Constant Solar Radiation Research Articles

Energy-efficient solar heat supply system based on hybrid photovoltaic collector

Following the commitments made under the Paris Climate Agreement, the scientific community has initiated a strategic increase in the share of renewable energy sources while gradually reducing dependence on traditional carbon fuels. Priority is given to the acceleration of the development of the photovoltaic industry, which has shown a constant increase in capacity over the past decades. According to the energy and climate strategies of the European Union, a significant increase in the amount of energy generation due to solar sources is planned. Therefore, the article is devoted to the development of a solar heat supply system based on a hybrid thermal photovoltaic solar collector with an improved design and analysis of the main characteristics of its operation using computer modeling. The authors have developed a 3D computer model of the proposed hybrid system with a solar collector by using SolidWorks software. The change in the temperature of the heat carrier in the hybrid thermal photovoltaic solar collector under constant solar radiation was analyzed. The temperature change of the coolant in the thermal accumulator of the system was also investigated. The results of the simulation of thermal processes revealed the key regularities of the temperature increase during the computer experiment, both in the hybrid thermal photovoltaic solar collector and in the thermal accumulator. The change in the instantaneous specific heat capacity of the developed solar collector was analyzed, and its average efficiency was estimated. The trends of changes in the thermal efficiency of the developed heat supply system during the computer experiment were determined. The novelty of the study is that the design of the hybrid thermophotoelectric solar collector has been improved, its 3D computer model has been developed, and the main thermal characteristics of the developed heat supply system with constant solar radiation have been obtained, which will contribute to the development of calculation methods for such heat supply systems with hybrid solar collectors in the future.

An investigation of serial connected U-pipe evacuated tube solar collector performance using TiO2/Water nanofluid

U-pipe evacuated solar collector is one of the efficient ways to convert solar energy to heat. In this study, different from the literature, thermal efficiency and pressure drop of a solar collector established with serial connected U-pipe evacuated tubes are investigated. However, a nanofluid has been used in the experimental studies with different concentration ratios. The experimental studies have been performed with water and TiO2/water nanofluid. Thermal efficiency and pressure drop of the collector have been experimentally investigated with different working concentration ratios of the fluid at constant solar radiation rate. Efficiency increased by 14.3% to 22.1% compared to water when using a 2% concentration fluid with decreasing reduced temperature. The highest collector efficiency was 80% approximately with using 2% TiO2 concentrated nanofluid. At the same time, the lowest value was almost 60% with water at 0.033 reduced temperature conditions. Pressure drop of working fluid increased 17.7% with using 2% concentration ratio than water at 40 ℃ average collector temperature. With increasing average collector temperature, pressure drop of working fluid decreased. Similarly, the maximum pumping power was obtained with a 2% concentrated fluid of about 52 W. The results of this study are expected to contribute to filling this deficiency in the literature.

Reply to Comment on “Potential Evaporation and the Complementary Relationship” by Jozsef Szilagyi

AbstractWe appreciate Dr Szilagyi's interest in our article on potential evaporation and the complementary relationship (CR). For his first concern on the assumption of constant net radiation versus constant net solar radiation in the estimation of potential evaporation, here we show that the constant net solar radiation condition is more universally applicable both in observations and from a theoretical perspective. For his second concern on the CR model calibration, we clarify herein that no calibrations were used in our applications of the various CR models. Instead, the parameter values were all directly taken from previous studies to ensure a fair and practically meaningful inter‐model comparison.

A robust MPPT approach based on first-order sliding mode for triple-junction photovoltaic power system supplying electric vehicle

