Solar panel degradation over 25 years?

celerity

Could someone knowledgable about panels and inverters please take a look at this link :
http://gizmodo.com/5514060/60-year-old-solar-panel-still-works

and see if this comment at the bottom of the page has a point? :

You are misinformed. In fact, solar cell output generally has lowered enough in two to three decades that they don't drive the electronics well enough to be useful, and need to be replaced. Most installations require the array output voltage to be above the battery voltage by enough that diode forward drops and IR drops still result in charge current. The problem with putting a switcher between the cell output and the charge system (to ensure constant voltage) is that (1), it's expensive, (2) reduces reliability due to more high energy components, (3) output power drops no matter what, because to pump up the output voltage, the switcher will draw more current from the cells (4) large arrays take multiple switchers.
About your 80% guarantee: BP is telling you the honest truth. Now go look at your charge electronics, and see what the minimum operating voltage is. If your stacked panels were putting out (just for example) 28 volts new, then at 80%, they're down to 22.4 volts. Will your system still charge batteries at that level? Will your inverters still work, or work efficiently, presuming they can work directly off the cells, as opposed to being limited to just the cells? And this is generally the case. If not, then the cell's usefulness is over.

I always assumed that if my panels degrade to 80% efficiency then all that would mean is that whereas today I may get 1000W for a given light level, in 25 years the same conditions would only produce 800W. If I am mistaken about this I'd like to know!



Thanks,


/\dam

Martyn1981

Celerity, I think you may want a response from an off-grider, who will have better knowledge than me about maintaining the right charging voltage for batteries.

Edit: Didn't make myself very clear there, I think the respondent is obsessing about PV charging batteries and maybe missing the point that the OP with BP panels, is presumably on-grid.

However, as you suspect, for on-grid, the inverter is outputting useable AC matched to the grid voltage (at any given time), so a 20% drop in efficiency, would simply mean a 20% drop in generation. No probs, well no probs since we expect it to happen, nicer if it didn't of course.

The only possible issue I can think of, and again, here we'd both benefit from the input of an electrician / installer, would be if the panel performance dropped off enough that the sum of the panels DC voltage was unable to meet the minimum required by the inverter. I'm only assuming here, but presumably when selecting an inverter, such issues are taken into account. Maybe you could even solve the problem 20 years down the line by adding another panel or 2, or replacing the inverter when it dies, with a slightly smaller and more efficient model?

Now, over to the experts!

Mart.