Running a Raspberry Pi with a Solar Panel

[Tone L]

TL;DR Summary

Calculating daily energy consumption of raspberry pi versus daily power regeneration of a solar panel.

The objective:
Determine the daily power draw of a Raspberry Pi (Watts per Day) and determine the average daily power generation of a solar panel. Will energy generated be greater than energy drawn?



Lets begin,
I have a 9 Watt, 18 Volt solar panel. This solar panel is charging a sealed lead acid battery (18 V to 12 V converter in-line), the battery is a 12 Volt, 12 Amp-hour battery. There is a Raspberry Pi (RPi) that is powered off this battery.

Consider, the RPi (3B+) requires 5 Volts to run, and on average I directly found it's power consumption is 3 Watts while I am running my processes. So, in 24 hours the total daily usage will be 72 Watt-hours per day (24 hours * 3 Watts).

Consider, the solar panel operates with full sunlight 6 hours per day. So 6 hours * 9 Watts = 54 Watt-hours per day generated.

Is my thinking correct, is there another way to approach this? A LOT of assumptions but, first I wanted to smooth out the details. I haven't considered partly cloudy conditions, etc, it is an average. But, there is a disparity of: 54 watt-hours per day - 72 watt-hours per day = -18 watt-hours per day.

 

[Borek]

I see nothing wrong in your approach, you have just proven that your solar panel won't suffice.

 

[sophiecentaur]

Ten out of ten marks for actually doing some sums before asking for PF's opinion. If your Energy calculations stand up to re- checking then you've shown that you just need a bigger solar panel. If you are serious about this then you must first look around for one of the many Energy Yield vs Location calculators. Alternatively , you could drive around your area and see if there are any / many Solar Farms around. If there are none then the conditions are less than desirable. But, bearing in mind that you may not want good value for money - just a facility and / or a fun project - then do the calculations for your latitude and add about 50% or double what you calculated.

 

[anorlunda]

I have a 9 Watt, 18 Volt solar panel.

That is very small. Is there a problem with finding a bigger panel?

 

[Tone L]

Ten out of ten marks for actually doing some sums before asking for PF's opinion. If your Energy calculations stand up to re- checking then you've shown that you just need a bigger solar panel. If you are serious about this then you must first look around for one of the many Energy Yield vs Location calculators. Alternatively , you could drive around your area and see if there are any / many Solar Farms around. If there are none then the conditions are less than desirable. But, bearing in mind that you may not want good value for money - just a facility and / or a fun project - then do the calculations for your latitude and add about 50% or double what you calculated.

Hmm, good idea on using a energy yield calculator!

 

[Tone L]

That is very small. Is there a problem with finding a bigger panel?

There is not, just the one I had laying around. I mean if we are talking bare minimum, I could just find a configuration that gets me 12 Watts. It’s a shame that the RPi is such an energy hog without any ability for sleep mode. I guess the Rasbian OS running in the background is the issue. Might need a Linux board with nothing fancy.

 

[sophiecentaur]

There is not, just the one I had laying around. I mean if we are talking bare minimum, I could just find a configuration that gets me 12 Watts. It’s a shame that the RPi is such an energy hog without any ability for sleep mode. I guess the Rasbian OS running in the background is the issue. Might need a Linux board with nothing fancy.

Sometimes, the solution is not to go for the smartest and most efficient. Just go for the one that works. It's only worth doing what you want to do if you are selling 10,000 units or a million of them and the actual cost is important to your profit. Have you costed your time on this exercise?

 

[Windadct]

Does the PI have to be running 24/7? Even without a sleep mode, building simple timer, that just cuts the power at some interval could help.