Solar 18650 shield usable?

Hi All,

I am planning to deploy the pico weather board with weather sensors to a place in the garden shed under the roof (within wifi reach of the house). There is no power so I want to try solar. Has anybody gathered some experience / tutorial about it?

What about this device :

They call the power output port ‘USB Output Interface(2Pin 2.0MM)’ but it seems to be just some 2-pin output. Not sure what voltage?? OK to connect to the picoc weather board?

With 10cm solar cell will there be enough charge to balance the pico weather board consumption? European weather conditions!

So many of these type of chargers do not allow charging and current draw on the battery at the same time. Will this one work?


I would advice against this charger for multiple reasons. The first is lack of documentation (e.g. you don’t get a schematic). The second is the limited input-range for the solar-panel: 4.5V-6V. If you use 6V panels, you will only have this voltage in bright sunlight. The third reason is that you don’t need to boost the voltage to 5V for a Pico. The Pico is happy with the voltage range that the LiPo provides (3.3V-4.2V).

My suggestion is that you measure the current consumption of the Pico in your real-life setup. You can find some measurements from me here: pcb-pico-datalogger/ at main · bablokb/pcb-pico-datalogger · GitHub. I don’t think you will be happy with anything but an on/off solution (i.e. the Pico is turned off between measurements). Even the low current of the Pico will drain any LiPo fast if you just let it run. If you refer to the “Enviro Weather (Pico W Aboard)” that should keep you covered.

Once you know your requirements, you can estimate what kind of LiPo and solar solution you need. This of course depends very much on how many hours of sun you expect and your “on”-time. From the charger perspective, I would recommend the Adafruit solar-breakouts. These let you charge even with active consumer. Don’t by one of the old breakouts. The newer variants limit the output-current to a sensible range.


Thank you the information. Could you send a link for a recommended charger unit? Will 18650 be a good choice of LiPo?


The charger: Adafruit Universal USB / DC / Solar Lithium Ion/Polymer charger - bq24074

Regarding the 18650: for your setup, this is probably not the right choice. These are industry cells that are usually unprotected (there are also some with protection). If you use an unprotected LiPo, you have to add the protection circuitry yourself. In addition, the 18650 support high currents, which you don’t need for the Pico in this setup.

I would go for one of the flat-type LiPos, e.g. LiPo Battery Pack - 1200mAh. The size depends on your needs. I would start with something like 1200mAh or 2000mAh. If your duty-cycle is low and you have enough sunshine, both will be probably too big, but this is hard to tell without the facts (and practical experiments).

Depending on where you live, it might make more sense to order the LiPos locally. I am in Germany and shipping is rather expensive from UK once you have a LiPo in your parcel.


That is very helpful data. Just a super simple estimation on my part: You have 12.7mAh, let’s say I want more measurement duty cycle and it will be 30mAh. At ca. 3-4V that’s 100mWh. Let’s switch to the supply side. A 1W or 2W solar and charge (let’s say the adafruit) gives about 10:1 ratio for charging under non ideal situation. The LiPo only needs to supply for the night and maybe a super dark day in winter. But it doesn’t have to run the circuit for weeks. I don’t have power measurement circuit for such small devices at this time so the estimate will have to be it.

Cheers & hallo from Berlin,

Sounds like a good starting point.

For power-measurement: I recommend the INA219. Very cheap (3,70€), very easy to use, and sufficiently accurate down to 1mA. Allows sampling up to 200samples/s (i.e. about every 5ms). The next class of tools start at 120€.