To make a better thermal storage system that uses air as the heat transfer fluid flowing through a packed-bed of ceramic spheres (Al 2 O 3 ) as thermal storage materials, the present work studied cases using multiple small-diameter thin tanks to replace a large-diameter big tank while keeping the same total volume and the same air flow rate. Performance analysis of thermal storage has been conducted for comparison and optimization. The long flow passage and faster flow velocity of air in the small-diameter tanks was found to significantly benefit thermal storage performance compared with that of a short big tank. It resulted in a longer duration of discharge of high-temperature airflow, if the same operation time is applied to the two situations. The faster airflow enhances the heat transfer between air and thermal storage material, although it incurs larger pressure loss. Overall, the energy storage efficiency of using several thin tanks can be significantly better than that of using a big short tank if the height-to-diameter ratio in the multiple thin tanks is properly optimized. The optimization methodology and results are of great significance to the development of thermal storage systems that use air as heat transfer fluid and rocks or ceramic spheres as the packed-bed material for thermal storage.

An integrated desalination system with a combination of electrical heating by power supply and solar heating by Fresnel lens with the sun tracking system was investigated in this study. The experiments were carried out under the climatic conditions of Kaohsiung City (22 deg36′58″ N, 120 deg18′47″ E), Taiwan. With only solar heating by the Fresnel lens, the temperature of the seawater is strongly dependent on the position of the seawater tray and climatic conditions, and seawater evaporation is not stable. To maintain the uniform evaporation of seawater, an electrical heating plate was also used to provide energy for the desalination process. The results indicate that there are two desalination processes: evaporation on the surface of the seawater and boiling inside the seawater. The production of distilled water is greatly improved with this solar/electrical desalination system, especially at the boiling temperature. The results indicate that the energy efficiency and recovery efficiency of this desalination system increase rapidly as electrical power increases. In this study, the commercial energy efficiency of the system can reach 85%, and the recovery efficiency can approach 56.52%. Additionally, a higher annual productivity (6036 l) is obtained, and the cost per liter of distilled water is about 0.152 (US$/l).

In this work, a humidification–dehumidification unit powered by solar energy was designed, constructed, and tested for brackish water desalination. In order to enhance the mass and heat transfer between feedwater and flowing air, 16 layers of wick were used as packing material. The results showed that the daily productivity increased by 28.28% when wick was used. The desalination unit with wick was tested at different temperatures and flowrates of feedwater. High significance positive relation between productivity and feedwater flowrate was found. The proposed system was also tested at a wide range of air flowrate. The results also showed that the peak value of productivity was achieved when the air flowrate was 0.0075 kg/s. It was also found that the daily productivity increased by 31.3% when the feedwater flowrate was increased from 0.114 to 0.171 kg/s when the air flowrate was 0.0075 kg/s.

Due to the increasing demand for air conditioners to maintain thermal comfort in buildings, it is necessary to search for alternatives that can reduce the soaring temperature and meet total air conditioning demands. There are several proven technologies for maintaining thermal comfort in buildings of which the use of phase change material (PCM) in buildings provides improved thermal comfort with fewer energy requirements. The present study analyzes the impact of the incorporation of PCM in roofs on the thermal behavior of buildings. The experiments were conducted in two identical model building roofs with and without the implementation of PCM. A numerical model was developed to find the effect of variation in the PCM layer thickness and month wise temperature variations. To get minimum variation in the results, the simulation was run continuously for 5 days assuming average climatic conditions. The results showed that temperature fluctuations in the room were reduced with the use of PCM, and also the average peak temperature rise was reduced by 2–4°C. The increased PCM layer thickness resulted in decreased energy demand for maintaining the required thermal comfort in buildings at an almost constant temperature.

This study numerically investigates the thermal behavior and airflow characteristics of the building-integrated photovoltaic (BIPV) façade. A three-dimensional model is developed based on the typical BIPV façade. Computational fluid dynamics (CFD) with the shear stress transport (SST) κ-omega turbulent model is used in the study. The effects of geometric configurations on the BIPV cell temperature in steady state are evaluated including the sizes of the bottom and top openings and the depth of the back air cavity (or so-called cavity depth). When the sizes of the inlet and outlet openings are the same, the effects on the decrease of cell temperature are limited. By enlarging the bottom (inlet) opening, the impact of ventilation in the cavity behind is more significant and the cell temperature decreases. Cavity depth is also a vital factor affecting BIPV cell temperature. The paper identifies the optimal cavity depth of approximately 100–125 mm. Flow disturbance and a vortex may be observed at the bottom and top of the air cavity, respectively, as the cavity depth increases which negatively affects the ventilation causing these flow disturbances to increase the cell temperature. Thermal effects of environmental conditions are compared with regard to two selected BIPV configurations. The wind velocity and the attack angle also have an obvious impact on cell temperature. Ambient temperature and solar irradiance exhibit a linear relationship with BIPV cell temperature as expected.

