Firstly the same Solarex SX 10 Panel was placed in 75% Sun and its temperature
measured every 5 seconds up to1/2 a minute then every 15 seconds up to 1 minute.
Results are graphed below.
The question is how much does a panel heat up during a race?
Consider the graph, after the panel is covered the temperature continues to rise. This lag
effect is due to the time it takes for the heat to travel from the front of the cell to the back
of the panel.
At worst case condition the cells will be hotter by this temperature, so if we add this
temperature rise to the temperature we recorded at the time of interest say 20 seconds for
an average race time. We will have a fair indication of actual cell temperature at that
time.
What is the temperature rise after 20 seconds?
Probable total temperature rise = temperature rise after 20 seconds + thermal lag
temperature rise, ie. 2.5 + 2 = 4.5 Deg C.
Panel testing has shown that a temperature rise of 4.0 Deg C results in an approximate
fall in maximum power point voltage of 0.54 volts. This leaves us with the option of
setting the electronics unit about ½ a volt below the maximum power point and only
being within a few % of the maximum power point at the end of a race.