This paper studies the problem of the energy system optimization for photovoltaic (PV) generator supplying the electric vehicle. The used photovoltaic generator was conceived around a high-efficiency triple-junction solar cell InGaP/InGaAs/Ge. To adopt the photovoltaic generator to the load and to track the maximum power points, a DC–DC converter feeding the electric vehicle is used. Due to the nonlinearity of the PV generator’s electrical characteristics on the one hand and meteorological conditions variations and load changes, on the other hand, robust control approach is used. It is based on the sliding mode control (SMC) technique. The maximum power point tracking (MPPT) approach for a PV system is well detailed. Moreover, a stability analysis of this approach is carried out. The PV system used in the comparative study is made up of a resistive load, a boost converter, and a high efficiency PV generator. Standard test conditions, a step change in solar radiation with a constant temperature, a step change in temperature with a constant solar radiation, a step change in load and solar radiation with a constant temperature, simultaneous step changes in load, temperature, and solar radiation, and partial shading conditions are the seven case studies that are investigated. They have the aim of evaluating the effectiveness and advantages of the SMC algorithm in comparison to those of perturb and observe (P and O) and three meta-heuristic algorithms. The latters are the particle swarm optimization (PSO), flower pollination (FPA) and the cuckoo search algorithm (CSA). Obtained results show that the SMC algorithm has the ability to sufficiently and rapidly track the maximum power points in the aforementioned cases. As a result, it is used in electric vehicles. The traction part of the electric vehicle is built around a three-phase permanent magnet motor (PMSM). The control strategy is based on indirect, field-oriented control. The conceived system and the control algorithms are all implemented in Matlab/Simulink. Significant results for a wide range of speeds, including the two operating modes under step changes in environmental conditions and under strong partial shading conditions, are presented and discussed.

Performance of Parabolic Trough Collector with Different Heat Transfer Fluids and Control Operation

Electricity generation from solar energy has become very desirable because it is abundantly available and eco-friendly. Mathematical modeling of various components of a Solar Thermal Power plant (STP) is warranted to predict the optimal and efficient operation of the plant. The efficiency and reliability of STPs are maximized based on different operating strategies. Opting for proper Heat Transfer Fluid (HTF), which is proposed in this paper, helps in reducing operating complexity and lowering procurement cost. The Parabolic Trough Collector (PTC) is the heart of STP, where proper focusing of PTC towards solar radiation is the primary task to maximize the outlet temperature of HTF. This maximum temperature plays a major factor due to diurnal solar radiation variation, and its disturbance nature, with the frequent startup and shutdown of STP, is avoided. In this paper, the PTC component is modeled from the first principle, and, with different HTF, the performance of PTC with constant and quadratic solar disturbances is analyzed along with classical control system designs. Through this, the operator will be able to choose proper HTF and resize the plant components depending on plant location and weather conditions. Furthermore, the thermal energy is collected for therminol oil, molten salt, and water; and its performance with different inputs of solar radiation is analyzed along with closed-loop controllers. Thermal energy extracted by therminol oil, molten salt, and water with constant solar radiation results in 81.7%,73.7% and 18.7%, respectively.

A numerical study of the double-glazed solar air heater (DG-SAH) performance using optimized gas-filled interspaces

The reduction of energy losses and destroyed exergy requires the optimization of the double-glazing space. The poor thermophysical characteristics of the air are a limiting factor in the attenuation of heat loss through the double-glazing of the solar collector.The aim of this study is to examine the effect of trapped gases (argon, xenon, krypton, and SF6) within the double-glazing and between the inner glass and the absorber on the efficiency, useful energy, overall heat loss coefficient, and outlet temperature of the back-plate solar air heater. This research was conducted by applying constant solar radiation of 1000 W/m2. The new Eismann correlation is implemented to iteratively evaluate the heat transfer coefficients in gas-filled interspaces and to optimally define these distances. Furthermore, the impact of these gases on exergy efficiency, destruction exergy, and system exergy has been studied. Among these rare gases, xenon leads to the best thermal performance, followed by krypton and argon, compared to air. Respectively, the efficiencies obtained are 51.8%, 50.6%, 48.8%, and 45.8% for xenon, krypton, argon, and air. The optimal gas-filled spaces corresponding to these efficiencies are 4 mm, 5 mm, 9 mm, and 10 mm. Similarly, the exergy approach leads to the same optimal widths of the gas-filled spaces.

Comparative analysis between constant and variable solar radiation reflectivity for exterior walls in the hot-summer and cold-winter zone

Abstract The thermal and optical performance in coating material of exterior walls affected the thermal action from the outdoor thermal environment indirectly, but there was the contrary thermal requirement in winter and summer, which could not be met by the constant-reflectivity coating. To overcome this drawback, the variable-reflectivity coating was analyzed and evaluated by taking three constant-reflectivity coatings as the references. The thermal transfer model with dynamic radiation reflectivity was built to simulate the thermal process of exterior walls in the whole year. Numerical results showed that the constant-reflectivity coating had poor seasonal adaptability with the best performance in some certain months and the poorest behavior in other months, while the variable-reflectivity coating had the better seasonal adaptability to dampen the heat gain in summer and promote the heat gain in winter. Although the variable-reflectivity coating could not show the optimal in all months, its overall performance played the best in the whole year. And compared with constant-reflectivity coating with radiation reflectivity of 90%, 50% and 10%, the variable-reflectivity coating could reduce the annual heating and cooling loads by 2.45%, 16.67% and 46.46%, respectively, in the studied Nanjing City of China.

