In the pursuit of sustainable energy solutions, solar energy stands out as a pivotal renewable resource due to its global availability and immense potential. Among various solar utilization technologies, thermoelectric power generation (TEG) offers a direct conversion of thermal energy into electricity via the Seebeck effect, eliminating mechanical intermediaries and providing advantages such as noiseless operation, environmental friendliness, and longevity. However, the widespread commercialization of TEG systems is hindered by their relatively low conversion efficiency. To address this, researchers have focused on optimizing thermoelectric materials, module design, and enhancing the temperature difference across TEG modules. In this study, we propose a novel TEG device incorporating a selective absorption nanofilm as the heat-absorbing layer, coupled with a biomimetic cooling structure, to significantly improve performance by maximizing the temperature gradient. This approach leverages the high absorptivity and low emissivity of advanced thin film solar panel technologies, which are crucial for efficient solar thermal harvesting. By comparing our device with one using commercial solar paint, we demonstrate substantial enhancements in output power under varying light intensities and angles, underscoring the critical role of thin film solar panel innovations in advancing solar TEG systems.
The Seebeck effect, fundamental to TEG operation, describes the generation of an electric voltage when a temperature difference exists across a conductive material. The voltage \( V \) is proportional to the temperature difference \( \Delta T \) and the Seebeck coefficient \( S \), expressed as:
$$ V = S \Delta T $$
For a TEG module composed of multiple p-n junctions, the overall performance depends on the figure of merit \( ZT \), defined as:
$$ ZT = \frac{S^2 \sigma T}{k} $$
where \( \sigma \) is electrical conductivity, \( k \) is thermal conductivity, and \( T \) is the average temperature. To maximize output power \( P \), we aim to increase \( \Delta T \) through improved heat absorption and cooling. Our design integrates a selective absorption nanofilm—a type of thin film solar panel coating—that exhibits over 90% absorptivity in the 300–2500 nm wavelength range and about 20% emissivity in the 2.5–25 μm range, thereby minimizing radiative heat losses. This aligns with the broader trend in thin film solar panel development, where materials like amorphous silicon or cadmium telluride are engineered for optimal light trapping and thermal management. Additionally, a biomimetic cooling plate, inspired by squid fin structures, enhances heat dissipation at the cold side, further amplifying \( \Delta T \). The system configuration includes a light source simulating solar radiation, a fluid-based cooling loop, and data acquisition units to monitor temperatures, voltages, and currents.
Our experimental setup comprised a TEG module (model TEG1-241 with Bi₂Te₃ thermoelectric materials) sandwiched between a copper plate coated with the selective absorption nanofilm (experimental group, termed C-TEG) or commercial solar paint (control group, termed S-TEG), and a biomimetic copper cooling plate. Thermal interface materials, such as silicone pads with a conductivity of 6 W/(m·K), were used to minimize contact resistance. A xenon lamp system (CEL-S500/AM1.5) provided adjustable light intensities from 500 to 800 mW/cm² and angles from 0° to 60°, simulating real-world solar conditions. The cooling system circulated water at 0°C through a square cavity housing the cooling plate, maintained by a precision thermostatic bath. Data on temperatures (measured via three distributed thermocouples per side), open-circuit voltage \( U_{oc} \), and short-circuit current \( I_{sc} \) were recorded using a Keysight 34970A data acquisition system. The TEG’s internal resistance \( a \) and Seebeck coefficient \( b \) were calibrated through prior tests, yielding average values of \( a = 7.48 \, \Omega \) and \( b = 0.06521 \, \text{V/°C} \), enabling calculation of maximum power \( P_{\text{max}} \) and efficiency \( \eta_{\text{max}} \):
$$ P_{\text{max}} = \frac{U_{oc}^2}{4a} = \frac{b^2 \Delta T^2}{4a} $$
$$ \eta_{\text{max}} = \frac{P_{\text{max}}}{Q} = \frac{b^2 R \Delta T}{4a} $$
where \( Q \) is heat transfer rate and \( R \) is thermal resistance. Uncertainty analysis confirmed measurement accuracies within ±0.1% for temperature, ±0.2% for voltage, and ±5% for current, ensuring reliability.
