The Peltier element is a thermoelectric converter. It can convert current energy for cooling. It has the opposite effect - the generation of electric current arising due to the temperature difference between the thermal and cooling elements.
It is a plate based on heterogeneous semiconductors. When passing current, energy is generated in the form of charged electrons. They are absorbed by another semiconductor, whose energy potential is higher. With the passage of current, at the contact point of the semiconductors, a cooling effect occurs. Due to its small size, it can be used as a cooler for the CPU, a home-made car fan and other devices.
When thermal energy is supplied through a Peltier converter in a self-made electric generator, a current is generated that is enough to charge mobile devices in the field. This is achieved due to the same heterogeneity of the elements. The higher the temperature difference, the greater the output voltage.
Cost: ~ 130