# Running RPi on Solar Panel and battery

Hi guys, I am quite new in electronic projects and my basics are quite limited. I've been reading a lot regarding this topic (refer to the tittle) and I am currently working out to buy the suitable solar panel and battery for my project. The price is expensive, so I need to ensure I made the right choices.

1. My project We assume the battery need to power the RPi for about 15 hours (assume 5pm – 8am without sunlight in Malaysia) without having the solar panel charging the battery. This means, it will rely on the battery solely for 15 hours. the power consumption is ~5.25 W or ~1200mA (with wifi dongle,camera,and IR sensor connected at GPIO)

In brief, a proper Power Supply to the RPi must be rated at 5V regulated, 2A and that the power consumption would be around 5.25 W.

How to proceed in calculating suitable Solar Panel, regulator and Battery?

1. Running RPi from Solar Power (and battery) Example

From viewtopic.php?f=63&t=13901 “…I used a 50 watt solar panel, a 20 Ah Lithium battery, and a charge controller that was made for that particular battery. I also used a USB car charger to convert the 12 volts from the battery down to 5 volts… this setup is working perfectly. I've had several cloudy days with no issues. The Pi keeps on running! I also see the controller charging the battery (and running the Pi) when there is fairly low light, so I think the 50 watt panel was the way to go…”

But this might be an overkill?

1. Some choices

Solar Panel http://www.lelong.com.my/20-watt-solar- ... -Std-P.htm

This one gives 12V 20W

12AH, 12V

Have you asked on the RPi forums?

If you plan to run on battery for 15 hours with no input charge and if your RPi and other parts consume 1.2 Amps, then you need to be able to supply 1.2Amps for 15 hours.

You will also need to allow the the power supply, from battery volts to 5Vdc as it will also havesome self consumption. You can calculate this by knowing the efficiency of the power supply.

But if we take a guess and say you need to be able to supply 1.5 Amps for 15 hours, which equates to 22.5 Amp/hrs of energy you will take from the battery.

Next, if you choose to use an old style lead acid battery, you will only be able to take 50% of the battery energy or risk early failure of the battery.

This means you then need a battery that has at least 50 Amp/hour capacity to work for you.

If you choose to use a LiFePO4 battery, then you can safely use 80% of its energy, which means you can use a battery that has a capacity of 30 Amp/hours.

Also, you will need a solar charger to regulate the energy from the solar panel to the battery. This is a must have as you can not just connect the solar panel directly to the battery, unless you use the solar panel in a trickle charge system, which this is not.

You need to size your solar panel on the minimum solar gain you expect each day, so, you already say you will not have solar gain for 15 hours each day, leaving you with only 9 hours of possible solar gain.

I expect you will also have additional ‘dark’ time on either side of solar maximum each day, lets take a wild guess and say that will be an additional 3 hours, thus leaving you with a total of 6 hours each day that you wil lget solar input to charge your battery.

If you have only 6 hours to charge a lead acid battery with 22.5 Amps plus the losses of the battery of say another 2.5 Amps, you will need to charge a total of 25 Amps back into the battery each day to maintain a working system.

A 50 Watt solar panel will give you around 4 Amps in good sun light. If you can get 6 hoours of this, then you will only get a total of 4 x 6, which is 24 Amp/hours.

This will not be enough to maintain the battery and no goo if you get a dull day.

At a mimimum, you will need a 60 Watt solar panel, but better to have a 80 Watt panel as minimum.

My suggestion would be to look more carefully at your toatl load and see how you can reduce this.
Next I would suggest you have a battery and solar system that will give you 2 days of autonomy.
This will mean doubling the capacity of your battery and solar panel.

Paul

The RPi is a poor choice for battery operated equipment. Unless you require very sophisticated calculations and/or multitasking, try something much less power hungry, like an Arduino.

Or like I use, a Cubieboard II.

I live off renewable energy and I selected a Cubieboard for its low power requirements. Imagine running a complete GNU/Linux system, with Ethernet, USB, HDMI, SD, 4GB NAND, 1GB SRAM all from a USB port from another computer.

Modern ARM based boards take very little electrical power and can offer so much in terms of application possibilites.

Paul