Let’s take a look at the solar power kit which is very interesting.
A solar panel converts light into electricity and the output of a solar panel depends on the amount of sunlight.
The solar panel provided is a 5V, 1.25W panel which means that the output voltage would be 5V when sufficient light shines on it. You could connect an LED or electronic device directly to the solar panel and it would work fine as long as it does not consume for than 1.25W and as long as there is constant light shining on the panel.
The reality is that it is not easy to get a constant source of light from the sun and that is why we use some sort of a storage element. This is the theory behind such a setup. When the sun shines on the panel, it will generate a voltage and current that will charge the storage element. This charge will then supply the load with energy if there is drop-in sunlight which causes a drop in the output of the solar panel.
The kit contains a supercapacitor which can be used as a storage element. It has a value of 1 Farad and with a maximum voltage rating of 5.5V. All the capacitors we have been using so far had a maximum value in the uF range, and 1F is 10^6 uF, that should give you an idea of how much storage a supercapacitor has.
This is what the schematic looks like. We have a screw terminal for the solar panel and another one for the load or output. The supercapacitor is directly connected in parallel with the solar panel.
The supercapacitor will start charging from 0 and as the voltage rises it will cause an increase in the current flowing through R3, which will eventually switch ON T1 & T2. The number of diodes present determine the switch ON voltage. You can also replace these with LEDs for a higher switch ON voltage. When T2 switches ON, the negative output terminal will be connected to ground switching ON the load.
When T1 switches ON, it will lower the base voltage of T3 and this will switch it ON. This injects voltage into the junction between R4 & R5 causing T1 & T2 to latch ON. As the supercapacitor starts discharging, the voltage across the rails will decrease and this will also decrease the voltage at the base of T3 and it will eventually switch OFF. T3 was responsible for latching T1 & T2 and these two transistors will also switch OFF, ultimately causing the output to switch OFF.
This way, we have control over the turn-ON and turn-OFF voltages.
Let’s assemble and test the circuit. Make sure you mount the supercapacitor with the correct polarity.
Let’s connect an LED to the output and let’s wait for the supercapacitor to charge. The turn ON and turn OFF voltages are shown on screen.
I’ve modified the circuit to power an Arduino microcontroller – a Piksey Pico in this case.
Here’s what the updated circuit looks like. You can increase the run time of the circuit by adding more supercapacitors in parallel. This way, you can drive even heavier loads like motors to create a solar-powered car or wind chime.
That’s it for this video, we will quickly recap some of the main components in the next few videos.