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Used Solar Panels from Santan Solar--Only 41% of the Rated Power?

MichaelK, yes, some of the numbers don't add up. But I find that's pretty common with web sites and spec sheets as the persons entering the data sometimes make errors.​

I've never seen more than about 41% of rated capacity out of these panels so far. I've been watching them since late April and the highest output I've seen is 2.71kW from the east facing array, just a few minutes to noon. South array, 2.41kW. What I'm finding is that I need a LOT more than forty panels to power our baseline loads. I've had to shut down my graphics workstation last night (saves idle 400w) and stop using the AC and day over day, the average battery charge left is decreasing by about 20% a day. I had to fire up the generator for an hour this morning to put some charge back into the batteries.

iamrich, the question that bugs me is when you have two arrays, one in shade and the other in sun, connected together into the same MPPT, is there a drastic loss of efficiency? I would think having dedicated MPPT for each array would allow getting the most out of the array that's shaded. But I won't know until I try. I'm not getting anywhere near 9600W out of this system. Not even close. Not even half that. I would expect close to 160 amps combined from both arrays, but I see 30-40 from one and low 30s from the other at noon.​


The other oddity is that the three BMS's don't balance the charge across all three battery banks. Always the case is that the bank with the lowest charge (bank 3) is always being discharged, while the high charge banks are receiving charge. So bank 3 always goes toward zero while the other two are charging during the day or less rapidly discharging at night. Even after selectively charging bank 3 to 100% yesterday, it is now down to 53% while the other two are at 72%. If all the banks are in parallel, they should all be the same charge level!
 

MichaelK, yes, some of the numbers don't add up. But I find that's pretty common with web sites and spec sheets as the persons entering the data sometimes make errors.​

I've never seen more than about 41% of rated capacity out of these panels so far. I've been watching them since late April and the highest output I've seen is 2.71kW from the east facing array, just a few minutes to noon. South array, 2.41kW. What I'm finding is that I need a LOT more than forty panels to power our baseline loads. I've had to shut down my graphics workstation last night (saves idle 400w) and stop using the AC and day over day, the average battery charge left is decreasing by about 20% a day. I had to fire up the generator for an hour this morning to put some charge back into the batteries.

iamrich, the question that bugs me is when you have two arrays, one in shade and the other in sun, connected together into the same MPPT, is there a drastic loss of efficiency? I would think having dedicated MPPT for each array would allow getting the most out of the array that's shaded. But I won't know until I try. I'm not getting anywhere near 9600W out of this system. Not even close. Not even half that. I would expect close to 160 amps combined from both arrays, but I see 30-40 from one and low 30s from the other at noon.​


The other oddity is that the three BMS's don't balance the charge across all three battery banks. Always the case is that the bank with the lowest charge (bank 3) is always being discharged, while the high charge banks are receiving charge. So bank 3 always goes toward zero while the other two are charging during the day or less rapidly discharging at night. Even after selectively charging bank 3 to 100% yesterday, it is now down to 53% while the other two are at 72%. If all the banks are in parallel, they should all be the same charge level!
A picture of the wiring of the batteries. Please also you NEED an MPPT to get even half of your power. A proper charge controller may cure your imbalance in charging. You will need at least two MPPT's as I have not seen many that will handle 9 KWs.
 
I bought some used panels from SS last year and have installed them they are 195-watt panels they are 14 years old I have 36 of them hooked up in 2 strings of 3s6p I get 92% of their rated power at noon they are all facing the same way and at the same angle. You state that at high noon you can only get 42% of your rated power you have not stated at what angle the panels are at and that HAS a BIG bearing on how much sun they will get, full sun means nothing when you fail to mention the angle to the sun, the panels have to be pedicular to the sun to get full sun and east and west-facing panels will never get full sun at noon.
 
iamrich, the question that bugs me is when you have two arrays, one in shade and the other in sun, connected together into the same MPPT, is there a drastic loss of efficiency? I would think having dedicated MPPT for each array would allow getting the most out of the array that's shaded. But I won't know until I try. I'm not getting anywhere near 9600W out of this system. Not even close. Not even half that. I would expect close to 160 amps combined from both arrays, but I see 30-40 from one and low 30s from the other at noon.
Two MPPT's are always going to be better than one (or at the minimum, at least as good). The way I understand solar strings is that as long as the voltage is the same (or close), the two strings will pull the maximum amperage they can.

