Powering by Solar Panel Help - New to this

Hi,

I’m very new to Arduino and this is my first project. I’m sure I’m missing something basic and hoping someone can shed some light on this.

I have an Arduino Leonardo and plugged in to it is a micro servo and a PIR. (See picture attached). When plugged in to the wall or computer via USB all works great.

I picked up a small solar panel from my local microcenter and thought I could power this with the panel plugged in to the barrel port on the arduino.

It’s the SC10072 http://osepp.com/products/solar-cells-arduino-compatible/ which says it is 7.2V and 100mA

If I get a decent source of light my voltmeter does show a voltage above 7V. When I plug it in and get to a nice light source the little green led on the arduino board turns on, though no other lights turn on and nothing else happens.

Is this just not enough V or AMPs? Am I missing something regarding powering these with solar panels? The people at microcenter thought I could just plug it in and it would work.

Thanks for any help given!

crickeys:
The people at microcenter thought I could just plug it in and it would work.

So now you know that they know zilch.

Your solar panel cannot produce enough current even in bright sunshine. It probaby doesn't even provide enough for the servo, never mind the rest of the kit.

But buying a bigger solar panel is not the complete answer either. You need a rechargeable battery that is kept topped up by the solar panel and which can supply enough current either when the light is a bit less bright or when the Arduino needs a bit more current.

And before you buy a battery you need to decide how much energy your Arduino needs each day. Things will be very different if the Arduino just runs for 1 hour in 24 compared to running it for 12 or 24 hrs in 24. If the usage is very low the solar panel you already have might produce enough watt-hrs to keep the battery charged. If the usage is very high then you will probably need a solar panel that can supply maybe 4 times the instantaneous demand of the Arduino and its attachments. And, of course, the intensity and duration of sunlight where you are also has a big impact.

...R

Thanks Robin,

Starting to get a little clearer. Could you help me understand the following:

Let’s say I’m in the best lighting conditions and 7.2V are coming out of the solar panel and I just hook that up to the arduino with nothing else plugged into the arduino. Is the current that comes out of the solar panel limited by the solar panel? Is that why it says 100mA or does it mean 100mA is a max current before something bad happens? Does 100mA flow through the arduino or does the Arduino itself dictate how much current is going to be pulled from the solar panel?

Maybe I’m confused between a battery and a solar panel. Do batteries have any max Current? If I short the positive and negative terminals of a battery is the current almost infinite?

I’m not sure I understand how current and voltage are being distributed amongst the various pins in the Arduino. If 7.2V is hooked into the arduino barrel port (whether with a solar panel or a battery) does the arduino just make sure every HIGH pin has 5V at all times? Is it the component that you plug in to the 5V pin that determines the current that will flow through the pin?

Here is the PIR sensor I am using for instance. How would I be able to calculate how much CURRENT it requires?
http://www.microcenter.com/product/390014/pir_sensor_-_rev_b

Thanks so much for your help!

There is an upper limit to the amount of current a solar panel can supply - probably 100mA in your case. However if the device it is connected to caan only take 50mA that is all the solar panel can supply. However the solar panel voltage may rise in that case. There will also be an upper limit to the solar panel voltage - the voltage it produces when not connected to any load (apart from the volt meter). And, like anything else, if you try to draw more current than it can provide the voltage will fall - to 0 when you have a short circuit.

If you study solar panel theory a bit more closely you will find that the reputable manufacturers produce a graph showing how voltage varies with current and with different levels of sunshine. For any given light intensity there will be an optimum balance between voltage and current at which the panel produces maximum power. Although not relevant to a small panel like yours MPPT controllers (Google them) are designed to keep the solar panel at its Maximum Power Point.

...R

If the sun goes in there may be insufficient power for your arduino.
Using a battery is a bit like a high value capaciror.
But if your cell does not produce enough power the battery never gets charged.

Solar cell specs for the smaller ones fromm the high street give current suply figures under ideal conditions.

They rarely meet expectations .
Especially if you live in a cloudy climate.
To be useful solar panels are often expensive.

From the solar cell you have and its size i would expect 100 ma in direct desert sunshine but not much else.

As an overall primer, voltage is supplied by the power supply, in this case the solar panel, and current is requested. A power source will only supply the current requested by a device connected to it, up to it's maximum. In you case the arduino and servo need more than the max the panel can supply, so they just don't work.

Now, onto the battery option. Running from solar power requires a panel, a battery, typically a lipo, a charger circuit to safely charge the lipo, and something to use the power, in this case your arduino

On top of all that the whole package needs to be designed so your battery is large enough to run the whole system for as many days as you expect you won't see any sun at all, and your panel needs to be large enough to charge your battery in the time it will get sun

This will give you something of an overview of whats required but you'll need to work out the above things by yourself with a multimeter. I would guess you'll actually need to kill power to the servo when it's not in use to have any chance of a viable solar system unless you use a big panel and battery

Solar panels are normally rated at whats called STC (Standard Test Conditions) which means the Solar Panel produces the stated output power with a irradiation intensity of 1000 W / sq meter and a cell temperature of 25 C.
These types of conditions you only get in a lab.
If you live close to the equator, you might get close to the above around noon, but in general you will get a lot less.
Powering anything with a Solar Panel requires a battery, which powers the hardware, and the Solar panel charges the battery.
Its the only way to get reliable results.