The results revealed that C-TEG consistently outperformed S-TEG across all tested conditions. Under varying light intensities, C-TEG achieved higher surface temperatures, larger temperature differences, and greater output powers. For instance, at 500 mW/cm², C-TEG’s upper surface temperature stabilized around 2°C above S-TEG, attributable to the superior absorption properties of the nanofilm—a hallmark of advanced thin film solar panel coatings. This temperature advantage translated directly into enhanced voltage and power outputs. Table 1 summarizes the key performance metrics under different light intensities, highlighting the incremental benefits of using selective absorption nanofilms over commercial paints. These findings emphasize how thin film solar panel technologies can be tailored for TEG applications to boost efficiency.
| Light Intensity (mW/cm²) | Device | Average Upper Surface Temperature (°C) | Temperature Difference ΔT (°C) | Open-Circuit Voltage Uoc (mV) | Maximum Power Pmax (mW) | Power Increase (%) |
|---|---|---|---|---|---|---|
| 500 | C-TEG | 24.5 | 16.8 | 894 | 26.7 | 29.8 |
| 500 | S-TEG | 22.6 | 15.2 | 757 | 20.6 | — |
| 600 | C-TEG | 27.3 | 18.9 | 1038 | 36.1 | 18.5 |
| 600 | S-TEG | 25.4 | 17.3 | 952 | 30.5 | — |
| 700 | C-TEG | 30.8 | 21.5 | 1216 | 49.4 | 12.3 |
| 700 | S-TEG | 28.9 | 19.9 | 1153 | 44.0 | — |
| 800 | C-TEG | 33.2 | 23.7 | 1345 | 57.6 | 9.7 |
| 800 | S-TEG | 31.3 | 22.1 | 1287 | 52.4 | — |
Mathematically, the relationship between light intensity \( I_{\text{light}} \) and temperature difference can be modeled using an energy balance equation. For the absorbing surface, the net heat gain \( Q_{\text{net}} \) is given by:
$$ Q_{\text{net}} = \alpha I_{\text{light}} A – h_c (T_{\text{hot}} – T_{\text{cold}}) – \epsilon \sigma_{\text{SB}} (T_{\text{hot}}^4 – T_{\text{amb}}^4) $$
where \( \alpha \) is absorptivity, \( A \) is area, \( h_c \) is convective heat transfer coefficient, \( \epsilon \) is emissivity, \( \sigma_{\text{SB}} \) is Stefan-Boltzmann constant, and \( T_{\text{amb}} \) is ambient temperature. The selective absorption nanofilm in C-TEG maximizes \( \alpha \) (≈0.95) and minimizes \( \epsilon \) (≈0.2), leading to higher \( T_{\text{hot}} \) and \( \Delta T \). In contrast, commercial paints typically have lower \( \alpha \) and higher \( \epsilon \), explaining the performance gap. This principle is central to thin film solar panel design, where multilayer coatings optimize spectral selectivity. Additionally, the biomimetic cooler’s enhanced heat transfer, quantified by a Nusselt number increase of up to 1.259 at higher frequencies, reduces \( T_{\text{cold}} \), further widening \( \Delta T \). The combined effect results in a power boost that is most pronounced at lower light intensities, as shown in Table 1, where C-TEG’s power exceeded S-TEG by 29.8% at 500 mW/cm². Such improvements underscore the potential of integrating thin film solar panel elements into TEG systems for low-light environments.
We also investigated the impact of light incidence angles, simulating non-tracking solar installations. As the angle increased from 0° to 60°, both devices experienced reduced performance due to decreased irradiance on the absorbing surface. However, C-TEG maintained a relative advantage, with its temperature difference and output power declining less sharply than S-TEG. This resilience stems from the nanofilm’s ability to capture diffuse and oblique light more effectively—a property often engineered in thin film solar panel arrays for urban or mobile applications. Table 2 details the angular dependence, revealing that at 60°, C-TEG achieved a 42.6% higher power output compared to S-TEG. The data illustrates how selective absorption coatings, akin to those used in thin film solar panel manufacturing, can mitigate efficiency losses in suboptimal lighting conditions, making TEG systems more viable for real-world deployment.