Low thermal conductivity is the main drawback of using paraffin wax as a latent heat thermal storage material in the solar air heater (SAH). In order to overcome this drawback, an absorber plate with extended surfaces through the paraffin wax was used. Two extended surface absorbers were used: a flat plate attached with downward fins and a V-corrugated plate. For the purpose of comparison, the SAH integrated with paraffin wax was tested using three proposed types of the absorber plate: flat, downward finned, and V-corrugated plates. The results showed superiority of the downward finned plate during the day. But the V-corrugated SAH remains the best choice for the applications in which the hot air is mostly needed during night as it is continuously operated for 7 h after sunset with the outlet air temperature of 8–11 °C more than the ambient air temperature.

With increasing energy consumption in buildings, energy efficiency measures are matter of prime concern. A huge portion of energy consumed in buildings is used for regulating the thermal comfort. A solution to this is to incorporate phase change material (PCM) within the building elements which increases their overall thermal capacity. In the present study, the temperature of inner room surface, with and without PCM incorporation, is calculated for composite climate of Delhi. The analysis of PCM sandwiched walls has been performed. The performance analysis of five PCMs, having different melting temperatures, is carried out with nodal temperatures as the output. The results show that a phase change temperature range of 34–38 °C is suitable for peak summer conditions of Delhi. It is also observed that due to the low thermal conductivity of PCMs, they act as both storage medium and insulation, thus reducing temperature fluctuation during summer/winter. Based on the simulation, three PCMs were found suitable and hence were experimentally tested for their characteristic charging and discharging properties and performance, using differential scanning calorimeter (DSC). Based on the characterization results, it is concluded that two commercially available PCMs (Eicosane and OM35) are suitable for Delhi. All the other PCMs have also been simulated for different climatic conditions in India and their impact on heat gain has been assessed.

The principle of solar chimney power plant (SCPP) is based on harvesting the thermal spectrum of solar radiation and converting it to mechanical energy by the means of a collector, a wind turbine, and a chimney. In this work, a number of experiments were performed on a modified model made up of one-third of the circular collector area. Field data from selected clear, sunny days were recorded and studied. The analysis focused on time-temperature relations for ambient, near chimney entry point and the collector periphery, in addition to hourly solar radiation intensity and air velocity inside the chimney. The results show that for this geometry arrangement, the maximum temperature of the air entering the chimney is achieved before the ambient temperature reaches its peak value. Air velocity inside the chimney depends on the intensity of solar radiation and the temperature difference between the air temperature entering the chimney and the ambient temperature. Solar intensity directly affects the temperature of air beneath the collector, and a part of this energy is stored in the ground. Later, when the solar radiation is impaired, the stored energy can be utilized. Air velocity of 2.1 m/s is obtained after the solar noon, when the solar intensity is 737 W/m 2 and the maximum temperature difference is 11.2 °C. Due to the unique geometrical shape of the rig, a minor temperature loss of up to 1.3 °C occurs for the air near the center of the chimney.

Missions to Mars need a power source, while, one of the most compatible sources for such a purpose is the photovoltaic system. Photovoltaic systems generate power based on the available energy from the Sun, and thus, solar radiation intensity at Mars should be known for design purposes. In this research, the feed-forward back-propagation artificial neural network is developed to predict solar radiation in terms of longitude, latitude, time of the day, temperature, altitude, pressure, amount of dust, and volume mixing ratio of water ice clouds. Data which are used to develop this model are obtained from the Mars Climate Database. The results of the developed method are accurate as compared with other methods whereas the correlation (R 2 ) coefficient for the developed model is 0.97. The developed model then is used to predict mean solar radiation and mean temperature for every location on Mars and then the data are presented on Mars maps in order to determine the best location for harvesting energy from the Sun by photovoltaic systems. According to results, the solar radiation-temperature belt on Mars is found to be between latitudes 20 deg south and 15 deg north.

