Solar The Solar Panel Thread

[Boots in Action]

An interesting read on basic solar- http://ecgllp.com/files/7014/0200/1304/5-Cells-Modules-and-Arrays.pdf

Thanks @G Daddy , that link has it all!!. If I had read that firstly, I would have most of the answers already and only had to do the practical in field testing to confirm what was on this link. Great stuff!! Now I can get my calculator out and work through the data. I have all the IV info on two panels and am following up on the last one panel "C". In my testing, I did not take into account another variable - increasing temperature of panels in the sun, as it got quite warm working in the sun and panels did get hot towards the end of the test.

I checked on the diodes on all three panels and all have 2 blocking diodes type 10A10 per single panel. None have the Schottky type as mentioned by @mikerezny which may have lower forward voltage drop.

I noted that the bypass diodes can be wired in parallel with the outputs of panels. All my panels consist of 2 folding type panels with each fold connected in parallel. As my MPPT controller has blocking devices in its circuitry, is there a need for the blocking diodes in the panels. If I removed these blocking diodes, perhaps I could connect Schottky type diodes in parallel with the outputs on each panel to assist output when one (or part of one) of the panels was partially or fully shaded?? Like hotting up a motor car!!
You expert advice and opinion would be greatly appreciated. I still have a lot to learn on this subject which really interests me!

 

[G Daddy]

Hi @Boots in Action , I am no expert I've had 40 odd years working on 12 volt and 240 volt gear mostly in transport refrigeration and I am still learning and making mistakes.
My understanding of diodes is quote
"This use of bypass diodes allows a series (called a string) of connected cells or panels to continue supplying power at a reduced voltage rather than no power at all.Bypass diodes are connected in reverse bias between a solar cells (or panel) positive and negative output terminals and has no effect on its output. Ideally there would be one bypass diode for each solar cell, but this can be rather expensive so generally one diode is used per small group of series cells" So removing them from a panel would effect the efficiency of the panel under shading conditions.
Blocking diodes are used in each circuit of a parallel setup as you are testing in A + B , A + C , B + C or A+B+C and in my opinion could help when one whole panel is shaded, ie roof top panel shaded and portable in full sun.

This is something I have been meaning to try as I have 1 panel on van & 1 portable panel connected through 1 MPPT controller. If I had 1 controller on each panel there would be no need for blocking diodes IMO.
Hope this helps

Further reading http://www.electronics-tutorials.ws/diode/bypass-diodes.html

 

[G Daddy]

Hi @Boots in Action , In relation to temperature most panels have a coefficient of -0.2% / deg C to -0.5% / deg C

In relation to voltage drop across diodes, Silicon 0.6 to 0.7 V , Schottky 0.2 to 0.5 V

 

[Boots in Action]

Hi @Boots in Action , In relation to temperature most panels have a coefficient of -0.2% / deg C to -0.5% / deg C
View attachment 56341
In relation to voltage drop across diodes, Silicon 0.6 to 0.7 V , Schottky 0.2 to 0.5 V

Thanks @G Daddy , more EXCELLENT information which would no doubt have affected my test results as panel temp would have been at least 28C. This information would have massive ramifications for all those who have their solar panel/s installed on top of vans with minimal distance between back of panel and roof of van. I have seen reference to the fitting of panels on van rooftops earlier in threads on this forum. So to get maximum output from your panel, it has to be in as direct sunlight as possible AND not get too hot. A very interesting scenario!!

The information about diodes is very valuable too. As I am handy with a soldering iron and a multimeter, I will probably replace all the existing diodes with Schottky type. 45 volt 15 A should do the job. It might help me squeeze a bit more out of my panels for only a couple of dollars.
Regarding the great links you have referred me to, there is one section which states that for series connections with dissimilar panels (same or close voltage outputs but differing amperage output), the voltage will be added, but current will NOT exceed the amperage output of the smallest panel. My test results do NOT confirm that as both "A" plus "B" reached 11.8 amps at 13.4 volts and "A" plus "C" reached 10.9 amps at 13.6 volts. The rated output of "A" was only 4.5A even though I was able to achieve 6.0 amps at 12.8 volts! Comments on that???
I am at the moment going through all the formulas and data calculations for all three panels to see exactly what's what. You have been a tremendous help and I shall be calling on your knowledge again shortly. I hope you do not mind. Best regards

 

[G Daddy]

Hi @Boots in Action , QUOTE My test results do NOT confirm that as both "A" plus "B" reached 11.8 amps at 13.4 volts and "A" plus "C" reached 10.9 amps at 13.6 volts. The rated output of "A" was only 4.5A even though I was able to achieve 6.0 amps at 12.8 volts! Comments on that???[/QUOTE]
Your current ( AMPS) were measured at the output (ie battery side) of the controller and therefor indicate that your controller is a true MPPT ,
If you are testing again can you record the Amps into the controller from the panels?

