A prototype wearable device I designed and made for charging handheld devices, smart watches, phones, video game devices, etc, using electricity harvested from body heat using a low voltage thermoelectric generator.
Thermoelectricity produced from bismuth-selenide peltier elements by the Seebeck effect produces a low voltage and a more or less stable current when a constant temperature differential is created across the element. This can be accomplished by having a constant heat source and a constant heat sink, i.e. a cooling apparatus. The low voltage can be boosted using a standard low voltage boosting circuit which boosts the voltage from millivolts to around 5V.
Such circuits have become more and more widespread as the field of energy harvesting grows, with thermoelectric flashlights such as the one demonstrated here being developed for mass production for sale to the public in the near future as people become more aware of renewable energy and as the renewable energy economy grows which will only increase the demand for such devices in the electronics industry over the next decade.
Making thermoelectric energy harvesting devices that charge devices with a more intensive energy demand than LEDs is a bigger challenge and requires the device to have more elements and a faster yet more continuous method of harvesting the energy as the temperature differential is diminished as is the case for devices which are cooled by the air as the cooler side eventually heats up itself.
As the user moves around, the change in the external environment will affect the amount of power produced. For example, walking or running outside with the device exposed will not only allow more heat to be harvested as the body expels waste heat but the movement will move air across the coolers which will sustain the temperature differential. In cold weather and environments the device will also work very efficiently. In warm weather or if the user is indoors and not moving the amount of power produced will be reduced. Hence the power harvested is intermittent.
Ultra-capacitors/Super-capacitors are therefore useful for storing the intermittent periods of a strong temperature differential forming across the elements as a voltage which is contained in the capacitor bank as long as the circuit is not switched. When power is required, the circuit is switched on and the capacitors are drained. The circuit is then switched off to let the charge rebuild again.
In this demonstration, the power is transferred periodically into a commercially available lithium-ion power watch which stores the electricity for further use in the range of portable rechargeable devices that people have grown accustomed to in the modern age. As progress continues, devices like this will be improved upon more and more until they are eventually commercially available and affordable for people to incorporate such technology into wearable devices and clothing to have more sustainable sources of energy to power potable technologies on the go without having to depend on power outlets.
In the future, it is hoped, that technology such as this will help replace our dependence on inefficient and environmentally unfriendly batteries and an over-reliance on using power outlets to charge small devices which is itself wasteful due to the waste heat created by transformation of current from AC to DC.
