Energy Harvester

Power harvester (PV) is a mechanism to convert a source of ambient energy (solar, heat, wind, chemicals etc) into another form of energy (electric). There are several types of power harvester such as fuel cells, piezoelectric, solar energy, thermo-electric etc. Fuel cell is a device that converts chemical energy of a particular fuel (such as hydrogen, metanol etc) to electrical energy as a result of the chemical reaction process. The application of fuel cell covers from portable power to military and aerospace applications. However the common disadvantage of fuel cell is low efficiency, long start up time or sensitive to fuel impurities. Piezoelectric is another power harvesting mechanism that converts mechanical force such as pressure, vibration and stress to electrical charge. In contrast to fuel cell power harvesting, piezoelectric provides very high power efficiency that is appealing for applications that required an effective and high power performance. Despite of its advantages, however its requires continuous motion to provide necessary force for power generation. This limits its application in various field especially those requires continuous power such as in biomedical applications. 

Solar energy is another promising method of power generation. It converts sunlight to electrical power when the solar panels expose to sunlight. Some of the popular applications that use solar power are photovoltaic, dye-sensitized solar cells, biohybrid solar cell etc. The advantage of solar energy are enhance sustainability, pollution free, and inexhaustible. Despite their advantages, solar energy system are capital intensive in nature due to the setup price and requires large surface area for efficient power harvesting. Obviously, it is not applicable for powering biomedical devices.

Thermoelectric emerging technology that could resolve the issues associated with the affore mentioned power harvesting method. Thermoelectric convert heat to electricity due to the Seeback Effect.Thermoelectric is generated when there is temperature differences between the junctions of two dissimilar metals. Thermoelectric power harvester offers advantages such as compact, simple and it is scalable. It can operate with small heat source and small temperature difference. Thermo-electric element could be utilized as a power source for micro devices  due to its flexibility in terms of fabrication method that enables it to be formed in microscale. Various materials have been proposed for obtaining thermo-electric power based on specific application including home appliances and also health care industries. Among the advantages of thermo-electric power generation are longevity, portability, flexibility of size and environmental friendly. Unlike solar energy, heat source that is required for thermo-electric power harvesting is not limited during day time. These features are very promising which provide huge opportunity of application ranging from personal devices to domestic power generation.
Figure 1: Example of thermoelectric harvester for wearable device application