In this paper, thermal-fluid modeling of nonporous/porous thermal coil filled by alumina nanofluid is discussed considering constant/variable solar heat fluxes. The fluxes are calculated for a parabolic concentrator at the solar paths for the city with a longitude of 59.20 deg and latitude of 32.87 deg in the clear sky at spring season. The governing equations are included as continuity, momentum, and energy conservations with considering variable solar flux by shadow effects of the coil on the parabolic concentrator. The numerical model is based on the finite element method by LU algorithm using the mumps solver. The results show that, in a porous medium, that the normalized temperature of the presented model has an acceptable agreement with experimental data with maximum errors of 3%. The existence of porosity significantly increases heat transfer parameters that improve transferred solar heat from the wall of the coil to nanofluid. The variable solar heat flux increases the temperature in the length of the coil rather than constant heat fluxes because of increasing exchanged heat to nanofluid.

Greenhouse drying shows a significant role in the bulk level of drying. In the present setup, a greenhouse dryer operating under natural convection mode was designed and fabricated. The sensible heat storage concept was applied to the bed of the drying chamber. Four different beds, namely, gravel bed, ground bed, concrete bed, and black painted gravel bed was being selected for the comparative heat transfer analyses of the proposed setup. The maximum heat gain takes place at the black painted gravel bed conditions, i.e., 53%, while for concrete bed, gravel bed, and ground bed, it is 33%, 49%, and 29%, respectively. Hence, black painted gravel bed condition is strongly recommended for maximum heat storage. The proposed setup was used for drying of tomato flakes in black painted gravel bed condition. It has been found that the moisture content in the tomato flakes has been removed from 96% to 9.10% in 13 h. The average drying efficiency of the proposed greenhouse dryer is found to be 23.49%. The comparative analysis of the performance evaluation has been done with other investigators, and it was found that the drying rate of the proposed setup shows superior performance as compared with others. The design of the proposed greenhouse setup with black painted gravel bed condition is strongly recommended for small-scale industries and farmers.

Solar air heaters (SAHs) are the simplest form of nonconcentrating thermal collectors. SAHs utilize solar thermal energy to increase the temperature of air for thermal applications of less than 80 °C. The energy efficiency of SAHs is significantly low due to poor convective heat transfer between the absorber and the air medium. In this present study, it is aimed to increase the convective heat transfer by modifying the absorber and the type of air flow inside the duct. Experimental studies were performed to study about the energy and exergy efficiencies of SAH with the absorber of longitudinal circular fins. The thermal analysis of the SAH is evaluated for five mass flow rates of 30, 45, 60, 75, and 90 kg/h m 2 flowing inside the duct of thickness 100 mm. The impact of the flow rate on the absorber and air temperature, temperature difference (ΔT), energy and exergy efficiencies, irreversibility, improvement potential, sustainability, and CO 2 reduction potential is studied. The experimental results show that the first and second laws of thermodynamic efficiency increase from 44.13% to 56.98% and from 24.98% to 36.62% by increasing the flow rate from 30 to 90 kg/h m 2 . The results conclude that the air flow duration inside the duct plays an important role in efficiency of the solar air heater. Therefore, lower flow rate is preferred to achieve maximum outlet air temperature and temperature difference.

The photovoltaic panel is characterized by a unique point called the maximum power point (MPP) where the panel produces its maximum power. However, this point is highly influenced by the weather conditions and the fluctuation of load which drop the efficiency of the photovoltaic system. Therefore, the insertion of the maximum power point tracking (MPPT) is compulsory to track the maximum power of the panel. The approach adopted in this paper is based on combining the strengths of two maximum power point tracking techniques. As a result, an efficient maximum power point tracking method is obtained. It leads to an accurate determination of the MPP during different situations of climatic conditions and load. To validate the effectiveness of the proposed MPPT method, it has been simulated in matlab / simulink under different conditions.

