Direct Beam Solar Radiation Research Articles

Experimental Investigations of Stagnation Temperature and Overall Heat Transfer Coefficient of Flat Receiver for Solar Parabolic Dish Concentrator System

The parabolic dish concentrator is one of the most efficient technologies to convert direct beam radiation into thermal energy for steam and power generation. The parabolic dish concentrates direct beam radiation from the sun on to a receiver at the focal point. The receiver plays a major role to transform the reflected solar radiation into thermal energy. The conversion efficiency of the dish is severely influenced by imperfection of the dish collector such as the contour of parabola, size of the facets aligned, positioning of the receiver and tracking of the system. These imperfections are mainly involved in the design, manufacturing, construction and operation of a parabolic dish collector. To overcome this imperfection, secondary reflector are normally deployed at the focal region of the receiver. The function of the secondary reflector reradiates the deviated rays from the primary concentrator onto the receiver. In this aspect, flat receiver is initially fabricated to evaluate the performance of the flat receiver without secondary reflector. In this paper, the experimental investigations on flat receiver for 12.6 m2 area of solar parabolic dish concentrator system to estimate the receiver temperature and overall heat transfer coefficient of the flat receiver. In order to estimate this, rectangular box type aluminium receiver is fabricated and placed at the focal point of 2.42 m from the base of the dish. The aperture area of dish concentrator system is 12.6 m2 area and it consists of 12 petals and in each petals 128 flat mirrors of size 7.5 cm × 7.5 cm with reflectivity of 0.95 are pasted on 1.2 mm thickness MS plate to form a parabolic dish concentrator. The azimuth and elevation manual tracking arrangements are made to track the dish continuously for different orientation of the sun. K-type thermocouples are used to measure the temperatures of the top and bottom of the receiver. To measure the maximum temperature of the receiver, experiments are carried out for stagnation conditions (without heat retrieval from the receiver). Experiments are carried out on 5th, 6th and 7th March 2018 from 10.00 am to 3.00 pm. For different direct beam solar radiation, the top and bottom temperatures, ambient temperatures are measured. The maximum temperature of 399°C is achieved at the bottom surface of the flat receiver for the beam radiation of 955 W/m2, and the corresponding top surface temperature of 58°C is achieved for the same flux. Based on the measured bottom surfaces temperatures, the overall heat transfer coefficient of bottom surface are estimated as 145.56 W/m2 K. Based on this study, further heat transfer analysis will be carried out for the developed flat receiver.

Impact of solar reflectance of wall and road on outdoor thermal comfort - experimental study in a street canyon setup

Thermal environment in an urban street canyon is primarily affected by prevailing air conditions, wind flow, solar radiation as well as thermal properties of the surrounding urban structures and pavement surfaces that affect the reflection, absorption and re-emission of solar radiation. Experiments were conducted in a 1:5 scale test setup consisting of North-South oriented street canyon (height to width ratio 1.7) located in Singapore. Test cases covering two levels solar reflectance of walls (0.35 and 0.57) and road (0.12 and 0.55) were conducted in a three-month period. Environmental parameters including direct beam and diffuse solar radiation, net radiation (incoming and outgoing shortwave and longwave radiation) and wind speed were continuously measured at the top of the canyon. Thermal comfort parameters including air temperature, relative humidity, air velocity and globe temperature were also monitored continuously inside the street canyon. When the solar reflectance of canyon surfaces increases, mean radiant temperature (MRT) reduces by up to 1.2°C during daytime and 2.5°C during the night. Such reduction leads to reduced occurrence of heat stress by 34% and 42% during the day and night times, respectively, as measured by the universal thermal comfort index (UTCI). This paper further discusses the effect of longwave radiation on MRT in the street canyon due to changes in canyon solar reflectance.

