system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't laptops convert waste heat into electricity instead of using even more power to run a fan?

Laptops and other devices get hotter during extended use. Various portable devices exist to turn heat into energy (camping stoves, as an example). Could laptops (and other devices) convert their own waste heat into power?

Edit: Thanks for the answers guys, and for putting up with my impression of a five year old asking "Why? Why? Why?"
gpt
Thermoelectric generators are very inefficient and relatively expensive. They'd cost a lot and wouldn't generate much power in return because, while a laptop generates plenty of heat, it's not in the range that's necessary to make such generators economical (you're looking at >200 degrees Celsius range). They'd take up additional space in the laptop and at current technology, you'd probably get better return using that same space to make a bigger or better battery.

Secondly, thermoelectric generators need low thermal conductivity to function - meaning they don't 'grab' heat very quickly. Combined with its low efficiency, this is makes it a lousy heat sink. If you used such a device in place of a cooling fan, your laptop would overheat very quickly.