Wednesday, July 15, 2009

Unit Idea... PowerPeak-Lifetime25 (or somesuch).

A Solar Cell performance degrades over time. The effective lifetime of Solar Panels are right now considered to be in the area of 25 years.

The rate at which a collection of cells degrades, on average, over the lifetime may not be a nice line.

I can only guess what the curve looks like for a standard Silicon, Wafer-based, Cell but I imagine that it's close to linear. If you have good data, I'd love to see it.

On the other hand, particularly when future cells have their efficiency enhanced by things like coatings, the curve could get alot more complicated. You might have a Silicon Solar Cell that will degrade linearly over 25 years, but the cell might be coated with a product that will increase its initial efficiency by a very significant amount, but which might degrade in effect completely after only 15 years.

Depending on the cost to add the coating, etc, it might very well be financially advantageous to buy this panel with a rapidly degrading initial phase, and a slowly degrading long term component.

The way I see it is that if, for example, a 100W panel were to degrade at 1% per year over its 25 year rated lifetime, then the effective Peak Power is really 87.5W. That's the effective peak power over the panel's lifetime, of PowerPeak-Lifetime25.

In the same way, if you had a panel of the same surface area area that was 160W, but it degraded at 2% per year for 15 years, and then 1% after that till 25 years, it would have an effective PowerPeak-Lifetime25 of 140W.

This would allow the customer to know what they're really buying over 25 years, even if it would take some estimations and tricky modeling on the part of manufacturers. They'd have to try to figure out with great care exactly what the FUTURE degradation curve of their product is going to look like. No worries, they'll appreciate the challenge. :)

In any case, if you're not reflecting rates of lifetime degradation in the cost per Watt, then there is trouble on the horizon for everyone involved.

EDIT: I suppose I spoke prematurely. I assumed that there wasn't a standard name for this. There must be. I ask then, what is it?

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