Thermophotovoltaic System Research Articles

Numerical investigation on the combustion characteristics and NOx emission of non-premixed H2/NH3/air in vase-shaped micro combustor

Hydrogen and ammonia, as currently popular zero carbon fuels, have received widespread attention. These two fuels have complementary advantages in combustion characteristics, cost, safety, etc. Based on the vase shaped micro combustor, a new structure proposed for application in micro thermophotovoltaic systems in our previous work. This article numerically investigated the combustion characteristics and NOx emission of non-premixed H2/NH3/Air in vase shaped micro combustor which proposed in our previous work. The variation patterns of flame temperature, wall temperature, flammability limit, and NOx emission with the blended ratio of NH3 and equivalence ratio were obtained. It was found that the flame cannot move and stabilize when the mixing ratio is 0.6. The rate of production (ROP) and sensitivity of NO and N2O were analyzed. Four precursors of NO, HNO, NH, N, N2 have been discovered. Under the conditions of this article, HNO is the key component affecting NO emissions. When the blending ratio is greater than 0.3, the lower reaction rate of HNO leaded to a decrease in NO. The elementary reaction R63: NH + NON2O + H is the key elementary reaction that affects NO consumption and N2O generation. The blending ratio of 0.4 and the equivalence ratio of 1.2 are the optimized operating conditions with the highest comprehensive performance.

Enhanced SWIR Absorption in PMMA‐Coated TiN‐Based Metamaterial

AbstractAchieving highly efficient absorption in the short wavelength infrared (SWIR) spectral region is crucial for advancing numerous technologies. SWIR absorption enhances energy harvesting in solar cells, improves the sensitivity of infrared sensors, and enables precise control of thermal radiative properties in thermal emission devices. These advancements are essential for applications such as thermal imaging, night vision, and thermophotovoltaic systems. The study presents a simple, cost‐effective design of a polymer‐coated multilayer perfect absorber (MPA) metamaterial optimized for the SWIR spectral region. The proposed MPA structure is composed of four distinct layers: a top layer made of polymethyl methacrylate (PMMA) polymer, a second layer featuring arrays of circular titanium nitride (TiN) disks, a dielectric middle layer consisting of a pure zinc oxide (ZnO) film, and a bottom metallic layer formed by a thin film of TiN. The results demonstrate that the MPA achieves near‐perfect absorption, with a remarkable 99% efficiency centered at a wavelength of 1.3 µm. The absorption properties are further investigated with respect to various structural parameters to ensure better performance of the absorber. These absorbers hold great promise for applications in energy absorption, infrared sensing, thermal emission, and related fields.

Antireflective all-dielectric metamaterials for thermophotovoltaic systems based on multiresonance

Antireflective all-dielectric metamaterials for thermophotovoltaic systems based on multiresonance

Thermal characterisation of isotopic heat sources for enhanced thermophotovoltaic systems

Radioisotope thermophotovoltaics (RTPVs) are playing an increasingly important role in the energy supply for deep space exploration. The output performance of RTPVs can be significantly improved by increasing the surface temperature of isotopic heat sources and reducing the high-temperature degradation effect of the thermophotovoltaic cells. This work proposes methods such as selective emission coating and adjusting heat source structure to improve heat source temperature and optimize heat distribution. Results showed that the surface temperature of the heat source could generally reach more than 1000 K by using the selective coating when the thermal power of the isotopic heat source was 500 W. The use of selective coatings can also make the thermophotovoltaic cells closer to the heat source, and the volume of RTPVs could be reduced from 1.23 × 10−3 m3 to 0.49 × 10−3 m3, with a reduction of ∼60 %. Under the condition of W@SiO2 selective coating and 500 W heat source, RTPVs could produce the maximum output power of 22 mW/cm2 when the distance between the InGaAs cell and the heat source is 2 cm. The results provided effective guidance for the design of the heat source and miniaturization of RTPVs in space applications.