Numerical analysis of a small sized water based solar photovoltaic-thermal collector

ABSTRACT Large-sized collectors suffer from heat loss from its top due to large aperture plane area. In this work, numerical investigation is performed on a small-sized solar-based photovoltaic thermal water collector using a channel type absorber to analyze its performance under different operating and ambient conditions. A 3D numerical model is developed using COMSOL multi-physics software and the thermal and hydraulic performances of the PV-T collector are carried out. The influence of Reynolds number on the Nusselt number is enumerated for a given operating temperature range and solar radiation level. The variations of PV cell temperature, channel water temperature, thermal and electrical efficiency, exergetic efficiency are studied under different mass flow rates, fluid inlet temperatures, and solar radiations, which majorly control the PV-T performance. It has been observed that with increase of Reynolds number heat transfer rate also increases, and as rate of flow increases from 0.004 kg/s to 0.08 kg/s, the electrical and thermal efficiencies also increase and achieve a maximum 89.96% and 11.47%, respectively. Moreover, uniform temperature distribution has been observed for varying mass flow rates under constant inlet temperature and solar radiation. In addition, a maximum total exergy efficiency of 14.68% is achieved at a mass flow rate of 0.02 kg/s, inlet temperature of 32°C and solar radiation of 900 W/m2. On the basis of the present investigation, a small-sized PV-T collector is recommended for future use as an efficient collector that can provide hot water and also electricity for small-scale domestic or industrial applications.

Modelling and Numerical simulation of Nano-enhanced PV-PCM System for Heat Transfer Augmentation from the Panel

Phase change materials (PCMs) can effectively cool photovoltaic (PV) panels by the passive cooling technique, thereby enhancing its direct energy conversion efficiency. However, generally, PCMs have low thermal conductivity, and different methods can be employed to improve the heat transfer rate. Cooling techniques based on phase change materials (PCMs) enhanced by nano-sized solid particles are very promising. In this paper, a mathematical model is developed to simulate the performance analysis of PV attached with nano-enhanced PCM (NEPCM) integrated with fins and compare the same with that of pure PCM case. The system is oriented in a horizontal position and subjected to constant solar radiation flux of 1000 W/m 2. The PCM selected is RT25HC, and the nanoparticle used is CuO for the numerical study. The effects of volumetric concentrations (0%, 2%, and 4%) and fin number on the performance of the system are investigated numerically. Results show that adding nanoparticles is more effective in no fin case compared to finned cases. The maximum reduction in average PV temperature of 2.02 °C is obtained for no fin case with the nanoparticles’ volumetric concentration of 4%. Further enhancement in liquid fraction and energy storage in NEPCM is also achieved compared to the pure PCM system.

Thermal performance of nanofluid with employing of NEPCM in a PVT-LFR system

A photovoltaic thermal- linear Fresnel reflector (PVT-LFR) modified with integration of phase change material (PCM) was investigated numerically in current paper. The impact of the different mass flow rates and influence of adding Al2O3 nanoparticles to the coolant and PCM on the performance of collector is evaluated. In order to model the PVT-LFR system a transient solver is chosen. The governing equations of the PVT-LFR are solved using CFD (computational fluid dynamic) approach. The SIMPLE algorithm was applied for coupling of velocity and pressure. The simulation is done under the constant solar radiation of 750 W/m2 for 20,000 s. The results show, that electrical efficiency of the system is reduced by decreasing mass flow rate and adding nanoparticles to the PCM, however, with adding nanoparticles to coolant, the electrical performance of the system is enhanced. The thermal output of the system enhances with increasing mass flow rate. Furthermore, adding nanoparticles to the water and phase change material has positive effect on the thermal output of collector.

