Last week I designed a solar regulator that costs 66c (US 7¢) per Watt. That compares very favourably with R175 ($17.50) for 25 Watts, on offer in the city, which is ten times the price. However, a number of things are crucial to such a design -- not least the voltage of the solar panel. The shop informed me that the panel put out "17.2 volts maximum". But as soon as the sun came out, I could feel that this was badly wrong (heat). I double-checked. The manufacturer claimed that the panel put out "17.2 volts at maximum power. 22.2 volts open circuit". That's a very big difference -- and it seemed to explain my troubles. I adjusted the circuit. But I could see that even the manufacturer was wrong, as the voltage floated up and up, well beyond 22.2 volts -- under load, never mind open circuit. OBSERVATION: I find that, in science, practice frequently diverges from theory.
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