The most modern thermophotovoltaics technology of solar heat conversion to electricity uses semiconductor materials that absorb thermal heat or technically called infrared radiation or photons from high-temperature sources like concentrated solar power systems and converts them into electrical power.
What are Photovoltaic and Thermophotovoltaics?
Photovoltaic (PV) technology or simply called Solar Technology refers to the process of converting sunlight into electricity using semiconductor materials. It is a renewable energy technology that powers a wide range of devices, from small gadgets for residential uses to large-scale electricity grids.
The basic principle behind photovoltaic cells is the photovoltaic effect where sunlight strikes the surface of a solar cell most commonly made from silicon, which excites electrons in the semiconductor material. These electrons are then knocked loose and can flow through the material, creating an electric current. This current is what generates electricity.
Unlike photovoltaics, thermophotovoltaics technology is also a type of renewable energy technology which instead of using sunlight, converts infrared radiation or commonly called sun heat into electricity using specially engineered photovoltaic cells.
As the global focus on clean and sustainable energy intensifies, researchers are exploring most advanced technologies for efficient heat-to-electricity conversion. Known for their silent operation and lack of moving parts, TPV systems offer a low-maintenance and potentially cost-effective energy solution.
How Thermophotovoltaics Technology Works
A high temperature emitter mostly the sun, radiates thermal energy through infrared radiation which are then directed toward a photovoltaic (PV) cell that produces electricity. Apart from the sun, the emitter can be heated by any high-temperature source, such as waste heat or nuclear fission etc.
While thermophotovoltaic generators utilize the photovoltaic effect to convert heat into electrical power, many other potential heat sources can be interfaced with TPVs, including fuels, variable renewable electricity, and high-temperature waste-heat streams.
When heat is supplied to the thermal emitter, it drives radiative emission to the cold-side photovoltaic cell. When high-energy photons are absorbed in the cell, it excites electron-hole pairs, while low-energy thermal radiation may be suppressed or reflected to minimize the heat input. Ultimately, photoexcited carriers are separated, inducing a voltage across the junction that drives current across a load.
TPV conversion is a promising approach for a number of energy applications. TPV generators also provide silent power generation near the point of use using a range of heat sources, offering advantages over fuel-run generators and conventional power cycles.
Additionally, low-grade heat generated as a byproduct of this system could be used for domestic hot water and space heating. Moreover, TPVs enable high-temperature thermal battery approaches for grid-scale storage of electricity which have superior energy density and cost metrics compared to electrochemical batteries.
The efficiency of TPV-based energy systems is largely dependent on how effectively energy losses are mitigated at each conversion step. Important channels of such losses include emission and absorption of out-of-band photons, thermalization of in-band photons, electron-hole pair recombination, Ohmic losses along the conduction channel, and parasitic heat losses to the backdrops.
Presently, TPVs are being utilized for application in space exploration, which requires high specific power and remote power generation. However, in broader applications, like grid-scale energy storage, waste-heat recovery, and direct solar energy conversion, advanced researches and experiments are in progress for more improvements in cost and conversion efficiency.
While the total system efficiency of TPV generators captures primary energy conversion and heat-transfer losses, TPV-based energy systems are fundamentally limited by conversion of heat into thermal radiation and radiation into electricity. Other factors directly impacting total system efficiency depend on the heat source like solar thermal efficiency, burner efficiency, and adiabatic efficiency.
Although total system efficiencies of solar, chemical and nuclear-sourced TPV generators are relatively low (4%–8%) as compared to well-established energy systems such as natural gas combined-cycle power plants, TPVs are generally too technologically immature to be compared at that level.
More research efforts and resources are to be established to develop current TPV components at the necessary scale for prototypical generators to reach the potential efficiencies set by the emitter and cell materials. These challenges will motivate progress in the development of high-performance cell and emitters.
Is Thermophotovoltaics Technology Efficient?
Currently the TPV systems based on Silicon Photovoltaic Cells, Crystalline Photovoltaic Cells and Thin Film Photovoltaic Cells are typically less efficient than solar cells because they operate at lower temperatures.
However, researches are being carried out to make TPV systems more cost and energy efficient by using multi-junction cells made from non-silicon materials like Gallium Indium Phosphide (GaInP), Indium Gallium Arsenide (InGaAs), and Germanium (Ge). However, MJSCs are not currently commercially available in bulk and are comparatively more expensive.
In 2023, the global thermophotovoltaics market was valued at $10.72 billion, with a projected annual growth rate of 7.2%. By 2036, the market is expected to reach $26.47 billion.
Currently the rise in adopting thermophotovoltaics technology in Space Nuclear Power Systems is the most stimulating factor for its market expansion. These systems provide electricity for spacecraft and similar applications.
TPV cells can convert a large portion of heat generated by nuclear reactors and most commonly the sun into electric power. The conversion efficiency of such systems reaches up-to 50% which makes this technology ideal for use in space applications where there is a need of reliability and high efficiency. Therefore, an increased adoption of TPV technology in this sector is projected to boost the TPV market growth in other commercial sectors in near future.
The industry is expected to grow in North America as many countries including United States are actively forecasting to find solutions to reduce their dependence on fossil fuels and shift towards more sustainable energy resources and thus fueling the TPV market dynamics of North America.
Thermophotovoltaics - Challenges and Development Overview
One of the main challenges TPVs face is the cost, particularly in terms of materials and manufacturing. It is projected that as the technology matures at larger scales, further advancements in materials could reduce costs, making them more viable for residential and commercial use.
Efficient thermal management will be key to developing practical TPV systems. The ability to utilize ways that enhance conversion efficiency is an area of ongoing research where multi-junction cells made from non-silicon materials are considered more energy efficient like Gallium Indium Phosphide (GaInP), Indium Gallium Arsenide (InGaAs), and Germanium (Ge).
Thermophotovoltaics systems have a strong potential in emerging markets globally where they could be used for localized power generation from waste heat or other thermal sources.
Conclusion
The future of thermophotovoltaics technology holds substantial market projection in a wide variety of applications, from waste heat recovery to space exploration and portable energy systems.
However, improvements in materials, thermal efficiency, cost of materials, and scalability are required to make TPVs a mainstream energy technology. As the demand for cleaner, more efficient energy sources grows, TPV technology will contribute a crucial role in meeting these needs, especially when combined with other renewable energy technologies.
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