Panels and power loss during slight amount of shade

panels loose output from shade lines, depending on how the cells are wired/oriented.

And go buy yourself a lottery ticket, old HF panels still working = lucky man

That was my assumption being the way the panels are wired internally and lucky maybe or possibly these old panels were just a good quality. They were expensive, even purchased on sale I paid 390.00 plus tax for a 135w total combing 9 15w panels. At the time we had power outtage issues often and being self employed I needed to be able to run a few lights, drill, grinder ect. while the power was out. Now that much of the surrounding farm land has what looks like million dollar homes everywhere we rarely have grid failure but still do ocassionally. What do I look for when I search for well performing panels? I could easily go to 24v but would have to replace my inverters.

Maybe I should rephrase my Question. I do understand that all panels will loose a certain amount of output when a small amount of shade crosses them but what do I look for to get the least amount of loss in a panel before I purchase more panels?

icy cold, bright, windy winter days

IMHO, only NASA engineers need to worry if a panel fades 1% or 1.2% from heat. The difference might matter for a mountain top radio repeater.

As Mike wrote, panels are separated into subpanels and wired together with bypass diodes. For best shade output, you want a panel that is separated into as many subpanels as possible. Common panels are divided into 3 subpanels. Half-cut panels are divided into 6 subpanels. I think that's where terms like "duo" in the model name come from. Another tipoff that a panel is half-cut is that the junction box is centered on the panel, rather than on one end. A large panel supplier like AltE or Renvu will be able to tell you which of their panels are half-cut.

Thank you very much bob-n, I knew there was a reason for the my issue. Now I know what to look for and believe or not you really brightened my day this morning. I asked the same question on here 2 years ago and no one could help.
And I've known all along about heat and power loss. Several years ago I bought some panels and pulling them out of the boxes I saw the black border trim and just put them back in the boxes thinking how ignorant can a manufacturer be.

Two different technologies with different reactions:

1) The Harbor Freight panels are "film" panels. Notice that they don't have any silver grid traces across any of it.
2) Mono or polycrystalline cells are different and original tech. Notice the grid wires across each cell.

Film: Shading such as a branch or cable, or even wet-leaf across a film panel only puts the shaded part out of commision - the rest still works. Technically, the shaded portion is reverse-biased, but the part of the film panel that is exposed to direct light is able to pass current past the shaded parts easily.

Mono/Polycrystalline:
Shading just one of these cells put the cell into reverse-bias. Since it is wired in series with the rest of the other cells, it can totally inhibit the current coming from the exposed cells. In most cases, current *will* pass through it, but not fully, and but being reverse biased that shaded cell gets hot.

What most modern panels do is actually wire the panel into two "halves" or in effect electrically two-panels in parallel separated by blocking diodes inside the junction box.

So, now, when a shadow, wet-leaf etc puts a cell into shadow, only half the panel current will try to pass through the reverse-biased shaded cell, so the cell lives longer in that reverse-bias condition.

It's a very wordy way to say that mono/poly panels should not be shaded at all, whereas film-type panels can handle that condition better. Ie, a mono/poly panel with slight shading can result in severely degraded current until the shadow passes.

Note that I have not gone into any sort of film vs mono panels for longevity, build quality etc. But if you are not going to babysit or do a site-survey of shadowing, especially in long-shadow winter conditions, then a film panel might be your best bet. Would I put film panels as a long term solution on my house? Not currently as film panels degrade faster than mono/poly panels.

For me, film is camping / hobbiest stuff - and can do very well. Permanent 20 year installations? Mono/Poly currently.

All of this can be proven easily by the hobbiest by merely placing a piece of cardboard over a mono panel and a film panel, and taking measurements.

Moral: try not to shadow *either* of these different tech panels.