Direct Radiation Research Articles

The Direct Radiative Effect of CO2 Increase on Summer Precipitation in North America

AbstractPrecipitation changes in full response to CO2 increase are widely studied but confidence in future projections remains low. Mechanistic understanding of the direct radiative effect of CO2 on precipitation changes, independent from CO2‐induced SST changes, is therefore necessary. Utilizing global atmospheric models, we identify robust summer precipitation decreases across North America in response to direct CO2 forcing. We find that spatial distribution of CO2 forcing at land surface is likely shaped by climatological distribution of water vapor and clouds. This, coupled with local feedback processes, changes in convection, and moisture supply resulting from CO2‐induced circulation changes, could determine North American hydroclimate changes. In central North America, increasing CO2 may decrease summertime precipitation by warming the surface and inducing dry advection into the region to reduce moisture supply. Meanwhile, for the southwest and the east, CO2‐induced shift of subtropical highs generates wet advection, which might mitigate the drying effect from warming.

Building Mass Optimization to Reduce Solar Radiation in High Rise Building by Using Parametric Approach

Buildings use 40% of global primary energy, therefore their design and use affect climate change. Building performance analysis can assist architects predict performance before construction with parametric design tools. Radiance can be reduced via a parametric mass, lowering cooling load and energy use. The study uses theoretical and computational research to explain, forecast, and analyze events, whereas parametric design optimizes complicated geometries using mathematical parameters and algorithms. Environmental analysis in Grasshopper with the Ladybug plugin uses Rhinoceros. This plugin provides solar radiation, and climate analysis capabilities. To determine the most energy-efficient building design, the research links independent and dependent variables such solar radiation intensity and building mass. The study uses Surabaya weather data and high rise buildings. The land is formed like a square, with a 15-degree slope to the north and is flanked by low-rise buildings. As a result, the location receives the most direct sunlight during the day. Then, solar radiation analysis. It helps optimize passive solar design solutions. According to the modelling results, solar radiation on the top and west sides are particularly large and dominant in 65.37 and 32.69 kWh/m2. Meanwhile, the north, east and south sides receive very little solar radiation. The following simulation considers the optimal direction, which is to extend west-east and face to the south. A multi-towered megastructure is a high-rise building that responds best to solar radiation. The total solar radiation value is 3,718,100 kWh. It can accommodate large spaces with large mass composition but relatively low total solar radiation values. The building towers provide shade to each other, thereby reducing direct radiation from the sun to the building. The sides of the building's podium are also shaded, so the top of the building is partially red.

More Accurate Quantification of Direct Aerosol Radiative Effects Using Vertical Profiles of Single‐Scattering Albedo Derived From Tethered Balloon Observations

AbstractAerosol single‐scattering albedo (SSA) is the most critical factor for the accurately calculating of aerosol radiative effects, however, the observation of vertical profiles of SSA is difficult to realize. Current assessments of aerosol radiative effects remain uncertain because of the lack of long‐term, high‐resolution vertical profiles of SSA observations. High‐resolution SSA vertical profiles were observed in a semi‐arid region of Northwest China during winter using a tethered balloon. The observed SSA vertical profiles were used to calculate the aerosol direct radiative forcing and radiative heating rates. Significant differences in the calculated radiative forcing were found (e.g., a 48.3% relative difference for the heating effect in the atmosphere at 14:00) between the observed SSA profiles and the constant assumption with SSA = 0.90. Diurnal variations in the vertical distribution of SSA decisively influenced direct radiative forcing of aerosols. Furthermore, high‐resolution vertical profiles of absorbing aerosols and meteorological parameters provide robust observational evidence of the heating effect of an elevated absorbing aerosol layer. This study provides a more accurate calculation of aerosol radiative forcing using observed aerosol SSA profiles.

