I need help powering a raspberry pi by a solar panel

I want to power my raspberry pi model 1B(not plus) with a solar panel I have. I know that there is a built in voltage regulator so what is the voltage range I can put in? I know 5 volts works but what about 3.5 or 10? Also how many amps will I need? I've heard from 1/2 an amp to 1 amp. Will I need an external rechargeable battery or external voltage regulator? And what size solar panel will I need?

• Given the information you have provided it is impossible to tell if you need an external battery, voltage regulator, or the size of the solar panel you need.
– joan
Aug 17 '15 at 14:36

Well, feeding the Pi directly from a solar panel won't work since the current from a panel (and by extension the voltage) varies wildly, depending on the light conditions.

At a minimum you need a battery, a solar charger, a 5 volt regulator and some voltage monitoring so you can safely shut down the Pi when the voltage of the battery drops below a minimum.

A possible setup would be a solar panel that can charge a 12 volt battery, a small 12 volt 'gel' battery, a suitable solar charger, a 12-to-5 volt regulator (use a switching power type, not a simple downregulator like a 7805). That should power your Pi. The Pi itself needs about an Amp at full power. A small 1.2 Ah gel battery would last about an hour then.

The next problem is a voltage monitor so the Pi can shut itself down cleanly if the battery voltage gets too low (i.e. at night and cloudy days). A simple resistor network connected to a analog input of the PI could do that. However, the next problem is starting up the Pi again when the battery is charged again. You need an external circuit that monitors the battery voltage, and either pulses the reset pin on the Pi or turns on the power (assuming the shutdown circuit turned it off). Something with an opamp and zener diode comes to mind...

You can feed the remaining electronics either directly from the 12 volt battery or 5 volt power supply. It would make sense to also add a circuit that powers down the peripherals when the Pi powers down and vice versa.

• the pi does not have any analog pins. Aug 18 '15 at 1:02

If we assume your solar panels won't be providing enough current all the time(when there's not enough sun) you need a rechargeable battery.

If your rechargeable battery outputs a voltage out of the voltage range 4.75V-5.25V then you'll need to make some voltage regulation for sure.

As joan said you'll need amps enough to cover consumption which depends on what you are planning with Pi. If you lack power then Pi will malfunction and you won't want it.

The Pi is meant to be powered from the microUSB socket. That was chosen in part to ensure only a safe voltage would be fed into the Pi. The Pi expects 5V +/- 0.25V, i.e. between 4.75V and 5.25V.

Only you know what you will be powering so you will have to work out how many amps you need.

The Pi usually takes a little less or more than 5V (give or take 0.25V). 1000 mA works but it can need as much as 2000 mA depending on the peripherals connected to it.