A Hybrid Photovoltaic-Thermoelectric Energy Harvester for Day and Night Automobile Applications

Abstract

Automobiles and other industries waste substantial energy as heat. Conventional photovoltaic power generation in daylight is unavailable at night. In this study a portable hybrid photovoltaic–thermoelectric energy-harvesting prototype is developed to generate electrical power from solar energy during the day and thermal energy at night. The daytime subsystem used a monocrystalline-silicon photovoltaic panel positioned between adjustable aluminum reflectors. Reflector angles, voltage, and electrical power were measured with a protractor, multi-meter and power meter, while an Arduino-based photoresistor circuit monitored light intensity. The nighttime subsystem used four bismuth-telluride thermoelectric generators connected with an aluminum plate and heat sink; voltage was measured under clear and cloudy nighttime conditions. Dual reflectors increased photovoltaic power efficiency by up to 34%, with an optimum reflector angle near 43°, and the measured prototype results in power generation of 130 W m?², extrapolated to a potential 156 W for a typical windshield area. The thermoelectric subsystem produced a mean 62.97 mV under clear sky and 45.1 mV under cloudy sky, corresponding to reported power densities of 35.9 and 18.4 mW m?², respectively. The prototype demonstrates complementary day/night energy harvesting, although full-scale automobile validation and higher-output thermoelectric materials are needed.

Introduction

The text describes the design and experimental evaluation of a portable automobile-oriented energy-harvesting system that combines photovoltaic (PV) solar generation during the day with thermoelectric generation at night. The main goal is to recover otherwise unused ambient energy and provide an additional source of electrical power.

Main concept

The proposed device combines two complementary energy-harvesting mechanisms:

• Photovoltaic generation: A monocrystalline-silicon solar panel converts sunlight into electricity during the daytime.
• Thermoelectric generation: Bi?Te? thermoelectric generators (TEGs) convert a temperature difference into electrical voltage through the Seebeck effect, enabling nighttime energy harvesting.

The system is designed specifically for use around automobiles and aims to demonstrate that multiple low-power energy sources can be integrated into a single portable device.

Prototype design

The researchers developed five prototypes before arriving at the final design. The final prototype consists of:

• A foldable trifold solar concentrator.
• A 215 × 155 mm monocrystalline-silicon PV panel.
• Two adjustable aluminum reflectors.
• An Arduino Uno R4 Wi-Fi microcontroller.
• An LDR (light-dependent resistor) for continuous light monitoring.
• Four Bi?Te? TEG modules connected in series.
• Aluminum plates, thermal paste, and a finned heat sink.
• A power meter, multimeter, and power bank.

The solar subsystem captures and concentrates sunlight using adjustable reflectors. The thermoelectric subsystem uses the temperature difference between a hot automobile environment and a cooler radiating surface to generate electricity.

Solar-concentrator experiment

The researchers tested the PV panel under three configurations:

1. No reflector.
2. One reflector.
3. Two reflectors.

They also tested the system in front of and behind an automobile windshield and varied the reflector angles to identify the most effective configuration.

The results showed that adding reflectors increased solar output, with the dual-reflector configuration producing the greatest improvement.

Solar results

The main reported findings were:

• Single reflector: approximately 28.9% maximum increase in power efficiency.
• Dual reflectors: approximately 34.2% maximum increase.
• Optimal dual-reflector angle: approximately 43°.
• At around 43°, the efficiency gain was approximately 34.2% in front of the windshield.
• Behind the windshield, the gain was approximately 21.8%, reflecting losses caused by windshield transmission.
• An estimated 156 W of potential power was projected for a standard 1.5 m × 0.8 m windshield area.

The 156 W figure is an area-scaled engineering estimate, not a measurement from a full-size vehicle. Real-world performance could be affected by windshield losses, nonuniform illumination, reflector positioning, temperature, wiring losses, and available mounting area.

Light monitoring

An LDR connected to an Arduino Uno R4 Wi-Fi was used to continuously monitor light intensity. The measurements were recorded through the Arduino development environment, and the study also demonstrated wireless data transmission using an HC-06 Bluetooth module.

