Hello, I'm trying to make my arduino Uno run by solar energy, however, its not working and I think some of you may have some experience with this. There are 11 solar cells in series. 1 cell generate 0.14 Wp, 0.28 Imax, 0.5 Vmax. Adding pictures of solar panel. I'll be glad for any help.
So let's assume you have 11x0.5 = 5.5V. Where do you feed that into the Uno?
I use "external power supply" connector. I'll better show a picture. I know it's not the best way, but it's just a temporary solution, until it starts work properly. I tried to power arduino using alligator clips(like in pic.) with 9V battery and it worked. So I don't think way of connection should be problem. Or do I need higher input volatge?
Slovakia33:
Or do I need higher input volatge?
It says here that:
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable.
So yep, you need more volts.
What is the measured output of your solar cells? If it is ~6v or less you might be able to directly connect the solar cell output to the arduino +5v pin and ground just as a test.
I haven't measured it yet, because i don't have any measuring tools right now..but I will try to measure it later..if cells are working too(i'm amateur at solar energy so I'm not sure if that panel is good)..i'd rather not put it in +5v pin, because it can damage arduino, am I right?
Slovakia33:
i'd rather not put it in +5v pin, because it can damage arduino, am I right?
Says here:
Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
I have an old arduino board that the onboard regulator chip failed to regulate properly (how i know the board can withstand 8v+ for a short duration), so used an external 7805 chip directly to the board +5v pin. I think if you look at an arduino schematic you may see that the board is directly supplied +5v from the USB port.
You will have more success if you run your Uno off a rechargeable battery, and use the Solar Cells to charge the battery.
Running anything directly off Solar cells is extremely difficult, as Solar Cells behave like current sources, and most
Micros require a voltage source.
mauried:
Solar Cells behave like current sources
Can you elaborate on that please mauried? I just bought a panel to experiment with, and was wondering what its supply characteristics are under a) different ambient light and b) different loads
Solar cells have a VI curve characteristic which has a peak power point at one voltage level and one current point.
The output current from a Solar Cell is directly proportional to the sunlight intensity, but the voltage is not.
The OC (open circuit ) voltage from a solar cell will be close to its specified value , even under low light conditions, but the cell will be unable to supply any current , if its loaded.
If you try and run something directly off a Solar Cell, the output power of the cell will vary greatly over the course of the day, peaking at noon.
Most Microcontrollers need a constant voltage like 5V, and draw a fixed amount of current , so need a voltage source to feed them.
What generally happens with using a Solar Cell directly, is that if the power demand from the Microcontroller is less
than what the Solar cell is currently able to produce at a given time of the day, the Micro will work, but as soon as
the solar intensity on the cell falls to where the cell is unable to supply the current the Micro needs, the Solar cells voltage collapses.
Hence the need for the battery to act as a voltage source for when the Solar Cell is unable to provide enough power.
The normal usage is for the Solar Cell to charge the battery, and the battery acts like a voltage source to run the Micro.
Thanks for that mauried.
I'll be doing some simple testing today. Not a cloud in the sky as the airfield webcam shows (well, as I type this; storms later probably).
Hi, you regard a PV cell as a current source rather than a voltage source.
You will need a storage device.
Tom....... 
You said you don't have a voltmeter.
You really, really need one, if you are going to pursue this hobby!
Don't imagine it needs to be an all-singing WonderBeast....
...costs $15, and would serve you well for many, many needs.
And that's certainly not the cheapest suitable one out there... but, while Sparkfun DOES charge a premium for serving hobbyists, I haven't been let down by their product selection or customer service. Serving hobbyists has overheads. I don't begrudge them. (Nor do I have any connection beyond happy customer. When I want something, I often go there, if only out of laziness. If I were buying 20 meters, to set up an electronics course... I would shop harder. But for a one off, I just spend a little more for the quiet life.)
mauried:
You will have more success if you run your Uno off a rechargeable battery, and use the Solar Cells to charge the battery.
Running anything directly off Solar cells is extremely difficult, as Solar Cells behave like current sources, and most
Micros require a voltage source.
Okay, thanks. I think that your idea is better, so I'll do it that way.
Anyway, I'm still confused a bit about those solar cells. What does that white line stand for? Because on some cells it's full and on some 1/4, 2/3, 1/6 (adding picture).
And also I'm running 5 servos with this arduino. I'm powering servos with 7.2V 2700NiMh battery through pins. So won't be it better, if instead 9V I will put that 7.2V directly to "external power supply" to run both arduino and servos and recharge that battery with that solar panel?
If you only want to operate the Arduino from your solar cell and do not propose any storage options, and if the cell generates about 8V open-circuit, then in this particular case, you operate it with a shunt regulator - which is to say, you simply put a 5.1V Zener diode of about 5W rating (given that the solar cells are guaranteed not to generate more than 5W) in parallel across the solar cell and feed this directly to Vcc.
That is the simpler way of operating solar cells.
Note that you may have to calibrate the brownout threshold of the Arduino to cope with a slowly applied (and removed) supply voltage.