Solar Power

[admin]

Hi Guys,

Now that the major issues with the design are more or less mitigated, i started thinking on what would be the next level.
Up to now i've consistently avoided using batteries, as this adds another level of complexity. So i decided to pay some skilled freelancer to do the schematic design this time. The question is what would be the requirements for a battery powered device. What i am thinking of is:

- Power consumption of a wireless device is in the range of 2-8 ma/h (send each 10 min, vs each 2 min), mostly consumed by the Wifi module while sending data - for 3-4 seconds @ 250ma/h.
- The CO2 sensor consumes ~ 8ma/h while active, and it takes ~60 seconds to get stable results, so if it is switche on each 5 minutes for 1 minute, this would reduce it to 1-2 ma/h
- Temperature sensor does not consume anything

So this totals to about 50-100 mah per day

Standard AA cells have 2000 MA, C cells have 5000, D cells have 10000
14500 lipos have ~1000 ma
18650 can have up to 5000 ma

So now in any case the device has a limited lifetime before the batteries are dead.

This is why i started wondering - what if i add also some 5x5cm solar panel. If it can deliver up to 10-20ma per hour during the day (even if not every day) this would be enough to cover the daily consumption.

Has any of you thought about this?
I saw a similar comment of Rene Arts in one forum. But maybe others have also thought about this

Regards, Vladimir

[René Arts]

With a little charging circuit this could be a nice solution. I think there should be a few nice solutions which can both charge lithium cells and convert power to 3V3 (or 5V). Also the ESP can be brought to a (programmable timed) deep sleep, power consumption then goes down to few uA (if done correctly, mind that a simple LED consumes a few mA already). I guess there should be a few integrated solutions already available for this, e.g. on Aliexpress. 
For instance a LM3671 could serve as a nice voltage regulator, it is quite suited for being used with LiPo cells. 
You also might have a look at Aliexpress, there are several cheap solar charging PCBs available. These circuits are all quite simple, it shouldn't be a huge problem I think
A nice video on this topic is provided by Andreas Spiess (the guy with the Swiss accent ). A must-watch if you are considering reducing ESP power consumption:
https://www.youtube.com/watch?v=IYuYTfO6iOs

[admin]

Thanks a lot!

This buck-regulator seems to be a perfect fit, and the guy really tells interesting stories : have to spend more time watching some of his videos 
I will  check then about those things in more detail

[René Arts]

Also have a look at this project:
https://hackaday.io/project/13260-lifepo4weredsolar1