Riddle Me This

[friedorian]

What governs a solar panel's current flow output besides load? for example my panel is rated to put out 5 amps. Never have I seen it reach that peak with loads. Max I have seen with loads are 3a (seems like its struggling) I have tried completely dead batteries, full batteries both with and without controller, even plugged my necked sister (for tanning purposes. . not really but . . . . ) The only times I've seen the amp meter reach 5amps while connected in full sun is when a battery charger was doing its job. Open circuit full sun the panel puts out something close to 3.8 There is some damage as the glass is spidered but not too many shadows. I need to know for factoid reasons. (cuz this @#$* is bugging mah)

Panel stats: 180w @5.4a /72 cell
open circuit output: 37-40v @ 3.8a Load output: 14.4v @ 2 - 2.8a max amp)

So my questions are:

1) WHAT DETERMINES CURRENT FLOW/OUTPUT IN FULL SUN BESIDES LOAD RESISTANCE. (shade, ambient light, amount of light, and my sister have already been considered)

2) Can there be a shortage, broken cell or broken connection causing the short fall in amps? (one cell heats up much hotter (cant touch it) than area cells. Direct sun beam va mirror on this and surrounding cells makes the current increase .8 - 1.2 amp. Direct pressure on this cell will cause complete loss of current)

3) With out direct sun light, how many amps can one expect a panel to put out (ex: 5 amp mono in average day light no sun) What % of rated amps can I expect?

Thanks all. The correct responder will win the satisfaction of helping a person live happily-ever-after (fixing this @#$%& problem ) Making this world a better place . . one solar panel owner at a time

[Sunking]

Panel stats: 180w @5.4a /72 cell
open circuit output: 37-40v @ 3.8a Load output: 14.4v @ 2 - 2.8a max amp)

Ok here is one problem, your stats are wrong. Panels have two current ratings to be concerned with:
1. Imp = current at maximum power.
2. Isc = current at short circuit.

Isc will always be greater than Imp. So you have a huge and error in the stats you posted. You quoted 180 watts @ 5.4 amps. Sounds like you transposed Isc with Imp. I suspect your Imp which is what you would be looking for is 3.8 amps, and 5.4 amps is Isc which is a test condition. Now post these values

Voc
Vmp
Isc
Imp

[friedorian]

Ok here is one problem, your stats are wrong. Panels have two current ratings to be concerned with:
1. Imp = current at maximum power.
2. Isc = current at short circuit.

Isc will always be greater than Imp. So you have a huge and error in the stats you posted. You quoted 180 watts @ 5.4 amps. Sounds like you transposed Isc with Imp. I suspect your Imp which is what you would be looking for is 3.8 amps, and 5.4 amps is Isc which is a test condition. Now post these values

Voc
Vmp
Isc
Imp

Thanks for the correction. The 3.8 is actual current readings I get when testing open in full sun. Isc=4.9 and Imp=5.4. The focus of the question is to determine IF and WHERE my short fall is and to get a start point of Isc. Understanding real world situations like shade, dimness, clouds, shadows from broken glass, time of day and yes my sisters tanning, Im looking for information to better my understanding in fixing this problem to get more amps or a better current. Rite now in an ideal day (temp and sun) all I can get is 2.6a regardless of battery condition both low or high. As stated, if I put a mirror reflected sun on that cell which heats up the most, the amps jump up .80 - 1.3a

Im feeling this panel can put out much more. My goal is to get somewhere in the range of 3-3.5a or better of constant current in mild to full sun. Im willing to do surgery on this but want to make sure before cutting it up. I need to find where the current is shorting if that is the case. Not sure if this IS a shortage or just standard output.

[Sunking]

Thanks for the correction. The 3.8 is actual current readings I get when testing open in full sun. Isc=4.9 and Imp=5.4.

You still have the specs wrong.

There can be no current in a open circuit test, only voltage which is Voc spec. Imp cannot be greater than Isc.Try again. What are the panel specification values of:

1. Voc = Voltage open circuit
2. Vmp = Voltage at maximum power
3. Isc = Current short circuit
4. Imp = Current maximum power
5. Pm = Power maximum @ STC

Better yet solar panel manufacture and model number.

Now to get to the heart of your question.

• I suspect you have a off-grid battery system?
• Is that correct?
• If so what charge controller type are you using? MPPT or PWM?

[friedorian]

You still have the specs wrong.

There can be no current in a open circuit test, only voltage which is Voc spec. Imp cannot be greater than Isc.Try again. What are the panel specification values of:

1. Voc = Voltage open circuit
2. Vmp = Voltage at maximum power
3. Isc = Current short circuit
4. Imp = Current maximum power
5. Pm = Power maximum @ STC

Better yet solar panel manufacture and model number.

Now to get to the heart of your question.

• I suspect you have a off-grid battery system?
• Is that correct?
• If so what charge controller type are you using? MPPT or PWM?

Sunking, although I DO appreciate your reply, the corrections and the banter, it is somewhat annoying that its obvious my Isc and Imp are reversed. Yes this is an off grid battery system set up to charge my RV batteries. Im using a PWM, but have tested with out. I do get a amp reading from the line off the panel when on load and no load.

Skipping past the basic of what when where and how, the nature of my problems has been clearly stated, but ANY answer to the specific questions has yet to be given. Did I not provide enough detailed information for a technical reply?

[Sunking]

Ok answer is simple you have a battery system with a PWM charge controller. Batteries are like a glass of water sitting out in the dessert or a sponge, they can only hold so much water. Anything else is wasted.

