Direct Absorption Of Solar Radiation Research Articles

Bulk ceramics of lanthanum hexaboride with enhanced spectral selectivity and photothermal efficiency for novel hybrid thermal-thermionic solar absorbers

Lanthanum hexaboride (LaB6) single-crystals are known from a long time for their excellent thermionic and field-assisted electron-emitting properties. Recently, multi-crystalline ceramics, which offer several technological advantages over single-crystals, have been studied as well, proving a low work function and Richardson constant, in addition to favorable optical properties for high-temperature solar radiation absorbers. However, to fully disclose to LaB6 ceramics the novel application of a double-function bulk thermionic emitter, enabled by the direct absorption of solar radiation, and, at the same time, thermodynamic solar absorber for Concentrating Solar Power (CSP), their optical properties should be further optimized. The ideal result, consisting in the selective increase of the solar absorptance and decrease of the thermal emittance, thus increasing both the spectral selectivity and the photothermal efficiency of the absorber, has been obtained in this work by realizing Laser-Induced Periodic Surface Structures (LIPSS) on the ceramic surface by means of femtosecond-laser treatments. LIPPS formation has been investigated as a function of the accumulated laser fluence.

Long-term climatology and spatial trends of absorption, scattering, and total aerosol optical depths over East Africa during 2001-2019.

The unprecedented increase in anthropogenic activities, coupled with the prevailing climatic conditions, has increased the aerosol load over East Africa (EA). Given this, the present study examined the trends in total, absorption, scattering, and total aerosol extinction optical depth (TAOD, AAOD, SAOD, and TAEOD) over EA, alongside trends in single scattering albedo (SSA). For this purpose, the AOD of different optical properties retrieved from multiple sensors and the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) model between January 2001 to December 2019 were utilized to estimate trends and assess their statistical significance. The spatial patterns of seasonal mean AOD from the Moderate-resolution Imaging Spectroradiometer (MODIS) sensor and MERRA-2 model were generally characterized with high (>0.35) and low (<0.2) AOD centers over EA observed during the local dry and wet seasons, respectively. Also, the spatial trend analysis revealed a general increase in TAOD, being positive and significant over the arid and semi-arid zones of the northeastern part of EA, which is majorly dominated by locally derived dust. The local dry (wet) months generally experienced positive (negative) trends in TAOD, associated with seasonal cycles of rainfall. High and significant positive trends in AAOD were dominated over the study domain, attributed to an increased amount of biomass burning, variations in soil moisture, and changes in the rainfall pattern. The trends in TAEOD showed a distinct pattern, except over some months that depicted significant increasing trends attributed to changes in climatic conditions and anthropogenic activities. At last, the study domain exhibited decreasing trends in SSA, signifying strong absorption of direct solar radiation resulting in a warming effect. The study revealed patterns of trends in aerosol optical properties and forms the basis for further research in aerosols over EA.

Methodology for assessing the danger of erosion and formation of soil protection agro-landscapes

Purpose. On the basis of an in-depth analysis of the erosion safety of the soil cover of Ukraine, to determine the theoretical and applied principles of the formation of an agrolandscape with guaranteed soil protection, mainly by engineering methods. Methods. System comparative analysis of erosion hazard. Mathematical modeling of erosion processes. Physical simulation of anti-corrosion protection. Results. The main causes of progressive soil erosion in Ukraine have been revealed. Classified distributed soil erosion by types and species. The main reason for the development of erosion processes and the imbalance of modern agricultural landscapes of Ukraine, which is excessive plowing of the territory and agricultural lands, has been revealed. Annual erosion losses from arable lands of Ukraine are indicated. The main degradation processes of the soil cover have been identified. The main problems in land use and land protection, which are not solved and become chronic, are formulated. Generalized negative ecological consequences of soil erosion of the chernozem habitus. It has been proven that arable land is the main element of the entropy of “chaos” in the landscape. Algorithms for the construction of soil protection agrolandscape are formulated. The ability to use the hydromechanical model has been proven Ts. E. Mirtskhulava, which we have moderated for the assessment of erosion danger in the formation of agricultural landscape structures mainly by engineering methods, for a certain probability of manifestation of erosion danger and individual factors of soil erosion. Conclusions 1. The soil cover of the Earth is degraded by almost 100%, the greatest “weight” among degradation processes is occupied by the processes of water (36%) and wind (28%) erosions. 2. One of the most significant destabilizing factors is arable land. When natural vegetation is destroyed, the soil is destroyed as a result of a sharp increase in the direct absorption of solar radiation. 3. A reliable method of protecting soils from erosion is an agrolandscape – an engineering structure (structure) that must be designed and built mainly by engineering methods on a calculated and quantitative basis, which requires the presence of appropriate mathematical models verified in every way, those processes that determined the stability and productivity of lands. The “zero” cycle is the basis of the construction of the agro-landscape is the anti-erosion protection system. 4. For the formation of anti-erosion protection in the agricultural landscape, a mathematical model of erosion is necessary as a calculation quantitative base, preference should be given to theoretical models that adequately and physically conditionally describe natural processes. Keywords: soil erosion and degradation, agricultural landscape, mathematical models of erosion, erosion hazard.