An analysis of a priori and empirical solar radiation pressure models for GPS satellites

Abstract. Among the different non-conservative forces acting on GPS satellites, solar radiation pressure (SRP) has the greatest influence and inappropriate modeling of it can introduce an acceleration with the order of 1 × 10−7 m s−2. There are a variety of empirical, analytical, and hybrid empirical-physical models to describe the SRP effect. Among them, the empirical model developed at the Center for Orbit Determination in Europe (CODE) and analytical models based on a box-wing prototype, namely box-shape bus with solar panels, are widely used in the International GNSS Service (IGS) community. To investigate the effects of different a priori SRP models on top of empirical parameterization, two sets of parameters based on the Empirical CODE Orbit Model (ECOM) and two a priori models including the analytical box-wing model and the empirical GPS Solar Pressure Model (GSPM) are tested for the different GPS satellites. Orbit comparison of different SRP scenarios shows that: (1) the two parameterizations of ECOM perform differently for Block IIA and IIR/IIR-M satellites but lead to fewer differences for Block IIF satellites in terms of orbit difference pattern. The 3D RMS of orbit difference of two parameterizations are 25, 30 and 21 mm for each block type. (2) Adoption of a priori model or change of the ECOM parameterization mainly lead to orbit differences varying with both elevation of the Sun w.r.t. the orbit plane and the satellites' argument of latitude w.r.t. the noon point, which is supposed to be related to the special geometry and attitude of every block type. These differences are especially obvious in radial direction. Analysis of estimated parameters of ECOM indicates that (3) the GSPM.04 performs better than box-wing model to describe the main constant solar radiation. It is found (4) that the asymmetry of estimated ECOM parameters in B direction (i.e., the direction completing the orthogonal system with D direction and satellite's solar panel axes), observed for three Block IIR satellites, causes corresponding asymmetrical orbit differences in radial direction when reduced ECOM parameters are used. This does not apply to the extended ECOM parameterization tested in this study, which indicates the insufficiency of reduced ECOM to parameterize asymmetrical satellites.

Reliability Analysis and Maintainability for the Design of Grid and Hybrid Solar Power Plant Systems in Wonogiri Regency

Indonesia has the potential for large solar power plants. It has relatively constant solar radiation because it is close to the equator. Besides, solar energy includes renewable energy that is more environmentally friendly and easier to apply in office areas, especially Wonogiri. However, it turns out that the solar power plant projects that have been built are not yet fully functional, and some have even failed. A lack of responsibility and maintenance causes this carried out after the project is complete. For this reason, it is necessary to estimate the reliability of these components and determine the maintenance schedule before the project is carried out. So that later they have a picture and be better prepared when this project is already underway. The fault tree method's failure factors are expected to create a picture to maintain reliability and determine the prioritized components for maintainability. For the results obtained to be more appropriate, apart from seeing the quantitative analysis output, the fault tree also needs to be adjusted to the component manual or datasheet to determine the replacement of spare parts and their maintenance. So that the resulting schedule for maintenance and replacement of spare parts. Thus, the solar power plant project that has been built will be more reliable and can be appropriately utilized.

Dynamics of Melting Process in Phase Change Material Windows Determined Based on Direct Light Transmission

Detailed analyses of melting processes in phase change material (PCM) glazing units, changes of direct transmittance as well as investigation of refraction index were provided based on laboratory measurements. The main goal of the study was to determine the direct light transmittance versus time under constant solar radiation intensity and stable temperature of the surrounding air. The experiment was conducted on a triple glazed unit with one cavity filled with a paraffin RT21HC as a PCM. The unit was installed in a special holder and exposed to the radiation from an artificial sun. The vertical illuminance was measured by luxmeters and compared with a reference case to determine the direct light transmittance. The transmittance was determined for the whole period of measurements when some specific artefacts were identified and theoretically explained based on values of refractive indexes for paraffins in the solid and liquid state, and for a glass. The melting process of a PCM in a glass unit was identified as a complex one, with interreflections and refraction of light on semi layers characterized by a different physical states (solid, liquid or mushy). These optical phenomena caused nonuniformity in light transmittance, especially when the PCM is in a mushy state. It was revealed that light transmittance versus temperature cannot be treated as a linear function.