The concentration ratio of the parabolic dish solar collector (PDSC) is considered to be one of the highest among the concentrated solar power technologies (CSPs); therefore, such system is capable of generating more heat rate. The present paper focuses on the integration of the PDSC with the combined cycle (gas cycle as the toping cycle and steam cycle as the bottoming cycle) along with the utilization of waste heat from the power cycle to drive the single effect lithium bromide/water absorption cycle. Molten salt is used as a heat transfer fluid in the solar collector. The engineering equation solver (EES) is employed for the mathematical modeling and simulation of the solar integrated system. The various operating parameters (beam radiation, inlet and ambient temperatures of heat transfer fluid, mass flow rate of heat transfer fluid, evaporator temperature, and generator temperature) are varied to analyze their influence on the performance parameters (power output, overall energetic and exergetic efficiencies, outlet temperature of the receiver, and as coefficient of performance (COP) and exergy efficiencies) of the integrated system. The results show that the overall energy and exergy efficiencies are observed to be 39.9% and 42.95% at ambient temperature of 27 °C and solar irradiance of 1000 W/m 2 . The outlet temperature of the receiver is noticed to decrease from 1008 K to 528 K for an increase in the mass flow rate from 0.01 to 0.05 kg/s. The efficiency rate of the power plant is 38%, whereas COP of single effect absorption system is 0.84, and it will decrease from 0.87 to 0.79. However, the evaporator load is decreased to approximately 9.7% by increasing the generator temperature from 47 °C to 107 °C.

In the present work, an effort is carried out to enhance the distillate yield of a single-slope basin-type solar still by increasing the heat input through its transparent walls and providing hanging wicks to increase the evaporation–condensation rates. A modified basin-type single-slope multi-wick solar still (MBSSMWSS) was proposed and fabricated to increase the productivity and improve the low efficiency of the recently designed modified basin-type single-slope solar still (MBSSSS). Experiments were conducted on both the solar stills to assess their performance, productivity, and efficiency (thermal and exergy) for the same basin area and water depth for the climatic condition of Prayagraj, Uttar Pradesh (U.P.), India. Results showed that the productivity, overall energy (thermal) efficiency, and maximum values of measured instantaneous exergy efficiency of the MBSSSS and MBSSMWSS systems were found to be 3.2 l/m 2 day and 4.22 l/m 2 day, 18.16% and 26.89%, and 4.28% and 5.31%, respectively. Furthermore, thermal modeling was also done using the energy balance equations, and then, a theoretical analysis was carried out to validate with the respective experimental observations. A good agreement was found between experimental and theoretical results. Finally, based on the results of the evaluation parameters and comparative analysis, the modified solar still with wick was found to be a better system compared with that of the system without wick and might be a good option as a solar desalination system.

The present study aims to develop a compact experimental facility to trap solar energy. Line focusing concentrators, i.e., Fresnel lens and secondary reflectors, are coupled to enhance the photothermal conversion efficiency. Two types of receiver tubes are used, a plain copper tube and an evacuated glass tube embedded with a copper tube. Surfactant-free multiwalled carbon nanotubes–Therminol55 nanofluid with concentrations of 25, 50, 75, and 100 ppm are used in this study. The characterization of the nanoparticles and nanofluids is presented. In the visible range, a maximum absorbance and extinction coefficient of 0.75 and 1.7 cm −1 are obtained for 100 ppm concentration. The thermal conductivity is also enhanced by 6.29% compared to base fluid. A maximum fluid temperature of 78.15 and 89.58 °C is observed for plain receiver tube and receiver tube in evacuated space, respectively, and the corresponding efficiencies are 12.65 and 17.36%

Air quality in major cities is reaching worrisome levels across the planet owing to large-scale industrialization. As a result, air purification systems are becoming a fertile and emerging field for research. Here, consideration is given to the use of a small-medium scale air purification system for cities using a kind of solar thermal panels by inducing local convective currents intended to be used in parks, housing estates, or similar urban places providing a local improvement of the quality of the air. The main difficulty which arose when attempting to use these convective currents is that the upward flow of hot air, which has been cleaned from contaminant particles during its upward travel, must be returned back to the ground. To accomplish this, air must be cooled during the travel in order to obtain an effective buoyancy. Several possible solutions have been proposed in the past, for example, the use of a dedicated cooling system as is the use of water spraying systems which could be an attractive option for large towers. However, for small-medium scale air cleaners, dedicated spraying cooling systems are out of question either because of the requirement of water flow or because of the high local humidity generated which can be uncomfortable for humans. One possible solution could be taking advantage of vertical panels in which a side of the panel is permanently irradiated and the other is permanently in the shadow; in this way, heating and cooling could be performed eliminating the need for specialized cooling systems, and although the effective buoyancy—and then the purified air mass flow—of such a system is considerably reduced, nevertheless, it could still be acceptable for local small-scale applications. Utilizing a simplified physical model, the effective buoyancy and attainable air mass flow were calculated. It is shown that for a small panel of 5 m-height or thereabouts, an air flow per unit of width ∼0.4 kg/s is attainable, and for a 10 m-height panel, an air flow per unit of width 0.6 kg/s is attainable. Computational fluid dynamics simulations were performed which agree with the analytical results within ±30 %.

