Solar Energy

The finiteness of the Earth's fossil-fuel reserves are discussed and the world energy needs are projected to show that alternative energy sources to nuclear power merit consideration. A satellite solar power station is proposed to generate power to meet future requirements. Considerations are given to orbital location, solar energy conversion devices, transmittal equipment and Earth-receiving stations. The use of photoconductive organic materials to form thin film solar collector surfaces and generation of microwave radiation to transmit energy to an Earth-based antenna are discussed. The design considerations and the development tasks for a large satellite solar power station are reviewed and the potential technological needs are identified. The suggestion is made that the technology developed for the space program may find application in a satellite solar power station to generate power for use on Earth.

The thermal radiative properties of glass are calculated using the optical constants data that are recently published in the literature. The directional-spectral reflectivity, absorptivity and transmissivity of glass are computed from 0.32 to 206 μm. These properties are also integrated to obtain the directional-total and hemispherical-total properties. The systems under investigation include a glass surface, a bulk glass plate and multilayer glass systems. Prediction equations are given to show that in the far IR various property equations can be reduced to a function of surface reflectivity. According to the calculated results, only under the normal incidence condition inside the far IR, the glass has a total reflectivity of 0.107 which is very close to the present design value (0.1). However, if the incident energy is coming from all directions as what is normally encountered in practice, the present design value makes, at least, a 50 per cent underestimation of reflectivity. To facilitate application of data presented in the far IR, an equation is also correlated that relates the glass hemispherical-total properties with temperature. While the glass properties are also evaluated inside the solar spectrum in this paper, these properties have been reported elsewhere and therefore, are not elaborated.

By recent developments in imaging-furnace techniques it is possible to obtain fundamental data on the thermal properties and phase-diagrams of high-melting-point ceramic oxides by a solar furnace.With a heliostat-type solar furnace, temperature and emissivity measurements have been investigated, using a brightness pyrometer designed by our Solar Research Laboratory.Brightness temperature of an opaque body having a specular reflection surface, can be measured by shadowing the marked area of the target surface, rejecting the reflected solar radiation. Spectral reflection is measured after the shadowing mask is removed, and thus the spectral emissivity and true temperature of the specimen can be calculated.In the case of a diffuse-reflection surface, a rotating sector is used to separate the emitted and reflected radiation from the target.The results of freezing-point measurements on HfO2, ZrO2, and Al2O3 are 3026 ± 20 deg K, 2979 ± 20 deg K, and 2322 ± 15 deg K respectively by the use of specular-reflection method.

Three typical polymeric, heat-shield materials and three refractories were evaluated under high radiant fluxes. Properties such as surface recession rate, surface temperature, re-radiated flux, emittance, and heat of ablation were measured where possible. An anomaly in the behavior of two of the refractories regarding their emittance-temperature relationship was noted. Possible mechanisms are suggested to explain the apparent anomaly.

Thermochemical methane reforming by a reactive redox system of WO3 was demonstrated under direct irradiation of the metal oxide by a concentrated, solar-simulated Xe-lamp beam below 1173 K, for the purpose of converting solar high-temperature heat to chemical fuels. In the proposed cycling redox process, the metal oxide is expected to react with methane as an oxidant to produce syngas with a H2/CO ratio of two, which is suitable for the production of methanol, and the reduced metal oxide which is oxidized back with steam in a separate step to generate hydrogen uncontaminated with carbon oxide. The ZrO2-supported WO3 gave about 45% of CO yield and 55% of H2 yield with a H2/CO ratio of about 2.4 in a temperature range of 1080–1160 K at a W/F ratio of 0.167 g min Ncm−3 (W is the weight of WO3 phase and F is the flow rate of CH4). The activity data under the solar simulation were compared to those for the WO3/ZrO2 heated by irradiation of an infrared light. This comparison indicated that the CO selectivity was much improved to 76–85% in the solar-simulated methane reforming, probably by photochemical effect due to WO3 phase. The main solid product of WO2 in the reduced WO3/ZrO2 was reoxidized to WO3 with steam to generate hydrogen below 1173 K.

In April 2001 the new European Standard EN 12975:2000: “Thermal solar systems and components––Solar Collectors” was established. With the publication of this European standard all national standards, related to the same topic, have to be withdrawn by the nations of the European Community. Now only one standard for testing solar collectors is valid throughout Europe.This European Standard specifies test methods for validating the durability, reliability and safety requirements for liquid heating collectors. The standard also includes two alternative test methods for the thermal performance characterization for liquid heating collectors. Apart from the well-known test method under steady-state conditions according to ISO 9806-1, ISO 9806-3 and ASHRAE 93-77 the EN 12975 permits a quasi-dynamic test method for the thermal performance characterization of solar thermal collectors.This paper presents the improved approach to outdoor performance testing of solar thermal collectors under quasi-dynamic test conditions. The test requirements and collector theory are closely connected to those long agreed on for steady-state testing, as described in the ISO and ASHRAE standards mentioned above. The most important effects for the all day performance of the collector are taken into account. The test method covers most collector designs on the market today (except ICS type). Only some correction terms are added to the basic collector models of the present steady-state test methods. Still this limited change will allow test data to be collected and used from whole days.An important fact is that the collector model used for the parameter identification is written so that the error in collector output power is minimized. Therefore an accurate long-term prediction of the collector performance can be an integral part of the test method, where the same collector model and parameters are used for both testing and prediction.

