Incident Solar Intensity Research Articles

An accurate real time neural network based irradiance and temperature sensor for photovoltaic applications

The functioning of photovoltaic (PV) systems mainly depends on the climatic conditions, including incident solar irradiance intensity and module temperature. Thus, irradiance and operating temperature are key factors for assessing and monitoring the performance of PV systems. This work develops a PV solar cells-based sensor for accurate measurement of both incident irradiance and the PV operating temperature. The proposed sensor relies on a Neural Network (NN) soft sensor, trained to estimate PV modules incident solar irradiance and operating temperature without direct measurements. The trained NN model uses the short circuit current (ISC) and open-circuit voltage (VOC) of a reference PV module as inputs of the estimation. The accuracy of the proposed sensor is validated through indoor and outdoor experiments using a PV emulator and a real panel, respectively. Indoor results affirmed the accurate tracking capability of the proposed estimator for both irradiance and module temperature, in constant and rapidly changing conditions, including sudden irradiance changes. The estimator achieved an exceptional level of performance with a Mean Absolute Percentage Error (MAPE) of 1.45% for irradiance and 1.64% for temperature. Similarly, the outdoor experiments using real-time data further validate the obtained results with a Normalized Root Mean Square Error (NRMSE) of 1.22% for irradiance and 3.50% for temperature, outperforming other methods published in the literature.

Selective absorber and emitter boost water evaporation and condensation toward water collection

Solar evaporation has attracted much attention for water collection. However, previous studies on the traditional interface evaporation pay little attention to the selective spectral properties of solar absorbers, leading to mid-infrared radiative heat loss. Besides, during the vapor condensation, the scatter and absorption of the droplets reduce the incident solar intensity on the evaporation interface below. In this work, a freshwater collection strategy combining solar selective absorber and daytime passive radiative cooling techniques is proposed. The solar selective absorber achieves a high solar thermal conversion efficiency (ηevap = 0.894 at 1 sun) to enhance solar evaporation. The passive daytime radiative cooling coating achieves a high solar reflectance R¯solar = 0.927 and thermal emittance ε¯LWIR = 0.929 in the atmospheric transmission window to cool the condensation surface and enhance vapor condensation. In addition, the contact angle is optimized to be 79° by manipulating the hydrophilicity of the condensation surface to ensure the droplet nucleation and shedding. Indoor experiments show that the water collection rate reaches 0.43 kg m−2 h−1. This work provides a promising water collection strategy through solar heating and radiative cooling.

A simplified model for calculating heat transfer through the double skin facade

Double skin façade (DSF) has been recognized as a flexible type of envelope that can adapt to various building needs, such as insulation, solar heat gain, ventilation, and shading. This adaption ability makes the DSF a potentially high performance envelope. However, the reliable calculation of the heat flow in the DSF has been a challenging task due to the complex heat transfer process involved in the DSF. In this study, we propose a simple model that aims to simplify the heat transfer calculation involved in the DSF. In this model, a characteristic function of heat transfer coefficient (CFHTC) was proposed for the heat transfer between the inner layer and the outside air, which would otherwise call the complex convective heat transfer in the cavity. We use experimental data to demonstrate that this function can be expressed as a function of the incident solar intensity. This CFHTC is supposed to be dependent on the geometry of the DSF. With the CFHTC, the calculation of the heat transfer between the inner layer of the DSF and the outside air is simplified and can be incorporated in energy simulation tools.

Investigation of the performance parameters of a sloped collector solar chimney model – An adaptation for the North of Iraq

This work examines the geometrical parameters of the solar chimney power plant using three dimensional CFD simulation. The collector design considers the ground slope, the cover tilt angle, and the inlet opening height. The performance indicators are the temperature, pressure, and velocity with emphasis on the chimney inlet temperature and the incident solar intensity for the estimation of monthly plant performance. The considered collector slopes reflect the alpine nature of the ground for the research area in the suburbia of the city of Erbil on 36th parallel, to the North of Iraq. With a fixed plant height, the actual chimney length is reduced with the increase in the ground slope as the collector inclination increases from the periphery to the center of the collector. At 35° optimum ground slope, there is 18% reduction in horizontal span and 36% in chimney height for the same system volume on flat ground. For this ground slope, a collector cover tilt of zero (parallel to the ground) has shown better results. The inlet height yields little change in temperature and velocity. The pressure profile is unfamiliar and pushes the turbine location into the chimney. Sloped collector solar chimney can play a role in alpine regions with electricity shortages. The simulation results for output power peaked in July with 47.7 kW.

