It's a solar panel with some 200 mAh 1.2 V lipo battery, five led lamps. The logic is that it charges as long as there's enough of light. And when the light is low enough, it lights the leds as long as there's charge.
Without knowing anymore specs, could one assume that one could connect three of these to get a 3.6 V system to run some 3.3 V Arduino? One would have to make all three follow only one circuit's decision of when to charge and when to discharge.
In that case I remember wrong the lipo, but right the 1.2 V. It must have been NiMh. Let's forget about the stuffing for a moment. 1.2 V rechargeable, some 200 mAh.
Well, if I have three separate devices, each performs on its own a logic, where it charges its 1.2 V battery while there is enough light on its solar panel. When the light drops, at one point it stops charging. At an even lower point it lights the led. If I'd want to use three of these devices and connect their batteries to get 3.6 V, I still want to use their charging system, if possible. But to assure all three start to charge at the same time, they should have a common signal to tell them when to charge and when to deliver power to the leds or to whatever I want to power.
All this can be achieved with dedicated solar power charging circuits. My idea is simply to try to instead use something very cheap found on the market.
No, they might be using a cheap photoresistor to tell whether it's dark enough or not. Or some of them might even be using the solar cell as one to tell whether it's dark or not.
If you can show us a photo of the solar circuit then we can tell you how it works. They might simply be using diodes to get that effect.