 

[Boots in Action]

Hi @Boots in Action , QUOTE My test results do NOT confirm that as both "A" plus "B" reached 11.8 amps at 13.4 volts and "A" plus "C" reached 10.9 amps at 13.6 volts. The rated output of "A" was only 4.5A even though I was able to achieve 6.0 amps at 12.8 volts! Comments on that???

Your current ( AMPS) were measured at the output (ie battery side) of the controller and therefor indicate that your controller is a true MPPT ,
If you are testing again can you record the Amps into the controller from the panels? [/QUOTE]

Hi @G Daddy , the wonders of a genuine and good MPPT solar controller are now more evident. Regarding the "A" plus "B" test, I was able to calculate the current from the panels without another test as I had already recorded the panel input voltage and placed it in the data.
So given that the MPPT controller is 98% efficient in operation as advertised, battery voltage 13.4 volts, current into battry is 11.8 amps and panel voltage is 32, then current from panels to controller can be calculated as follows:
13.4 X 11.8 divided by 98, X 100, divided by 32 comes out at 5.04 amps. This is in accordance with the theory of dissimilar panels (same/close voltage) but uneven current output - max 4.5A for panel "A" as against panel "B" max 10.01 A. It appears that input current to controller was definitely limited to the output of the smaller panel of only 5.04 A, but because voltage was 32 volts, the MPPT controller was able to re-configure this to 11.8 A at a battery voltage of 13.4 volts to charge battery and carry load of 4.5 A as well!!
Please tell me that this is correct. If so, then the value of a true (and good) MPPT is obvious.

I have done the same calculation for other readings and came up with "A" plus "C" as 5.07 A which is consistent with "A" plus "B" above. The result for "B" plus "C" comes out at 7.83 A which is well down on expectations as panels are rated at 10.01 A and 10.87 A respectively. I will now investigate the efficiency of these two panels to see if they can be improved. Even if unable, an amount of 15.8 A at 13.8 battery volts is still substantial. Will keep you informed as I delve deeper into the intricacies of solar power and control. Cheers
PS. @mikerezny and @Bellbirdweb may be interested in these figures??

 

[mikerezny]

Hi @G Daddy,
I knew that hotter panels generated less power, but until your post I didn't know by how much.
I also thought that hotter panels aged quicker. Is that your understanding?

I combined those two facts and usually avoid putting my solar panel out during the hot part of the day.
On good days, I can put the panel out in the cool morning and have the battery fully charged in less than an hour then keep it on float for another hour. If, I don't get it all done in the morning, I put it out again in the afternoon.

cheers
Mike

 

[mikerezny]

Hi @Boots in Action,
I have been looking at the table of your results posted by @G Daddy. There seems to be something very wrong with the results of the 180W and 200W panels. The 80W panel achieved 76.8W, the other two panels 120W of 180W and 110W out of 200W.
IMHO, you would be better o hold off on any further testing of testing panels in series or parallel, or buying schotky diodes for bypass and blocking until you can get close to the panel rating for each of these panels. They have a long warranty and if they are not up to scratch, it would be worth getting them replaced.

These are the specs you posted earlier:
"A" rated at 80 watts is 17.6 volts Vmp and when multiplied by max power current (Ipm) 4.55A comes to 80.0 watts - correct.
"B" rated at 180 watts, 18.0 volts by 10.01 comes to 180 watts - correct.
"C" panel rated at 200 watts, 18.3 volts by 10.92A comes to 199.83 watts - close enough

Is it possible to put each panel out in good sunlight and confirm that you actually can get Isc with a S/C and a current clamp?
You will need to do these tests quickly before each panel heats up in the sun.
Since both B and C are over 10A, it will exceed the ratings for a normal multimeter.

Can your controller display solar panel input voltage and current?
I googled but couldn't find the manual for your controller.

On a good cold panel, the MPPT should be finding something close to Vmp and Imp.
But your tests indicate otherwise. Take panel C: Vmp = 18.3V and Imp 10.92A = 199.83W
But your MPPT controller found a maximum at 14.7V. It would be really useful to also have the actual panel current.

