Custom charger with solar cell

Question

I want to make kind of autonomous power supply for my RPi.

So that I am planning to use 12V solar cell and batteries for this project.

Also I will use Arduino to controll all of this stuff - to monitor the voltage both of solar cell and battery and to switch power destribution.

I suggest 3 working states:

1. Battery low - solar cell charges battery and powers up RPi
2. Battery full - solar cell powers up RPi only
3. Solar cell low - battery powers up RPi

This is the exemplary scheme

The idea is to measure voltage both of solar cell and the battery and implement simple logics to switch power destribution unit and to charge battery if it is low.

Btw I don't want to use any power bank because there is no built in interface for reading remaining charge.

It would be great if you recommend me solar cell and battery setup/assembly for this purpose and correct my scheme.

This is the preliminary list of items:

1. 5V regulator
2. switch
3. batteries
4. solar cell
5. battery charger module

Any advice will be appreciated, thanks!

Answer 1

With only a voltage regulator on the the output of the solar cell, the efficiency will be low. Use an MPPT tracker module before the voltage regulator to mach the solar panel output with the load. The MPPT tracker is not essential but will allow you to use power from the solar cell in a wider variety of lighting conditions, and at higher deficiencies.

In the place of SW2 you could use a double diode configuration to automatically use either supply (or a mosfet solution which is more efficient) : OR-ing power supplies (diode or mosfet)