Improved performance of thermophotovoltaic energy conversion with Tamm plasmon emitters enabled by back gapped reflectors

A thermophotovoltaic (TPV) system that can convert thermal radiation from terrestrial heat sources into electricity, plays an important role in energy utilization, waste heat recovery and so on. In order to enhance the conversion efficiency of a TPV system having a narrow-band thermal emitter, we propose to add a back gapped reflector (BGR) to recover more out-of band (OOB) photons. We first design a Tamm plasmon thermal emitter to yield a narrow-band emission peak matching well with the bandgap of the InGaAs cell. Then, we add a BGR on the PV cell to regulate the absorption spectrum of the cell. Results show that, compared to the back surface reflector (BSR), the TPV system with the Au BGR cell has a higher power conversion efficiency (PCE), because more OOB photons are reflected back to the emitter by the Au BGR cell, so that the absorbed power by the cell decreases while the output power is improved. Due to the contribution of recycled OOB photons, at 1500 K, a 1.7 % OOB reflectance gain of the BGR (h = 0.2 μm, t = 1.2 μm) can actually increase the PCE by about 4 %. In addition, a thin PV cell and an appropriately thick air gap layer of 0.4–0.6 μm are suggested to obtain a high η × Pout. The PCE of the TPV system based on the Tamm plasmon emitter is higher and becomes saturated at a lower temperature than the broad-band SiC emitter. This work may facilitate high-performance TPV energy conversion.

Symmetric engineered central cross-shaped broadband metamaterial absorber with high absorption and stability for solar sailing and solar energy applications

We propose a theoretical design and analysis of a broadband metamaterial absorber (MMA) with significant potential for solar sailing applications which is a method of spacecraft propulsion that usages the momentum of sunlight to propel a spacecraft through space. The absorber features a metal-dielectric-metal configuration with a tungsten (W) based resonator and ground plane, and a Silicon-dioxide (SiO₂) substrate. Addressing the critical need for materials that can efficiently harness solar radiation for propulsion in space, our design achieves an average absorption of 99.15 % over a broad spectrum from 250 nm to 1200 nm, covering the UV–Visible–NIR regions, with near-unity absorption peaks at 362 nm and 915.8 nm. It maintains high absorptions of 84.9 % and 86 % under transvers electric and transvers magnetic modes respectively, demonstrating excellent wide incident angle stability and polarization insensitivity due to its symmetric design. PCR values close to zero confirm its functionality as an absorber rather than a polarizer. The MMA shows minimal deformation across temperatures from 500 K to 1750 K and remains stable under various mechanical stresses, proving its durability and efficiency in space. Additionally, in solar thermophotovoltaic (STPV) systems, the MMA demonstrates high photothermal conversion efficiency (PTCE) over a wide temperature range (500 °C to 1500 °C) and different concentration factors. This dual functionality highlights its potential for both efficient space exploration and terrestrial solar energy harvesting, making it a versatile tool for future technological applications.

Techno-economic analysis of a solar thermophotovoltaic system for a residential building

Techno-economic analysis of a solar thermophotovoltaic system for a residential building

Experimental Study of Near-field Radiative Heat Transfer Between Large-Area Polar Dielectric Films

Utilizing polar dielectric films can improve the performance of near-field thermophotovoltaic system. To confirm the enhancement of near-field radiative heat transfer (NFRHT) achieved by large-area polar dielectric films, we built an experimental setup and observe NFRHT between two 250 nm-thick SiO2 films on intrinsic Si substrate with an area 5 × 5 mm2. The two films are supported by SiO2 nano-spacers with a height of 302 nm. Temperature difference between the two films varies from 13 K to 42 K at room temperature. The observed near-field radiative heat flux closely matches the theoretical values, which surpasses substrate-only system by up to 9.87 times and could reach up to 7.45 times that of blackbody radiation due to excitation of the surface photon polaritons modes. These results demonstrate the effectiveness of polar dielectric films in enhancing NFRHT.

Investigation on H2-fueled combustion characteristics and improvement of thermal performance in a micro-planar with arranged inlet-fins and bluff-bodies for micro-thermophotovoltaic

To improve the energy conversion and efficiency, a micro-planar with arranged inlet-fins and bluff-bodies is proposed for H2-fueled micro thermophotovoltaic system. Effects of inlet-fins and bluff-bodies setting and combustor dimensions on combustion properties, heat transfer and energy conversion are investigated and analyzed under various operating conditions. The results illustrate that the flame stability and heat transfer in combustion chamber with arranged inlet-fins and bluff-bodies are enhanced, where heat recirculation is formed and radiation temperature is boosted. According to the field synergy analysis, coupling effects of inlet-fins and bluff-bodies on burning and thermal process can be improved by the optimization of bluff-bodies setting, and the flow limit is also expanded. There is a balance of the burner dimensions effects on the augment of radiation surface area and the reduction of radiation temperature for micro power generation. Particularly, the micro-planar with La/L = 0.62 contributes to achieve a higher radiation density, and the highest electrical output Pe = 3.16 W is adopted in combustor C2-0.62 at mf = 6.751 × 10−5 kg/s. It is beneficial to promote energy output of micro-planar and the energy efficiency of micro-thermophotovoltaic system.

