just saving money. It reduces the consumption of other energy while it operates. What we don't hear is how much energy went into its development and production. For it to be an overall savings, it must last long enough to produce more energy than it took to make and install it. I don't think there are or could be any accurate figures regarding this. Sometimes, however, the endeavor to save leads to new products and technology spin offs that do benefit or help us to improve what we'd originally intended.
I know I'm not answering your question. As for electrical output with age, I think we're just about to learn more about that over time. It may be that some cells will fail ahead of others...or be damaged. Perhaps if enough cells fail it will necessitate replacement of entire panels even if most are working.
As for the affect on your wallet, my personal guess is that it's unrealistic to think that reducing energy consumption will make it get heavier in the long run.
Three years ago I did some research into photovoltaic panels for my house. Cost per voltage output was prohibitive and only by factoring tax rebates did there seem to be a financial gain. Bottom line I did not do it.
Today in the local newspaper I read about a state building that was fitted with custom photovoltaic panels. After working through some factoring based on figures from the article, the electric output from the panels will cost 1.7 times more money than just purchasing the power from the electric company.
At first I just thought this was a case of feel good politics, but then I thought if the electric rate triples in the next few years these photovoltaic panels would turn out to be a good deal. This is based on the idea of being able to sell the power back to the electric company. If you shoot for electrical independence, the cost of rechargeable batteries makes the project prohibitive again.
The unresolved problem areas seem to me to be. How long would the photovoltaic panels be good for, when would replacement/repair be needed? Does the panel produce at the same rate over its life, or drop off? As the homeowner, do I need/can I get insurance for the panels from storm damage?
I?m interested in real world experience, so if anyone out there has taken the plunge please respond. I have looked at the site http://en.wikipedia.org/wiki/Photovoltaics but can't make sense of it.