Ventilation performance of a naturally ventilated double skin façade with low-e glazing

Natural ventilation through double-skin façades shows promising effects in building energy saving, but the possible potential and behind mechanisms with low-e glazing remain to be explored. To fill the research gap, this study compared the normal clear glazing and the low-e glazing in the use of a naturally ventilated double-skin façade (NVDSF), together under impacts of spectral optical properties, environmental factors and configurations. Results reveal a significant enhancement - 13% more ventilation rate by replacing clear glass with low-e glass. However, the ventilation performance is sensitive to low-e glazing’s spectral optical properties, where a higher portion of absorptivity is more advantageous for natural ventilation. Besides, environmental factors - solar incident angles and solar intensities - show predominant impacts on ventilation performance, which are correlated in the form of power functions. Results suggest that NVDSFs with small incident angles (<40°) is better. At similar trends, the NVDSF performance is also better under solar intensities larger than 600 W/m2. On the other hand, configurations of NVDSFs also exert primary influences. The optimal cavity gap is found ranging between 0.15–0.3 m, and the ventilation rate increases until a vent height of 0.4 m. This study demonstrates that a significant improvement in ventilation efficiency can be achieved simply by changing the glazing type.

Simulation of solar irradiation assessment for power generation

Solar Energy forms the perennial source to all living processes existing on Earth, directly or indirectly owing to its widespread usage to support the primary energy producers of the eco-system. The solar energy has been an important driver to all activities, supporting the civilizations as it has been used in different applications ranging from, drying of hide to sophisticated application of powering a satellite. The world today has found relief, through use of eco-friendly sources, of which solar energy has been primary form. The study has identified typical solar system design for household application through computational tool. The solar power module performance and variation in incident solar intensity on both horizontal and inclined surfaces are compared with load variation. The energy gain by integrating equations for Hubballi city was evolved, along with its comparison with locations like Delhi and Hamburg (Germany). It was observed that existing fixed SPV device was inadequate to meet the anticipated energy demand. The four different types of solar tracking modes were investigated using Empirical equations on MATLAB computational tool as a measure to enhance energy gain at the location. It was observed that operating in sun-tracking mode, SPV module programmed on basis of the objective function to minimize incidence angle, yielded higher solar energy throughout the year.

Performance optimization of a solar adsorption chiller by dynamically adjusting the half-cycle time

The half-cycle time effect on the performance of a solar single-stage dual-bed adsorption chiller, in Athens, Greece, in July, is investigated. The adsorption chiller coupled with the solar system is simulated, in real time, during the day for a) constant and b) adjusted half-cycle times and the system performance is monitored. In the former case, the half-cycle time is fixed, while in the latter one is dynamically adjusted according to the varying solar radiation intensity. Using a wide range of constant half-cycle times it is found that the maximum daily cooling capacity is obtained at some constant half-cycle time, which is larger than the optimum one of a single adsorption cycle. Similarly, using a wide range of adjusted half-cycle times, the one, providing the maximum cooling capacity is defined. The analysis is performed in a systematic manner through a proposed algebraic expression. It is found that the dynamically optimized adjusted half-cycle time operation mode provides about 12% higher daily and monthly cooling capacities than the corresponding maximum constant ones. This significant increase has been also confirmed for various incident solar radiation intensities.

Performance analysis of solar thermophotovoltaic system with selective absorber/emitter

Selective spectra of absorber and emitter have great effects on the solar thermophotovoltaic (STPV) performance. In this work, a systematic thermal analysis of the STPV system was conducted to optimize the selective absorber and emitter. For the ideal absorber and emitter, the maximum STPV efficiency can be achieved at the cutoff wavelength of 1.2 μm for the ideal absorber and emitted spectrum width of 1.0 μm for the ideal emitter. Increasing concentrated factor of solar radiation from 1 to 100 can enhance the total STPV efficiency from 10.4% to 20.3%, indicating that the large incident solar intensity can enhance the STPV efficiency. In addition, increasing ratios of length to gap (eg: l/d to be ~ 30) and length to width (eg: n to be ~ 6) can further increase the STPV efficiency by reducing the radiation loss. Compared with an original meta-surface serving as both absorber and emitter, the designed selective absorber and emitter can achieve a STPV efficiency of 9.5%, which ~ 20% higher than that of the original meta-surface (7.9%) while it is still lower than that of ideal absorber/emitter. These results indicate that the selective spectrum of the absorber and emitter is of significant to improve the STPV performance, giving valuable insights into design opportunity for the selective absorber and emitter in the STPV system.