The influence of radiation modeling on flame characteristics and emissions prediction in microcombustors with Ammonia/Hydrogen blends

This study advances numerical methodologies for designing microcombustor-based thermophotovoltaic systems by incorporating comprehensive analyses of radiation models and absorption coefficients. It examines the impact of non-premixed hydrogen-ammonia-air fuel blends on the micro combustion process using three-dimensional CFD simulations on a Y-shaped microcombustor under atmospheric conditions.Key to this research is modeling radiative heat transfer from multiple species, including ammonia (NH3), nitric oxide (NO), and water vapor, ensuring accurate predictions and optimization of thermal behavior and efficiency. Three modeling approaches were compared: a multispecies Planck-mean approximation radiation model (PMAC), a narrowband model for water vapor, and a scenario excluding radiation effects.The PMAC model, incorporating the absorption coefficients of ammonia and its products, consistently produced lower errors in flame length compared to the NB method across all equivalence ratios, with errors ranging from 0 % to 7 % for PMAC and 10 % to 30 % for NB, with the lowest error observed at Φ = 1.0. Additionally, the prediction of laminar burning velocity (LBV) differed by approximately 4 % between the two models.Considering different fuel blends, two scenarios were compared: constant input thermal power and constant fuel flow rate. Efficiency in the constant input thermal power scenario maintained higher radiation efficiency, in the range of 32–38%. Additionally, radiation efficiency initially increased with increasing H2 content but subsequently decreased for high H2 values due to effects on flame area, flame position, and temperature.

Influence of roughness and temperature on the emissivity of molybdenum in RTPV system

In this paper, the effect of different surface roughness and temperature on molybdenum's emissivity was studied. We measured and analyzed the emissivity of molybdenum with surface roughness ranging from 5 to 103 nm at 25, 600, 800, and 1030 °C. The emissivity of molybdenum increases with the temperature and surface roughness. For molybdenum with a flat surface, the emissivity is relatively low within the temperature range of 600–1000 ℃, with an average emissivity of less than 0.1. Whereas for samples with large roughness, the average emissivity is greater than 0.1 and changes significantly with temperature. Considering the cutoff wavelength of 2.2 μm for InGaAs cell, the proportion of the spectrum emitted by the samples at 600 ℃ in the 1–2.2 μm is around 10 %. At 1030 °C, the proportion reaches 44.1 % for the flat molybdenum and gradually declines with the surface roughness. Moreover, the effect of the surface roughness of molybdenum on the radioisotope thermophotovoltaic (RTPV) system was analyzed. The results show that a molybdenum emitter with larger roughness can improve the conversion efficiency of the RTPV system.

Efficient solar energy harvesting via thermally stable tungsten-based nanostructured solar thermophotovoltaic systems

Electromagnetic radiations are a key energy source, which, by deploying bandgap-engineered devices, are directed onto PV cells to maximize their utilization. In this regard, the Solar Thermophotovoltaic (STPV) systems are vital, consisting of an intermediate absorber-emitter assembly between sunlight and solar cells. A theoretical and computational demonstration of a highly thermally robust, angularly stable, polarization-insensitive, and compact tungsten-based broadband absorber and spectrally selective emitter in symmetric metal-insulator-metal (W-SiO2-W) configuration has been presented. The nanoscale absorber consists of four differently-sized cylinders forming a supercell, and the emitter is cylindrical. The absorber has been optimized over a range of operating temperatures and solar irradiances, manifesting a very high absorption for the visible region with an average of 98.09 % for 400 – 800 nm, exhibiting > 99 % absorption for a BW of 225 nm with a peak of 99.99 % at 674 nm. The emitter has been optimized with 99.72 % emissivity at the desired spectral location. The absorber’s intermediate efficiency is 99.91 % for 5000 suns at 800 °C, which is as high as 72.33 % at a target temperature of 3200 °C. This study aims to match a higher bandgap of 1.5 eV perovskite solar cells and realize higher efficiency than tandem solar cells. The solar cell efficiency is 42.39 %, which results in solar-to-electricity efficiency of 42.38 %, exceeding the Shockley-Queisser (SQ) limit. As a proof-of-concept using a simulation program SCAPS-1D, a perovskite solar cell is illuminated using a bandgap-matched photon, increasing its efficiency from 26.67 % to 45.79 %. Thus, the presented idea achieves cell efficiency beyond the SQ limit without employing complex tandem cells.