A High-Precision Sub-Grid Parameterization Scheme for Clear-Sky Direct Solar Radiation in Complex Terrain—Part I: A High-Precision Fast Terrain Occlusion Algorithm

In atmospheric modeling, sub-grid parameterization is an important method for studying the topographic effects of solar radiation using high-resolution Digital Elevation Model (DEM) data. For reducing the amount of computation, some approximate methods that can lead to errors are used in existing sub-grid parameterization schemes for clear-sky direct solar radiation (SPS-CSDSR). The lack of a high-precision fast terrain occlusion algorithm (HPFTOA) remains one of the biggest constraints in this field. This study proposed an HPFTOA. It mainly uses two kinds of acceleration algorithms. One method is to use a dynamic, lossless, and fast occlusion search radius. Another way is to use the rectangular grid for calculations within the accuracy of DEM data to avoid coordinate projection conversions. The test results indicate that the HPFTOA can carry out large-scale computation based on DEM data with a resolution of 90 m. Because it rarely uses approximation algorithms and considers the curvature of the Earth, SPS-CSDSR can achieve unprecedented precision. The HPFTOA can also be used in the fields of mountain solar energy assessment, remote sensing, and telemetry, including terrain-obscuring the probe. As computer performance improves and algorithms and execution code are optimized, the application prospects will be very broad.

Experimental study of electricity generation from solar energy using organic phase change materials and thermoelectric generator

The study investigates using edible oils (ostrich, mutton, beef, coconut) as natural phase change materials for solar energy absorption and storage. Exposed to 900 W/m2 direct radiation by a solar simulator, these materials harness captured energy at a specific depth to generate electricity through a thermoelectric device. The experimental results showed that coconut oil exhibits the highest thermal energy storage efficiency among others, measuring at 39 %, while mutton tallow shows the lowest performance at 16.59 %. Additionally, the performance of a system employing coconut oil as the best material, in combination with iron oxide nanoparticles and carbonized sawdust (CS) was experimentally evaluated at different mass fractions (0.3 %, 0.6 %, and 0.9 %) to enhance thermal conductivity and sunlight absorption. The carbonized sawdust and its nanoparticles increased the thermal energy storage efficiency of the system by 62 % and 53 %, respectively. Moreover, the stored exergy by the phase change materials indicates that coconut oil and beef tallow had the highest and lowest exergy efficiencies of 6.3 % and 3.3 %, respectively. The combination of coconut oil with iron oxide nanoparticles and carbonized sawdust leads to 10 % and 7.9 % increased exergy efficiencies respectively.

Informing solar blind radioluminescence imaging through a calibrated spectrum

While direct radiation detection methods offer great insight into the origin of ionizing particles and photons, their use to locate contaminated areas or concealed radioactive sources can lead to undue exposure of personnel and equipment to ionizing radiation or the potential for contamination. These same sources induce ultraviolet (UV) optical photon fluorescence in air – a process referred to as radioluminescence – that may be imaged from low dose regions over larger attenuation lengths than ionizing radiation. However, most optical detection methods are limited to low lighting conditions to image the more abundant ultraviolet-A (UV-A) photons. To extend this capability to room light or daytime conditions, the solar blind region (Ultraviolet-C (UV–C), <280 nm) can be tapped. Though the emission yield of UV-C photons is roughly two orders of magnitude lower than that in the UV-A regime, the UV-C offers dramatic improvements in signal-to-noise ratios under bright lighting conditions due to decreased background interferences. The yield of specific UV-C lines, if present in the literature at all, varies widely, which has a large impact in modeling and analyzing standoff UV-C measurement scenarios. Thus, we have captured improved radioluminescence spectra over 250–400 nm and identified observed emission peaks in ambient air. Many of the UV-C photons produced by ionizing radiation excitation result from high-energy, molecular nitrogen Gaydon-Herman transitions which have had limited study to date for this application. Relating these findings to published UV-A yields, we estimate emissions between 0.15 and 0.19 photons/MeV over 250–280 nm. We also use a commercial corona-discharge imaging camera to demonstrate outdoor UV-C radiation mapping of alpha and gamma emitters from 50 to 75 m standoffs, respectively. The imaged “counts” are compared to optically modeled values and show the same trend over distance.

