May 10, 2010
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We get a lot of questions about how to run an Arduino off of solar panels. We decided to do a bit of testing and came up with three pretty simple ways to run an Arduino even if you aren’t near your computer or an AC plug.
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Direct to a Solar Panel – We plugged our 2.0 Watt, 6Volt panel into the Arduino’s 5.5mm x 2.1mm DC Jack via our Generator Circuit Box. On a hazy day and through a screen, it lowered the basic blink application. Of course, this will only work when there is sunlight and your application can work with extended downtime. The circuit box set has two outs so you can send power to another part of your application if needed. The panel is also available from Adafruit.
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A 5Volt Battery with a USB Port – There are a number of battery packs out there with an integrated USB port. Our 3,000mAh USB Battery connects to the Arduino via a USB A/B Cable. It is also included with many of our solar chargers. The major downside is that there is a one hour shut-off in our battery if the load is drawing less than 50mA. This is great for preserving battery life in the pack but not great if you need to run the Arduino for over an hour. You can restart the battery by pressing the Power Button.
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Solar & Battery Hybrid – We were pointed towards these Tenergy Lithium-Ion Cells (3.7V 2600mAh) and this smart battery case (puts two Li-Ion 3.7V cells in series) by office neighbors Breakfast NY. We connected three of our 10Volt panels in Parallel with our Generator circuit box (As an alternative, you could wire two of our 2.0 Watt, 6Volt panels in series to charge this configuration), connected the circuit box to the Arduino’s DC Jack, then connected the second out from the circuit box to the 2 Li-Ion cells.
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The circuit box has a blocking diode which prevents power from draining from the batteries into the panel. When the sun goes down or is obscured by clouds, the batteries will kick in and provide power to the Arduino. When the sun is up, excess power goes into the batteries for later. Both the batteries and the battery case have built-in protections against overcharge and short circuit which simplifies the amount of supporting circuitry you need to do.
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The arduino would be getting around 7.4V as the panels and the battery are in parallel. The panels drop down to 7.4 Volts when connected to the load. So in sunlight and in darkness, the output to the arduino should be *roughly* the same.
The blocking diode in the circuit box sits between both outs and the panels as we didn’t want any battery connected to the panels to drain.
We recognize that this is not the most sophisticated circuit. Our batteries have lots more going on: separate power ins and outs, overcharge protection, short circuit protection, boost circuit to deliver constant voltage, etc. Our auto-shutoff on our USB battery eliminates it as an option for longer term use, however.
How does the solar/battery hybrid option work in that configuration. It would seem there would be some sort of short. Is the arduino getting 17.4 volts (battery and solar panels) in sunlight? Or does it somehow switch between charging and powering the arduino when there is no sunlight? I realize that is what the article says, but don’t you need some sort of circuit for that? If I understand right, there is no blocking diode on the Second Out of the circuit box, only the Battery Out?
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I bought a load of solar-powered LED yard lights at Lowes last year for cheepcheep. They have a little solar cell and an AA battery in them, and some kind of charging circuit I guess. I was thinking to do something with them to make them more interesting than a yard light, it might be possible to rig up something to charge the batteries and run the Arduino for some time.
http://www.prize-pony.com/blog/renewable-energy/arduino-solio/
For short-term use, something like this is great http://www.maplin.co.uk/Module.aspx?ModuleNo=222899
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