Enhancing overall performance of thermophotovoltaics via deep reinforcement learning-based optimization

Thermophotovoltaic (TPV) systems can be used to harvest thermal energy for thermoelectric conversion with much improved efficiency and power density compared with traditional photovoltaic systems. As the key component, selective emitters (SEs) can re-emit tailored thermal radiation for better matching with the absorption band of TPV cells. However, current designs of the SEs heavily rely on empirical design templates, particularly the metal-insulator-metal (MIM) structure, and lack of considering the overall performance of TPV systems and optimization efficiency. Here, we utilized a deep reinforcement learning (DRL) method to perform a comprehensive design of a 2D square-pattern metamaterial SE, with simultaneous optimization of material selections and structural parameters. In the DRL method, only the database of refractory materials with gradient refraction indexes needs to be prepared in advance, and the whole design roadmap will automatically output the SE with optimal Figure-of-Merit (FoM) efficiently. The optimal SE is composed of a novel material combination of TiO2, Si, and W substrate, with its thickness and structure precisely optimized. Its emissivity spectra match well with the external quantum efficiency curve of the GaSb cell. Consequently, the overall performance of TPV is significantly enhanced with an output power density of 5.78 W/cm2, an energy conversion efficiency of 38.26%, and a corresponding FoM of 2.21, surpassing most existing designs. The underlying physics of optimal SE is explained by the coupling effect of multiple resonance modes. This work advances the practical application potential of TPV systems and paves the way for addressing other multi-physics optimization problems and metamaterial designs.

Novel composite could vastly improve thermophotovoltaic systems

Neural network identifies novel material that could help power future green engines from hybrid electric vehicles on Earth to spacecraft for deep space exploration.

Design and optimization of near-field thermophotovoltaic systems using deep learning

Design and optimization of near-field thermophotovoltaic systems using deep learning

A novel micro-combustor with dual-inlets hedging and center opening for enhancing comprehensive performance of micro thermophotovoltaic system

Micro-combustor outer wall temperature uniformity is a critical bottleneck in the widespread application of micro thermophotovoltaic system. In this study, we proposed a novel micro-combustor with dual-inlets hedging and center opening structure to improve the wall temperature distribution and achieve a stable and high-energy of micro thermophotovoltaic system output, and we applied the overall performance evaluation criteria to evaluate the performance of micro thermophotovoltaic system comprehensively. Initially, we conducted a comparative analysis among the traditional micro-combustor, the single rectangular center opening, and the double rectangular center opening micro-combustor. The findings indicate that the double rectangular center opening micro-combustor exhibits superior comprehensive thermal performance, showcasing a mean outer wall temperature and temperature standard deviation of 1362.05 K and 32.77 K, bringing better temperature uniformity. Then, the center opening distance of the double rectangular center opening micro-combustor was optimized from 0.5 mm to 3.0 mm, the results reveal that the double rectangular center opening micro-combustor with a distance of 2.5 mm possesses the best comprehensive performance, specifically, temperature standard deviation and overall performance evaluation criteria values of 23.17 K and 4.882. Ultimately, the effect of inlet velocity on the thermal performance was investigated, revealing that an increase in inlet velocity stimulates the output energy, but concurrently diminishing the energy conversion efficiency, leading to a reduction in overall thermal performance. This study introduces a novel concept for designing micro-combustor structures for promoting overall performance of micro thermophotovoltaic systems.

Hot-carrier thermophotovoltaic systems

A thermophotovoltaic (TPV) energy converter harnesses thermal photons emitted by a hot body and converts them to electricity. When the radiative heat exchange between the emitter and photovoltaic cell is spectrally monochromatic, the TPV system can approach the Carnot thermodynamic efficiency limit. Nonetheless, this occurs at the expense of vanishing extracted electrical power density. Conversely, a spectrally broadband radiative heat exchange between the emitter and the cell yields maximal TPV power density at the expense of low efficiency. By leveraging hot-carriers as a means to mitigate thermalization losses within the cell, we demonstrate that one can alleviate this trade-off between power density and efficiency. Via detailed balance analysis, we show analytically that one can reach near-Carnot conversion efficiencies close to the maximum power point, which is unattainable with conventional TPV systems. We derive analytical relations between intrinsic device parameters and performance metrics, which serve as design rules for hot-carrier-based TPV systems.