It seems that you might get better results in A+C by just having A+A (2 x 80W panel delivering 160W) instead you are only getting 144W or 148W depending on how they are conected.

cheers
Mike

 

[Boots in Action]

Hi @Boots in Action,
I have been looking at the table of your results posted by @G Daddy. There seems to be something very wrong with the results of the 180W and 200W panels. The 80W panel achieved 76.8W, the other two panels 120W of 180W and 110W out of 200W.
IMHO, you would be better o hold off on any further testing of testing panels in series or parallel, or buying schotky diodes for bypass and blocking until you can get close to the panel rating for each of these panels. They have a long warranty and if they are not up to scratch, it would be worth getting them replaced.

These are the specs you posted earlier:
"A" rated at 80 watts is 17.6 volts Vmp and when multiplied by max power current (Ipm) 4.55A comes to 80.0 watts - correct.
"B" rated at 180 watts, 18.0 volts by 10.01 comes to 180 watts - correct.
"C" panel rated at 200 watts, 18.3 volts by 10.92A comes to 199.83 watts - close enough

Is it possible to put each panel out in good sunlight and confirm that you actually can get Isc with a S/C and a current clamp?
You will need to do these tests quickly before each panel heats up in the sun.
Since both B and C are over 10A, it will exceed the ratings for a normal multimeter.

Can your controller display solar panel input voltage and current?
I googled but couldn't find the manual for your controller.

On a good cold panel, the MPPT should be finding something close to Vmp and Imp.
But your tests indicate otherwise. Take panel C: Vmp = 18.3V and Imp 10.92A = 199.83W
But your MPPT controller found a maximum at 14.7V. It would be really useful to also have the actual panel current.

It seems that you might get better results in A+C by just having A+A (2 x 80W panel delivering 160W) instead you are only getting 144W or 148W depending on how they are conected.

cheers
Mike

Hi @mikerezny , the points you raised are pertinent and noted for future action. Still coming to grips with all the data my MPPT controller can provide. Rather sophisticated!! The figures on my test sheet show the panel voltage provided by controller BEFORE entering MPPT adjustment phase. The controller DOES have a readout for PV power available. This is shown in watts and I did not record it in first test. MY figures Also show OCV for each panel. 21 volts for panel "A", 21.6 volts for panel "B" and 19.1 volts for panel "C" which is close to spec shown. I will probably be able to do further testing for Isc sometime this week as this is SUNNY Queensland.
The first figures in my test data show INDIVIDUAL outputs for each panel with "A" putting out an impressive 6.0A. Panel :B" was 9.2A which is close to Imp of 10.01A . Panel "C" is rather disappointing at 8.3A but I have just realized it has less solar cells at 16 per panel (albeit much larger surface area) compared to 72 per panel (smaller) on panel "B" and 36 cells per panel on panel "A". Will delve into there anomalies more and report back. @G Daddy .....HELP!!!!

 

[Boots in Action]

Hi @G Daddy,
I knew that hotter panels generated less power, but until your post I didn't know by how much.
I also thought that hotter panels aged quicker. Is that your understanding?

I combined those two facts and usually avoid putting my solar panel out during the hot part of the day.
On good days, I can put the panel out in the cool morning and have the battery fully charged in less than an hour then keep it on float for another hour. If, I don't get it all done in the morning, I put it out again in the afternoon.

cheers
Mike

Hi @mikerezny , that is a luxury I cannot afford with the demands placed on my battery system on extended stays off grid. If they last at least 10 to 15 years, then that will probably see me out of camping. I note that the panels on my roof are subject to the harshest conditions most of the time and have a 30 year warranty on at least 80% production after that time, so I do not consider the heat degradation problem too much. Same on my portable panels.

 

[G Daddy]

Hi @mikerezny In relation to ageing (

I also thought that hotter panels aged quicker. Is that your understanding?

My understanding on ageing is there quite a few factors involved including heat, conductor breakdown inside the panels, vibration (even vibration caused by wind on house panels), UV light and others, so excessive temperature is only one of the effects.

Cheers

 

[G Daddy]

Hi @Boots in Action , Solar cells have a voltage of 0.05 to 0.06V, therefor the voltage output of the panel depends on the configuration (series and parallel) circuits within the panel. Does that make sense?

 

[G Daddy]

Hi @Boots in Action ,I've added your formulae to the spreed sheet, just looking it appears the panel voltage on B and C are very low compared to the VPM spec for those panels, may need to recheck.

 

[G Daddy]

Hi @Boots in Action ,Here is a voltage printout from the new controller I fitted last week. I have the charts with watts and amps if your interested?

 

[Boots in Action]

Hi @Boots in Action , Solar cells have a voltage of 0.05 to 0.06V, therefor the voltage output of the panel depends on the configuration (series and parallel) circuits within the panel. Does that make sense?

