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russ_watters is offline
Feb14-10, 11:54 PM
P: 22,001
Quote Quote by OmCheeto View Post
I'm very interested in your system voltage vs. temperature. I learned yesterday that most solar panel manufacturer's under-rate their panels, knowing that they have a certain degradation over time....
That's not quite right. Manufacturers rate their panels according to a set 3rd party standard. Like any other device, mechanical or electrical, performance will vary based on test conditions, so *someone* has to decide on a standard set of conditions unless the industry is to be a free-for-all. The rating point is then based on a set of conditions near the top of what is likely to be seen, but there is no such thing as perfect conditions, so there is no real set maximum.

Here's an article about the Standard Test Conditions for rating panels (on which, Artman's panel's 220W nominal rating is based).
1.Irradiance (sunlight intensity or power), in Watts per square meter falling on a flat surface. The measurement standard is 1 kW per sq. m. (1,000 Watts/m2)
2.Air Mass refers to “thickness” and clarity of the air through which the sunlight passes to reach the modules (sun angle affects this value). The standard is 1.5.
3.Cell temperature , which will differ from ambient air temperature. STC defines cell testing temperature as 25 degrees C.

Because of #2, #1 seems to me that it should be the irradiance at the top of the atmosphere. The real value varies from 1.321-1.412 kW/sq m, so I would think if you mounted one of these on the top of Mt Everest, it would put out a good 285W. I'm not really sure of what #2 means in terms of real-world conditions, though.

#3 is significantly cooler than what you'll actually get in summer, so that one works against you.

....speaking of which, does anyone make a combo solar water heater and power panel? I'd think that you could collect nearly as much heat as with a regular solar water heater while also significantly improving the electrical output of the panel.