Modelling solar enhanced waste stabilization pond

Abstract Solar enhanced waste stabilization pond (SEWSP) was modeled in this research. In the analysis, SEWSPs of varying sizes, made of metallic tanks with inlet and outlet valves and solar reflectors, were constructed to increase the incident solar intensity. Wastewater samples collected from the inlet and outlet of the SEWSPs were examined for physico-chemical and biological characteristics for a period of twelve (12) months. The parameters examined were temperature, pH, detention time, total suspended solids, dissolved oxygen, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), algae count, faecal coliforms and E. coli. The efficiencies of the SEWSPs with respect to these parameters fluctuated with depth, location of reflectors and variation in width. The SEWSP with a width of 0.2 m whose reflector was installed at the outlet position gave the highest treatment efficiency. The conventional model was modified to account for solar irradiation. The faecal bacteria removal was significantly higher in the enhanced pond than in the conventional pond at 0.10 level of significance. The verification of the conventional model gave a good correlation of r = 0.882 between the measured and calculated Ne/No with a low standard error of s = 0.010, while the irradiated pond gave a correlation and standard error of r = 0.959 and s = 0.012 respectively. The research revealed that with the incorporation of solar radiation in WSPs, a length/ width/depth ratio of 1:0.2:0.2 can be used in the design of SEWSPs for maximum treatment efficiency.

Experimental and numerical investigation of the thermal performance of evaporative cooled greenhouses in hot and arid climates

The controlled microclimate of greenhouses is vital for producing quality yield. This paper investigates the thermal performance of an evaporative cooled greenhouse operating in Qatar. Three design factors affecting the greenhouse thermal performance were assessed, namely the greenhouse geometry, operational parameters, and its geographical location. Geometrical parameters include induction fan elevation, roof shape, and aspect ratio. Operational parameters refer to the air flowrate. The greenhouse location dictates the incident solar intensity that was studied. Computational Fluid Dynamics (CFD) was used to model a typical ASHRAE compliant greenhouse. The simulation results were validated using measured data of a greenhouse inner air temperature, relative humidity, and the global incident solar radiation, showing good agreement. Simulation results showed that induction fans located at or below the crop height resulted in lowering the average temperature of the greenhouse. Doubling of the greenhouse ventilation rate from 20 ACH to 40 ACH further decreased the greenhouse air temperature. Temperature rise due to high incident solar radiation is reduced by increasing the ventilation rates. The uneven span greenhouse roof shape resulted in the lowest average inner temperature. For the same greenhouse floor area and volume, the effect of the aspect ratio showed negligible differences.

CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light.

We demonstrate a method for the enhancement of CO2 photoreduction. As the driving force of a photocatalytic reaction is from solar light, the basic idea is to use concentration technology to raise the incident solar light intensity. Concentrating a large-area light onto a small area cannot only increase light intensity, but also reduce the catalyst amount, as well as the reactor volume, and increase the surface temperature. The concentration of light can be realized by different devices. In this manuscript, it is realized by a Fresnel lens. The light penetrates the lens and is concentrated on a disc-shaped catalyst. The results show that both the reaction rate and the total yield are efficiently increased. The method can be applied to most CO2 photoreduction catalysts, as well as to similar reactions with a low reaction rate at natural light.

Excellent growth of ZnS shell on Ag2S QDs using a photochemical-microwave irradiation approach and fabrication of their indoor QD thin film solar cells

ABSTRACTIn this report, a new two pots method using microwave-photochemical approaches was suggested for the fabrication of Ag2S@ZnS core-shells. UV-Vis and photoluminescence spectroscopies clearly proved the growth of ZnS shell on Ag2S cores. X-ray diffraction, Energy dispersive x-ray spectroscopy and transmission electron microscopy also indicated the formation of core-shell structure. To identify excellence growth of ZnS shell, Ag2S@ZnS core-shells were implemented for the fabrication of thin film solar cells. The fabricated cells showed a J-V character with 0.4%, 1 mA.cm−2 and 0.43 V and 54% as efficiency, JSC, VOC and fill factor, respectively. The cells showed also an increasing efficiency up to 0.8% upon the decrease of incident solar intensity to 10% of its standard. The results proved the cells are stable under sun light illumination that is promising for environmentally friendly fabrication of QD thin film solar cells.

Determination of critical low light limit and adaptive physiological and biochemical traits regulating growth and yield of mustard (Brassica juncea Coss.).