Air Temperature Modification of an Urban Neighborhood Park in Summer

In order to investigate the effect of air temperature reduction on an urban neighborhood park, air temperature data from five inside locations (forest, pine tree, lawn, brick and pergola) depending on surface types and three outside locations (Suwon, Maetan and Kwonsun) depending on urban forms were collected during the summer 2016 and compared. The forest location had the lowest mean air temperature amongst all locations sampled, though the mean difference between this and the other four locations in the park was relatively small (0.2-0.5℃). In the daytime, the greatest mean difference between the forest location and the two locations exposed to direct beam solar radiation (brick and lawn) was 0.5-0.8℃ (Max. 1.6-2.1℃). In the nighttime, the mean difference between the forest location and the other four locations in the park was small, though differences between the forest location and locations with grass cover (pine tree and lawn) reached a maximum of 0.9-1.7℃. Comparing air temperature between sunny and shaded locations, the shaded locations showed a maximum of 1.5℃ lower temperature in the daytime and 0.7℃ higher in the nighttime. Comparing the air temperature of the forest location with those of the residential (Kwonsun) and apartment (Maetan) locations, the mean air temperature difference was 0.8-1.0℃, higher than those measured between the forest location and the other park locations. The temperatures measured in the forest location were mean 0.9-1.3℃ (Max. 2.0-3.9℃) lower in the daytime than for the residential and apartment locations and mean 0.4-1.0℃ (Max. 1.3-3.1℃) lower in the nighttime. During the hottest period of each month, the difference was greater than the mean monthly differences, with temperatures in the residential and apartment locations mean 1.0-1.6℃ higher than those measured in the forest location. The effect of air temperature reduction on sampling locations within the park and a relatively high thermal environment on the urban sampling locations was clearly evident in the daytime, and the shading effect of trees in the forest location must be most effective. In the nighttime, areas with a high sky view factor and surface types with high evapotranspiration potential (e.g. grass) showed the maximum air temperature reduction. In the urban areas outside the park, the low-rise building area, with a high sky view factor, showed high air temperature due to the effect of solar (shortwave) radiation during the daytime, while in the nighttime the area with high-rise buildings, and hence a low sky view factor, showed high air temperature due to the effect of terrestrial (longwave) radiation emitted by surrounding high-rise building surfaces. The effect of air temperature reduction on the park with a high thermal environment in the city was clearly evident in the daytime, and the shading effect of trees in the forest location must be most effective. In the nighttime, areas with high sky view factor and surface types (e.g., grass) with evapotranspiration effect showed maximum air temperature reduction. In the urban areas outside the park, the high sky view factor area (low-rise building area) showed high air temperature due to the effect of solar (shortwave) radiation during the daytime, but in the nighttime the low sky view factor area (high-rise building area) showed high air temperature due to the effect of terrestrial (longwave) radiation emitted surrounding high-rise building surfaces.

Direct Beam Solar Radiation Received by Parabolic Trough Collector with Dust Accumulated on Its Surface

This article has been retracted to straighten the academic record. In making this decision the Editorial Board follows COPE's Retraction Guidelines. Aim is to promote the circulation of scientific research by offering an ideal research publication platform with due consideration of internationally accepted standards on publication ethics. The Editorial Board would like to extend its sincere apologies for any inconvenience this retraction may have caused.

Solar Energy Potential and Performance Assessment of CSP Plants in Different Areas of Iran

Concentrating solar power (CSP) plants only exploit direct beam solar radiation in order to generate electricity. It is generally assumed that CSP systems are economic only for locations with direct normal irradiation (DNI) above 1800 kWh/m2/year(about 5 kWh/m2/day). In the present study, talented regions of Iran to install CSP plants are identified by using the available measured data of global horizontal irradiation (GHI) from 21 cities. A computational code converts the measured GHI to DNI and by comparing the calculated data, six most talented city areaof Iran are selected as the case study. By applying geographical, radiation and meteorological parameters to SAM software, the generation of electricity for a typical CSP plant for these locations are evaluated. The selected CSP plant is a parabolic trough (PT) power plant with capacity of 100MW and 6hour thermal storage. Results show that areas around the cities of Bandar-e Abbas, Bushehr, Esfahan, Kerman, Shiraz, and Yazd have more solar energy potential to establish CSP plants in Iran. Annual electricity power for these cities are calculated to be about 234GWh, 245GWh, 283GWh, 318GWh, 321 GWh and 318GWh, respectively. Furthermore, employment of solar energy in these areas for electricity generation, considerably conserve fossil fuels and reduces CO2 emission.Also, a comparison of DNI and power plant electricity generation in the 6 talented cities of Iran and 4 cities of Algeria are performed.

