It's been 13 years I've never seen one

At just 14 years old, Ann Makosinski harnessed the warmth of her own hand to create a flashlight that needs no batteries. 💡

Her inspiration came from a friend in the Philippines who told her she couldn't study at night and was failing in school because her family had no electricity for light.

Ann wanted to find a way to help. She knew she could capture energy from many sources, including the heat from a human body.

She looked into Peltier tiles, which produce an electric charge when one side of the tile is heated and the other is cooled.

Ann realized that the heat from a person's hand on one side, and the ambient air cooling the other, could generate enough power for an LED light.

Using this principle, she designed the Hollow Flashlight. The design allows air to flow through the device, keeping the outside cool while the inside is warmed by the user's hand.

In 2013, at age 15, her invention won her top prize for her age group at the Google Science Fair.

Her simple, yet brilliant, device showed a new path for sustainable, off-grid energy solutions. 👋 #InnovativeYouth #SustainableEnergy #InventionSpotlight #fblifestyle

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DeWayfarer · 61-69, M

The problem is the difference between the ambient air and the the body heat makes it worthless in temperatures near the body heat of 92.6°f. There needs to be a very large temperature difference.

Better is the lights that you shake. And those have been around for decades.

ninalanyon · 61-69, T

@DeWayfarer Better still would be treating a basic amount of electricity as a human right. But you are quite right in a climate like the Philippines such a torch would not be useful.

I'm sceptical of the whole idea. The only paper I could easily find has such ridiculous errors in it that it is difficult to believe that the Seebeck effect is at all practical for generating electricity.

In addition Peltier devices used to generate electricity are very inefficient, <5%. An LED producing enough light to comfortably read by is probably at least 100 mW so you need to supply 2 W through your hands to do that. That's implausible too as the total energy dissipated by an average human is only about a hundred watts. See https://physics.stackexchange.com/questions/116960/how-much-energy-in-form-of-heat-does-a-human-body-emit

I found the patent which confirms my opinion. In it it says:

Example 1

In order to determine the feasibility of using heat from the hand of a user to power a flashlight, calculations had to be performed. An average human dissipates around 350,000 Joules per hour, or 97 watts. The average surface area of the human skin is 1.7 m2 or 17,000 cm2, so the heat dissipation equals to (97/17000)*1000=5.7 mW/cm2. A useful area of the palm is about 10 cm2. This implies that 57 mW could be available. The thermal efficiency of a Peltier module is cited at about 6%, hence the palm of the hand may be able to generate 3.4 mW. At least 25 microwatts is needed to light an LED and about 100 microwatts is needed to obtain usable LED brightness.

https://patents.justia.com/patent/10178713

Smoke and mirrors.

Gibbon · 70-79, M

Hmm? I wonder where this went. It's not unbelievable. Thermal differences are currently used for energy generation. Iceland and Greenland both make use of this.

ninalanyon · 61-69, T

@Gibbon On the contrary, it is quite unbelievable! It didn't go anywhere because it is ludicrously ineffective and expensive.

The thermal differences in the Icelandic power systems are huge in comparison and the available power is also huge. The geothermal source are mostly used directly to heat houses, pavements, swimming pools etc. not to generate electricity in ridiculously inefficient Seebeck effect devices.

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