• Energy Research

Abstract The upward energy demand, along with the depletion of conventional energy sources, demands improved utilization of renewable energy resources. Among all renewable energy resources, solar energy is the most appropriate alternative to conventional energy sources owing to its inexhaustibility and green property. Solar collectors are devices that convert solar radiation into heat or energy. However, the efficiency of the solar collector is still not adequate. The competent step to enhance the efficiency of the solar collector is to use nanofluids. This study is carried out different phases viz. characterization and stabilization while both qualitative and quantitative methods used to evaluate the stability of nanofluids thermophysical properties of Al2O3 and CNC nanofluids such as thermal conductivity measured at four different temperature using KD2 Pro, viscosity and specific heat determined at similar temperature range by viscometer and differential scanning calorimetry respectively. The experiment is executed with a fixed flow rate and in steady-state conditions under extensive solar radiation. The experimental study has revealed that up to 2.48% and 8.46% efficiency of solar collector enhanced by using 0.5% Al2O3 and 0.5% CNC nanofluids respectively. Moreover, nanofluids show good to moderate stability performance. Besides, the thermal conductivity of nanofluids increased while viscosity is in a decreasing trend with increasing temperature. Nanofluids could enhance the efficiency of a flat-plate solar collector.

The traditional approach of open-sun drying is facing contemporary challenges arising from the widespread adoption of energy-intensive methods and the quality of drying. In response, solar dryers have emerged as a sustainable alternative, utilizing solar thermal energy to effectively dehydrate vegetables. This study investigates the performance of a single-basin, double-slope solar dryer utilizing natural convection for drying bottle gourds and tomatoes, presenting a sustainable alternative to traditional open-sun drying. The solar dryer exhibited superior moisture removal efficiency, achieving a 94.42% reduction in tomatoes and 83.87% in bottle gourds, compared to open-sun drying. Drying rates were significantly enhanced, with maximum air and plate temperatures reaching 54.42 °C and 63.38 °C, respectively, accelerating the dehydration process. Moisture diffusivity analysis revealed a marked improvement in drying behavior under solar drying, with values ranging from 3.12 × 10-11 to 4.31 × 10-11 m2/s for bottle gourds, and 4.65 × 10-11 to 2.31 × 10-11 m2/s for tomatoes. Energy efficiency assessments highlighted the solar dryer's advantage, with exergy efficiency peaking at 61.78% for bottle gourds and 68.5% for tomatoes. Furthermore, the activation energy required for drying was significantly lower in the solar dryer (29.14-46.41 kJ/mol for bottle gourds and 27.16-55.42 kJ/mol for tomatoes) compared to open-sun drying, enhancing energy conservation. Visual inspections confirmed the superior quality of the solar-dried vegetables, free from dust and impurities. An economic analysis underscored the system's viability, with payback periods of 2 years for bottle gourds and 1.6 years for tomatoes. Overall, this study demonstrates the efficacy of solar dryers in optimizing vegetable preservation while promoting energy efficiency, aligning with global sustainability goals by reducing post-harvest losses and supporting eco-friendly practices.

Sustainable development goals not only contributes towards a clean environment but also towards better climatic conditions. Within Asia next to China and India, the Association of Southeast Asian Nations (ASEAN) are the actively developing countries in terms of economy and technologies. On the verge of achieving development, the ASEAN countries highly depend on fossil fuels for their energy needs. The ASEAN countries have taken visionary steps towards increasing the renewable energy mix with the conventional grid without hampering the ongoing development; this study presents the solar energy utilization policies, potential, progresses, and challenges adopted in ASEAN countries; furthermore, in these nations there is a huge potential of solar energy being located near the equator, therefore, they should focus on both solar to electrical and solar to thermal energy applications; however, in order to meet the peak demand and ensure the reliability of renewable energy like solar power, the development of advanced energy storage systems could be the key areas, and concrete efforts are required. Therefore, this article is a spotlight on government policies and goals focusing on energy potential, major progress in terms of energy storage and challenges in implementation of renewable energy systems in ASEAN countries; furthermore the recommended highlights on policies to accelerate the exploitation of renewable energy usage among the people are also discussed in detail, besides, the insights on reduction of carbon footprints over the next decade through incorporation of advanced energy storage systems. The issues discussed in this article will be helpful for exploring the desired energy storage systems and energy policies to be followed, which will eventually attract the stakeholders for small and medium-scale entrepreneurs for the development of renewable energy business in the region, if implemented on the ground.

