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Solar energy demand is growing for future energy needs in different sectors to replace fossil fuels, which leads to a reduced carbon footprint and global warming. Evacuated tube solar collectors (ETSC) harness solar thermal energy for air heating, water heating, and drying in domestic and industrial sectors. The review paper comprises ETSC technology categorization, influencing factors like fin arrangement, integration of phase change material, tilt angle, solar radiation, and airflow rate on the performance of ETSC-based solar air heaters and dryers. The thermal performance parameters, like the collector efficiency, dryer efficiency, energy and exergy efficiency, thermal profile, zone temperature, relative humidity, heat loss during operations, etc., are reviewed. The developed ETSC-based air heating systems and solar dryers for drying agricultural products are performed effectively. However, research progress on improving the thermal performance integrated with nanofluids and phase change materials was discussed. CO 2 mitigation analysis and global standards for ETSC-based air heaters and dryers are compiled. A large scope exists by use of solar air heaters (SAH) for food commodity drying with a suitable drying chamber and improving the designs of ETSC-based solar dryers. The work accomplished by various researchers has been analyzed in this study for prospective research gaps in the context of future design and development. Graphical abstract

An indirect-type forced convection solar dryer implementing a phase-changing material (PCM) as the energy-storing medium was designed, fabricated, and investigated in this study. The effects of changing the mass flow rate on the valuable energy and thermal efficiencies were studied. The experimental results showed that the instantaneous and daily efficiencies of the indirect solar dryer (ISD) increased with the initial increase in mass flow rate, beyond which the change is not prominent both with and without using the PCM. The system consisted of a solar energy accumulator (solar air collector with a PCM cavity), a drying compartment, and a blower. The charging and discharging characteristics of the thermal energy storage unit were evaluated experimentally. It was found that after using PCM, drying air temperature was higher than ambient air temperature by 9–12 ℃ after sunset for 4 h. Using PCM accelerated the process by which Cymbopogon citratus was effectively dried between 42 and 59 °C of drying air. Energy and exergy analysis of the drying process was performed. The daily energy efficiency of the solar energy accumulator reached 35.8%, while the daily exergy efficiency reached 13.84%. The exergy efficiency of the drying chamber was in the range of 47–97%. A free energy source, a large reduction in drying time, a higher drying capacity, a decrease in mass losses, and improved product quality all contributed to the proposed solar dryer’s high potential.

Regarding the detrimental impacts of using non-renewable energy resources on the environment and the importance of increasing heat transfer in heat exchangers, this research is aimed to increase the heat transfer surface of the collector pipe in contact with the absorber plate at the flat-plate solar collector by designing the pipe in a zigzag shape instead of conventional straight pipe. The 3D coupled investigation of fly ash–Cu/water hybrid nanofluids and analyzing the thermal performance of the proposed solar collector comprising zigzag pipe are the innovation of this research. Also, the effect of variations in mass flow rate, fluid inlet temperature, the volume fraction of nanoparticles on thermal efficiency, Nusselt number, pressure drop, Rayleigh number, and rate of heat transfer coefficient in three irradiations with two types of working fluids have been investigated. Results indicate that due to the enhancement in heat transfer surface in the case where the fluid path is zigzag, the thermal efficiency has improved compared to the straight pipe. In addition, with enhancing mass flow rate, temperature, and irradiation, the average Nusselt number increased. The heat transfer coefficient and pressure drop have the highest value by utilizing 0.5% and 3.5% nanoparticle concentration up to 10.84% and 7.603%, respectively, at a mass flow rate of 0.0089 kg/s, and irradiation of 800 W/m 2 . Finally, by calculating the efficiency index of the proposed flat-plate solar collector, the proper volume concentration for using copper–fly ash/water hybrid nanofluid is obtained at fraction of 0.5% and a mass flow rate of 0.0045 kg/s.

