If you have a commercial solar panel the label will most probably specify the power at
AM 1.5. What does this mean? (Caution: The power listed on your panel is probably only
nominal not an actual measurement.)
AM 1.5 refers to the energy and spectrum of Sunlight after it has passed through a
distance of 1.5 times the thickness of the atmosphere. (Note 1.5 times the atmospheric
thickness occurs when the angle between the vertical and the sun is 48.2 Deg.) The
actual energy striking the earths surface at AM 1.5 is 970 Watts / square metre but it is
rounded up to 1000 Watts / square metre in the standard.
For full details see: Applied Photovoltaics Second Edition by Stuart R Wenham, Martin
A Green, Muriel E Watt and Richard Corkish.
Previously (prior to 2010) solar panel power at the Victorian Model Solar Vehicle
Challenge was not measured to this standard. We used the maximum Sun power expected
here in Melbourne as the 100% Sun datum for our measurements. The light box we (and
all other states) use is fitted with quartz halogen globes, these do not have the same
spectrum as Sunlight introducing a slight error.
To better align us with international standards, the National regulations now specify
100% Sun to be AM 1.5 In Victoria and Nationally all solar panel power measurements
will be referred back to this datum.
CALCULATED SUN POWER VARIATION:
The following graph was produced as an aid to understanding. It shows the calculated
power variation in Melbourne over the course of a year.
It’s 100% is based on the power measured at midday Sun time 23 December, this is the
power previously used as the 100% Sun datum for setting the light box at the Victorian
Model Solar Vehicle competition.
NOTE: It is only calculated and assumes that power losses are linear with distance
travelled through the atmosphere, which is not strictly accurate particularly as the Sun
angle becomes large.