A New Cloud Screening Algorithm for Ground-Based Direct-Beam Solar Radiation

AbstractCloud screening of direct-beam solar radiation is an essential step for in situ calibration and atmospheric properties retrieval. The internal cloud screening module of a Langley analysis program [Langley Analyzer (LA)] used by the U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Program (UVMRP) is used for screening the uncalibrated direct-beam measurements and for deriving Langley offset voltages for calibration of the UV version of the Multifilter Rotating Shadowband Radiometer (UV-MFRSR). The current LA cloud screening module utilizes data from extended clear-sky periods and tends to ignore shorter periods that typify periods of broken cloudiness, and as a result, fewer values are generated for sites with higher frequencies of cloudy days (cloudy sites). A new cloud screening algorithm is presented that calculates the total optical depth (TOD) difference between a target point and pairs of points, and identifies the target as cloudy if the mean TOD difference exceeds a certain threshold. The screening is an iterative process that finishes when no new cloudy points are found. The result at a typical clear/sunny site shows that values from partly cloudy days are consistent with those from cloud-free days, when the new method is employed. The new cloud screening algorithm picks up significantly more values at cloudy sites. The larger decrease of the annual mean value of at cloudy sites than at relatively clear sites suggests the potential for improving calibration accuracy at cloudy sites. The results also show that the new cloud screening method is capable of detecting clear points in short clear windows and in transitional regions.

Application of Universal Thermal Climate Index (UTCI) for microclimatic analysis in urban thermal environments

Microclimatic effects were investigated for human thermal sensation on human bioclimatic maps in summer, 2009 using the Universal Thermal Climate Index (UTCI). Study locations were downtown Nanaimo, BC, Canada and Changwon, Republic of Korea. Air temperatures and humidities of several sites were collected at the two locations. Mean radiant temperatures of outdoor study areas in high resolution were simulated with the HURES human-urban radiation exchange simulation model. Wind speeds estimated using the ENVI-met model were corrected using collected wind speed data and adjusted from one to ten meters above the surface via UTCI's wind speed converting formula. Greatest heat stress was around mid-afternoon. Sunny areas had moderate to strong heat stress, 28–38°C UTCI. Shady areas had no thermal stress to moderate heat stress, 20–27°C UTCI. Narrow streets had lower UTCI's than open spaces in both areas. A 1ms−1 reduction in 10m height wind speed (u) increased UTCI by 1°C. In this study, u varied by up to 3.3ms−1. Observed direct beam solar radiation variations changed UTCI by three heat stress levels, diffuse and reflected solar radiation and longwave radiation changed it by 1.5 levels and u altered UTCI by half a level. UTCI is an accepted, easy to determine human thermal index whose results can be mapped as human bioclimatic maps and should be a useful tool for analyzing possible outdoor human thermal effects of urban and landscape planning and design.

Using a shading matrix to estimate the shading factor and the irradiation in a three-dimensional model of a receiving surface in an urban environment

In an urban environment, grid-connected building integrated photovoltaic (PV) systems can be subject to complex shading patterns. The study of the shadows projected by nearby buildings and other elements around a PV surface permits cutting down energy losses due to the module’s partial shading and improving the system’s performance ratio, so that the energy production costs can be lower. This paper presents a methodology that estimates the shading factor and irradiation on a three-dimensional model of a receiving surface in an urban environment. The main innovations introduced by this methodology are the building of a shading matrix composed by direct shading factor values around the whole sky dome and the analysis of the shading impacts on direct beam, isotropic diffuse, circumsolar diffuse and horizon brightening diffuse solar radiation components. The shading matrix improves the time spent on long simulation periods and permits an easy numerical integration over the sky to obtain the diffuse shading factors. Using this feature, a plug-in to the Google SketchUp three-dimensional modeling software was built to test this methodology. A series of similar results were obtained between actual measurements and estimates conducted by the plug-in.