A hybrid approach of surface and direct absorption of solar radiation on parabolic solar collector.

This paper presents a novel approach of utilizing a spectrally selective coating inside the absorber tube of a solar parabolic collector for enhanced photothermal conversion. The photothermal performance of a hybrid system that incorporates an internal coating and nanofluid is analyzed in the present work. The internal coating developed is a composite of PMMA/CuO/Epoxy and as applied using the simple dip-coating technique. The maximum weighted solar absorptance of the internal coating was found to be 57.51%. The significance and interactions of the coating process variables, like concentrations of PMMA and CuO and the number of dips, were analyzed using the central composite design (CCD) of response surface methodology (RSM). An optimized coating (Concentration of PMMA and CuO: 4997.7 and 170.8 mg/30 ml, Number of Dips: 4) was arrived at based on the desirability function. Prior to the introduction of internal coating on the parabolic solar collector, a lab-scale photothermal conversion study was carried out using the optimized internal coating. The results revealed the superior performance of the internal coating when compared with that of pure surface absorption and direct absorption. Finally, the optimized internal coating was incorporated in a parabolic collector, with CuO nanofluid as a working fluid. Maximum efficiency of 62.80% was obtained for the hybrid system the internal coating and CuO nanofluid, compared to 31.6% for a direct absorption solar collector.

Investigation of Nanofluids Circulating in a Volumetric Solar Receiver

Abstract Single-wall carbon nanohorn (SWCNHs)-based nanofluids have been proven to be promising media for the direct absorption of solar radiation due to their favorable optical properties and potential low cost. Still their stability in real working conditions is an open issue because they have been studied mainly under stagnant conditions, while limited information is available on the performance of these nanofluids during circulation in real systems. In the present work, the optical behavior of SWCNH-based nanofluids has been investigated with the aim of detecting possible effects of circulation and exposure to radiation, avoiding other effects such as thermal instability. An ad hoc experimental apparatus has been realized to check the stability of the circulating fluids in situ using a novel approach based on the use of pyranometers. Three suspensions are tested, two are surfactant stabilized and one is based on preoxidized and functionalized SWCNHs. Efficiency values higher than 90% were measured for more than 65 h of circulation. The effects of fluid circulation and exposure to solar radiation have been addressed, finding that the absorption efficiency decreases during tests due to the degradation of the optical properties and the nanofluid circulation is the main responsible for such degradation.

Design and characterization of a solar-enhanced microwave plasma reactor for atmospheric pressure carbon dioxide decomposition

The decomposition of carbon dioxide (CO2) is a primary step in carbon re-utilization approaches aimed to fulfill fuels and chemicals demands and mitigate environmental emissions. Plasmachemical CO2 decomposition processes can be highly efficient; however, their reliance on electrical energy can limit their economic viability and sustainability advantage. In contrast, solar thermochemical CO2 decomposition approaches can have limited efficiency, but their direct use of the most abundant form of renewable energy affords them the greatest sustainability potential. Solar-enhanced microwave plasma (SEMP) chemical synthesis, based on the direct interaction between microwave plasma and concentrated solar radiation, is investigated as a novel approach to combine the advantages of plasmachemical and solar thermochemical processes. SEMP is motivated by the potential for synergistic effects between solar photons and plasma species, implied by the markedly greater spectral absorption of nonequilibrium CO2 plasma compared to that of equilibrium CO2, to lead to enhanced chemical decomposition. The design, development, and characterization of a SEMP reactor for atmospheric pressure CO2 decomposition is presented. The reactor is powered by a 1.25 kW magnetron and by up to 525 W of incident radiative power from a high-flux solar simulator. Experimental results reveal that the microwave plasma absorbs up to 20% of concentrated solar radiation at a solar-to-electrical power ratio of 0.5, and that relative absorption decreases with increasing solar input power. However, conversion efficiency and plasma energy efficiency increase with increasing solar power, up to 9% and 25% respectively, for a solar-to-electrical power ratio of 0.75. The enhanced process performance appears to be a consequence of the greater power density in the plasma caused by the direct absorption of solar radiation.

