Solar panel too small for charging?

[Jordi]

Hello people,

I have been building a small solar set up as a test for building a bigger one. This has a 12V solar panel from Aliexpress supposed to provide 30W but as indicated in product comments from other buyers, it really just provides 10W, a voltage regulator, a 2,6Ah battery made out of 4 18650 of 3,7V each connected in series (14,4V approx.) and a power inverter.

To evaluate the input of the solar panel I have connected all the elements to the voltage regulator and in the solar panel circuit I have added a wattmeter. The result of the wattmeter is that I obtain a voltage but no amperage (so effectively no power).

I have tested the wattmeter with the battery and it works. I have tested the panel with a power sink and it does provide some power (don't know how much). I have made sure that the battery is only half full. I am wondering why I can not measure any power when the solar set up is assembled.

Could it be that the solar panel is too small for which no power can reach the battery?
I don't understand what might be happening because my understanding from voltage regulator is that it will manipulate the solar panel voltage regardless of the battery voltage to always charge it. Or am I wrong?

 

[gnubie]

Is this a current limited regulator? If it's not your batteries will likely load everything to the point where the panel is not supplying enough current to allow the regulator to work.

If you want to use solar panels as a power source you need a charger, a small PWM is best for your situation not even a $20 ebay special - smaller than those blue things, or at the least a power supply (regulator) that allows a current limit to be set low enough to allow everything to operate.

 

[Jordi]

Hi gnubie, thanks a lot for your answer. The funny part is that I already have a PWN for max. 10A and for which I can not find any minimal current required. The PWN or voltage regulator (as I call it) was sold together with the panel and so theoretically are compatible.

Cheap PWM I bought from Aliexpress

Maybe you have experience with this type of cheap PWN from Aliexpress?

Is there any way I can test the power supply from the panel either at its maximum levels or at a desired one. To do that now I use a device that consumes 1W, another 10W and the last 20W. As only the device of 1W switches on, I know at least 1W is supplied, but more I do not know.

This way I can estimate the current required by the PWN to initialize.

I will make a battery pack with for instance 8-10 AA batteries in series (10-12V) and test If that is willing to take current? Let you know what happened.

Lastly I understand from your answer that even thought having a bigger panel is not the right answer, it could solve the problem because it would provide a higher current.

 

[JoeHam]

What voltage does your panel achieve?

With most MPPT Solar Charge Controllers it will need to get up near or past 18v to drive current into a 14.4v battery.

For your current test you can just use a resistor I would think. That could drive amps at any voltage.

 

[Jordi]

The panel achieves in general 16V under sun, sometimes a bit more during summer months.

I will get resistors. Good tip.

 

[JoeHam]

Here’s an option:

Amazon.com

 

[gnubie]

Maybe you have experience with this type of cheap PWN from Aliexpress?

That's the sort of thing I was talking about when I said cheap blue off ebay, they are all the same thing just in different boxes. TBH I haven't played with one to the extent of working out any minimum power requirements. At worst, hook it up and see what happens. Just make sure it's charging voltages are compatible with your battery. You don't want to over-voltage them.

I will make a battery pack with for instance 8-10 AA batteries in series (10-12V) and test If that is willing to take current? Let you know what happened.

Lastly I understand from your answer that even thought having a bigger panel is not the right answer, it could solve the problem because it would provide a higher current.

The trick with lithium batteries is they will take as much current as you can give them. Trying to run them off a conventional power supply connected to a small solar panel is not going to work and connecting to a big panel is likely to provide enough current to damage the cells or burn out / shutdown the normal power supply too. You will need a solar charger or at the least a current limited power supply.

 

[Jordi]

Thank you all guys. You are being very helpful and giving me a lot of ways and ideas to keep testing my little experimental set-up.

Now is the time for me to get hands on work.

I will probably make a show and tell when I am done; but for sure more challenges will come on the way of completion.

 

[Jordi]

Update 14/10/2020
A sunny day gifted me the chance to make some tests.
The 30W 12V solar panel open circuit voltage was slightly over 20V, encouraging!

I attached the panel to the cheap PWN with the wattmeter in between attempting to measure the PWN consumption. While those were connected, the PWN was not functioning well and could not measure any current.

I attached 8 AA rechargeable of 1,2V each in series = 10V approx. to the PWN. Immediately after attaching them, the PWN started working correctly and the panel voltage dropped to 11V but yet no current flow, a cloud was passing by at that moment. As soon as the sun came back, the panel voltage went up to 12,5V and the PWN started receiving charge. Just 2W.

Not sure about where those 2W are really going thought. Are they feeding the well functioning PWN? Or are they feeding the AA battery pack?

So for now, the following conclusions:
- A bigger solar panel would solve this issue.
- A lower voltage battery would probably help completing the solar set-up.

(Maybe?) - Due to the low power point voltage of the panel at medium sunny weather; the voltage upgrade needed to feed a battery of 14,4V reduces even further the already low current. In this condition, the resistance of the PWN blocks the inlet of current from the panel. I guess because If not, the battery would fry the panel. Again, another sign of the panel being too weak.

11,5V at 0,17 Amp = 2 W so If this was to be converted at 16V to charge 4 18650; just 0,125A. The PWN resistance might be somewhere between 0,125 - 0,17 Ampere.

 

[Kugel8x57]

Not to be anal, but the proper term is PWM (Pulse Width Modulated).

I am by no means an expert or very experienced, but one thing I remember from a lot of reading on this forum is:
FIRST - connect your batteries to the charge controller.
SECOND - connect your PV array to the charge controller.

My understanding is that the batteries are the proper power source for the charge controller, and if you do not connect them first, it can "confuse" the charge controller, causing it to not work properly.

Hope this helps and God Bless!

Kugel

 

[Jordi]

Not to be anal, but the proper term is PWM (Pulse Width Modulated).

I am by no means an expert or very experienced, but one thing I remember from a lot of reading on this forum is:
FIRST - connect your batteries to the charge controller.
SECOND - connect your PV array to the charge controller.

My understanding is that the batteries are the proper power source for the charge controller, and if you do not connect them first, it can "confuse" the charge controller, causing it to not work properly.

Hope this helps and God Bless!

Kugel

Good tip. I am such a noob yet.
Better to be corrected that keep being wrong over and over.