# Solar panel powered arduino problem

#### zazas321

Joined Nov 29, 2015
437
Hello Guys. I am working on a project and I need to power arduino and the rest of the system with solar panel. The solar panel that i have is Voc=21V
Vpm=17V and a P=10w.

When i measure the voltage of the solar panel in ambien light i get about 11Volts. When i connect to Arduino the voltage drops to about 1.8V and just 2mA of current. Could someone help me figure out whats happening and why is happening? Thank you

#### ericgibbs

Joined Jan 29, 2010
9,561
hi 321,
What is the solar panel output , when driving the load, in bright sunlight.?
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#### zazas321

Joined Nov 29, 2015
437
I cant really tell that at this moment. I am sitting in the lab. I am just using room lamps as a reference. I know its not very accurate but still. why does it drop down from 11V to 1.8V. My load currently just arduino uno. I am not powering anything through arduino just arduino itself.

#### ericgibbs

Joined Jan 29, 2010
9,561
hi,
Without the Arduino load, you are measuring the open circuit output voltage, which could be ~11v.
With the Arduino connected it is loading the solar panel, so the voltage will drop to say ~2v.

The ambient light in the Lab is too low to drive the solar panel, when a load is connected.

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#### zazas321

Joined Nov 29, 2015
437
But the room is quite bright and I am working directly below the lamp. What are my options to increase the voltage? should I use DC to DC converter? but then i would need to use some sort of DC voltage for the converter. Is there any other way?

#### AlbertHall

Joined Jun 4, 2014
9,310
Is there any other way?
More light or a bigger panel.
The DC-DC converter will not increase the available power.

Joined Feb 20, 2016
3,322
But the room is quite bright and I am working directly below the lamp. What are my options to increase the voltage? should I use DC to DC converter? but then i would need to use some sort of DC voltage for the converter. Is there any other way?
Inside lights may seem bright but they really are not.
For interest, just have a look at the wattage of the lamp you are using.
A quick look found...
https://www.dial.de/en/blog/article/efficiency-of-ledsthe-highest-luminous-efficacy-of-a-white-led/
The efficiency of the lamps are not 100%, then the light spreads out. Solar cells are themselves not real efficient either. And they do not respond to all the light wavelengths.
So as an exercise, see if you can figure out roughly what power lamps you would need to drive the pannel.
The sun is a pretty big lamp!

#### zazas321

Joined Nov 29, 2015
437
I have left the room for today. Next time I will try putting the solar panel next to a window towards the sun light and I will see if it makes any difference. Thanks for the replies guys

#### ebp

Joined Feb 8, 2018
2,332
No matter how bright indoor light is, it is a very small fraction of what sunlight is.

PV products are normally characterized at an "insolation" of 1000 watts per square meter. Imagine a 1000 W artificial lamp illuminating 1 square metre. Pretty bright. Divide by 4 or 5 or so to get what portion of that kilowatt is actually turned into light if the source is near state of the art production LEDs or other high-efficacy source.

The short circuit current of a PV module quite accurately reflects the amount of illumination. Voltage varies primarily with temperature. The fact you were getting open-circuit voltage of 11 volts says the illumination was vastly below 1000 watts per square metre. PV voltage does not vary much with illumination until you get way down near the bottom end.

Indirect sky light on a day with uniform light cloud can be pretty bright, but likely to be less than 20% of direct sun.

#### zazas321

Joined Nov 29, 2015
437
Okay thank you for the answer. If my solar panel is not enough to power the arduino, could i charge the power bank instead with solar panel that would be able to powet arduino. Im trying to avoid using power supply as this is the main goal of the project being able to operate without external power supply and mostly on solar energy

#### ericgibbs

Joined Jan 29, 2010
9,561
hi,
It is possible to charge a battery using a solar panel, you should have an efficient converter.
Problem with most batteries you basically have to put more energy in than you get out, some batteries are only around 65% efficient.
What type and capacity battery did you have planned.?
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#### zazas321

Joined Nov 29, 2015
437
hi,
It is possible to charge a battery using a solar panel, you should have an efficient converter.
Problem with most batteries you basically have to put more energy in than you get out, some batteries are only around 65% efficient.
What type and capacity battery did you have planned.?
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I havent really looked into that yet it was just an idea. Would a power bank that I use to charge my phone would work?

#### ericgibbs

Joined Jan 29, 2010
9,561
hi,
To answer that, we need the specification of the power bank.
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#### ebp

Joined Feb 8, 2018
2,332
It seems almost all power banks around these days are based on lithium ion cells which are extremely efficient in terms of discharge power available relative to charge power required.

A battery will do absolutely nothing for you unless the total energy input available is at least as great as the total energy output required over the period of operation. This often is the case with photovoltaic systems. One hour of bright direct sunlight on the PV module might be enough to keep your circuit powered for 24 hours. But if all you have is room light that can't run the circuit directly, the battery will do nothing unless you operate the circuit only intermittently.

If the MPP voltage of the panel is 17 V and you want to charge a single lithium ion cell, then you will require an MPP "tracking" charging circuit that will keep the panel operating at or near the MPP voltage. An ordinary buck converter that regulates the output voltage will simply "collapse" the input voltage to nearly equal to the output voltage. You would get something around 20% of the nominal power of the PV module that way. The implication of MPP tracking is that the output voltage must be allowed to vary and it is hard to say how a power bank, with an internal charge circuit, would respond.

#### zazas321

Joined Nov 29, 2015
437
Im not sure if its a good choice then. Because powering arduino is the easy part. I need most of my solar panel generated energy to turn on some other device. Basically the idea of the project is to create a system that would be able to turn on some hone device remotely if there is enough energy generated. Im working with low voltages and in the future this could be done with an actual residential houses to turn on lets say washing machine. In my case, i want to turn on an LED or charge a phone or something else. I will be sending and receiving signals through Xbees 2. But Im struggling to find a way how to power my arduinos at the moment

#### ericgibbs

Joined Jan 29, 2010
9,561
hi zazas,
I have Deleted the second Thread, you Created a few minutes ago, for the same problem.
Moderation.

#### zazas321

Joined Nov 29, 2015
437
Okay. Im still trying to figure out why my 20V panel is not capable of powering arduino UNO which only requires 5V and little current. Open circuit voltage from my solar panels drops from arround 10-15V to arround 1.5V when connected to arduino. I cant believe that 20V solar panel is not enough to power arduino

#### ericgibbs

Joined Jan 29, 2010
9,561
hi,
What level of sunlight was illuminating the solar panel when you carried out this test.?
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#### zazas321

Joined Nov 29, 2015
437
It was fairly sunny but not 100%. Ideally i would have imagined that my solar panel would be able to run arduino even when there is little sun because i do not need its full power (18V) to power the arduino.

#### AlbertHall

Joined Jun 4, 2014
9,310
Okay. Im still trying to figure out why my 20V panel is not capable of powering arduino UNO which only requires 5V and little current. Open circuit voltage from my solar panels drops from arround 10-15V to arround 1.5V when connected to arduino. I cant believe that 20V solar panel is not enough to power arduino
If the voltage drops that much when drawing minimal current then there was not enough light.
Wait til the sun comes out and stick the panel in that sun shine and then see what happens.