A Thermophotovoltaic (TPV) cell is a type of energy conversion device that generates electricity directly from heat radiation (thermal energy) using the principles of thermophotovoltaic effect. It converts thermal radiation emitted by a hot surface into photons, which in turn, are absorbed by a photovoltaic (PV) cell to generate electrical power.
Here's how the thermophotovoltaic cell works:
Thermal Emission: The process begins with a hot surface, often referred to as the emitter, which is maintained at a high temperature. This temperature difference between the emitter and its surroundings creates a flow of thermal energy. According to Planck's law of blackbody radiation, a hot object emits electromagnetic radiation, including photons, with a spectrum that is dependent on its temperature. The emitted radiation spans a wide range of wavelengths, from infrared to visible light.
Photon Emission: The emitted thermal radiation contains photons that carry energy. However, not all of these photons are suitable for energy conversion. To improve the efficiency of energy conversion, selective spectral control is applied. This involves designing the emitter's material and structure to enhance the emission of photons within the optimal wavelength range for absorption by the photovoltaic cell.
Absorption in Photovoltaic Cell: The emitted photons are directed towards a photovoltaic cell, which is specifically designed to absorb photons in the desired wavelength range. This PV cell can be a traditional semiconductor-based photovoltaic material, such as silicon, gallium arsenide, or other advanced materials designed to optimize the conversion of incoming photons into electrical current.
Photoelectric Conversion: When the absorbed photons strike the photovoltaic material, they transfer their energy to electrons within the material. This energy excites the electrons to a higher energy state, creating electron-hole pairs. This phenomenon is known as the photoelectric effect. The material's inherent properties then allow these electron-hole pairs to be separated, generating a voltage potential difference across the PV cell.
Electricity Generation: The voltage potential created across the PV cell due to the separation of charges results in an electric current flow when an external circuit is connected to the cell. This flow of electrons constitutes the generation of electrical power.
Heat Recycling: After the thermal radiation is converted into electrical power, some residual heat might remain in the system. In some TPV designs, this heat can be recycled by using heat exchangers to transfer it back to the emitter, improving overall efficiency.
The efficiency of a thermophotovoltaic cell depends on several factors, including the spectral match between the emitter's radiation and the PV cell's absorption spectrum, the quality of the photovoltaic material, and the ability to manage heat losses and maintain a temperature gradient. TPV technology has the potential to be used in applications where waste heat is abundant, such as industrial processes and concentrated solar power systems, helping to increase overall energy conversion efficiency.