Growth and physio-biochemical traits under different incident solar light intensities (100, 67, 50 and 25%) were studied in mustard in a semi-arid agroclimate region of Central India. Our comprehensive studies revealed that incident solar light intensities below about 67% were highly detrimental in mustard for its growth and grain yield. Major factors that contributed to the differential responses under varying light intensities were identified which holds importance for better understanding of low light adaptability in an important oilseed crop like mustard. Biomass index (ratio of dry biomass to height) has been established and evaluated for the differential growth performance of the crop under different light intensities. Biomass index progressively declined from 0.48 (open sunlight) to 0.11 (25% sunlight). Physio-biochemical factors were identified that were playing major role in manifestation of the differential growth and grain yield. Mustard exhibited its low light adaptive trends through differential down-regulation in the rates of net CO2 assimilation (PN), stomatal conductance, transpiration, thylakoid electron transport rate (ETR) and leaf wax level. For example, PN decreased from 35.88 (open light) to 11.64µmolm-2s-1 (25% sunlight). Photochemical events showed critical impact as evidenced by decreased PSII quantum yield, photochemical quenching (qP) and higher non-photochemical quenching (qN) that were clearly associated with physiological efficiency of the plants under varying light intensities. Leaf wax level decreased from 1.69mgg-1 fresh weight (open light) to 0.96mgg-1 fresh weight (25% sunlight). Our results indicated that limited ETR supply across photosystem II (PSII) decreased the photochemical efficiency and carbon gain under low light which resulted in reduction of biomass index and grain yield. Besides, it was found that overexpression of protein band around ~ 26kDa in low light could be another adaptive feature for mustard related to light harvesting complex. Our findings would augment selection of traits for optimizing growth and grain yield of mustard for low light or light limiting agro-ecosystem.

Optical and Thermal Switching of Liquid Crystals for Self‐Shading Windows

AbstractA liquid crystal light shutter whose transmittance can be controlled by ambient conditions, such as incident solar UV intensity and outdoor temperature, is demonstrated. Self‐shading by optical or thermal switching between transparent and opaque states is achieved by liquid crystals doped with push–pull azobenzene and can be used for energy‐saving smart windows. The self‐shading light shutter is transparent during cool weather or under weak sunlight, which could save the energy used for heating and lighting, and can be switched from transparent to opaque during warm weather or under strong sunlight, saving energy used for cooling.

Experimental investigation of a solar collector integrated with a pulsating heat pipe and a compound parabolic concentrator

The paper reports an experimental investigation of a newly proposed solar collector that integrates a closed-end pulsating heat pipe (PHP) and a compound parabolic concentrator (CPC). The PHP is used as an absorber due to its simple structure and high heat transfer capacity. The CPC has a concentration ratio of 3.4 and can be readily manufactured by three-dimensional printing. The CPC can significantly increase the incident solar irradiation intensity to the PHP absorber and also reduce the heat loss due to the decrease in the area of the hot surface. A prototype of the solar collector has been built, consisting of a PHP absorber bent by 4mm diameter copper tube, CPC arrayed by 10×2 CPC units with the collection area of 300×427.6mm2, a hot water tank and a glass cover. HFE7100 was utilized as the working fluid at a filling ratio of 40%. The operating characteristics and thermal efficiency of the solar collector were experimentally studied. The steady and periodic temperature fluctuations of the evaporation and condensation sections of the PHP absorber indicate that the absorber works well with a thermal resistance of about 0.26°C/W. It is also found that, as the main factor to the the thermal performance of the collector, thermal resistance of the PHP absorber decreases with increasing evaporation temperature. The collector apparently shows start-up, operational and shutdown stages at the starting and ending temperatures of 75°C. When the direct normal irradiance is 800W/m2, the instantaneous thermal efficiency of the solar collector can reach up to 50%.

MEDIUM SIZE DUAL-AXIS SOLAR TRACKING SYSTEM WITH SUNLIGHT INTENSITY COMPARISON METHOD AND FUZZY LOGIC IMPLEMENTATION

Nowadays, renewable energy such as solar power has become important for electricity generation, and solar power systems have been installed in homes. Furthermore, solar tracking systems are being continuously improved by researchers around the world, who focus on achieving the best design and thus maximizing the efficiency of the solar power system. In this project, a fuzzy logic controller has been integrated and implemented in a medium-scale solar tracking system to achieve the best real-time orientation of a solar PV panel toward the sun. This project utilized dual-axis solar tracking with a fuzzy logic intelligent method. The hardware system consists of an Arduino UNO microcontroller as the main controller and Light Dependent Resistor (LDR) sensors for sensing the maximum incident intensity of solar irradiance. Initially, two power window motors (one for the horizontal axis and the other for the vertical axis) coordinate and alternately rotate to scan the position of the sun. Since the sun changes its position all the time, the LDR sensors detect its position at five-minute intervals through the level of incident solar irradiance intensity measured by them. The fuzzy logic controller helps the microcontroller to give the best inference concerning the direction to which the solar PV panel should rotate and the position in which it should stay. In conclusion, the solar tracking system delivers high efficiency of output power with a low power intake while it operates.