인간 열환경 지수를 이용한 생기후지도 작성 및 도시·조경계획 및 디자인에의 적용방안

이 연구는 대구광역시에 위치한 중심상업지역을 포함한 국채보상운동공원과 2.28공원지역을 대상지로 미기후 실측과 컴퓨터 시뮬레이션을 이용해 여름철 인간 열환경 지수를 분석하고, 그 지수를 토대로 인간 생기후지도를 제작하여 향후 도시 조경계획 및 디자인에 이용할 방안을 모색하는데 목적을 두었다. 인간 열환경 지수를 분석하기 위해 필요한 자료들로서 기후자료(기온, 습도, 풍속, 태양 및 지구 복사에너지)와 도시공간 구성자료(건물의 위치와 높이; 수목의 위치와 높이; 수목의 종류와 건물 벽, 지표면의 재질; 태양 복사에너지 반사율과 지구 복사에너지 방사율)를 지리정보시스템 자료와 실측을 통해 구축하였다. 그 결과, 풍속이 약할수록 도시중심상업지역이 공원보다 높은 기온을 나타냈으며, 습도는 반대의 현상을 보였다. 특히, 주풍 방향의 길들은 지역풍의 영향으로 주풍과 직각방향의 길들보다 더 낮은 기온을 나타냈다. 여름철 열환경 지수에서 가장 큰 영향을 미치는 기후요소는 태양직사광선으로 나타났으며, 도시공간에서 그늘 조성이 가장 효과적인 열환경 개선 방법이었다. 그 방법 중 파고라에 수목그늘을 이중적으로 조성하는 방법이 가장 효과적이었으며, 북향의 건물 벽 앞에 수목그늘을 조성하는 것이 그 다음으로 효과적이었다. 또한, 수종 선택뿐만 아니라 식재방식에도 중점을 두어야 하는 것으로 나타났다. 양지의 열환경 지수는 따뜻한 정도(warm)에서 매우 더운 정도(very hot)로 나와, 음지의 중간(neutral)에서 따뜻한 정도(warm)에 비해 불쾌한 열환경이 조성되었다. 특히, 양지는 넓은 광장형태의 지역들이 좁은 길보다 더 불쾌한 결과를 보였다. 재질의 반사율을 건물 벽 0.15, 지표면 0.1 낮췄을 때, 열환경 지수가 음지에서는 한 단계 중 1/6만큼, 양지에서는 1/3만큼 감소됨을 알 수 있었다. 이와 같은 미기후적 접근방식이 도시 열환경 개선방안을 찾는데 효과적일 것이다. The purpose of this study is to find applicabilities of human bioclimatic maps, using human thermal sensation(comfort) in summer, with microclimatic in situ data and computer simulation results at the study site of downtown Daegu. This includes the central business district(CBD) area and two urban parks, the Debt Redemption Movement Memorial Park and the 2.28 Park, for urban and landscape planning and design. Climatic data and urban setting information for the analysis of human thermal sensation were obtained from in situ measurement and the geographic information system data. As a result, the CBD had higher air temperature than the parks when the wind speed was low. Relative humidities were opposite to the air temperature. Especially, same directional streets with local wind direction had lower air temperature than streets perpendicular to the wind direction. The most important climatic variable of human thermal sensation in summer was direct beam solar radiation. Also, creating shadow areas would be the most relevant method for modifying hot thermal environments in urban areas. The most effective method of creating shadow patterns was making a tree shadow over a pergola, and the second best one was making a tree shadow on the front of north directional building walls. Moreover, how to plant trees for creating shadow patterns was important as well as what kind of trees should be planted. The results of human thermal sensation were warm to very hot at sunny areas and neutral to warm at shaded ones. At the sunny areas, wide, squared shape areas had a little bit higher thermal sensation than those of narrow streets. The albedo change of building walls 0.15 and ground surface 0.1 could change 1/6 of a sensation level at the shaded areas and 1/3 at the sunny ones. These microclimatic approaches will be useful to find appropriate methods for modifying thermal environments in urban areas.

Direct beam and hemispherical terrestrial solar spectral distributions derived from broadband hourly solar radiation data

Multiple junction and thin film photovoltaic (PV) technologies respond differently to varying terrestrial spectral distributions of solar energy. PV device and system designers are concerned with the impact of spectral variation on PV specific technologies. Spectral distribution data are generally very rare, expensive, and difficult to obtain. We modified an existing empirical spectral conversion model to convert hourly broadband global (total hemispherical) horizontal and direct normal solar radiation to representative spectral distributions. Hourly average total hemispherical and direct normal beam solar radiation, such as provided in Typical Meteorological Year (TMY) data, are spectral model input data. Default or prescribed atmospheric aerosols and water vapor are possible inputs. Individual hourly and monthly and annual average spectral distributions are computed for a specified tilted surface. The spectral range is from 300nm to 1800nm. The model is a modified version of the Nann and Riordan SEDES2 model. Measured hemispherical spectral distributions for a wide variety of conditions at the Solar Radiation Research Laboratory at the National Renewable Energy Laboratory, Golden, Co. and Florida Solar Energy Center (Cocoa, FL) show that reasonable spectral accuracy of about ±10% is obtainable with exceptions for weather events such as snow. Differing cloud climatology and variable albedo and aerosol optical depth atmospheric conditions can lead to spectral model differences of 30–40%.

