The most abundant energy source on Earth is low-temperature differential. Heat flowing from one reservoir, slightly hotter than the cold reservoir. There have been many solid-state heat engines designed to be put in that heat flow and produce mechanical work, but none successful in being commercially available to the public. I want to change that.
Here is my idea of the solid-state heat engine published under TAPR Open Hardware license:
Subscribers to my Youtube channel get the model for free. Let me know you subscribed over e-mail, which is published in the video.