Keep in mind, I am a novice at this myself. :p
 

labeeman, my arrays are mounted at 45° angles. One faces southeast and the other southwest actually. I've tested single panels with a 4 ohm load resistor and a volt meter and found that I have to vary the angle by more than 20° to see a change in voltage of more than a couple %. Singlely, one 240W panel produced 20V across 4 ohms in January. The same panel produced 29.2V across the same load in April.​

I hope you are correct about not getting half the rated power without an MPPT. My only analogy that I can understand is from the perspective of an amp repair tech and that is impedance matching. If a vacuum tube amp makes 40 watts into an 8 ohm load with it's 8 ohm output tap, doubling the load to 4 ohms would drop the power transferred to the load by about half. The load must be matched to the amplifier output impedance. I know there's no impedance with DC power, but there may be an optimal load resistance range and it probably varies with light levels. If the MPPT handles this and can double my useable output, then I will hit BUY on two Growatt MPPT modules that another participant in this discussion recommended. Thank you for mentioning that you are getting 92% of rated power on 14 yo panels. That's more inline with what I expect in terms of degradation.​


iamrich, I think I'm going to buy the two Growatts (was it you who linked to them?) and try this out. If it's true that 50% of the power is wasted when connecting direct to the batteries, then this is the solution.​

 

labeeman, my arrays are mounted at 45° angles. One faces southeast and the other southwest actually. I've tested single panels with a 4 ohm load resistor and a volt meter and found that I have to vary the angle by more than 20° to see a change in voltage of more than a couple %. Singlely, one 240W panel produced 20V across 4 ohms in January. The same panel produced 29.2V across the same load in April.​

I hope you are correct about not getting half the rated power without an MPPT. My only analogy that I can understand is from the perspective of an amp repair tech and that is impedance matching. If a vacuum tube amp makes 40 watts into an 8 ohm load with it's 8 ohm output tap, doubling the load to 4 ohms would drop the power transferred to the load by about half. The load must be matched to the amplifier output impedance. I know there's no impedance with DC power, but there may be an optimal load resistance range and it probably varies with light levels. If the MPPT handles this and can double my useable output, then I will hit BUY on two Growatt MPPT modules that another participant in this discussion recommended. Thank you for mentioning that you are getting 92% of rated power on 14 yo panels. That's more inline with what I expect in terms of degradation.​


iamrich, I think I'm going to buy the two Growatts (was it you who linked to them?) and try this out. If it's true that 50% of the power is wasted when connecting direct to the batteries, then this is the solution.​

To test if your panels are in the direct sun put a beer can on it and if it cast a shadow it is not getting full sun. You are correct on matching the internal resistance of the panel to your load you cannot get full power above or below that figure there is an instrument to measure that it is used to measure internal resistance on batteries. I was expecting more degradation. With your panels at 45° angles, you may be losing power that 45° seems a little steep to me I sure would not like to be on your roof that is if I could stay on it.

I am using a Growatts charge controller for my panels If I were you only purchase one and see if it will improve your power on one set of panels. It is not in the manual but it has two MPPT inputs if you only hook up one of them you will only get half the power it is rated for you need to split up the set of panels into two groups and hook up both inputs to panels.


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iamrich, I think I'm going to buy the two Growatts (was it you who linked to them?) and try this out. If it's true that 50% of the power is wasted when connecting direct to the batteries, then this is the solution.
There might be less expensive options for MPPT, but that was what I found when looking. I can vouch for Watts247 as a seller. Two of those units will allow you to expand your strings if you have room as well. You could probably run at least another 4 panels per string. Maybe run 6S4P on each controller (open circuit 225v, 33a). Even if the panels hit 100% by some magic, you are under the max listed by a good margin. 5S5P would work as well (5 more panels). You have a lot of options if you have the real estate.
 