The author reports an experimental investigation of the thermal performance of a multipurpose photovoltanic (PV) solar wall with phase change material (PVSW-PCM). The PVSW-PCM configuration was made of double layers. The external layer consists of a 12 Wp photovoltaic panel attached to a 15 cm thick PCM tank integrating water pipes. The internal wall is an ordinary clear glass pane. There is an 8 cm air gap between the two layers. The PVSW-PCM was integrated into the southern side of a small house of 4.05 m 3 volume built by autoclaved aerated concrete block walls 0.07 m thick. On top of the external layer, three glass blocks (3 × 0.2 × 0.2 cm 2 ) are installed to ensure indoor illumination. The absorbed solar radiation by the PV panel and PCM heats the water in the pipes and the air in the gap. The hot water produced is stored in a 10 liters tank located near the roof. At the inner lower part (room side) and the external upper part (ambient) of the gap, a small DC fan (12 V, 0.48 A) box was installed. The fans were connected to the PV panel directly to enhance indoor ventilation. The investigation considered both natural (fans OFF) and PV assisted ventilation. Another similar house without the PVSW-PCM referred to as glass wall (GW) was built and used as a reference for comparison. The experimental results revealed that the indoor temperature of the PVSW-PCM house was considerably lower than that of the GW house. Moreover, the PVSW-PCM could produce hot water temperature of 55–62 °C and induce a ventilation rate proportional to the intensity of solar radiation. Indoor illumination was sufficient for general house use. Therefore, the PVSW-PCM offers a new alternative for architects and engineers to reduce electric energy use for producing hot water and ventilation and save electrical energy consumption of air conditioner, as the indoor temperature is lower than that of the conventional house.

The performance of a solar collector with wax as a phase change material (PCM) located in a set of staggered pipes configuration was simulated computationally in this work. For the solar radiation of Chile, the accumulation of heat in the PCM system and the heat release at different time intervals were analyzed during the process of energy capture in summer: (a) without wax and with airflow, (b) with wax and without airflow, and (c) with wax and with airflow. Furthermore, the effects of solar radiation (summer and winter) airflow in the collector were analyzed on the performance of the system. The simulation results show that the use of a PCM in a solar air heater allows to store greater amounts of energy and it helps to extend the period of time when the air coming out of the collector has an elevated temperature. By increasing the airflow rate, the efficiency of the system increases and also the energy released to the air to be absorbed.

The performance of the photovoltaic-thermoelectric (PV-TE) hybrid system was examined using three types of PV cells and a thermoelectric generator (TEG) based on bismuth telluride. The investigated PV cells are amorphous silicon (a-Si), monocrystalline silicon (mono-Si), and cadmium telluride (CdTe). The results showed that the TEG contribution can overcome the degradation of the PV cell efficiency with increasing temperature at the minimal working condition. This condition corresponds to the critical temperature difference across the TEG that guarantees the same efficiency of the hybrid system as that of the PV cell alone at 298 K. The obtained results showed that the critical temperature difference is 13.3 K, 44.1 K, and 105 K for the a-Si, CdTe, and mono-Si PV cell, respectively. In addition, the general expression of the temperature difference across the TEG needed for an efficiency enhancement by a ratio of r compared with a PV cell alone at 298 K was given. For an efficiency enhancement by 5 % (r = 1.05), the temperature difference required is 30.2 K, 61.3 K, and 116.1 K for the a-Si, CdTe, and mono-Si PV cells, respectively. These values cannot be achieved practically only in the case of the a-Si PV cell. Moreover, a TE material with a high power factor can reduce this temperature difference and improve the performance of the hybrid system. This work provides a tool that may be useful during the selection of the PV cell and the TE material for the hybrid system.