Thanks @ G Daddy , I was aware of this from the links you have provided. As mentioned to @mikerezny , I will be doing further in depth testing of EACH panel, checking against specs provided on back of panels and from any other sources. I did not notice the difference in the number of cells per panel at first so it will be interesting to fully check them out. My MPPT controller does have a readout of panel power available (in watts) which I have not as yet compared on individual panels and in different circuit combinations.
I just need another point clarified if you would please. When recording amps into battery from controller, does this include replacing the load placed on battery at the time or is the load draw additional current just to keep voltage down so there is a lower voltage for the controller to sense to charge battery??

 

[Boots in Action]

Hi @Boots in Action ,Here is a voltage printout from the new controller I fitted last week. I have the charts with watts and amps if your interested?
View attachment 56407

Great chart @G Daddy . I notice that solar voltage is 20 volts most of the time in good light and that battery voltage is pretty stable at 15 volts for nearly 3 hours (bulk charge??) before dropping to about 13 volts as battery charge come up. And no load applied too. It that the correct interpretation of your chart?? Should I also do tests without any load applied and see what the readings are???
And yes, I would be interested in you charts of watts and amps produced.

 

[G Daddy]

Hi @Boots in Action , [QUOTE, When recording amps into battery from controller, does this include replacing the load placed on battery at the time or is the load draw additional current just to keep voltage down so there is a lower voltage for the controller to sense to charge battery??[/QUOTE]
Most MPPT controllers act just like a 3 stage battery charger, so yes what you have said is basically correct. MPPT controllers switch to PWM mode when on float mode until the battery voltage drops below a set voltage point (on my controller this is adjustable) at which point they switch back to MPPT.
As seen in the chart above and below where at 3:40 pm the current similar. I have yet to record the upward switching.

Amp Chart

Watts Chart


These charts are from an old 140W portable panel I have mounted flat on the van roof using a EPSolar EPEver Tracer A Series 30 Amp

 

[Bellbirdweb]

Hi @Boots in Action , [QUOTE, When recording amps into battery from controller, does this include replacing the load placed on battery at the time or is the load draw additional current just to keep voltage down so there is a lower voltage for the controller to sense to charge battery??

Most MPPT controllers act just like a 3 stage battery charger, so yes what you have said is basically correct. MPPT controllers switch to PWM mode when on float mode until the battery voltage drops below a set voltage point (on my controller this is adjustable) at which point they switch back to MPPT.
As seen in the chart above and below where at 3:40 pm the current similar. I have yet to record the upward switching.

Amp Chart
View attachment 56411
Watts Chart


These charts are from an old 140W portable panel I have mounted flat on the van roof using a EPSolar EPEver Tracer A Series 30 Amp[/QUOTE]
What controller are you using @G Daddy ?

 

[mikerezny]

What controller are you using @G Daddy ?

Hi @Bellbirdweb ,
in his previous post, he said it was a:

EPSolar EPEver Tracer A Series 30 Amp

cheers
Mike

 

[Boots in Action]

Hi @Boots in Action , [QUOTE, When recording amps into battery from controller, does this include replacing the load placed on battery at the time or is the load draw additional current just to keep voltage down so there is a lower voltage for the controller to sense to charge battery??

Most MPPT controllers act just like a 3 stage battery charger, so yes what you have said is basically correct. MPPT controllers switch to PWM mode when on float mode until the battery voltage drops below a set voltage point (on my controller this is adjustable) at which point they switch back to MPPT.
As seen in the chart above and below where at 3:40 pm the current similar. I have yet to record the upward switching.

Amp Chart
View attachment 56411
Watts Chart


These charts are from an old 140W portable panel I have mounted flat on the van roof using a EPSolar EPEver Tracer A Series 30 Amp[/QUOTE]
Hi @G Daddy , a good chart showing what is happening on a time scale. Noted that your panel achieved a peak charge of 3.5A at 20V before settling down to a steady 1.5A at 20V as battery charged up, because no load. Also obvious is the change to PWM charging as panel voltage dropped to 15V, yet battery voltage was maintained at 13.8V (float charging setting??) I too have an adjustable float voltage setting. Currently in the cooler weather, I have it set at 13.8V which should be fine for my 120Ah AGM battery. As it gets hotter, I will probably set the float voltage a little lower at say 13.6V. My unit has a remote temp sensor to monitor battery temp and adjust charging accordingly. That is why I knew the battery temp when doing test was only 11C!!
After looking at some of the videos on Utube, I saw how angle of panel towards the sun could affect output. Any idea how much your 140w panel could be capable of when sun more favorably in position?