Thermal modeling and exergetic analysis of a thermoelectric assisted solar still

The present study is devoted to a comprehensive thermodynamic modeling of a novel portable solar still through the first and second laws analysis. In this new solar still, a thermoelectric module is employed to elevate the temperature difference between evaporating and condensing zones. Energy and exergy balance equations have been written for all components of the solar still including glass cover, thermoelectric module, saline water, and basin-liner. A new approach is used to evaluate evaporative heat transfer coefficients. Comparison of distilled water calculated by the present approach and the results obtained by employing various semi-experimental models proved the accuracy of the proposed thermodynamic modeling. It is also found that the exergy stored within the body of saline water, which was neglected in the most previous studies, is important and should be considered.It is shown that the daily average energy and exergy efficiencies of the solar still are 19.8% and 0.95%, respectively. It is seen that the exergy efficiency is much lower than the energy efficiency. Furthermore, it is found that the rate of exergy destructions in solar still components is proportional to the incident solar intensity. The largest exergy destruction belongs to the thermoelectric module, which is 63.4% of the total exergy destruction, while the glass cover has the smallest share. It is concluded that although the energy efficiency associated with this type of thermoelectrically assisted solar still is higher than its counterpart simple passive solar still one, however, its exergy efficiency is lower.

Experimental assessment of two-phase bubble pump for solar water heating

The research goal is to develop a new solar water heater system (SWHS) that uses a solar bubble pump instead of an electric pump. The pump is powered by the steam produced from an evacuated tube collector. Therefore, heat could be transferred downward from the collector to a hot water storage tank. The designed system consists of two sets of heat-pipe evacuated tube collectors, a solar bubble pump installed at an upper level and a water storage tank with a heat exchanger at a lower level. Discharge heads of 1 and 5 m were tested. The bubble pump could operate at the collector temperature of about 90–100 °C and vapor gage pressure of 80–90 kPa. It is found that water circulation within the SWHS depends on the incident solar intensity and system discharge head. Experimental investigations are conducted to obtain the system thermal efficiencies from the hourly, daily and long-term performance tests. The thermal performance of the proposed system is compared with conventional solar water heaters. The results show that the proposed system achieves system characteristic efficiency of 10% higher than that of the conventional systems using electric pump if taking the consumption of electric power into account. And the former is a zero carbon system.

Solar disinfection of drinking water (SODIS): an investigation of the effect of UV-A dose on inactivation efficiency

The effect of solar UV-A irradiance and solar UV-A dose on the inactivation of Escherichia coli K-12 using solar disinfection (SODIS) was studied. E. coli K-12 was seeded in natural well-water contained in borosilicate glass tubes and exposed to sunlight at different irradiances and doses of solar UV radiation. In addition, E. coli K-12 was also inoculated into poly(ethylene) terephthalate (PET) bottles and in a continuous flow system (10 L min(-1)) to determine the effect of an interrupted and uninterrupted solar dose on inactivation. Results showed that inactivation from approximately 10(6) CFU mL(-1) to below the detection level (4 CFU/mL) for E. coli K-12, is a function of the total uninterrupted dose delivered to the bacteria and that the minimum dose should be >108 kJ m(-2) for the conditions described (spectral range of 0.295-0.385 microm). For complete inactivation to below the limit of detection, this dose needs to be received regardless of the incident solar UV intensity and needs to be delivered in a continuous and uninterrupted manner. This is illustrated by a continuous flow system in which bacteria were not fully inactivated (residual viable concentration approximately 10(2) CFU/mL) even after 5 h of exposure to strong sunlight and a cumulative dose of >108 kJ m(-2). This has serious implications for attempts to scale-up solar disinfection through the use of re-circulatory continuous flow reactors.

Experimental studies of a new solar water heater system using a solar water pump

Abstract The research goal was to develop a new solar water heater system (SWHS) that used a solar water pump instead of an electric pump. The pump was powered by the steam produced from a flat plate collector. Therefore, heat could be transferred downward from the collector to a hot water storage tank. The designed system consisted of four panels of flat plate solar collectors, an overhead tank installed at an upper level and a large water storage tank with a heat exchanger at a lower level. Discharge heads of 1, 1.5 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 7–14 kPa. It was found that water circulation within the SWHS ranged between 12 and 59 l/d depending on the incident solar intensity and system discharge head. The average daily pump efficiency was about 0.0014–0.0019%. Moreover, the SWHS could have a daily thermal efficiency of about 7–13%, whereas a conventional system had 30–60% efficiency. The present system was economically comparable to a conventional one.