Improving passive daytime radiative cooling via incorporation of composite nanoparticles into sheath of PU-PVDF core-sheath nanofiber film

Climate change has recently caused more severe temperatures, increasing demand for personal thermal management outdoors. Radiative cooling fabrics, known for their potent cooling ability, play a crucial role in regulating the thermal balance of the human body in high-temperature environments. In this study, an innovative PU (polyurethane)-SiO2/TiO2@PVDF (polyvinylidene fluoride) core-sheath nanofiber film was developed by incorporating SiO2/TiO2 composite nanoparticles (STNs) into the sheath of the nanofibers through coaxial electrospinning. The PU-STNs@PVDF composite nanofiber film with thickness of ∼100 μm achieved a reflectance of 92 % in the visible to near-infrared spectral range and an emittance of 91 % within the atmospheric transparent window. The temperature of the PU-STNs@PVDF core-sheath nanofiber film was reduced by 6.9 °C and 4.7 °C compared with that of the cotton fabric and PU-PVDF nanofiber film, respectively. Under direct solar radiation in summer, the temperature of the PU-STNs@PVDF core-sheath nanofiber film was 7.7 °C lower than that of cotton fabric. The PU-STNs@PVDF core-sheath nanofiber film elongated at a break of 127.5 % and a tensile strength of 4.3 MPa, implying it promising flexibility. The PU-STNs@PVDF core-sheath nanofiber film possesses huge potential in personal thermal management.

Novel feature selection based ANN for optimal solar panels tilt angles prediction in micro grid

Predicting PV system electricity output is necessary for daily operational management and annual power system planning when integrating solar collector-based photovoltaic (PV) stations into micro grids. Tilting the panels at the ideal angle to maximize solar energy capture is necessary to maximize PV station production. This optimal tilt angle (OTA) must be predicted as it is a nonlinear function of the total solar radiation, diffuse solar radiation, and direct solar radiation. This research explores the use of feature selection-based artificial neural networks (ANN) with various machine learning algorithms to predict the OTA for PV systems at specific locations, aiming to maximize PV output in micro grids. The study identifies global solar radiation, diffuse solar radiation, clarity index, and global solar radiation on inclined surfaces as the most critical inputs for predicting OTA, while extraterrestrial radiation is deemed the least significant. Implementing the appropriate input variables significantly enhanced prediction accuracy from 38.59 % to 90.72 %. Among the neural networks evaluated, the Elman neural network demonstrated the greatest improvement.

A dataset of topographic correction coefficients for shortwave downward radiation over the Pan-Third Pole

Prevalent Shortwave downward radiation (SWDR) estimates assume a flat surface, neglecting topographic effects and leading to significant errors in mountainous regions. We introduce SWDR topography correction coefficients (TCCs), based on the mountain radiative transfer model tailored for the Pan-Third Pole region. This dataset effectively bridges the disparities between flat-surface SWDR and rugged-surface SWDR, forming part of the Long-term Earth System spatiotemporally Seamless Radiation budget dataset (LessRad). Validation results using a three-dimensional radiative transfer model demonstrate the efficacy of this method in correcting solar direct radiation, sky diffuse radiation, and SWDR under diverse conditions. At a spatial resolution of 2.5 arc-minutes, the correction accuracy for solar direct radiation is characterized by a coefficient of determination (R²) of 0.998, a relative root mean square error (rRMSE) of 2.4%, and a relative bias (rbias) of 0.8%. For sky diffused radiation, an R² of 0.965, a rRMSE of 1.2%, and a rbias of −0.8%. SWDR corrections under clear and cloudy skies also show high accuracy, demonstrating the robustness of the TCCs approach.