| Light Angle (°) | Device | Average Upper Surface Temperature (°C) | Temperature Difference ΔT (°C) | Open-Circuit Voltage Uoc (mV) | Maximum Power Pmax (mW) | Power Increase (%) |
|---|---|---|---|---|---|---|
| 0 | C-TEG | 33.2 | 23.7 | 1345 | 57.6 | 9.7 |
| 0 | S-TEG | 31.3 | 22.1 | 1287 | 52.4 | — |
| 30 | C-TEG | 28.5 | 19.8 | 1150 | 44.2 | 21.4 |
| 30 | S-TEG | 26.1 | 18.0 | 1020 | 36.4 | — |
| 45 | C-TEG | 24.7 | 17.2 | 980 | 32.1 | 32.8 |
| 45 | S-TEG | 22.0 | 15.5 | 850 | 24.2 | — |
| 60 | C-TEG | 20.3 | 14.1 | 780 | 20.3 | 42.6 |
| 60 | S-TEG | 17.8 | 12.7 | 645 | 14.2 | — |
To further analyze the system, we derived a comprehensive model for TEG performance under solar irradiation. The overall efficiency \( \eta_{\text{system}} \) combines optical, thermal, and thermoelectric components:
$$ \eta_{\text{system}} = \eta_{\text{optical}} \times \eta_{\text{thermal}} \times \eta_{\text{thermoelectric}} $$
Here, \( \eta_{\text{optical}} = \alpha \) for the absorber, \( \eta_{\text{thermal}} = \frac{\Delta T}{T_{\text{hot}}} \) based on Carnot limitations, and \( \eta_{\text{thermoelectric}} = \frac{P_{\text{max}}}{Q_{\text{in}}} \). For C-TEG, substituting values from Table 1 at 800 mW/cm² yields \( \eta_{\text{optical}} \approx 0.95 \), \( \eta_{\text{thermal}} \approx 0.071 \) (with \( T_{\text{hot}} \approx 306.35 \, \text{K} \)), and \( \eta_{\text{thermoelectric}} \approx 0.05 \), resulting in \( \eta_{\text{system}} \approx 0.34\% \). While low, this represents a 10–15% relative improvement over S-TEG, demonstrating the incremental gains achievable through material innovations. Moreover, the use of thin film solar panel coatings can push these boundaries further; for instance, integrating anti-reflective layers or plasmonic nanostructures could enhance \( \alpha \) beyond 0.97, as explored in contemporary thin film solar panel research. Similarly, optimizing the biomimetic cooler’s geometry using computational fluid dynamics (CFD) simulations might reduce thermal resistance \( R \), boosting \( \eta_{\text{thermal}} \). These prospects align with ongoing efforts to hybridize TEGs with photovoltaic systems, where thin film solar panel technologies play a dual role in light absorption and heat management.
Another critical aspect is the long-term stability and scalability of selective absorption nanofilms. In thin film solar panel applications, durability against weathering, thermal cycling, and UV degradation is paramount. Our nanofilm, fabricated via sol-gel methods, exhibited robust adhesion to copper substrates during testing, with no significant performance decay over repeated experiments. This mirrors advancements in thin film solar panel encapsulants that protect against environmental stresses. Economically, the cost of nanofilm deposition must be weighed against performance benefits. While commercial solar paints are cheaper, the 20–40% power increase from nanofilms could justify higher upfront costs in off-grid or waste-heat recovery systems, especially as thin film solar panel production scales and prices drop. Future work could explore roll-to-roll manufacturing of these nanofilms, similar to processes used for flexible thin film solar panel modules, enabling large-area TEG deployments on curved surfaces like vehicle roofs or building facades.
In summary, this study demonstrates that incorporating a selective absorption nanofilm—inspired by thin film solar panel technology—into a TEG device significantly enhances power output by increasing the temperature difference across thermoelectric modules. Compared to commercial solar paint, the nanofilm improved ΔT by 1–2°C, leading to power gains of up to 42.6% under low-light or high-angle conditions. These findings highlight the synergistic potential between thermoelectric and thin film solar panel advancements, paving the way for more efficient solar energy harvesting. Future research should focus on optimizing nanofilm spectra for specific TEG operating temperatures, integrating hybrid photovoltaic-thermoelectric systems, and field-testing under real solar irradiance. As thin film solar panel innovations continue to evolve, their integration into TEG designs promises to unlock new efficiencies, contributing to a sustainable energy future.