인간 열환경 지수(HumanThermal Sensation)를 이용한 조경계획 및 디자인 방법

이 연구는 인간 에너지 균형 모델에서 출발한 인간 열환경 지수 분석 방법을 이용하여 캐나다 BC주에 있는 나나이모시 상업지구안 좁은 길과 경상남도 창원시 중심상업지구에 있는 소공원을 연구 대상지로 2009년 여름철 열환경을 분석한 것이다. 기후 입력 자료는 기온, 상대습도, 풍속, 태양 및 지구 복사에너지이었으며, 그 결과 인간 열환경 지수에 가장 크게 영향을 미치는 요소들은 태양 직사광선, 건물시계지수 그리고 풍속이었다. 음지는 약간 더운 정도의 열환경을 조성하는 것으로 나타나 매우 덥게 나타난 양지에 비해 훨씬 좋은 열환경을 조성하는 것으로 나타났다. 나나이모 연구 대상지에 있는 좁은 길들은 주변의 넓은 장소들에 비해 주변 건축물에서 나오는 태양 반사광선과 지구 복사에너지들이 더 많이 영향을 미쳐 훨씬 덥게 나타났다. 낮은 풍속에 의해서 인체에서 방출되는 현열과 잠열의 양이 현저히 줄어듦으로서 더 더운 열환경이 조성되는 것으로 나타났다. 기후요소를 조경에 접목하기 위해서, 인간 열환경 지수 분석 방법을 이용하는 것은 열환경적으로 쾌적한 옥외 공간조성에 영향을 미칠 것이며, 도시 열섬 완화와 기후변화 연구에도 잘 이용될 수 있을 것이다. Human thermal sensation based on a human energy balance model was analyzed in the study areas, the Changwon and Nanaimo sites, on clear days during thesummer of 2009. The climatic input data were air temperature, relative humidity, wind speed and solar and terrestrial radiation. The most effective factors for human thermal sensation were direct beam solar radiation, building view factor and wind speed. Shaded locations had much lower thermal sensation, slightly warm, than sunny locations, very hot. Also, narrow streets in the Nanaimo site had higher thermal sensation than open spaces because of greater reflected solar radiation and terrestrial radiation from their surrounding buildings. Calm wind speed also produced much higher thermal sensation, which reduced sensible and latent heat loss from the human body. By adopting climatic factors into landscape architecture, the human thermal sensation analysis method promises to help create thermally comfortable outdoor areas. The method can also be used for urban heat island modification and climate change studies.

SOLAR RADIATION TRANSMISSION THROUGH PLASTIC SHADING NETS

Plastic shading nets are being used extensively in hot and sunny regions to protect plants from intense solar radiation. However, the choice of net to fulfill specific shading requirements often depends on empirical or economic criteria, not on scientific considerations because parameters used to characterize the different types of nets is not available. Solar radiation transmission is the most important parameter characterizing nets. A simple measuring method is presented and used to quantify global, diffuse and direct beam solar radiation transmission trough seven plastic shading nets. Nets with colors and nominal shading factors that are most commonly used in the Arabian Peninsula were selected for the study. The results showed that the behaviors of the plastic nets and their radiative properties under solar radiation conditions were similar to translucent materials. Accordingly, investigating equivalent optical constants (i.e., refractive indexes and extinction coefficients) for plastic nets similar to translucent materials is possible. Determining these constants can help to predict the radiative properties of the net without the need of measurements. Solidity and color of the net had significant effects on the radiative properties. The shading factor of a plastic net depends on the time of the day and on the design and meteorological parameters. Daily integral of the shading factor, solidity and the total radiative properties are appropriate parameters describing a net whereas, nominal shading factors provided by the producers cannot be used.