Modeling and analysis of optical properties of nanoparticles and nanofluids for effective absorption of solar radiation and their heating

This review presents a comprehensive analysis of the recent studies and advances related to optical properties of nanoparticles, their heating under solar irradiation and heat conversion, relevant equations and theoretical modeling approaches and application of nanofluids for direct absorption of solar radiation. A lot of papers including theoretical, numerical and experimental up-to-date works are reviewed and summarized carefully to give a panoramic overview of the role of the nanoparticles. Modern nanotechnology can produce various homogeneous and hybrid (core–shell) nanoparticles from different metals and materials which have unique optical and thermal properties. It was found that the application of nanoparticles selected on the basis of the presented analysis has shown remarkable properties and offers unique advantages over conventional fluids in optical absorption, thermo-physical and heating properties of nanofluids. This fact can play a crucial role in increasing the efficiency of solar energy harvesting.

Optical properties of nanoparticles and nanofluids for direct absorption of solar radiation

Theoretical investigation and selection of the optical properties of homogeneous metallic (titanium Ti, gold Au) and metal core–oxide shell (Ti–TiO2) nanoparticles with the radii 50, 75, 100 and 125 nm and their nanofluids have been carried out in the spectral interval 200–2500 nm for the purpose of effective absorption of solar radiation. Selected Ti and Ti–TiO2 nanoparticles with the radii 75–100 nm, in some cases up to 125 nm, are good absorbers in the visible and infrared spectral intervals and can be proposed for their use in solar thermal systems. Extinction and absorption of solar radiation by nanofluids (nanoparticles and water) are determined by the dominant influence of the system of Ti and Ti + TiO2 nanoparticles with concentration 109 cm−3 in the spectral interval 200–800 nm for the radii 50–75 nm and in interval 200–1100 nm for the radii 100–125 nm, and water dominantly influences the radiation extinction by nanofluid in the spectral range 1200–2500 nm.

Determination of absorption coefficient of nanofluids with unknown refractive index from reflection and transmission spectra

It has been shown that the absorption coefficient of a nanofluid can be actively tuned by changing material, size, shape, and concentration of the nanoparticle suspension. In applications of engineered nanofluids for the direct absorption of solar radiation, it is important to experimentally characterize the absorption coefficient of nanofluids in the solar spectrum. If the refractive index of the base fluid (i.e., the solution without nanoparticles) is known a priori, the absorption coefficient of nanofluids can be easily determined from the transmission spectrum. However, if the refractive index of the base fluid is not known, it is not straightforward to extract the absorption coefficient solely from the transmission spectrum. The present work aims to develop an analytical method of determining the absorption coefficient of nanofluids with unknown refractive index by measuring both reflection and transmission spectra. The proposed method will be validated with deionized water, and the effect of measurement uncertainty will be carefully examined. Finally, the general applicability of the proposed method will also be demonstrated for Therminol VP-1 as well as the Therminol VP-1 - graphite nanofluid.

Algoritmo teórico para la estimación de la radiación solar global para una atmósfera despejada

En este trabajo se desarrolló un algoritmo para la estimación de la radiación solar global, para una atmósfera despejada, mediante el modelamiento de las ecuaciones teóricas de transferencia radiativa de onda corta (0,3 µm - 2,8 µm). Se determinaron las transmitancias espectrales de la radiación solar directa, debidas a la dispersión de Rayleigh y Mie. Mediante el software Propiedades Ópticas de Aerosoles y Nubes (Optical Properties of Aerosols and Clouds, OPAC) se calculó la Profundidad Óptica de los Aerosoles (Aerosol Optical Depth, AOD) para cuatro diferentes tipos de atmósferas, indispensable para la determinación del índice de turbidez de Ångström. Así mismo, se calcularon la transmitancias espectrales por absorción de la radiación solar directa, incluyendo aerosoles, vapor de agua, ozono y aire seco (mezcla de gases). El contenido de O3 se obtuvo de los datos diarios existentes en base de datos de la NASA. Para la componente difusa de la radiación solar, se dedujo una nueva expresión para el cálculo de la fracción de la radiación solar dispersada por los aerosoles hacia la superficie terrestre. La comparación estadística entre los resultados obtenidos con el algoritmo desarrollado, los datos medidos de la radiación global (estación Potsdam - Alemania) y los resultados de otros tres modelos radiativos, entre 2012 y 2014, muestra que el nuevo modelo permite calcular los valores horarios de la radiación solar global con suficiente precisión. © 2018. Acad. Colomb. Cienc. Ex. Fis. Nat.

