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APPENDIX A: PERFORMANCE OF MOTOR AND PANEL

The following information relates to the performance of a solar panel when connected to an electric motor. Its main purpose is to assist in explaining the importance of selecting the correct gear ratio to suit the prevailing light conditions.

NOTE: The explanation is somewhat simplistic so the basic ideas can be understood more easily. See appropriate Texts for complete and accurate descriptions. * PANEL PERFORMANCE (SILICON CELLS) The solar panel produces electricity from the energy in the light which falls on it. The current it produces varies directly with the intensity of the light which falls on it.

Low light levels give low current and high light levels give high current. At a given light level, the panel behaves like a constant current source. At a particular light level, the panel can deliver current UP TO the maximum current available at that light level. 33 Assume a high resistance electrical load on the panel, the current drawn will be low (Ohms law applies V = R x I ). If the load resistance is lowered more current will flow through the load.

If the resistance is lowered to a value that would allow more current flow than the panel can provide at that light level, the panel provides its maximum current and the voltage at the panel output drops very rapidly. Because the voltage is reduced, so too is the power reduced in the load (i.e. the car motor). In the extreme, if you place an ammeter directly across the panels output you will read current but the voltage will have fallen to near zero.

This means the POWER output from the panel is near ZERO. (Power = Volts multiplied by amps) The onset of this voltage drop occurs suddenly with practically no warning, the voltage dropping to near zero almost instantly. In this discussion, we will call this situation “Panel Stall”

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