Prediction of Hourly Solar Radiation on Horizontal and Inclined Surfaces for Muscat/Oman

In this paper, hourly terrestrial radiation: direct beam, diffuse and global solar radiation are modelled and calculated based on daily measured data for a horizontal surface. In addition, the same parameters were modelled for inclined surfaces. Most of the parameters modelled in this work represent a part of the input data required by building thermal simulation and solar energy systems software. Important trends of the solar radiation on tilted surfaces as a function of time and direction are being presented and discussed. The comparison of some of the results with measured data from other sources shows good agreement. The effect of tilt angle and orientation on the incident solar radiation fluxes arepresented along with optimum surface tilt angles and directions for maximum solar radiation collection in Muscat area. The results presented in this paper are quite useful for quick estimation of solar radiation for calculations of cooling load and solar collector performance. Also, the models and the computer code developed in this work form the backbone of any computer-aided building thermal design and solar systems design calculations.

Lag‐time effects on a naturally ventilated large thermometer screen

AbstractSystematic natural ventilation effects on measured temperatures within a standard large wooden thermometer screen are investigated under summer conditions, using well‐calibrated platinum resistance thermometers. Under low ventilation (2 m wind speed u2 < 1.1 m s−1), the screen slightly underestimates daytime air temperature but overestimates air temperature nocturnally by 0.2°C. The screen's lag time L lengthens with decreasing wind speed, following an inverse power law relationship between L and u2. For u2 > 2 m s−1, L ∼ 2.5 min, increasing, when calm, to at least 15 min. Spectral response properties of the screen to air temperature fluctuations vary with wind speed because of the lag changes. Ventilation effects are particularly apparent at the higher (>25°C) temperatures, both through the lag effect and from solar heating. For sites where wind speed decreases with increasing daytime temperature, thermometer screen temperatures may consequently show larger uncertainties at the higher temperatures. Under strong direct beam solar radiation (>850 W m−2) the radiation effect is likely to be <0.4°C. Copyright © 2011 Royal Meteorological Society

Measuring and evaluating solar radiative properties of plastic shading nets

Plastic shading nets are being used extensively in hot and sunny regions to protect plants from intense solar radiation. Different varieties of these nets are commercially available. However, the choice of net to fulfill specific shading requirements often depends on empirical or economic criteria and not on scientific considerations because essential information used to characterize the different types of nets is not available. In order to replace expensive measuring facilities that use artificial lighting to investigate the radiative properties of plastic shading nets, a simple method was presented to investigate these properties under global, diffuse and direct beam solar radiation conditions. Measurements were performed on clear sunny days, (December 28, 2008–February 10, 2009). Nets with colors and shading factors that are most commonly used in hot regions were selected for the study. The results showed that the behaviors of the plastic nets under solar radiation conditions were similar to those of translucent materials. Accordingly, it is possible to (i) treat plastic nets as translucent materials and (ii) investigate the equivalent optical constants (i.e., refractive indexes and extinction coefficients) for plastic nets as functions of the net solidity, texture type and color. Solidity and color of the net had significant effects on the radiative properties and the effect of color was much more than the effect of solidity. The shading factor of a plastic net, is a function of the daytime, depends on several design and meteorological parameters, so it cannot be used to describe a net. However, the net solidity together with color, and the daily integrals of the shading factor and of the radiative properties are appropriate parameters for describing a net.

Modeling Stream Shade: Riparian Buffer Height and Density as Important as Buffer Width1

DeWalle, David R., 2010. Modeling Stream Shade: Riparian Buffer Height and Density as Important as Buffer Width. Journal of the American Water Resources Association (JAWRA) 46(2):323‐333. DOI: 10.1111/j.1752‐1688.2010.00423.xAbstract: A theoretical model was developed to explore impacts of varying buffer zone characteristics on shading of small streams using a path‐length form of Beer’s law to represent the transmission of direct beam solar radiation through vegetation. Impacts of varying buffer zone height, width, and radiation extinction coefficients (surrogate for buffer density) on shading were determined for E‐W and N‐S stream azimuths in infinitely long stream sections at 40°N on the summer solstice. Increases in buffer width produced little additional shading beyond buffer widths of 6‐7 m for E‐W streams due to shifts in solar beam pathway from the sides to the tops of the buffers. Buffers on the north bank of E‐W streams produced 30% of daily shade, while the south‐bank buffer produced 70% of total daily shade. For N‐S streams an optimum buffer width was less‐clearly defined, but a buffer width of about 18‐20 m produced about 85‐90% of total predicted shade. The model results supported past field studies showing buffer widths of 9‐11 m were sufficient for stream temperature control. Regardless of stream azimuth, increases in buffer height and extinction coefficient (buffer density) were found to substantially increase shading up to the maximum tree height and stand density likely encountered in the field. Model results suggest that at least 80% shade on small streams up to 6‐m wide can be achieved in mid‐latitudes with relatively narrow 12‐m wide buffers, regardless of stream azimuth, as long as buffers are tall (≈30 m) and dense (leaf area index ≈6). Although wide buffers may be preferred to provide other benefits, results suggest that increasing buffer widths beyond about 12 m will have a limited effect on stream shade at mid‐latitudes and that greater emphasis should be placed on the creation of dense, tall buffers to maximize stream shading.