When a battery is discharge significantly it will draw every bit of current the source can deliver. Once it gets somewhat charged up the charge current tapers off to ZERO and current stops flowing.

With a PWM CC you have the most inefficient system money can buy, and like a glass of water in the dessert you loose most of you water to the sand from dumping, or overfilling before the valve shuts off.

Think of it like a toilet valve. When you flush and empty the tank, the valve opens up fully. As the tank fills, the valve starts to close, the water flow reduces gradually until it stops.

So what I am telling you is it is normal. Discharge your battery to 50% DOD and wait until a bright sunny day and you will see the max the system can produce. In other words you are not using what the system is capable of generating which is exactly what a battery system should be designed around. A battery system cannot tolerate a deficit, they must operate in surplus mode or they die.

Lastly a solar panel will never deliver the specified voltages and current. What is specified are labortory conditions which you will never experience unless you live on a mountain, on the Equator, 0% humidity. 0 degrees, clear skies on March 21 or Sept 21. Otherwise only about 80 to 90% at the terminals. On a battery system around 50%. So your system is working fine.

[john p]

Fredorian look at this example..
You reed a new car specs it says top speed 120mph .. ok? but that is with one person on board windows closed no air con.. now put 5 people in it air con on and go up a long steep hill , ok? top speed mabe 90mph..
Another if you want to fill a bucket up to a certain mark on the side of the bucket at first you open tap wide let in large amount then as you get near the mark you close the tap down to very small amount so you dont over fll it.. All very similar to what Sunking has told you..

[friedorian]

John and Sink thank you very much. Love the 5 people thing. Reminds me of high school buddies and nights out driving around. Understood on both. I still think i have a shortage in that cell (area) that get very hot, almost untouchable. Rest of the panel gets a normal heat but this cell is like oven hot by itself. A small mirrored reflected sun beam or some (not much) pressure from the back on that cell ( if you can touch it) makes the current jump up .8 - 1.2amps. Pressure from the front side same spot causes the amps to cut completely off or down to .2 - .50 max. left alone and amps don't reach higher than 2.8 regardless the amount of sun or demand from loads either completely dead battery all the way to full. The current range should adjust itself to fit a demand up to its limits which in reality should be UP TO 4.9 in direct sun light. (water analogy, and PWM concepts) (Ive had some really good sunny cloudless days here) So on one of them days I put some pressure on that super hot cell area and the amps shot up to 3.7 . let it back to rest and amps crept down to 2.4? short in the cell? I've inspected the cell and dont see any physical damage or breaks. Im wondering if it is broken or damaged connections on the backside. This is the main reason for my questions and why i need to know some figures on current. What do you think? I can bypass this cell and jump it with wire (surgery) but my problem is its on the end row next to the junction box so im not sure if this cell wires directly to one of the four thick tabs surfacing from the box. The box does not get hot, just this cell area two cells away on the edge row. Its a 72 cell panel 12 length X 6 rows. This heat problem cell is position 1 on both row 1+2 same edge as junction box and what seams like my end connection to the box or over the thick tabs that run to the box - BTW this cell area only gets super hot under loads. . . when no load cell stays same temp as rest in full sun.

[Mike90250]

If you have a panel changeing amps, by pressure front or back, you have a BAD INTERNAL connection. get it replaced under warranty. As you note, it gets hot. Eventually, the cell and plastic will discolor, or if really bad, melt. This is where homemade wood and plastic panels catch fire.

[friedorian]

If you have a panel changeing amps, by pressure front or back, you have a BAD INTERNAL connection. get it replaced under warranty. As you note, it gets hot. Eventually, the cell and plastic will discolor, or if really bad, melt. This is where homemade wood and plastic panels catch fire.

Thanks again MIke. This is why I needed to know what governs current blah blah. Im fuguring by jumping this cell i can get full current back. Im wondering if a cracked cell will produce less current flow??

[Mike90250]

could be a cracked cell, loose metal contact strip, cracked metal contact strip. Even a shorted bypass diode. If you dig into the panel, you void any warranty and break the hermetic seal. But, yes, if you can locate the exact bad cell, and jumper around it, you will get full amps back, at the loss of 0.5V (the voltage contribution of each cell)

[friedorian]

could be a cracked cell, loose metal contact strip, cracked metal contact strip. Even a shorted bypass diode. If you dig into the panel, you void any warranty and break the hermetic seal. But, yes, if you can locate the exact bad cell, and jumper around it, you will get full amps back, at the loss of 0.5V (the voltage contribution of each cell)

Well that's exactly what i did. I jumped the bad cell and boom the current went up. I don't have a warranty so not worried about that. The panel was broken when I bought it dirt cheep brand newish. . fell off a truck during delivery. . . so I patched it up and she puts out. Best readings one day while open 40v @ 4.3a. I just seem to loose current when a load is on her . . I may have more broken connections somewhere making the current lower.

Just want to tweak it to get max amp. A small project to learn from. Waiting till full sun to see improvement. Thank you for your imput and wisdom

[friedorian]

I fixed it

OK all, I just fixed my problems with this panel. She is putting out 90% + now. Current shot up to 3.8+ (day is cloudy) but have seen 4.3a out of her. She is averaging about 3.8 constant. (still cloudy) Yeah! ! ! What I did was jump the broken cells. I drilled through glass, cut connection from the 8 damaged cells, and wired over them continuing the connection. Now she cranks the amps. In the process I only loose 4v which is not an issue considering its WAS 180w to start. . . now its a 160w. . still cooking for what I need.