Heat transfer in a molten salt filled enclosure absorbing concentrated solar radiation

Numerical simulations of the natural convection driven by the direct absorption of concentrated solar radiation by a high temperature molten salt filled enclosures for height to diameter ratios (H/D) of 0.5, 1 and 2 and Rayleigh numbers 107–1011 is presented. The domain of interest consists of a fluid cavity bounded by rigid adiabatic vertical walls, a heat-conducting bottom wall of finite thickness and an open adiabatic top surface, directly irradiated by a non- uniform concentrated solar flux. The salt volume is first heated non-uniformly by direct absorption of solar radiation and subsequently from the lower absorber plate which is heated by the absorption of the radiation transmitted through the salt.A Finite Element Method is used to solve the time dependent two dimensional Navier Stokes equations that includes a depth dependent volumetric heat source and temperature dependent thermophysical of molten salts.Numerical results presented in terms of isotherms and streamlines show a nonlinear temperature profile consisting of distinct layers where thermocapilarity and buoyancy effects are evident. Fluid flow development in the lower layer is found to vary significantly with time and exhibits an initial stage, transitional stage and quasi-steady stages. The magnitude of the natural convection and the duration of each stage is found to decrease as the aspect ratio increases from 0.5 to 2. Calculation of the average heat transfer reveals that the Nusselt Rayleigh number relationship is not uniformly linear and the average heat transfer over the lower boundary surface increased with increasing Ra.

Experimental Study of Water‐Based Al2O3 Nanofluid Flow in Direct Absorption Solar Collector

SummaryTo overcome the limitations of conventional tube in plate type solar collector such as low collection and conversion efficiency, direct absorption solar collectors using nanofluid as heat transfer media has been proposed. Direct absorption of solar radiation and mixing of nanoparticles in the base liquid improves the optical and thermo physical properties of the base liquids, resulting to an increase in the efficiency of solar collectors. In the present experimental work, the effect of Al2O3–H2O nanofluid, as heat transfer fluid on the efficiency of a direct absorption solar collector was investigated. The ASHRAE standard was used to calculate the instantaneous efficiency. The results show that, in comparison with water as direct solar absorption medium, nanofluid increases the efficiency. For 0.001 vol% the increased efficiency was 12.8%. There is a continuous increase in the efficiency by increasing the volume fraction from 0.001% to 0.01% and beyond that increase in volume fraction values, the solar collector efficiency gets a reverse trend and becomes constant.

Thermo-optical properties of copper oxide nanofluids for direct absorption of solar radiation

In this paper, the optical and thermophysical properties of CuO nanofluid as the working fluid of low temperature direct absorption solar collector which is prepared by dispersing the CuO nanoparticles into mixture of distilled water and ethylene glycol (70%:30% in volume) as the base fluid is investigated at the different temperatures for different volume fractions. The results showed that the nanofluids had higher absorption coefficient compared to the base fluid in the whole wavelengths for solar energy, ranging from 200 to 2500nm. The absorbed energy fraction of CuO nanofluid with only 100ppm (volume fraction 0.01%) nanoparticle volume fraction is 4 times more than that of the base fluid at solar collector depth of 1cm. The viscosity increased with the increasing volume fraction and decreased exponentially with the increasing temperature. The thermal conductivity of CuO nanofluids increased with the increase of CuO volume fraction in the base fluid and temperature. At the investigated volume fractions, the thermal conductivity of the nanofluids was found to increase with respect to the base fluid up to about 13.7% for the 100ppm CuO nanoparticle volume fraction. Higher thermal conductivity and lower viscosity of CuO nanofluids by increasing temperature, together with the appropriate optical properties, introduce this kind of nanofluids as an appropriate candidate to effectively enhance the direct absorption solar collector efficiency.