Renewable cooling via absorption chillers being supplied by various green heat technologies such as solar collectors has been widely studied in the literature, but it is still challenging to get positive economic outcomes from such systems due to the large expenses of solar thermal systems. This study offers the use of a new generation of solar collectors, so-called eccentric reflective solar collectors, for driving single-effect absorption chillers and thereby reducing the levelized cost of cooling. This article develops the most optimal design of this system (based on several different scenarios) using multi-objective optimization techniques and employs them for a case study in Brazil to assess its proficiency compared to conventional solar-driven cooling methods. For making the benchmarking analyses fair, the conventional system is also rigorously optimized in terms of design and operation features. The results show that the eccentric solar collector would enhance the cost-effectiveness by 29%. In addition, using optimally sized storage units would be necessary to get acceptable economic performance from the system, no matter which collector type is used. For the case study, at the optimal sizing and operating conditions, the levelized cost of cooling will be 124 USD/MWh and an emission level of 18.97 kgCO 2 /MWh.

Food product drying is a crucial stage in the preservation of crops and agricultural by-products that are used as raw materials for numerous end applications. The novelty of the study is the application of a phase change material in a solar dryer to improve the effectiveness of drying and reducing the overall drying period for drying while retaining/improving the quality parameters of the dried dhekia ( Diplazium esculentum ). The modified indirect thermal storage integrated solar dryer made up of a single-pass solar collector is attached with the drying chamber of 16.5 kg capacity. A thermal energy storage system prepared with paraffin wax embedded inside the drying cabinet was used. The proposed solar dryer has a thermal efficiency that is 11 ± 0.2% greater than the conventionally constructed solar dryer and reduces drying time by 40 ± 2.1%. Drying kinetic analysis of dhekia was performed, and two new drying kinetic models were proposed to predict moisture ratio. From statistical analysis, it was found that the chi square value and root mean square error value fits well for the proposed models. The anti-oxidant, total phenolic content, and total flavonoid content values of samples dried in solar dryer exhibit better results compared to fresh, tray dried, and open sun-dried samples. The developed dryer shows better results in saving drying time and quality of the product. Due to its affordability and long-term solution for drying fresh farm goods, this dryer can be very helpful to small-scale farmers. Graphical abstract

Since the solar irradiation is accessible in many parts of our planet, it is a viable replacement for fossil fuels, so commissioning photovoltaic (PV) power plants are increased, rapidly. One of the main problems that this technology faces is the increase in the temperature of solar cells. In this paper, streaming water layer over the upper side of PV modules is considered as a cooling method. This technique not only lowers the surface temperature, but also keeps the surface clean. Four different water flow rates of 0.5, 1, 2, and 4 lit/min were used so that two different flow patterns, water streaks and water film, were formed. In addition, the negative effect of the residual water layer over the surface of the PV panel on the absorbed radiation was evaluated experimentally. As results, temperature drops of 20.6 °C and 29.7 °C were measured for flow rates of 0.5 and 2 lit/min, respectively. Also, for the case of 4 lit/min, the efficiency is increased by 6.7% compared to the conventional case. Moreover, it was observed that after the formation of a water layer, the water flow rate no longer has a significant effect on cooling. Finally, a comparison between the electrical efficiency enhancements of this study with those of similar researches was performed.

Uneven drying is the key drawback of a conventional multi-tray dryer. Therefore, an improved active solar dryer with and without integrated sensible heat storage (SHS) was proposed. A unique feature of this dryer is its movable walls from the sides of the dryer to transform it to an indirect or mixed-mode as and when necessary. Garcinia Pedunculata (GP) is a local seasonal medicinal fruit in Northeast India . Drying kinetics of GP, the dryer performance and economic analysis of dryer were evaluated in the indirect solar dryer without SHS (Exp. I), mixed-mode solar dryer without SHS (Exp. II), indirect solar dryer with SHS (Exp. III), mixed-mode solar dryer with SHS (Exp. IV), and open sun drying (OSD). The dryer’s average efficiencies were 18.12%, 22.37%, 21.74%, and 24.46% for Exp. I, Exp. II, Exp. III, and Exp. IV, respectively. The moisture content of GP was reduced to 12.09% in wet basis (w.b.) from 87.99% (w.b.). The overall drying time for Exp. I, Exp. II, OSD, Exp. III and Exp. IV were 31, 26, 53, 28, and 10 h, respectively. From the eleven drying models, the Two-Term model was the best-fitted model for Exp. I, Exp. II, OSD and Exp. III, and Midilli and Kucuk model was for Exp. IV. The final product’s fragrance and colour are better for Exp. IV. Developing this dryer for Exp. I, Exp. II, Exp. III and Exp. IV, the price required was around 25,000, 27,000, 26,000, and 28,000 INR (1 US$ = 74.57 INR), respectively, while the economic payback periods are 1.6 years, 0.9 year, 1.4 years, and 0.59 year, respectively.

