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Comment by dvh | Hacker News Reader

12 microwatts per 1 cm2

0.12W per sqM

for an intuitive sense, it would take 125 hours to charge a standard phone with 1 sqM device

Or in other words it would be possible to continually power an iPhone with the temperature difference and area available in a tent. I think the context is important to whether this is presented as something negilable or something useful. Though there is absolutely no doubt that we aren’t going to see extreme amounts of power from this in tiny devices.

It also depends hugely on the nature of the generator - if it's a flexible sheet which can be used to make a tent, then awesome. If it's a rigid sheet then you'd be far better off making your tent out of solar panels even if they only saw an hour a day of sunlight.

They are not mutually exclusive though. And your tent would tend to have a higher temperature gradient during the night when there’s no sun.

A 2 cubic meter tent has a surface area on the order of 10 square meter. The temperature differential can easily exceed 10 kelvin during a cold night, else your face will freeze off.

So the potential for the application you cite is whole watts of power, enough to recharge a phone or a lantern overnight. (though, at current silicon fabrication costs, the price would be prohibitive)

So photovoltaics from the sun + waste heat is used by this on the backside. If cheap enough.

For the lowest-possible power wireless transmitter and camera (black and white, VGA), how big an area would you require then?

Right. But (I am an ignorant, sorry), how much wifi power can you get for how long?

Thanks.

The total power of the signal of a wifi router is around 2W. (Should I multiply it by x2 or x3 to power the internal system, the blinking leds, heat loss, ...?)

For 2W you need ~20m² (~200sqft). That is the size of two rooms. Probably using the surface of your whole roof you can get 4W or 5W.

Yes, but that’s for a 5°C difference. It isn’t clear if that changes with larger differences.

Thanks a lot. No IoT with this yet, then...

https://www.thingsquare.com/blog/articles/sensortag-power/ You would be suprised what you can pull off with wireless sensors. These people pulled off 1 year with a 2032 battery.

This could potentially power a low power beacon every so often. It doesn't seem practical for IOT wearables or for anything industrial at that power density. I'd be curious about the cost, in particular what manufacturing process size can be used for this. 1cm² of wafer can still be quite pricey at .000012 watts.

5°C Delta T generation is pretty impressive though. There are some commercial systems that can operate with 60°C temperature Delta (organic rankine cycle) and recover about 12% of that energy.

They'd need to adapt to something like aluminium foil or UHMWPE film (made like paper from the fiber-spinning solution) as a base and coat that with poly-Si. Even if it is only half as efficient, it should be a lot cheaper and possibly strong enough to be laminated into fabric like e.g. Gore-Tex membranes (extruded microporous PTFE film). A reverse electric blanket would be fancy...

By the sounds of it this is intended for use with things like Zigbee or LoRAWAN.

or 1000x less than a conventional photovoltaic technology

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