type. However, I only have 145W of panels and so would expect more like 24A if I had 380W.

Amps going to battery will of course be much lower if batteries are well charged. In fact, I have to set charge V limit to 15.0V to avoid the regulator throwing away useful Amps. Otherwise it tends to dump most of the input when at 80% if left at default setting and I only see a few Amps going to the domestic bank. Battery V never gets anywhere near 15V though (often only 14.6V if lucky and Trojan would prefer 14.8V).

Have you got an MPPT controller? If so I would think the controller would be in it's float/equalization modes if the batteries are well charged? If you "up" the Battery V setting are you in danger of over charging?
 

AndrewB

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It does sound a bit on the low side if your batteries are accepting full charge. My 200W installation has been giving 8-9 amps during the central part of the day recently in Greece.

Suggest you check the output from each panel independently - the total should be the sum of all four. But sometimes it seems that multiple panels can work against one another. I have had this problem at times, even with blocking diodes installed, but do not know what the answer is.
 

Poecheng

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This doesn't sound correct to me.

If the batteries are near fully charged then the MPPT should be either on bulk charging mode (about 14.6v) or have dropped down to float charge mode (about 13.8v). The amps may drop off somewhat if on float charge.

If as you say the batteries are not near full then the MMPT should be on bulk charge mode (showing a voltage at the battery of about 14.6v) and banging in the maximum amps that it can (you seem to have low voltage and low amps).

A very rough calculation (not based on any, or any solar, research) would be that you might get 90% efficiency from the panels (380W x 0.9 = 342W) and lose another 10% via resistance and the efficiency of the MPPT box (342W x 0.9 = 307W] Lets say you have a real 300W to play with then you should still have far greater amperage and voltage (300W / 15v = 20A) coming out of the MPPT box.

Therefore
a) are the readings correct? can the voltage be checked by multimeter rather than the MPPT box?. Turn off the domestic supply temporarily to see what is happening without any load
b) is the MPPT box upto the task - can it take the amperage that should be flowing in?
c) is each panel working and wired correctly to each other? [if they were wired incorrectly then one panel would cancel out the other leaving you with a 150W system which would give about 10A - it might do other damage as well but it is a thought !]
d) Depending on your MPPT, instead of wiring all in parallel so that the total output is "12v" (in reality an open voltage of about 18V), you could make two separate banks of two panels where the two panels in the same bank are wired in parallel but in series with the other bank. This would give you a "24v" panel input to your MPPT (which by connection to the battery knows it is a 12v system) which converts it to 12v charging. The MPPTs work better with higher voltages and do not need to be fed a "12v" supply.
[my knowledge of MPPT is limited to Victron; I have a 75/15. Once connected to the battery it knows it is 12v system. You can then feed it upto 75volts supply and it converts it to a 12v charging voltage upto a max of 15A. Apparently it is better at a higher voltage and, further, the cable resistance is favourable as Volts do not create resistance, Amps do]

Good luck
 

Nostrodamus

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Thank you all for your help.
You seem to agree that I should be getting more amps so I need to check the system all the way through. I will start with individual multi meter readings from each panel and work back to the batteries.
Thank you all for letting me know what I should be checking.
 

Mistroma

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Have you got an MPPT controller? If so I would think the controller would be in it's float/equalization modes if the batteries are well charged? If you "up" the Battery V setting are you in danger of over charging?

No, not an MPPT unit. Battery bank is quite large and I never get anywhere near too high Voltage unless on shore power and batteries at 100%. I always reset to factory default in a marina but have an annoying hardwired alarm set at around 14.7V so struggle to get the 14.8V I'd like without setting it off anyway. Trojan spec. is for daily 14.8V charge and I read a nice article by a guy living off-grid confirming Trojan were correct. He had lots more problems with T105s before starting to follow Trojan's instructions and now get more years life from them.
 

William_H

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A simple test of each panel is to remove the positive wire from the panel to the controller and connect via an amp meter (your multimeter might do it on amps) directly to the battery +ve. the negative hopefully will go direct to the battery negative. Current should be in the order of 4.5 amps in good overhead sun. You may be able to try temporarily tilting the panel towrds the sun. Each panel should give a similar result when tested.
This arrangement will give the max current into the battery at up to near 20 volts so is regardless of battery condition. (charge state) If all panels were connected that way you would get near 20 amps into the batteries which would in time overcharge them.
Hence the controller's roll is to reduce charge current as the batteries reach fully charged. Hence any actual charge current is going to be less except with very flat batteries. Or a large load on at the same time.
Like alternator charge controllers or battery chargers the solar controller may have progressive charge max voltage stages. So larger charge voltage at first to get max current in then reducing charge voltage to trickle or maintain the battery condition. Or it may be just a dumb fixed voltage controller (regulator) like a simple car alternator regulator which will then take much longer to recharge the batteries. This because the voltage of the battery tends to rise rapidly when charged out of proportion to actual charge percentage. So solar charge current with a regulator (controller) will always be the lesser of what the batteries will take and what the panels will supply. An MPPT regulator will provide some more current as a capability but is still constrained by what the batteries will take.
So my guess is that panels are probably OK given the flat mount, sun conditions and battery charge state. good luck olewill
 

geem

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install a digital ammeter before the solar regulator and you will see what the panels are making before the regulator reduces the output for charged batteries. it is possible that you have a lose wire on one of your panels.
 

William_H

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install a digital ammeter before the solar regulator and you will see what the panels are making before the regulator reduces the output for charged batteries. it is possible that you have a lose wire on one of your panels.

I don't think this is a safe statement to make. Regulators with a dumping resistor to shed the load may be OK to rely on the amp meter between the panel and the regulator but most pulse width and MPPT types will suck less current from the panel when the batteries are charged. So low amp meter reading here may not indicate bad panels. olewill
 

geem

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I don't think this is a safe statement to make. Regulators with a dumping resistor to shed the load may be OK to rely on the amp meter between the panel and the regulator but most pulse width and MPPT types will suck less current from the panel when the batteries are charged. So low amp meter reading here may not indicate bad panels. olewill
ok, that interesting. My regulator is a dumping resistor type. The meter does show the current available from the panel.
 
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