Evaluating direct and diffuse solar radiation components through global radiation measurements from three fixed directions

Solar systems are deemed to play a pivotal role within the process which should lead to the reduction in the carbon intensity of the worldwide energy use. However, for the analysis of solar system performance, the availability of data regarding the various components (direct and diffuse) of solar radiation is crucial.Nevertheless, the measure of either direct or diffuse solar irradiance requires sun tracker apparatuses (pyrheliometers) or shadow devices (e.g. shadow-band pyranometers) which involve mechanical appliances needing constant maintenance and articulated measurement protocols; therefore, these data are usually derived from global solar radiation measured records, by using empirical functions.With a view to trying to address these issues, the article proposes a methodology for the assessment of the direct and diffuse components of solar radiation from both global solar irradiance and infrared radiation data, all measured on three planes differently tilted and oriented.Therefore, no tracking or moving devices are involved, whereas the real configuration and weather conditions of the site (Sky View Factor, clouds, climate conditions, presence of reflective surfaces, etc.) are taken into account. Therefore, the results should possibly characterize the site, so that its actual potential for solar system installation can be properly assessed.Comparisons with different correlation models demonstrate good agreement, showing correlation coefficients ranging from 0.75 to 0.89 for diffuse radiation and from 0.97 to 0.99 for direct radiation. Notably, the proposed method tends to produce lower values for diffuse radiation. These discrepancies may be due to the peculiar features of the site.

Design and experimental validation of a metamaterial-based sensor for microwave imaging in breast, lung, and brain cancer detection

This study proposes an innovative geometry of a microstrip sensor for high-resolution microwave imaging (MWI). The main intended application of the sensor is early detection of breast, lung, and brain cancer. The proposed design consists of a microstrip patch antenna fed by a coplanar waveguide with a metamaterial (MTM) layer-based lens implemented on the back side, and an artificial magnetic conductor (AMC) realized on as a separate layer. The analysis of the AMC’s permeability and permittivity demonstrate that the structure exhibits negative epsilon (ENG) qualities near the antenna resonance point. In addition, reflectivity, transmittance, and absorption are also studied. The sensor prototype has been manufactures using the FR4 laminate. Excellent electrical and field characteristics of the structure are confirmed through experimental validation. At the resonance frequency of 4.56 GHz, the realized gain reaches 8.5 dBi, with 3.8 dBi gain enhancement contributed by the AMC. The suitability of the presented sensor for detecting brain tumors, lung cancer, and breast cancer has been corroborated through extensive simulation-based experiments performed using the MWI system model, which employs four copies of the proposed sensor, as well as the breast, lung, and brain phantoms. As demonstrated, the directional radiation pattern and enhanced gain of the sensor enable precise tumor size discrimination. The proposed sensor offers competitive performance in comparison the state-of-the-art sensors described in the recent literature, especially with respect to as gain, pattern directivity, and impedance matching, all being critical for MWI.

Investigation of Dust‐Induced Direct Radiative Forcing Over the Arabian Peninsula Based on High‐Resolution WRF‐Chem Simulations

AbstractThis study investigates the impact of dust on radiation over the Arabian Peninsula (AP) during the reported high, low, and normal dust seasons (March–August) of 2012, 2014, and 2015, respectively. Simulations were performed using the Weather Research and Forecasting model coupled to a Chemistry module (WRF‐Chem). The simulated seasonal horizontal and vertical dust concentrations, and their interannual distinctions, match well with those from two ground‐based AERONET observations, and measurements from MODIS and CALIOP satellites. The maximum dust concentrations over the dust‐source regions in the southern AP reach vertically upto 700 hPa during the high dust season, but only upto 900–950 hPa during the low/normal dust seasons. Stronger incoming low‐level winds along the southern Red Sea and those from Iraq bring in higher‐than‐normal dust during the high dust summers. We conducted a sensitivity experiment by switching‐off the dust module to assess the radiative perturbations due to dust. The results suggest that active dust‐module improved the fidelity of simulated radiation fluxes distributions at the surface and top of the atmosphere vis‐à‐vis Clouds and the Earth's Radiant Energy System (CERES) measurements. Dust results in a 26 Wm−2 short‐wave (SW) radiative forcing in the tropospheric‐column over the AP. The SW radiative forcing increases by another 6–8 Wm−2 during the high dust season due to the increased number of extreme dust days, which also amplifies atmospheric heating. During extreme dust days, the heating rate exhibits a dipolar structure, with cooling over the Iraq region and warming of 40%–60% over the southern‐AP.