Analysis of the exergetic performance of the reverse-side absorber-plate shallow solar pond

Results of exergetic performance analysis of three shallow solar pond (SSP) types – the CSSP, the RASSPgc, and RASSPins – are presented for the first time. The study shows that the highest irreversibilities are encountered in the components of the RASSPgc and that better exergetic performances in SSPs may be obtained by improving the surface properties: absorptivity, reflectivity, and transmissivity. Steady-state analysis also shows that exergy ‘losses’ in the SSPs due to irreversibilities in their water masses are significant and result from the direct absorption of solar radiation. Transient analysis reveals that the RASSPgc achieves the highest overall exergetic efficiency (4.37%), followed by the RASSPins (3.96%) and then the CSSP (2.87%). At the end of a 24 h operation, the exergy content of the water masses in the RASSPgc and the CSSP is negligible, whereas the water mass in the RASSPins retains 0.057 MJ of the exergy accumulated during daytime heating.

A Novel Integrated Direct Absorption Self-Storage Solar Collector

The present work introduces a novel integrated solar collector with direct absorption of solar radiation and self-energy storage. The proposed system has compact size without the need for any connecting pipes. The working fluid absorbs the incident solar radiation directly and passes it to the storing fluid container that has been implemented within the core of the novel system. A mathematical model has been presented to describe the thermal behavior of the proposed system. Moreover, an expression has been derived to predict the system efficiency, outlet temperature, and utilized heat transfer. Simultaneously, a comparison of the performance of the novel solar system with that of the conventional solar collector reveals that the performance of the proposed system is much better than that of the conventional collector. The proposed direct absorption collector has a collector efficiency factor, F′ = 1 which is 20% more than that of well-manufactured conventional collectors. This yields about 20% increase in the heat removal factors and efficiency of the integrated system as compared with that of the conventional collectors over the entire range of overall heat loss coefficients and for the same operating conditions regarding working fluid mass flow rate, inlet fluid temperature, ambient temperature, and incident solar radiation. However, it is found that the performance of the integrated collector is more sensitive to the variation in the overall heat loss coefficient and working fluid mass flow rate as compared with the conventional collectors.

The influence of the IR reflection of painted facades on the energy balance of a building

The investigation on the effect of painted facades with spectrally selective properties on the energy balance of a building is made by comparing real measured data from an outdoor test of facade samples with data calculated using the ESP-r simulation program. The following factors were investigated: influence of solar radiation, calculated with a solar model, the absorption of direct solar radiation as a function of the angle of incidence, IR radiation exchange and the influence of heat loss caused by convection. During this investigation, it was determined that the influence of solar radiation and especially the heat loss caused by convection are the most dominant influences on the examined energy balance of a building. After adapting the simulation program in order to simulate the data correctly, the influence of selective facades is investigated using an office model as an example. In the case of the location of Freiburg, Germany, two different types of outer walls are investigated and described in this publication: A well-insulated wall with a U-value of 0.42 W/(m 2 K) and a poorly insulated wall with 1.95 W/(m 2 K). The savings in the heating demand are higher in the case of poorly insulated walls than in well-insulated walls. In contrast to this effect, the cooling demand increases nearly in the same way for both types of walls. The tendency for condensation is also weakened, as is documented in [4].

Satellite- and ground-based observations of atmospheric water vapor absorption in the [formula omitted] region

Ground-based measurements of direct absorption of solar radiation between 9000 and 13,000 cm −1 (770– 1100 nm ) with a spectral resolution of 0.05 cm −1 are compared with line-by-line simulations of atmospheric absorption based on different molecular databases (HITRAN 2000, HITRAN 99, HITRAN 96 and ESA-WVR). Differences between measurements and simulations can be reduced to a great amount by scaling the individual line intensities with spectral and database dependent scaling factors. Scaling factors are calculated for the selected databases using a Marquardt non-linear least-squares fit together with a forward model for 100 cm −1 wide intervals between 10,150 and 11,250 cm −1 as well as for the water vapor absorption channels of the Medium Resolution Imaging Spectrometer (MERIS) onboard the European Space Agency's (ESA) ENVISAT platform and the Modular Optoelectronic Scanner (MOS) on the Indian IRSP-3 platform, developed by the German Aerospace Centre (DLR). For the latter, the scaling coefficients are converted into correction factors for retrieved total columnar water vapor content and used for a comparison of MOS-based retrievals of total columnar atmospheric water vapor above cloud-free land surfaces with radio soundings. The scaling factors determined for 100 cm −1 wide intervals range from 0.85 for the ESA-WVR molecular database to 1.15 for HITRAN 96. The best agreement between measurements and simulations is achieved with HITRAN 99 and HITRAN 2000, respectively, using scaling factors between 0.9 and 1. The effects on the satellite-based retrievals of columnar atmospheric water vapor range from 2% (HITRAN 2000) to 12% (ESA-WVR).

