Originally Posted by bigskypc50
If thatís the case solar numbers and ratings are a jokeÖ. But ya thatís spot on, 60% of 720.
Solar Panel "STC" ratings, don't often reflect real world results, especially on vehicles, but they aren't entirely' a joke, they are just misunderstood by many, and misleading to the uninitiated.
The "STC" rating (which is the Watt rating they advertise), is a test done under standardized test conditions, to make comparing between panels somewhat of an apples to apples comparison, this rating can be thought of roughly as an ideal
rating that you might see occasionally, but should not count on.
Things that affect the efficiency of your panels:
1. Heat, the hotter the panel, the lower the efficiency
2. Angle, the most efficient panels are angled directly at the sun
3. Air Gap, (this comes back to heat, without an air gap panels can get really really hot
4. Shade, (this one is obvious, but even a small bit of shade can have a devastating effect)
5. Dust/Dirt on the panels, or Dust/particulate in the atmosphere
6. Undersized wiring, an undersized controller, poor connections, an undersized lead acid battery bank, or basically anything else that adds resistance.
8. Probably a bunch more things that I am forgetting
Long story short, STC rating is not representative of what you will see day to day, but is a useful metric, there are other (less used) metrics which try to estimate 'real world' but there are so many variables that these will be closer to realistic but still a rough estimate, since conditions vary by location/region/conditions/system. Its a complicated and involved process to estimate real world solar yield for a given system/location.
I believe STC test conditions are panel temp of 25*C (77*F), directly angled at the "sun" with an intensity of 1000W per m^2, and proper airgap (or maybe no backing).
Probably there could be more representative test conditions (for instance the 25*C panel temp is pretty unrealistic in the real world)