that is specced as 5.5v 100mA panel.

and i just exposed it to full sun, 5.1v open circuit, 75mA shorted. when connected to extn cord it was like 70mA.

then added one 1k pot across it, in series to a multimeter for current measurement, also connected another mm parallel to load for voltage measurement. came out the best wattage is available at the range of 3-3.5v load voltage, current being 57-44mA, while current dropped sharp from load voltage 4v - 32mA@4v, 22mA@4.25, 11mA@4.5v......

i think i need some efficient 3.3v buck regulator for this, then charge one nicd AAs with a current limit of 50-60mA.

or somekind of current limiter driver, limiting @60mA ........

 

Thanks for doing some good panel testing there, that makes it a lot easier for people to suggest a good solution.

If your goal is to charge NiCd AA size cells it looks like the panel is ideal to charge two AA cells in series; 3v at 57mA. NiCds run at 1.2v and charge at about 1.4v per cell. So your panel is great at 2.8v output (2 AAs in series).

From memory, AA NiCds are about 1200mAh capacity? So you don't really need any circuitry. The panel max current will be about 60mA into the cells which is 20 times less than their C rating.

That's about ideal for a trickle charge, and with the panel only providing peak power for maybe 4 hours a day it's not likely to overcharge the NiCds, it will take a few days to full charge them.

 

So you don't really need any circuitry

If the panel doesn't already have one, you will need a series diode to prevent the NiCds discharging into the panel when the panel voltage drops.

 

Most commercial small solar appliances don't use the protect diodes. They use low voltage panels and batteries, and because the battery voltage is low the reverse leakage even in total darkenss is only a few uA.

In this case with two NiCds the battery will be max about 2.4v so the leakage into a 5.5v rated panel will be close to zero.

The reverse diodes are more critical where there are higher voltages at the battery; in 12v and especially 24v systems.

 

thats quite simple solution, even though a bit slow. thanks for suggesting.

harvesting natural energy seems expensive, but sooner or later i m gonna try out some 5-10w panels.