Numerical model simulations of boundary-layer dynamics during winter conditions

A mesoscale numerical model, incorporating a land-surface scheme based on Deardorffs’ approach, is used to study the diurnal variation of the boundary layer structure and surface fluxes during four consecutive days with air temperatures well below zero, snow covered ground and changing synoptic forcing. Model results are evaluated against in-situ measurements performed during the WINTEX field campaign held in Sodankyla, Northern Finland in March 1997. The results show that the land-surface parameterization employed in the mesoscale model is not able to reproduce the magnitude of the daytime sensible heat fluxes and especially the pronounced maximum observed in the afternoon. Additional model simulations indicate that this drawback is to a large extent removed by the implementation of a shading factor in the original Deardorff scheme. The shading factor, as discussed in Gryning et al. (2001), accounts for the fact that in areas with sparse vegetation and low solar angles, both typical for the northern boreal forests in wintertime, absorption of direct solar radiation is due to an apparent vegetation cover which is much greater than the actual one (defined as the portion of the ground covered by vegetation projected vertically). Moreover, the observed asymmetry in the diurnal variation of the sensible heat flux indicates that there might be a significant heat storage in the vegetation. The implementation of an objective heat storage scheme in the mesoscale model explains part of the observed diurnal variation of the sensible heat flux.

Progress in understanding of land surface/atmosphere exchanges at high latitudes

This paper summarises some of the key results from two European field programmes, WINTEX and LAPP, undertaken in the Boreal/Arctic regions in 1996–98. Both programmes have illustrated the very important role that snow plays within these areas, not only in the determination of energy, water and carbon fluxes in the winter, but also in controlling the length of the summer active season, and hence the overall carbon budget. These studies make a considerable advance in our knowledge of the fluxes from snow-covered landscape and the interactions between snow and vegetation. Also some of the first measurements of greenhouse gas fluxes (carbon dioxide and methane) are reported for the European arctic and sub-arctic. The measurements show a considerable variability across the arctic, with very high instantaneous values from sub-arctic birch and fen areas and extremely low fluxes reported from the polar desert in the high arctic. The overall annual budgets are everywhere limited by the very short active season in these regions. The heat flux over a high latitude boreal forest during late winter was found to be high. At low solar angles the forest shades most of the snow surface, therefore an important part of the radiation never reaches the snow surface but is absorbed by the forest. This indicates that in areas with sparse vegetation and low solar angles, absorption of direct solar radiation is due to an apparent vegetation cover, which is much greater than the actual one.

埋設パイプ内通水による畝内地温制御時の地温分布に関する数値シミュレーション

For a long time in the protected cultivation of fruit vegetables, there has been a practice of circulating warm water in pipes buried in soil ridges to control soil temperature in the root zone. Recently this technique has been applied to soil cooling in the cultivation of strawberry or ornamental plants such as Alstroemeria L. However there is little research on temperature distribution in the soil during the temperature control process or on the effects of ridge geometry, physical properties of the soil, climate conditions, pipe arrangement, water temperature and other factors on soil temperature. The authors have conducted numerical simulations of temperature distribution in ridge soil using the finite difference method to clarify the problems mentioned above and to optimize the system. In this paper, numerical solutions were conducted to explore the effects of free-convection heat transfer between the ridge surface and ambient air and the absorption of direct solar radiation at ridge surface, assuming that the effect of moisture in ridge soil on heat transfer is negligible. Results are shown for the cases of soil cooling during the high temperature period and soil heating during the low temperature period in Japan. In addition, the effects of physical properties of the soil, ambient air temperature, direct solar radiation absorbed at ridge surface, and the surface temperature of pipes on soil temperature distribution were examined.In conclusion, (1) the effect of solar radiation absorbed at the south side of ridges with E-W orientation on soil temperature is slight during the high temperature period, but significant during the low temperature period because of low solar altitude; (2) the effects of soil physical properties and ambient air temperature are small for both processes; (3) the effect of the surface temperature of pipes is comparatively large in both processes.