Dynamic SNR, Spectral Efficiency, and Rate Characterization in 5G/6G mmWave/sub-THz Systems with Macro- and Micro-Mobilities

The performance of 5G/6G cellular systems operating in millimeter wave (mmWave, 30–100 GHz) and sub-terahertz (sub-THz, 100–300 GHz) bands is conventionally assessed by utilizing the static distributions of user locations. The rationale is that the use of the beam tracking procedure allows for keeping the beams of a base station (BS) and user equipment (UE) aligned at all times. However, by introducing 3GPP Reduced Capability (RedCap) UEs utilizing the Radio Resource Management (RRM) Relaxation procedure, this may no longer be the case, as UEs are allowed to skip synchronization signal blocks (SSB) to improve energy efficiency. Thus, to characterize the performance of such UEs, methods explicitly accounting for UE mobility are needed. In this paper, we will utilize the tools of the stochastic geometry and random walk theory to derive signal-to-noise ratio (SNR), spectral efficiency, and rate as an explicit function of time by accounting for mmWave/sub-THZ specifics, including realistic directional antenna radiation patterns and micro- and macro-mobilities causing dynamic antenna misalignment. Different from other studies in the field that consider time-averaged performance measures, these metrics are obtained as an explicit function of time. Our numerical results illustrate that the macro-mobility specifies the overall trend of the time-dependent spectral efficiency, while local dynamics at 1–3 s scales are mainly governed by micro-mobility. The difference between spectral efficiency corresponding to perfectly synchronized UE and BS antennas and time-dependent spectral efficiency in a completely desynchronized system is rather negligible for realistic cell coverages and stays within approximately 5–10% for a wide range of system parameters. These conclusions are not affected by the utilized antenna array at the BS side. However, accounting for realistic radiation patterns is critical for a time-dependent performance analysis of 5G/6G mmWave/sub-THz systems.

Passive ventilation for building not subjected to solar radiation

Some small-height buildings are not exposed to direct solar radiation due to shading from neighboring buildings. Therefore, for these buildings to be ventilated naturally, it was necessary to develop a method using a thermal chimney. This is done by using hot water resulting from the solar heater at the top of the building to heat the base of the chimney instead of direct solar radiation. In this paper, the solar chimney system used to generate power, using some modifications, to be used in ventilation operations is investigated. The effect of different variables on the airflow rate inside the chimney ventilation air drawn was studied. From the experimental result, the ventilation air flow rate increase with the chimney height and diameter. Also, the increase of heated plate area and the heater capacity increases the ventilation air flow rate. Increasing the inlet air gap thickness decreases the ventilation air. For the divergent chimney, the ventilation air increases with the increase of the conical angle.

Prototype solar dome designed to function as a solar calendar

ABSTRACT The experiment aimed to create a prototype of a calendar dome that shows the days of the year using solar light passing through specific holes in the dome’s covering. Specific openings are placed on the dome to allow sunlight pass through daily all year round. Clear skies allow radiation to pass through and illuminate months plate. For more precise calculations, lenses can also be placed in the dome body to regulate and calibrate the location and orientation of reflected light. The light is then directed onto specific mirrors, which then reflect it onto a central control plate functioning as a fixed date reader in the center of the room. As bold characters are reversed and placed between the mirror and the central control plate, they display the exact day and time of the year. The date and time will be clearly shown on the control plate as a silhouette. To make it all done, the authors assessed the position, azimuth, latitude, and elevation angle of the sun to accurately determine the direction of solar radiation. This guarantees the precise and effective creation of the Solar Calendar Dome Prototype.