Effect of NH3/H2/O2 premixed combustion on energy conversion enhancement and NOx emission reduction of the segmented nozzle micro-combustor in thermophotovoltaic system

In the context of international carbon neutrality, ammonia as a carbon-free energy has attracted extensive attention and research, and its renewability is the most prominent advantage. However, ammonia combustion is unstable, and harmful nitrogen oxides will be generated at the same time. In order to enhance the combustion stability of ammonia and control the emission of nitrogen oxides, the premixed combustion of NH3/H2/O2 in a segmented nozzle micro-combustor is studied in this paper. The mean wall temperature of segmented micro-combustor is 11.5 K higher than that of non-segmented micro combustor, and NO emission is reduced by 7.91 % at most. When mass fraction of hydrogen in the gas mixture XH2 increases from 10 % to 30 %, radiation efficiency increases by 13.5 %, but NO emission also increases. Considering that fuel-rich combustion can reduce NO emission, when hydrogen equivalence ratio ΦH2 = 1.0 and ammonia equivalence ratio ΦNH3 = 1.2, NO emission is reduced by 13.3 %, while radiation efficiency remains above 60 %. In addition, the radiation efficiency of the combustor increases by up to 4.15 % when the dimensionless length of segmented channel L6 is 7.5 mm and the dimensionless width of segmented channel D4 is 2.5 mm, and NO emission is reduced by 5.14 %.

A Highly Efficient, Selective, and Thermally Stable Dielectric Multilayer Emitter for Solar Thermophotovoltaics

Herein, the design, optimization, fabrication, and characterization of a highly efficient selective emitter (SE) for solar thermophotovoltaic systems is presented. An SE consisting of three layers (SiNx–SiO2–TiO2) deposited on a tungsten substrate is optimized for use with photovoltaic (PV) cells based on III–V semiconductors, such as GaSb, InGaAs, and InGaAsSb. The fabricated SE shows an emitter efficiency (ηSE) of 50% when coupled with a PV cell having an energy bandgap of 0.63 eV. After thermal treatment carried out at 1000 °C for 8 h in a vacuum environment, ηSE of 46% is recorded, demonstrating the thermal stability of the proposed SE. Its behavior at high temperatures has also been studied using simulations based on the transfer matrix method and on refractive indices experimentally measured at different temperatures (up to 1000 °C). The results show ηSE of 44% in the energy bandgap range of 0.55–0.63 eV, proving that the proposed structure is promising and can operate at high temperatures. In addition, the behavior of a real PV cell is simulated, and calculations show a maximum PV cell efficiency of 15% at 1000 °C and 25% at 1600 °C, exceeding the Shockley–Queisser limit.

Improvement strategy evaluation from coupled energy-flow perspective on the GaSb thermophotovoltaic cell

Thermophotovoltaic (TPV) emerges as a novel high-efficiency generation technology, showcasing enormous potential in various sustainable energy solutions. Aiming to understand the complex conversion process between radiative, electrical and thermal energies within TPVs, a multi-physics coupled model is established. From the heat generation, temperature and carrier perspectives, the output performance is analyzed in detail. Under 1200 K black-body radiation, the energy loss distribution in the GaSb cell is analyzed meticulously, where Joule heat (40.4 %), surface recombination heat (23.1 %) and thermalization heat (20.8 %) play predominant roles. As it stands, the cell temperature rises to a maximum of 317.0 K with a cooling intensity of 300 W/(m2·K). The minimum of the average cell temperature (approximately 312.3 K) occurs at the optimized working voltage of 0.3 V. Subsequently, the electrical characteristics are illustrated. The results indicate a maximum output power underestimation of 4.6 % compared to the uncoupled isothermal case. Based on the coupled model, a quantitative analysis of the anti-reflection coating (ARC), the structural adjustment (SA) and the selective emitter (SE) is conducted. The results reveal that the ARC case exhibits the most enhancement in the output power (55.3 %) followed by the SA case, which effectively improves it by 12.2 %. Although the SE case partially decreases the output power (−9.8 %), it shows promise in promoting conversion efficiency. Integrating the above strategies, the TPV system achieves an impressive conversion efficiency of 29.38 %, representing a 76.46 % improvement compared to the prototype with the cell only.