Arduino Uno Solar Battery Charger ?

Hello everyone. Newbie here. 

My project is to make an environmental monitoring system that will be battery powered and charged using solar energy, when the system is not in use. The components I am using are listed below for reference. 

Parts List:
1. Solar Panel 
2. Rechargeable 9V Battery
3. Uno Rev 3
4. SD Module
5. Grove Dust Sensor
6. Grove Temp & Humidity Sensor
7. Grove Light Sensor
8. ESP8266 Transceiver
9. Grove Air Quality Sensor

All the components operate at 5v with the exception of the ESP8266 which is 3.3v. I have been looking at different methods of powering the system and noticed people using LiPo batteries. I'm aware that you shouldn't let there voltage drop too low and something about voltage regulators and boost converters that might be needed. 

Based on my system can anyone recommend the best method of powering everything using batteries and charging it through solar energy.  

I'm fairly new to the Arduino Eco system and this kind of work in general, so any help would be greatly appreciated. Thanks in advanced. 

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A 5.5 volt solar cell won't do a very good job at charging 9 volt battery without a voltage booster

hymcode (author)  Josehf Murchison15 days ago

Thanks for the response. I recently did some calculations (which might be wrong) and according to the numbers I would need a solar panel that was 54cm^2 in order to power just the Uno for the whole of December.

Source: @ 8:45

I would start with the hours of sun a month; where I live the sun only shines 55 to 80 hours a month for 6 months.

So to run a 5 watt device 24 hours a day for a month I would need to generate minimum 3600 watt hours during these months.

Rule of thumb watt hours times two for battery capacity.

Hours in a day times days in a month 24 x 30 = 720 hours in a month

Watts times hours in a month 720 x 5 = 3600 watt hours

Watt hours divided by hours of sun in a month, 3600 / 55 = 66 watt solar panels and about a 7200 watt hour battery.

When you only average 1.8 to 3 hours a day for six months solar is not very practical.

However the same formula goes when you get 360 hours of sun a month.

3600 / 360 = 10 watt solar cell and about a 20 watt hour battery.

Now I'm tight on the numbers here so you might want a 15 to a 20 watt solar cell for generation loss.

hymcode (author)  Josehf Murchison13 days ago

Thank you very much for this information. This is a great alternative method in comparison to my earlier calculations. By following this method I was able to generate the numbers shown below:

December 2017 we got 245 hours of sun

There are 31 days in December so: 24 x 31 = 744 hours

Watts times hours in a month: 744 x 5 = 3720 watt hours

Watt hours divided by hours of sun in a month: 3720 / 245 = 15.2 watt solar panel and roughly a 7740 watt hour battery (3720 x 2 = 7740)


So am I right to conclude that if I wanted to run a 5 watt system in December I would need a 15.2 watt hour solar panel and a 7740 watt hour battery.

A thought just struck me.

Is that 245 hours daylight or is that 245 hours of sun? (Full Bright Sun Light)

hymcode (author)  Josehf Murchison12 days ago

So 245 hours is regarding total daylight. The website I linked gives the times for sunrise to sunset for each day of the month, so I just added them into a excel document and I got a total duration of 245:37:26. Hope this helps.

You need bright sun light or full sun, when it is overcast solar cells don't work well.

A chart something like this is what you are looking for.

Solar Motor 0b.png
hymcode (author)  Josehf Murchison10 days ago

This diagram is much better then just the numerical data I have been going by. Where did you happen to find this, may I ask ?

Sorry for the long delay in my response couldn't get through to Instructables.

I have been doing a lot of research in free energy modeled for where I live.

I got that chart from the weather network before they changed the weather history on their webpage.

It takes research much of it done by the wind farms where I live.

Precipitation.pngSolar Motor 0b.pngWind Direction.pngWind Speed.png
hymcode (author)  Josehf Murchison9 days ago

Oh right I see. This visual data is very good. I will have to see if such data exists where I live.

Thank you for showing this information to me.

I messed up my math a little also.

15.2 watt solar cell is good.

But you shouldn't need more than a 200 amp hour battery just in case you get a few days of low light.

hymcode (author)  Josehf Murchison12 days ago

Where did you make your mistake sorry? Was it the 20 watt hour battery as I was not sure where you got that number from, or the 200 amp hour battery value. Thanks in advanced.

20 watt hour battery should have been 60 times 2 making 120 watt hour battery. missed the 1 when I was typing.

I guess I didn't explain the battery size with reliable sunlight.

15 watt solar panel 5 watt charging loss leaves 10 watts 5 used by circuit 5 to charge the battery.

12 hours in a day times 5 watts = 60 watts times 2 = 120 watt hours.

During the night 60 watt hours used leaving 60 watt hours in the battery for short day light and battery life.

The Grove stuff will, IIRC, work on 3.3 V. You can make an Arduino run on 3.3 V, and you can buy an Arduino WITH the ESP8266 BUILT IN.

Forget regulators, LiPo, boost converters and all that until you can answer the BASIC questions

How much data are you moving, how often ? How much power will it take to do that ? How much will the sensors pull ? How will you handle power management.

How long must the device work with no sun ?

hymcode (author)  steveastrouk15 days ago

Thanks for responding and providing me with some very valid and important questions that I need to answer. Do you have any recommended links for me to look at, which might help?

Forget the power system first.

Get your Arduino (preferably WITH ESP8266 on board) and your sensors.

Make sure I am right that your whole system CAN run on 3.3C.

Convert your Arduino to 3.3V operation. (It WILL run on 1.8V IIRC)

Get some working code that does the essentials, read sensors, send to WiFi etc.

Measure running current, measure when transmitting, measure when quiescent.

NOW start hacking !

Get that all together and report back. How can you save power ? Try ideas out. I hinted that the CPU can be put to sleep and rewoken.

That will enough clues for now, PM me and ask for further guidance perhaps, but I want to see YOUR ideas working first. That is how YOU learn.

Always happy to mentor, but I will NOT help people cheat

hymcode (author)  steveastrouk14 days ago

Thanks for the response. All the components I have listed above I already have at my disposal. Plus I have tested all the individual sensors using the the examples provided by Seeed Studio.

I do need to start hacking further indeed, to get a better understanding of how everything is working and start getting multiple sensors working simultaneously.

Thank you for offering to mentor. You sound like you know 100% more then me and I will definitely take you up on the PM offer.

I have NO intention of cheating I can assure you that. I'm in this to learn, develop and improve my skills. NO shortcuts !

iceng16 days ago

Depending on battery size and hobby photovoltaic area, most often a schottky low fwd diode is all you need to charge any rechargeable battery (see pic 3)...

The diode is a one way salve that prevents the battery discharging through the resistor of the array in the dark or during a cloudy eclipse !

solniteZE002.jpgSolar-lm317.jpgSolar .jPG
iceng iceng15 days ago

Joe is correct, I leave too much for you understood ;-)

Solar 9v .jPG
iceng iceng14 days ago

You do know, when you click the pic it shows the whole image..

hymcode (author)  iceng15 days ago

Thanks a lot for the information. I will definitely look into this further.

Your task has nothing to do with the
Arduino, its basic electronics. Assess the load your system is likely to
present to the battery FIRST, then decide how to accomplish it.

Hint: Your processor doesn't need to be awake continuously.

Hint: How does a 5.5V panel charge a 9V cell ?


Apart from not giving any help for school stuff:
Don't use a 9V battery, they simply won't provide enough power.
Either use a 5V power pack or better still a small 12V deep cycle battery.
A solar panel must always provide more power than what is used and be able to do this for around 3 days to compensate for bad weather, clouds and such things.
Same for the battery, especially if used in colder climates.