I^2 R) Not only that but the maximum power voltage is not around the expected 11.5 volts
but is several volts lower.
Let’s see what happens when the light level falls below 100%? At 50% the current will
drop to 0.5 amps and the power from our panel will drop to 3.25 watts. No it won’t!!! In
a perfect world the power from the unmodified panel would drop to 50% or 5.25 watts
but the power lost in the extra series resistor is not halved. The power in the resistor
equals the resistance times the SQUARE of the current so the loss is now 0.5 x 0.5 x 4 or
only 1 watt not 2 watts, meaning the resulting power output is 4.25 watts, a gain of 1 watt
or 31% over a ‘standard’ panel. And it only gets worse at lower light levels.
At 25% the expected power would be 6.5/4 or 1.625 watts. However, our modified panel
delivers 10.5/4 – 0.25 x 0.25 x 4 = 2.625 – 0.25 = 2.375 watts!!!! This is a theoretical
gain of 46% and you can see that this can be a huge advantage. In fact, at all light levels
below 100%, which is most of the time, a car equipped with such a panel will have a
significant advantage over other cars.
At very low light levels it performs like a 10.5 watt panel but only carries the weight of a
6.5 watt panel. You don’t need to be Einstein to work out which car will go better in low
light.
Because of this performance anomaly and the ease with which the fill factor of a solar
panel can be modified simply by inserting series resistance, the regulations have been
changed.
If you think that you know it all after reading the above think again!
The above article concentrated on the effect of series resistance we must not forget
parallel resistance. Please continue and read the following to obtain an overview of panel
performance including the effect of low parallel resistance.
SOLAR PANEL SELECTION
The Solar Panel you fit to your car can have a very significant effect on performance. In
fact it could easily mean the difference between winning and losing.
Let me explain. I am not thinking about the power output of the panel as all the modeling
done indicates that with the ballasting formulas now in use there is virtually no
performance difference between a low wattage and high wattage panel as long as they are
fitted to a “GOOD” car.
I am referring the characteristics of the panel. To understand this, consider the ballasting
formula prior to 2011. Ballast was calculated based on the panel power measured at ½
Sun and doubled. This means that any panel with a low Fill Factor FF (or if you prefer
Form Factor as used in some texts), due primarily to high series resistance will end up
carrying ballast weight for which there is no actual power available from the panel.