Solar energy is one of the most feasible options to produce energy in countries where unexploited desert areas or solar radiation are abundant. An energy tower is an effective system for electrical power generation that can perform more efficiently along with solar radiation. As the primary aim of the present study, effects of different environmental parameters on total efficacy of energy tower were investigated. In this study, the efficiency of the energy tower system is investigated experimentally by an indoor fully adjustable apparatus. In this regard, a comprehensive set of influencing parameters like air velocity, humidity, and temperature and the effects of tower height on the performance of the energy tower are individually assessed. It is demonstrated that there is a direct relationship between an increase in humidity percentage of the surrounding and performance of energy tower, meaning that a 274% increase in humidification rate led to 43% elevation in airflow velocity. The kinetic energy increases in the direction of airflow from top to bottom, and as the height of the tower lengthens, the kinetic energy enhances and subsequently increases the overall efficiency of the tower. An elevation about 2.7% in airflow velocity was seen due to an increase from 180 to 250 cm in chimney height. Although the energy tower performs efficiently in the nighttime, airflow velocity increases averagely about 8% during the daytime and at the peak of the solar radiation, the airflow velocity enhances by 58% compared to nighttime.

Recently, the increasing prevalence of solar energy in power and energy systems around the world has dramatically increased the importance of accurately predicting solar irradiance. However, the lack of access to data in many regions and the privacy concerns that can arise when collecting and transmitting data from distributed points to a central server pose challenges to current predictive techniques. This study proposes a global solar radiation forecasting approach based on federated learning (FL) and convolutional neural network (CNN). In addition to maintaining input data privacy, the proposed procedure can also be used as a global supermodel. In this paper, data related to eight regions of Iran with different climatic features are considered as CNN input for network training in each client. To test the effectiveness of the global supermodel, data related to three new regions of Iran named Abadeh, Jarqavieh, and Arak are used. It can be seen that the global forecasting supermodel was able to forecast solar radiation for Abadeh, Jarqavieh, and Arak regions with 95%, 92%, and 90% accuracy coefficients, respectively. Finally, in a comparative scenario, various conventional machine learning and deep learning models are employed to forecast solar radiation in each of the study regions. The results of the above approaches are compared and evaluated with the results of the proposed FL-based method. The results show that, since no training data were available from regions of Abadeh, Jarqavieh, and Arak, the conventional methods were not able to forecast solar radiation in these regions. This evaluation confirms the high ability of the presented FL approach to make acceptable predictions while preserving privacy and eliminating model reliance on training data.

The Internet of Things (IoT) stands out as one of the most captivating technologies of the current decade. Its ability to connect people and things anytime and anywhere has led to its rapid expansion and numerous impactful applications that enhance human life. With billions of connected devices and substantial power and infrastructure requirements, the IoT system can pose a threat to the environment. However, the IoT’s vast range of resources and capabilities can also be leveraged to assist in environmental conservation in the evolution of technologies due to massive CO 2 emissions, climate change, and environmental and health issues. In this study, with the two-way integration of IoT and green practices, two distinct concepts for green IoT are presented. Among green practices, energy solutions play a vital role in greening the IoT. In this study, the energy solutions for the IoT system are divided as reducing energy consumption and using green energy sources. Solutions for reducing IoT energy consumption are studied systematically through a five-layer framework to simplify its modular design and implementation. Then, the use of green energy resources is discussed for all components of the IoT ecosystem. Leveraging IoT to make the environment and other technologies green is the other concept of green IoT. IoT technology plays a crucial role in enhancing both energy management systems and the efficient harvesting of renewable energy sources. Switching to solar energy from fossil fuel energy is one of the most fundamental green practices today. In this study, the mutual relationship between solar energy harvesting and the IoT is addressed specifically. Several promising research directions in the realm of green IoT are also highlighted.