Raspberry Pi runs with solar power – Part 1

Some time ago I come up with the question: is it possible to run a Raspberry Pi only with solar power? This is not an easy question. It easy to compute how much power a solar panel should have to run a Pi, but you also have to consider, that there are times with little or no sunlight. For example at night. You have to do a research about possible technology and you also should known basics of electrical engineering.
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Theory

For my consideration, there are some different points that all have influence on this problem. This points are:

  • Consumption/Power of your Raspberry Pi
    A Raspberry Pi has a consumption of 3,5 Watt. You can guess it, because your Raspberry Pi needs 5 V with 700 mA. A USB plug always has 5 V, the current can be different. There are USB plugs for 500 mA up to 900 mA. The consumption is a maximum value, because it can never get more power. You can see this effect if you plug in more USB gadgets into your Pi and you will see, that there are problems. For example a mouse and a keyboard. External hard disks often does not work, because your Pi delivers too less energy. Hard disks often needs 1000 mA or more. Without consumption, a Pi may only needs 2 Watt. In some boards I read that a Raspberry Pi also runs with only 200 mA.
  • Efficiency solar panel
    If you want to use solar power, you will need to use a solar panel. Your solar panel should provide constant 5 V and 700 mA. Most commercial solar panels can do that. But you should be aware, that this numbers are only specified by manufacturers, so you do not know how they get this values. Normally this are only maximum values. So you should know, that your solar panel provides much less on average. Another problem is the night, winter and other different and changing weather conditions. Solar power is unreliable.
  • Battery
    Solar energy is not available around the clock. Normally solar power is only used to support an electrical system. For our needs, we will need an additional battery to cope with losses. Another important consideration is, that we need to charge the battery when the sunlight is available, so we need much more power for our solar panel. With all this in mind, we need a solar panel with a minimum of 100 to 130 Watt.
  • charge controller
    If you want to use your solar panel with a battery you will need a charge controller. A charge controller is important that your battery is not damaged or overloaded.

A short summery: you will need an efficient solar panel, a charge controller and a backup battery. In the next article, I will show additional information and will calculate planned costs for this project.

Part 2 | Part 3

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4 Responses

  1. raiden says:

    Is there a way to automatically Switch when there is no enough power from solar directly to “plug electricity” without battery?
    And from solar to battery and then to “plug electricity”?

  2. Dodutils says:

    You can also control “clean” power off/on schedule of your RasPi if you don’t need it to work 24/24 thru this module

    http://www.raspberrypi-spy.co.uk/2015/06/witty-pi-a-realtime-clock-and-power-management-for-your-raspberry-pi/

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