Design of Y-shaped tri-band rectangular slot DGS patch antenna at sub-6 GHz frequency range for 5G communication

This paper presents the design and development of a rectangular slot DGS patch antenna fed by a microstrip line, designed to operate across three distinct frequency bands at 4.0 GHz, 4.9 GHz, and 5.5 GHz for 5G wireless communication applications. The antenna design outlined in this study is implemented on a Fr-4 substrate with dimensions measuring 50.5 × 41.12 × 1.5 mm3. The antenna gains at three frequency bands are 2.69 dBi, 7.27 dBi, and 11.37 dBi having impedance bandwidths of 9%, 8.9%, and 5.1%, respectively. The attained bandwidths are 356 MHz, 443 MHz, and 287 MHz for the respective frequency bands. The radiation efficiencies of the proposed antenna are 90%, 82%, and 79% of the three respective frequencies. Antenna 1 in this study exhibits single-band behavior, effectively covering the single frequency band which is 5.5 GHz (5.3578–5.9519 GHz) 5G unlicensed band 5-GHz WLAN IEEE 802.11a frequency. On the other hand, Antenna 2 demonstrates dual-band characteristics spanning the S-band 3.7 GHz (3.5619–3.8544 GHz) and C-band range 5.1 GHz (4.8496–5.2008 GHz) suitable for mid-band 5G applications. Antenna 3 proposed antenna exhibits a tri-band functionality within the C-band spectrum. The results highlight multiple-band operation, consistent high gain, high directivity, and favorable directional radiation patterns.

Thermal comfort investigation of membrane-assisted radiant cooling in outdoor settings

The global warming and urban heat island effect call for mitigation strategies for improving thermal environments in open urban spaces. Radiant cooling can remove heat from the human body via direct thermal radiation, thereby creating the possibility to provide active cooling for people in outdoor environments. While using a transparent membrane, convection energy lost to the ambient airflow can be minimized. However, current research on the thermal comfort of radiant cooling systems is restricted to indoor applications, while outdoor applications remain unclear. To address this need, the study investigated the effect of membrane-assisted asymmetric radiant cooling on people's thermal perception in outdoor environments. A radiant cooling facility in an outdoor setting was built, and its cooling effects were assessed by using 248 human subjects across hot and transitional seasons. It is found that the radiant cooling facility can lower the mean thermal sensation vote (MTSV) by 0.6 to 1.5 units. The degree of cooling depends both on the panel temperature and environmental conditions. At the panel surface temperature of 14.3°C, MTSV was at the neutral zone (-0.5 ≤ MTSV ≤ 0.5) with the environmental UTCI as high as 38.1°C, whereas the thermal sensation of the group without radiant cooling was rated warm to hot. Under this condition, the ambient UTCI scope of no heat stress can be extended by 10.1°C higher. The strongest local cooling sensation appeared in the back, with an average decrease of 1.33 units in MTSV, contributing to lowering the overall thermal sensation of the body. For the first time, it is demonstrated that membrane-assisted radiant cooling panels can effectively improve thermal comfort in open outdoor settings.

A Radial Decrease in Kinetic Temperature Measured with H2CO in 30 Doradus

Feedback from star formation is a critical component of the evolution of galaxies and their interstellar medium. At parsec scales internal to molecular clouds, however, the observed signatures of that feedback on the physical properties of CO-emitting gas have often been weak or inconclusive. We present subparsec observations of H2CO in the 30 Doradus region, which contains the massive star cluster R136 that is clearly exerting feedback on its neighboring gas. H2CO provides a direct measure of gas kinetic temperature, and we find a trend of decreasing temperature with projected distance from R136 that may be indicative of gas heating by the stars. While it has been suggested that mechanical heating affects H2CO-measured temperature, we do not observe any correlation between T K and line width. The lack of an enhancement in mechanical feedback close to R136 is consistent with the absence of a radial trend in gravitational boundedness seen the Atacama Large Millimeter/submillimeter Array CO observations. Estimates of cosmic-ray flux in the region are quite uncertain, but can plausibly explain the observed temperatures if R136 itself is the dominant local source of energetic protons. The observations presented here are also consistent with the H2CO-emitting gas near R136 being dominated by direct radiation from R136 and photoelectric heating in the photodissociation regions.