Performance Analysis Of Solar Water Heating System With Plate Collector Integrated Pcm Storage

Availability of solar energy as a renewable energy source is very abundant and inexhaustible. Solar water heater is an equipment that utilizes solar energy as a source of energy. The thermal performance of a solar water heater system using absorber plate with phase change material (PCM) as thermal energy storage is presented in this study. Two design of solar water heater collectors with absorber plate variations, i.e. an absorber plate with PCM storage and absorber plate without PCM storage were investigated experimentally and numerically simulation. First, the material properties of paraffin wax as PCM storage was analized analyticaly. Every shape model of solar water heater systems were imported and simulated at three variations of constant solar radiation, i.e. 400 W/m2, 700 W/m2, and 1000 W/m2. The simulation using a computational fluid dynamic (CFD) fluent software. The results showed that the average collector efficiency between absorber plate with and without PCM storage is 70.98 % using experimental study and 67.73 % using numerical simulation study.

Modelling thermal and humidity transfers within green roof systems: effect of rubber crumbs and volcanic gravel

ABSTRACT The use of recycled materials and porous aggregates such as rubber crumbs and volcanic gravel (pozzolana) for the drainage layer can lead to improving thermal behaviour of the green roofs. On the other hand, the thermal performances of green roofs can be affected by the thickness of substrate and drainage layer. Therefore, the main objective of this study was to adapt modelling characteristics for different thicknesses of substrate and drainage layers used under constant and variable temperatures and solar radiation: specific rubber crumbs and volcanic gravel behaviour has been modelled. The simultaneous heat and moisture transfers within the green roof were estimated as well. According to the results, the 9 cm substrate was recommended to be used for the green roofs, once the thickness of drainage layer was 4 cm. Moreover, the optimum thickness of pozzolana and rubber crumbs as drainage layer was 6 and 7 cm, respectively, once the thickness of the substrate was kept constant (5 cm). By increasing the thickness of substrate and drainage layers, the fluctuation of internal ceiling temperature in the green roof models with the presence of humidity decreased, but not as much as that in the green roof models without the presence of humidity.

Evaluation of satellite-retrieved evapotranspiration based on a nonparametric approach over an arid region

ABSTRACT Daily evapotranspiration (ET) controlled by latent energy (LE) is an important variable used in the study of hydrology, meteorology, and ecology. A constant solar radiation ratio approach was introduced to the LE retrieval algorithm based on a nonparametric ET approach to upscale instantaneous LE temporally. On the basis of the proposed algorithm, this study retrieved the daily and eight-day LE using Moderate-resolution Imaging Spectroradiometer (MODIS) and China Meteorological Administration Land Data Assimilation System products and evaluated the daily and eight-day LE retrieval by using the ground observations and MOD16 product in Zhangye City during 25 June to 15 September 2012. Results show that the temporal-spatial distribution of retrieved result was reliable. The retrieved daily/eight-day LE could capture the dynamic change of ground observations, whereas the MOD16 LE was invalid. The retrieved daily (eight-day) LE was underestimated at all four (two) sites, with bias, root mean square error, and R2 of −7.9 to −2.2 W m−2 (approximately −5 W m−2), 19.8 to 39.0 W m−2 (approximately 10 W m−2), and 0.72 to 0.84 (approximately 0.9), respectively. The proposed approach showed more satisfactory performance than the triangle approach under clear sky condition. The eight-day LE retrieval was considerably better than MOD16 LE and had (no/slight) influence on MOD16 LE (eight-day retrieval). In addition, the accurate estimation of net radiation, soil heat flux, land surface temperature, and air temperature could aid in improving LE retrieval. Future studies would focus on the improvement of the retrieval algorithm, input accuracy, and residuals.