Here is a chart of my battery amps for today it is cloudy so the trace is a little crazy bottom is the time of day verticle is amps below 0 is coming out of the battery above is coming out of the charge controller into the battery and load at 1:30 battery is charged and the charge controller is just supplying the load.

Screenshot from 2022-06-08 16-27-24.png
 
You must have a better angle/facing than mine. I saw 80% once... :) But I am facing SE (more east) and the panels are almost flat.
Mine is facing South with about 15 degrees this time of year here they need to be almost flat.
 
Measure current flow between shaded and unshaded array. You may have cell shorts in some of the panels in shaded array which could cause them to absorb current in the shade when paralleled with illuminated array. This could explain your low efficiency. Ideally you want MPPT on each series string of panels if your panels are of unknown quality. Get small 20A MPPT controller and test each panel on it's own in full light. Forget messing with 4 ohm resistor. Panels have varying ideal load impedance with temperature and sunlight and you will never get it right with fixed load.
 
Measure current flow between shaded and unshaded array. You may have cell shorts in some of the panels in shaded array which could cause them to absorb current in the shade when paralleled with illuminated array. This could explain your low efficiency. Ideally you want MPPT on each series string of panels if your panels are of unknown quality. Get small 20A MPPT controller and test each panel on it's own in full light. Forget messing with 4 ohm resistor. Panels have varying ideal load impedance with temperature and sunlight and you will never get it right with fixed load.
The problem is that they are not using any SCC.
They have connected the panels directly to the batteries.
 
The problem is that they are not using any SCC.
They have connected the panels directly to the batteries.
I understand. That's main problem. But then paralleling 10x series strings of panels of unknown Vmp could be an issue too. Each panel needs to be verified to have correct Vmp before series/paralleling.
 
I understand. That's main problem. But then paralleling 10x series strings of panels of unknown Vmp could be an issue too. Each panel needs to be verified to have correct Vmp before series/paralleling.
Yup
Needs to go back to the drawing board and start over.
 
I have some used 255w Trina snail trails that delivered 100% rated output. Maybe the trails affect longevity, but don't appear to be affecting output.
I have seen 110% twice. I'm more than satisfied with my purchase. My future phases totalling 50kw will all be the same panels. (Snail Trails rule. lol)
 
I've mounted my panels on wooden racks that are ground mounted in the back yard. I shun the idea of roof mounted because they make roof maintenance a serious hassle. I chose 45° as a best year round angle. In June, the sun is a bit too high, but in Dec, it will be a bit too low. Probably early spring and late fall it will be perpendicular to panels. Sun is weaker in winter due to low angle, so panel angle takes that into account.

I read an article with schematics of DiY MPPT charge controllers and now I understand that solar panels are current sources--they behave like vacuum tube amplifiers and won't transfer all of their output without impedance matching device (in this case, an MPPT controller or at least a buck converter). According to the article, I could be losing 25% of PV output by connecting direct to battery.


There is an 80 amp version of the Growatt MPPT, but no stock anywhere. But that one is designed for 4800W of panels, so two of them, one for each array, seems ideal. I just need to find a dealer with stock around $269 each. Growatt SC 4880. Watts247 only lists the 120A version. I think the 80A version is just right for each array of 20 panels (4800W). It would have to be rewired for 5S4P.

I did find one panel with shorted cell the other day and disconnected it and its series partner. Made no difference in array output so it was consuming all the energy it produced with the shorted cell. Filed claim with Santan for replacement. 19 other panels all measured good across the three blocking diodes in each junction box. Based on the performance of the other array, all panels are working and no shorts.
 
I have seen 110% twice. I'm more than satisfied with my purchase. My future phases totalling 50kw will all be the same panels. (Snail Trails rule. lol)
That has happened to me too. Once I saw 130% for about 5 minutes. I rushed out to check the sky, and I could see wispy cirrus-type clouds high up. So, cloud lensing is a real phenomena. I haven't seen it happen since then. Nothing that can be counted on in a real-world sense.
 
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