I don’t have the circuit diagramed out, I just built it on a breadboard using what I had on hand already. I dug out the breadboard to at least give you what info I can.

It is an old project so I pulled some of the passive components for use elsewhere. But I can at least give some guidance.

I mis-spoke on the capacitance. I used two 4F supercapacitors in parallel, chosen based solely on voltage and economy for small purchase quantities.

I used a dual voltage comparator LM393 to detect full charge and the cutoff voltage and NPN switching transistor 2N222a to turn things off and on.

I used trimpots to set and tweak the on and off threshold voltages.

I didn’t bother with any output voltage conditioning because the application was to run a small air pump to aerate a tiny aquarium intermittently. The air pumps operate on a wide voltage range (4-6v are fine) so I opted for simplicity and lower losses. It ran for five months without a hitch, as I recall. The pump drew about 500ma steady state.

The research that I am really interested in is into biodegradable polymers for super capacitors. One of the main problems with batteries is the need for exotic materials that are expensive and harder to recycle when they inevitably wear out. There are so many applications that can be powered intermittently and eliminating batteries when possible can lower cost and circuit part count significantly.

Hope that helps.

I developed a simple circuit using 1 Farad supercapacitors and a power management IC, no battery. It buffers a 5v solar panel and provides smoother power when the aun is up. It even trickle charges the supercapacitors from just a bright security light outside the window at night.

The effect is that the capacitors store the trickle until they are full, then deliver a burst of steady full power, enough to power a node for 30 minites when busy. So with this circuit, a node cleverly placed near an outdoor light would operate continuously in daylight and intermittently at night with some artificial light nearby.