In a recent article published in the journal Case Studies in Thermal Engineering, researchers investigated the potential of solar energy to power a thermoelectric refrigerator (TER) for cooling purposes. They focused on designing, developing, and testing a solar-powered thermoelectric refrigerator (SPTR) with and without a solar tracking system (STS) under local climate conditions. They also assessed how dual-axial photovoltaic (PV) solar tracking impacts the SPTR's efficiency.
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Background
Thermoelectric cooling uses the Peltier effect, where an electric current generates a temperature difference across a thermoelectric module (TEM). This process moves heat from one side of the module to another, producing cooling on the cold side and heating on the hot side.
Compared to conventional refrigeration systems, thermoelectric cooling has several advantages: it has no moving parts, uses no refrigerants, operates quietly, boasts high reliability, and integrates easily with renewable energy sources.
Solar energy is a clean, abundant source of power that can be converted into electricity using photovoltaic (PV) panels. This electricity is then used to power various devices and applications.
Solar energy is particularly suitable in remote and rural areas with limited access to the power grid. However, solar energy effectiveness can fluctuate with weather conditions, time of day, and geographic location. Therefore, optimizing solar energy usage is crucial for maximizing efficiency across applications.
About the Research
In this paper, the authors introduced a compact-sized SPTR. Their setup included solar cells, the STS, a pyranometer, a data logger, a multimeter, thermocouples, and the TER.
The TER was constructed using acrylic, polyurethane, aluminum, and a TEM model TEC1-12706.
Heat dissipation from the TEM's hot side was managed with a sunflower heat sink and a cooling fan.
The TER's cooling load was determined by calculating the product, transmission, and miscellaneous loads. It had a volume of 7.50 liters and used water as the cooling medium.
Two 75 W PV panels powered the TER and the STS. The STS, made from cast iron, bearings, anemometers, gears, and motor systems, allowed the PV panels to track the sun's position throughout the day with dual-axis rotation.
The experiments were performed in two stages: first, with the PV panels fixed and directly connected to the TER, and second, with the panels mounted on the dual-axis STS.
Various performance parameters, such as voltage, current, power, temperature, heat transfer, cooling rate, and coefficient of performance (COP), were measured and recorded using various instruments and data logging systems.
Research Findings
The outcomes showed a linear relationship between the solar insolation rate, voltage, and current from the solar panels and the time of day, peaking around noon.
The STS significantly improved these values compared to the fixed solar panel, allowing the SPTR to capture more solar energy and generate more power.
The PV system's energy conversion efficiency (ECE) decreased until noon due to increased solar cell temperatures but improved for the rest of the day. The STS-based system achieved a 29% higher ECE than the fixed panel system.
The temperatures on the hot and cold sides of the TEM and the heat sink surface varied with ambient temperature. For the fixed panel SPTR, the cold side temperature dropped from 25 °C to 0 °C, while the STS-based SPTR showed a decrease from 25 °C to 5 °C.
The hot side temperature raised from 25 °C to 36 °C with the fixed panel, and from 25 °C to 37 °C with the STS-based system.
Inside the TER, water temperature was reduced from 25 °C to 1.5 °C with the fixed panel and from 25 °C to 0 °C with the STS-based system. These results indicate that the STS-based SPTR achieved better cooling performance and reached the desired refrigeration temperature faster than the fixed panel SPTR.
The system’s COP varied with input power and cooling rate. The highest COP occurred at the maximum cooling rate and the lowest input power.
The STS-based system exhibited a higher COP than the fixed system, with maximum values of 2.07 and minimum values of 0.39, compared to the fixed system's maximum of 1.19 and minimum of 0.27.
Overall, the STS-based system demonstrated greater efficiency and effectiveness, achieving a COP enhancement of 44-75% over the fixed system.
Conclusion
The SPTR demonstrated robustness, effectiveness, and efficiency in powering a TER for various cooling applications. It proved suitable for preserving food, medicines, and vaccines below ambient temperature and was feasible for use in remote and rural areas. It could also serve in other low-temperature applications, such as electronics cooling, thermal management, and air conditioning.
The SPTR offers a sustainable and environmentally friendly refrigeration solution as it operates without refrigerants, moving parts, or fluids, reducing greenhouse gas emissions and reliance on conventional energy sources.
Moving forward, the researchers recommend optimizing the TER's design and materials, integrating a battery or supercapacitor for energy storage, and performing a techno-economic analysis of the SPTR system.
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Source:
Qamar, A., et, al. Advancing sustainable cooling: Performance analysis of a solar-driven thermoelectric refrigeration system for eco-friendly solutions. Case Studies in Thermal Engineering, 2024, 60, 104781. DOI: 10.1016/j.csite.2024.104781, https://www.sciencedirect.com/science/article/pii/S2214157X24008128