Effects of digital elevation model spatial resolution on distributed calculations of solar radiation loading on a High Arctic glacier

AbstractHigh-resolution airborne lidar data are used to produce digital elevation models (DEMs) of an arctic valley glacier (midre Lovénbreen, Svalbard) at resolutions of 2.5–2000 m, using three different interpolation schemes. These data are used in a distributed model of solar radiation loading for glaciers. When the mean of all lidar measurements within a DEM cell is used to calculate cell height, the differences between the finest- (2.5 m) and coarsest-resolution (2000 m) DEMs for the calculated annual whole-glacier spatial means of total potential direct-beam solar radiation, potential duration of direct-beam solar radiation, and intensity of potential direct-beam solar radiation are 20%, 56% and −23% of the 2.5 m DEM values respectively. A resolution change from 2.5 m to 200 m affects the whole-glacier spatial mean summer net solar radiative flux by an average of 5%, and the summer melt production from the glacier by an average of 3% compared with the 2.5 m DEM values, for the years 2001–03. These changes are largely driven by underestimation of shading by surrounding topography at coarser DEM resolutions. This dependency is reduced in the second and third interpolation schemes, especially at resolutions finer than 50 m, which use the maximum lidar height measurement in some or all DEM cells. These results suggest that resolutions of ∼50 m are the coarsest that should be adopted in high-resolution glacier surface energy-balance models for glaciers of similar size and in similar topographic situations to midre Lovénbreen, and that the impact of DEM resolution on calculated solar radiation receipts can be reduced by an appropriate choice of DEM interpolation scheme.

Parameterization models for solar radiation and solar technology applications

Solar radiation is very important for the evaluation and wide use of solar renewable energy systems. The development of calibration procedures for broadband solar radiation photometric instrumentation and the improvement of broadband solar radiation measurement accuracy have been done. An improved diffuse sky reference and photometric calibration and characterization software for outdoor pyranometer calibrations are outlined. Parameterizations for direct beam, total hemispherical and diffuse sky radiation and solar radiation technology are briefly reviewed. The uncertainties for various broadband solar radiations of solar energy and atmospheric effects are discussed. The varying responsivities of solar radiation with meteorological, statistical and climatological parameters and possibility atmospheric conditions was examined.

RETROREFLECTIVE PROPERTIES CALCULATING METHOD BASED ON GEOMETRICAL-OPTICS ANALYSIS

If the albedo on the surface of a building is raised, it is expected that the effect of reducing the thermal load of a building, and also the depression effect of urban heat island phenomenon. If the retroreflectors are used in order to reflect solar radiation, it can reflect towards the incidence direction using the directivity of direct-beam solar radiation, therefore effective reflection may be able to expect. In order to evaluate the reflection performance to the direct-beam solar radiation, the optical properties of the retroreflectors are analyzed and the simple expressions which evaluates reflection performance are drawn. In this paper, the target retroreflectors are two sorts of a three-mirror type and a four-mirror type of corner reflectors.

NUMERICAL SIMULATION ON BASIC PROPERTIES OF RETROREFLECTORS

This paper aims at developing the solar-radiation reflector with retroreflective abilities, in order to aim at reduction of urban heat island effects, and building cooling loads of a summer season. However, although retroreflectors have some researches which should be referred to in the aspect of visibility, the knowledge on solar -radiation reflection is not accumulated. This is because the general purposes of the retroreflectors are reflecting plates, such as a road sign. Therefore, in this study, the numerical simulation which used the ray tracing method performed the case study, and the reflective property on a direct-beam solar radiation was analyzed. Furthermore, possibility that high reflection performance would be realizable compared with a diffuse reflection was shown.