surging solar

[thirteen]

What would cause a solar panel to surge? I got an old solar panel one that was given to me and in testing it the voltage jumps from 10 -26 v. In the bright sun it is around 26 v but will not stay with even voltage it changes from 26 - 23,  when the sun has even a little cloud it drops down to 11-12 v. It is supposed to be a 24v panel. There are no cracks that i can see but there is some darker shading on the upper left hand side about 1/16 of the panel. It is pretty old almost 24 yrs. I do not have a name for it, the guy was moving and needed a tarp and I had an old one so we traded for the panel and a splitting wedge.  It might work for a 12v system or it is probably having internal problems. My other new panels will be put up in January they are for a 24v system. I have a 12v system now. Old worn out mismatched batteries but they will make a fair back up if not used very much . 13

[ChrisOlson]

What would cause a solar panel to surge? I got an old solar panel one that was given to me and in testing it the voltage jumps from 10 -26 v. In the bright sun it is around 26 v but will not stay with even voltage it changes from 26 - 23,  when the sun has even a little cloud it drops down to 11-12 v

The voltage drop in the direct sun is probably from the cells heating up.  I would guess the panel is old technology, so doesn't have the performance of newer ones.  Solar panels also degrade with time - they lose a certain percentage of their output capacity with each year, but can't remember what the performance loss numbers are.

At 24 years old, that one is probably about "used up".
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Chris

[OperaHouse]

Solar panels are basicicaly very large diodes.  Each cell if cut up up could make possibly several hundred thousand diodes. Some will be bad, basically shorts. In older panels these bad sections could be seen as they would show overheating.  So each cell is a current generator in parallel with several shorts.  In a perfect cell the voltage/power point would remain the same regardless of sunlight level.  In bad cells these shorts represent a major load that the cell can not overcome with a small drop in sunlight.  It should be remembered that the output of a panel in linear and your eye is a log function.  A relatively hard to see change in sunlight is a prety major power drop for a panel.  I have some photowatt panels that were sold as factory 2nd grade.  After 12 years of just a couple months exposure each year they are basically junk now.  Bad sections of each cell are clearly visable.

[thirteen]

I am sure it is junk for the 24v system. I am going to hook it up to my 12v system and see if it will charge them. There are old junk batteries and they will be used for a emergency backup i have a charger controler that should handle the panel. It will be worth the effort. I have another small older (7yrs) panel 45W 12v that charges them now. I can hook them up together and see. the worst I could see is the controler shut down. Besides at this time they only get 2 hrs of sunlight a day. So a little more of a boost will not hurt them. They only handle two lights and sometimes a pump for a few minutes.
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