The Impact of Air Well Geometry in a Malaysian Single Storey Terraced House

In Malaysia, terraced housing hardly provides thermal comfort to the occupants. More often than not, mechanical cooling, which is an energy consuming component, contributes to outdoor heat dissipation that leads to an urban heat island effect. Alternatively, encouraging natural ventilation can eliminate heat from the indoor environment. Unfortunately, with static outdoor air conditioning and lack of windows in terraced houses, the conventional ventilation technique does not work well, even for houses with an air well. Hence, this research investigated ways to maximize natural ventilation in terraced housing by exploring the air well configurations. By adopting an existing single storey terraced house with an air well, located in Kuching, Sarawak, the existing indoor environmental conditions and thermal performance were investigated and monitored using scientific equipment, namely HOBO U12 air temperature and air humidity, the HOBO U12 anemometer and the Delta Ohm HD32.3 Wet Bulb Globe Temperature meter. For this parametric study, the DesignBuilder software was utilized. The field study illustrated that there is a need to improve indoor thermal comfort. Thus, the study further proposes improvement strategies to the existing case study house. The proposition was to turn the existing air well into a solar chimney taking into account advantages of constant and available solar radiation for stack ventilation. The results suggest that the enhanced air well was able to improve the indoor room air velocity and reduce air temperature. The enhanced air well with 3.5 m height, 1.0 m air gap width, 2.0 m length was able to induce higher air velocity. During the highest air temperature hour, the indoor air velocity in existing test room increased from 0.02 m/s in the existing condition to 0.29 m/s in the hottest day with 2.06 °C air temperature reduction. The findings revealed that the proposed air well could enhance the thermal and ventilation performance under the Malaysia tropical climate.

Experimental design of photo-fenton process decolorization of reactive red 120 by using mathematical statistics models

A statistical design of experiments was used to evaluate the potential use of clay catalyst (CuOFeB) during photo-Fenton process in which the concentration of hydrogen peroxide (H2O2), catalyst loading and pH values were select-ed as effective experimental factors in the process of dye decolorization. The photo-Fenton oxidation of Reactive Red 120 (RR120) has been investigated using a concentrating solar parabolic reactor with constant solar radiation of 950 W/m2 during summer period of the year. Under the optimal reaction conditions catalyst showed good catalytic activity in the processes with dye removal over 90%. Also, experiment confirmed that decolorization efficiency depends on the pH and concentration of H2O2 , wherein better results were achieved under lower pH values and higher concentration of H2O2.

Solar Radiation Model Applied to a Low Temperature Evacuated Tubes Solar Collector

A solar radiation model is applied to a low temperature water-in-glass evacuated tubes solar collector to predict its performance via computational fluid dynamics (CFD) numerical simulations. This approach allows obtaining the transmitted, reflected, and absorbed solar radiation flux and the solar heat flux on the surface of the evacuated tubes according to the geographical location, the date, and the hour of a day. Different environmental and operational conditions were used to obtain the outlet temperature of the solar collector; these results were validated against four experimental tests based on an Official Mexican Standard resulting in relative errors between 0.8% and 2.6%. Once the model is validated, two cases for the solar collector were studied: (i) different mass flow rates under a constant solar radiation and (ii) different solar radiation (due to the hour of the day) under a constant mass flow rate to predict its performance and efficiency. For the first case, it was found that the outlet temperature decreases as the mass flow rate increases reaching a steady value for a mass flow rate of 0.1 kg/s (6 l/min), while for the second case, the results showed a corresponding outlet temperature behavior to the solar radiation intensity reaching to a maximum temperature of 36.5 °C at 14:00 h. The CFD numerical study using a solar radiation model is more realistic than the previous reported works leading to overcome a gap in the knowledge of the low temperature evacuated tube solar collectors.

Effect of sowing density on yield and profitability of a hybrid corn under tropical conditions

A high sowing density in maize is a widely used management practice for increasing crop yield; this method increases intraspecific competition for solar radiation, nutrients and water, so yield per plant is reduced, but a greater number of plants is harvested. However, different corn hybrids present a differential behavior because some are tolerant and some are susceptible to this condition, as determined by their plasticity in adjusting their morphology and phenology. The aim of this study was to identify the optimum sowing density, in technical and economic terms, of a new hybrid corn named 30K73 YG RRFlex since no information is available for tropical conditions. This study was carried out in the province of Tolima, municipality of Valle de San Juan, Colombia, using a completely randomized block design in divided plots; five sowing densities determined by six spatial arrangements, two distances between rows (0.7 and 0.8 m) and three numbers of plants per linear meter (7, 8 and 9) were assessed. The treatments did not generate a nitrogen deficiency in the plants, and the evaluated hybrid developed morphological adjustments at the leaf level in order to maintain constant solar radiation interception. For yield, there were no significant variations, so the yield was similar for all of the evaluated treatments. The best treatment was 87,500 plants ha-1, with a yield of 9,916.66 ± 1,078 kg ha-1 and a profitability of 58%.