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). http://www.altestore.com/howto/Elect...s-PV-Modu/a87/
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.