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A little race

A project log for MPPT for low voltage solar harvesting

Microcontrollers + caps = MPPT in the time domain?

Simon MerrettSimon Merrett 09/18/2019 at 23:140 Comments

I took the lash-up in the previous log and raced it against a plain "connect your supercapacitor to your solar panel here" arrangement. I thought a fair and useful course to run would be to charge the supercapacitor from 2V to 3V, as this is usable for many microcontrollers, sensors and some colours of LED. There's not much point in testing lower voltages because hopefully in-use once the supercapacitor drops below 2V we've probably stopped being able to draw current from it (remember we're going to have to use a Schottky most likely so there will be an extra voltage drop at the microcontroller VCC pin).

Scores:

SetupTime (m:ss)
Pulsed (not true MPPT)5:48
Straight-connection6:01

So I wouldn't call this a straight-up victory, especially as I can't be sure I put the same illumination (distance between lamp and panel) on each time. However, even if they are roughly the same performance, I think there may be some scenarios where the pulsing could be more efficient. You also get a microcontroller running at 1MHz for free in the pulsed setup. Finally, this has got me thinking about a charge pump to maintain the reservoir caps (perhaps 3 or four in series) at a higher voltage.

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