This monitoring capability allows the system to relate changing light conditions to PV performance.

Thermoelectric energy harvesting

The nighttime subsystem uses four TEG modules connected in series between:

• A black-painted aluminum plate on the upper/cold side.
• A finned aluminum heat sink on the lower/hot side.

The black surface enhances radiative heat exchange with the night sky, while the heat sink facilitates thermal transfer from the automobile's warmer environment. The resulting temperature difference across the TEGs generates electrical voltage.

The researchers tested the system under clear and cloudy nighttime skies, recording the resulting voltage and estimating current and power using manufacturer specifications.

Overall significance

The study demonstrates the feasibility of combining solar PV and thermoelectric energy harvesting in a single automobile-focused portable system. The solar subsystem benefits from adjustable reflectors, while the thermoelectric subsystem provides a complementary nighttime harvesting mechanism.

The key finding from the solar experiments is that dual reflectors positioned at approximately 43° can significantly increase PV output, achieving a reported maximum efficiency gain of about 34%. The thermoelectric component further expands the concept by attempting to harvest energy when solar generation is unavailable.

Conclusion

The present study demonstrates a hybrid automobile-oriented approach to renewable energy harvesting using adjustable-reflector photovoltaics during the day and bismuth-telluride thermoelectric generators at night. Dual reflectors increased photovoltaic power efficiency by up to 34%, with an optimum angle near 43°, and the prototype data were extrapolated to a potential 156 W over a standard windshield area. At night, the TEG assembly produced higher output under clear sky (62.97 mV; 35.9 mW m?²) than cloudy sky (45.1 mV; 18.4 mW m?²). The results establish proof of concept for complementary day/night harvesting, but the thermoelectric contribution remains small relative to solar generation. Future work should measure electrical energy directly with the microcontroller, automate data collection, develop a mobile monitoring application, evaluate improved TEG materials and thermal interfaces.

References

[1] Mahlalela, S. et al. Electric Power Generation Potential Based on Waste Heat and Geothermal Resources in South Africa. Stanford Geothermal Workshop (2019). [2] Al-Ezzi, A. S.; Ansari, M. N. M. Photovoltaic Solar Cells: A Review. Applied System Innovation 2022, 5 (4), 67. [3] Jouhara, H. et al. Thermoelectric Generator (TEG) Technologies and Applications. International Journal of Thermofluids 2021, 9, 100063. [4] Pepitone, J. Be Your Own Power Plant: Energy Harvesting Tech for Wearables Is Hitting Its Stride. IEEE Spectrum 2023. [5] United Nations. Ensure Access to Affordable, Reliable, Sustainable and Modern Energy. United Nations Sustainable Development Goals. [6] Omair, Z.; Assawaworrarit, S.; Fan, L.; Jin, W.; Fan, S. Radiative-Cooling-Based Nighttime Electricity Generation with Power Density Exceeding 100 mW/m². iScience 2022, 25, 104858. [7] Bukit, F. R. A.; Sani, A.; Hasugian, I. A.; Butar-Butar, T. D. P. The Effect of Solar Panel Tilt Angle with Reflector on the Output Power Using Calculation and Experimental Methods. In 6th International Conference on Electrical, Telecommunication and Computer Engineering (ELTICOM), 2022. [8] Circuit Basics. How to Use Photoresistors to Detect Light on an Arduino. [9] Precedence Research. Waste to Energy Market. [10] Assawaworrarit, S. et al. Nighttime Electric Power Generation at a Density of 50 mW/m² via Radiative Cooling of a Photovoltaic Cell. Applied Physics Letters 2022, 120, 143901. [11] Global Market Insights. Solar Energy Harvesting Market. [12] Data Bridge Market Research. Global Thermal Energy Harvesting Market. [13] Green Car Reports. Fact of the Week: Internal Combustion Cars Still Waste 70 to 88 Percent of Energy.

Copyright

Copyright © 2026 Ayan Bera. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.