Abstract Thermal energy storage (TES) is a technique that is considered a very desirable technology with a high potential to overcome the gap between demand and supply. Phase change materials (PCMs) are considered to be a highly favourable thermal energy storage materials. Besides that, PCM has certain drawbacks, such as lower thermal conductivity and higher light transmission; owing to this, the heat transfer rate and energy storage density are less. The performance of the PCMs can be improved by adding highly conductive nanoparticles. In this study, various weight percentages (0.1% - 5.0%) of Copper (II) oxide nanoparticles are dispersed with salt hydrate phase change materials with melting temperature 50 °C and investigated the thermal and chemical properties using Thermogravimetric analyzer, thermal conductivity analyzer, and Fourier transform infrared spectrum. Results shows that the prepared nanocomposites have chemically and thermally stable up to 467 °C. The thermal conductivity was increased by 62.64%, at 3.0 wt% Copper (II) oxide with salt hydrate PCM. The developed nanocomposites have better thermophysical properties than pure salt hydrate, which may be applied for TES applications like solar water heating, photovoltaic thermal systems, and electronic cooling systems.

Due to intermittent nature of solar energy, scientists and researchers are working to develop thermal energy storage (TES) systems for effectively use the solar energy. One promising avenue involves utilizing phase change materials (PCMs), but primary challenge lies in their limited thermal conductivity, which results in slower heat transfer rate and lower thermal energy storage density. The present research work demonstrates, to develop and explore a PCM composite by embedding salt hydrate and coper (II) oxide to enhance the heat transfer mechanism for potential utilization of TES material. The optical behavior, and thermal conductivity were analyzed by using Ultraviolet visible spectrum, and thermal property analyzer. The developed copper oxide dispersed PCM composite displayed the thermal conductivity was energized up to 71.5 % without affecting the other properties. Also, the optical absorptance was remarkably enhanced and the transmittance reduced to 87 %. Increasing the concentration of copper oxide nanoparticles in the salt hydrate PCM improves the optical absorptivity and heat conductivity. With these extraordinary abilities the nanocomposite could play a significant role in progress of sustainable TES with significance to contribute towards sustainable development goal of affordable and clean energy and climate change.

This article offers a trend of inventions and implementations of photocatalysis process, desalination technologies and solar disinfection techniques adapted particularly for treatment of industrial and domestic wastewater. Photocatalysis treatment of wastewater using solar energy is a promising renewable solution to reduce stresses on global water crisis. Rendering to the United Nation Environment Programme, 1/3 of world population live in water-stressed countries, while by 2025 about 2/3 of world population will face water scarcity. Major pollutants exhibited from numerous sources are critically discussed with focus on potential environmental impacts & hazards. Treatment of wastewater by photocatalysis technique, solar thermal electrochemical process, solar desalination of brackish water and solar advanced oxidation process have been presented and systematically analysed with challenges. Both heterogenous and homogenous photocatalysis techniques employed for wastewater treatment are critically reviewed. For treating domestic wastewater, solar desalination technologies adopted for purifying brackish water into potable water is presented along with key challenges and remedies. Advanced oxidation process using solar energy for degradation of organic pollutant is an important technique to be reviewed due to their effectiveness in wastewater treatment process. Present article focused on three key issues i.e. major pollutants, wastewater treatment techniques and environmental benefits of using solar power for removal of pollutants. The review also provides close ideas on further research needs and major concerns. Drawbacks associated with conventional wastewater treatment options and direct solar energy-based wastewater treatment with energy storage systems to make it convenient during day and night both listed. Although, energy storage systems increase the overall cost of the wastewater treatment plant it also increases the overall efficiency of the system on environmental cost. Cost-efficient wastewater treatment methods using solar power would significantly ensure effective water source utilization, thereby contributing towards sustainable development goals.

Phase change materials (PCMs) are increasingly gaining prominence in thermal energy storage due to their impressive energy storage capacity per unit volume, especially in applications with low and medium temperatures. Nevertheless, PCMs have significant limitations regarding their ability to conduct and store heat, primarily due to their inadequate thermal conductivity. One potential solution for improving the thermal conductivity of PCMs involves the inclusion of nanoparticles into them. However, a recurring issue arises after several thermal cycles, as most nanoparticles have a tendency to clump together and settle at the container’s base due to their low interfacial strength and poor compatibility. To address this challenge, including surfactants such as sodium dodecylbenzene sulfonate (SDBS) has emerged as a prevalent and economically viable approach, demonstrating a substantial impact on the dispersion of carbon nanoparticles within PCMs. The foremost objective is to investigate the improvement of thermal energy storage by utilizing graphene nanoplatelets (GNP), which are dispersed in A70 PCM at various weight percentages (0.1, 0.3, 0.5, 0.7, and 1.0), both with and without the use of surfactants. The findings indicate a remarkable enhancement in thermal conductivity when GNP with surfactants is added to the PCM, showing an impressive increase of 122.26% with a loading of 1.0 wt.% compared to conventional PCM. However, when 1.0 wt.% pure GNP was added, the thermal conductivity only increased by 48.83%. Additionally, the optical transmittance of the composite containing ASG-1.0 was significantly reduced by 84.95% compared to conventional PCM. Furthermore, this newly developed nanocomposite exhibits excellent stability, enduring 1000 thermal cycles and demonstrating superior thermal and chemical stability up to 257.51 °C. Due to its high thermal stability, the composite NePCM is an ideal candidate for preheating in industrial and photovoltaic thermal (PVT) applications, where it can effectively store thermal energy.