Alibaba advertises a 156mm x 156mm solar cell with 4.38 watt output. The space on Minitec enclosure for membrane keypad is 34.7mm x 19.6mm, or 680 mm2. The solar cell is 24336 mm2. 24336 / 680=35.8. 4.38 watts / 35.8 = about 120mW.

This LiPo battery is 160 mAh * 3.7V = 0.592 watt-hours. 0.592 watt-hours / 0.120 watts = 4.9 hours to charge the battery using a piece of the advertised solar cell in direct sun at the equator at noon if it’s cool. It won’t work out exactly like that but at least it’s a possibility.
The iPod nano 6 LCD is about 32 x 33, or 1070 mm2. If it was replaced with a solar cell the output might be around 0.2 watts.
I still think the OKW Minitec is best solution we have available to us now. It would be interesting to see how much power a solar cell on the front of it would provide in normal use (worn on the wrist with a short-sleeved shirt on a bright day with all the window coverings open).

1 thought on “Solar charging by David

  1. That's great stuff David. Wouldn't it be cool if they didn't need to be plugged in ever.

    I just wrote you about V0.1 and V0.2 . I've pondered some more.

    Experience with TS teaches that the 0.1 enclosure will get opened and closed all the time to attach the JTAG. In fact it will be a long time before it gets to live in it's box at all. Does it still make sense to have solar charging for 0.1, or should we just assign a couple of the spare JTAG pins to an off-board charger, and also connect some serial pins RS232 uploads? I can imagine that a solar charging panel's wires will simply get in the way, and keep snapping off during the intense development pahse. During development I'll need to run it off a bench supply anyway I imagine?

    I'm less sure about anchor versions. They will also get their software upgraded at regular intervals too – but not as often. Perhaps 0.1 anchors should have an external charger too.

    Maybe you should provision V0.1 as a test-bed for a range of charging ideas?

    Not sure if 0.1 should even count Coulombs, or have a uSD. It's a waste of effort if the basic idea sucks. Maybe you could just make it easy to solder them on to 0.1 if we get that far. Only the wearable will need it.

    Just thinking out loud. What do you think?

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