Numerical computation of heat transfer, moisture transport and thermal comfort through walls of buildings made of concrete material in the city of Douala, Cameroon: An ab initio investigation

The buildings of the city of Douala in Cameroon have been experiencing degradation for several decades due to the climate characterized by high humidity and oppressive heat. As a result, large grayish or black stains can be observed on these buildings. We sometimes witness the subsidence of the slab of the balconies, the cracking of the walls and the collapse of the buildings worn by the humidity. These damages are generally caused by infiltration and capillary rise. In addition, it has been demonstrated that people living in damp buildings are at risk of illnesses such as asthma and lung infections. Therefore, the novelty of this work is threefold: (i) it proposes for the very first time a numerical study of the transport of humidity and heat through the porous walls of buildings constructed with concrete material, the main construction material in the city of Douala; (ii) It was determined what level of indoor thermal comfort was appropriate for sleeping inside a real three-dimensional G+1 complex residential building constructed with concrete blocks; and (iii) Using the geographical coordinates, and time data, the sun radiation's direction of incidence was assessed throughout the simulation. The computation was performed using Comsol Multiphysics 6.0 software. The distributions of temperature, relative humidity as well as moisture level were presented at various periods. It appears from the results that face to this high humidity, the concrete material retains a large quantity of water for a considerable periods of time, which weakens the steel reinforcement of concrete which is corroded by rust. The computation of thermal comfort in the 3D building showed that the various rooms of the building were not comfortable during the night since temperature inside the building increased progressively due to diffusion of heat. In addition, the numerical solutions indicated that the energy stored within the walls diffused from the external walls to the internal walls during the night. It was also demonstrated that the walls of the building were warmer than the windows, doors and the roof at the computational times, which simply revealed a greater storage capacity of heat in the concrete blocks material. The findings highlighted that the temperature decreased rapidly in a thickness of 0.06 m of the concrete block during the nine days and this decrease was attenuated in the second part of the thickness of the concrete block (0.14 m).

Designing an absorber for solar photovoltaic thermal systems: a heat pipe approach and comparative evaluation

Abstract Renewable energy power generation is extensively promoting for the global objective of mitigating greenhouse gas emissions. Solar energy leads all renewables due to its ubiquitous nature which can be harvested by solar thermal and solar photovoltaic devices. Solar PV is used widely because of its flexibility in working with both direct and diffuse radiation. However, PV systems experience efficiency loss for every degree rise of solar cell temperature above room temperature. Solar photovoltaic-thermal (PVT) collectors are proposed for co-generation of electrical and thermal energy by utilizing excess heat generated in the PV layer. The low heat transfer rate, energy-intensive nature, and freezing of working fluid in colder regions are some problems that persist in water- and air-based PV/Ts, leading us to consider alternatives. Thus, the present study addresses the current opportunities by utilizing heat pipes as PV/T absorbers. Heat pipe PVT is a passive system which operates in phase transition facilitating a tremendous amount of heat transfer enhancement. To enhance the efficiency of PV/T systems, the integration of advanced technologies, like heat pipe thermal absorbers, becomes imperative. Incorporating cutting-edge solutions, such as heat pipe thermal absorbers, is essential to optimize the performance of PV/T systems. Hence, the current study provides insight into heat pipe design through a case study on the application of heat pipes as thermal absorbers for photovoltaic systems. The existing absorbers with fluid flow configurations like Raster, Spiral or Rectangular spiral, etc. used in PV/T are considered as reference. Copper as tube material and water as working fluid are found to be compatible with each other for the proposed heat pipe. The maximum heat input of 0.55kW is computed by the inadequacy of the mentioned existing PVTs to extract the maximum available heat from the PV surface. Additionally, an analytical approach used to define the optimum size of the system and calculation of minimum requirement of tubes. The optimized design of copper heat pipes was found to be ½ inch in diameter and at least ten heat pipes were required to transfer a computed heat flux of 466kW/m 2 per pipe to outperform the existing PV/Ts.