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On Tue, 13 Apr 2004 09:18:00 +0300, Paul Keinanen
wrote: The solar cell operates as a (badly) regulated power supply with current limiting. At low load currents, the cell operates nearly as a constant voltage source, but after a specific current (for a given illumination) it operates nearly as a constant current source and deliver approximately that current even into a short circuit. The largest power from the cell (for a specific illumination) is obtained at the point it switches from constant voltage to constant current mode, in which both the voltage is quite close (within 30 %) of both the maximum voltage (as measured at open circuit) and maximum current (as measured at short circuit). This maximum power point varies with illumination, but if the switcher always loads the cell at this maximum power point, the largest available energy at a specific time is extracted from the cell independent of illumination. Even if the losses in the maximum power point tracker is 10-20 %, usually more energy can be obtained than running the module in some non-optimal constant voltage or constant current mode. Paul I have seen elegant ckts where a simple switcher was used, regulating the *input* voltage coming from the solar cell, keeping it in max efficiency mode at all loads. This obviously only works with flexible loads such as slow chargers or such. -- - René |
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