Power Raspberry PI using Solar Panel

12V battery is probably more scalable but the initial cost might end up being quite high. Depends if you are planning on adding additional load in the future. There should be lots of off-the-shelf kits available due to off-grid camping.

Wesley did an off-grid solar project over on element14 presents which may be of interest:

/challenges-projects/element14-presents/project-videos/w/documents/28102/episode-598-how-to-build-a-portable-solar-charged-off-grid-power-station

However, you have previously stated that the 10000mAh power bank provided sufficient capacity to power the R-Pi 4 setup, and that it works being charged off the solar power bank. You could perhaps just use that as a solution and increase the size of the powerbank if needed. 

However, it should be possible to get around 10500mAh out of the Waveshare solar powerbank using 3x 3500mAh 18650 cells. So perhaps worth taking a closer look at your existing '3350mAh' cells and replace them with known high quality ones that will give the full stated capacity. It's the neatest solution but those higher capacity cells can be quite expensive.

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Alternatively you could perhaps look at using an external 3.6V power pack with the solar charger, using 4x 2500mAh cells which probably works out cheaper to give similar capacity of around 10000mAh.

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The 3-cell battery holder looks like it plugs into the circuit board so would just need unplugging and a slot cutting in the cover to pass a power cable through and allow it to be plugged in. 

There is potential to expand this to 13400mAh if required, either using an off-the shelf pack containing 4x 3350mAh cells

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or building a custom pack (with appropriate protection). I think the Waveshare battery holder is just three cells in parallel, I didn't notice  any fuses to protect against shorted cells. 

If using external batteries, there are also the larger higher capacity 26650 sized cells. 

However by this stage, replacing the Waveshare solar powerbank with the likes of a Voltaic laptop one might end up being better value 

https://voltaicsystems.com/v88/ 

as although is is at around $149 you are getting around 24000mAh capacity which sounds like it would be enough to power your setup for 2-3days.

Another thing to consider is your solar charging capacity over the typical year. As nights grow longer and there are less sunny days, then you may need additional solar collection and storage to keep things running through the night. You may want to power down the R-Pi during daylight hours to conserve power rather than adding batteries and panels.

Well, I've been reading and reading - something I did before, but probably not so thoroughly as I should have - thank you for your comments .  This is mainly from projects that uses the PiJuice hardware - that I have - I did support them on KickStarter.

I need at least a 20W solar panel - That I have.

The battery is the crux of this . They recommend at least 12.000 mAh battery - or at least 5000 mAh or above - that I don't have.  My main problem with this is:

- The Pi will be sitting on a waterproof box - in the sun - lots of heat. a lipo battery will be suffering with this and I don't want to burn down the house. I'm talking of temperatures around 45º C or more. I will have some openings (protected from rain) to vent, but the temperatures inside will be around that value.

- So, probably Li-ion batteries should be the choice.

Since a 10000mAh power bank can power the Pi and still has juice left (from experience), I'm going to guess that the batteries in the Waveshare power solar Manager are the key .

Will have to see how are they connected - serial or parallel.

The other version that waveshare sells has an 10000mAh li-po battery inside.

Tonight will try with a Raspberry PI Zero W 2 !

Thank you all

Here's some links :https://sustainablewww.org/principles/how-to-build-a-solar-powered-raspberry-pi-with-pijuice

feiticeir0 said:

I'm talking of temperatures around 45º C or more.

This high ambient temperature will also likely affect the efficiency of your solar panel. The power ratings are usually for a panel operating at 25ºC.

Thank you beacon_dave for the information.

I would love to keep using the Waveshare Solar Charger - I've bought it for this purpose . I will take a look at those batteries.

beacon_dave said:

The 3-cell battery holder looks like it plugs into the circuit board so would just need unplugging and a slot cutting in the cover to pass a power cable through and allow it to be plugged in. 

There is potential to expand this to 13400mAh if required, either using an off-the shelf pack containing 4x 3350mAh cells

I'm not against this - heck, I would prefer this. Need to dig a bit further on the solar charger to see if I can replace that.

I have 3 cell packs at home for a LED cube project - that sits there - and I don't mind to use them..

Again, thank you.

I have this ones at home

Will see if I can use them

I am so stu....

Because of your post, I'm checking what I already have at home regarding solar - all I was missing was a good solar panel.

After all, I have this:

That I can connect one of those 1s4p 10400 mAh packs...

I have one of these as well. Be careful on the polarity of the battery connector - I've noticed that some are reversed from Waveshare/Adafruit polarity.

Looks like it should be comprised of 4x 2600mAh cells.

However the price looks a bit on the low side.

To power a Raspberry Pi, the solar panel needs to output at least 5V. The wattage and current ratings of the solar panel will determine how fast the battery charges. This means a 2W solar panel can charge a battery twice as fast as a 1W solar panel.

My first thought was to increase the voltage of the battery pack by adding another battery bank in series, but the battery manager isnt rated for it. 

I myself would do an experiment, with case open, add another battery in parallel with jumper clips. It would add 2 hours to operation, hopefully the MPP tracking is going to limit the charging volts and long time current regardless of additional battery load.  The solar panel is going to sag big time anyway, the difference between full load and short circuit is 6 mA.