The UV instruments described in part I of this paper have been applied for measurements of solar global UV radiation in three different wavelength regions (310–320 nm, 315–391 nm, and 296–388 nm). UV radiation values obtained since 1985 are analyzed. Different types of regression equations were compared as to how much information on UV radiation is contained in total global radiation measurements (400–2800 nm). Applying those regression equations allows us to estimate UV radiation from measurements of total global radiation, which are readily available.

In hot humid climates, like that of Madras, a coastal city, it is attractive to dehumidify room air using an absorbent solution and desorb the water from the solution by solar heating. If a desorption tower is used for transfer of water from the solution to the outdoor air, a blower is required to produce the air flow. It is found by analysis, however, that it is possible to achieve this desorption in the solar collector itself. Water is transfered to the ambient air which flows through the solar collector-cum-desorber by thermo-siphon action. The performance characteristics of the proposed collector-cum-desorber were found to be excellent by theoretical calculations. These have been confirmed by experiments.

A selection of eight high performance clear sky solar irradiance models is evaluated against a set of 16 independent data banks covering 20 years/stations, altitudes from sea level to 1600 m and a large range of different climates. Their performance evaluated on very clear condition measurements are within 4% in term of standard deviation.The conclusions are that the accuracy of the input parameters such as the turbidity is crucial in the validity of the obtained radiation components, and that the choice of a specific model is secondary. The model selection criteria should be based upon either implementation simplicity, input parameter availability (Linke turbidity or aerosol optical depth) or the capacity of the model to produce spectral radiation.

Central receivers for use with power-generating equipment require compact boiler and superheater designs to effectively concentrate the solar heat input and to improve system power cycle efficiency. Solar thermal collectors employ a central receiver that must be compact to effectively utilize the high concentration ratios of sunlight energy. The demonstration of lightweight, long-life receiver designs is a technology issue that must be resolved if the concept is to be attractive for power generation. The receiver must be lightweight to minimize the cost of the supporting tower structure. Current applied aerospace technology in compact steam boilers and rocket thrust chamber designs can be directly applied to the design and fabrication of solar central receivers.

The long-term performance of a residential solar heating system has been determined for a system which has been operating continuously since 1957 with no maintenance. This residential solar heating system is the Colorado Solar House located in Denver, Colorado, designed and operated by George O. G. Löf. The performance of this system was determined during the 1959-1960 heating season, and the results were publised. The performance of this system was redetermined during the 1974-1975 heating season so that changes in performance occurring over a period of 15 yr could be determined. The collector is an Overlapped-Glass Plate Solar-Air Heater. The system is completely automatic with provision for water heating in addition to space heating. Solar heat is stored in a rock bed of primarily granitic rock approximately 1.3-2.5 cm in diameter. The ratio of useful collected solar heat divided by the total solar radiation on the collector dropped to 71.8 per cent of its original value in 15 yr. For both seasons, the useful collected solar heat was correlated with the ratio of degree days per month divided by the total solar radiation on the collector. For the same value of this ratio, less useful collected solar heat was delivered during the latter season. Additional work that will be published at a later date includes the detailed performance of the hot water heating system.

For the first time solar disinfection of liters of water containing wild Salmonella sp. and total coliforms was carried out in a compound parabolic collector (CPC) photoreactor at temperatures of almost 50 °C. Using surface water with high turbidity, this treatment was efficient in completely inactivating Salmonella sp. without regrowth during the subsequent 72 h of dark sterile storage. However if the solar treated water is poured in a non- sterile container, bacteria regrowth occurs even if 10 mg L−1 of H2O2 is added before the storage. On the other hand, 30 mg L−1 of H2O2 added when the irradiation started was completely depleted within 2 h and did not prevent bacterial regrowth during post-irradiation storage in non-sterile containers, demonstrating that storage of large volumes of water treated by solar irradiation was not optimal. Finally, total coliforms (Escherichia coli included) showed a far higher sensitivity than Salmonella sp. and demonstrated to be an inappropriate indicator for monitoring bacterial contamination in water during solar disinfection processes.Highlights► In this study a 18 L solar CPC reactor was successful to inactivate wild Salmonella sp. bacteria present in Burkina Faso real raw waters. ► Inactivated wild Salmonella sp. did not show regrowth after 72 h of dark sterile storage. ► Addition of H2O2 did not prevent bacterial regrowth during post-irradiation storage in non-sterile containers.

Angular distribution of the diffuse light essentially varies with the physical state of a disperse media. The main factors influencing the optical behaviour of the Earth’s atmosphere are the total optical thickness, the scattering ability of atmospheric layers, and also the reflectance of underlying surface. Any model aspiring to be more universal and still satisfactory accurate must at least account for these quantities. The paper presents the theoretically derived equation simulating the sky luminance/radiance under various meteorological conditions. Because the radiative transfer equation in plan-parallel atmosphere is solved exactly, the proposed approximation formula is physically well-founded. Compared with other, predominately empirical models, the presented approach accepts the basic principles of light scattering in a turbid environment and the model is spectral in its nature (contrary to empirical models in current use). In addition, the contribution of multiple scattering is taken into account. A set of free parameters, otherwise used as weighting factors for individual optical effects, makes the model easily scalable and applicable for a wide range of optical states of the atmosphere.

In Part I of this paper, thermal devices developed up until 1950 were reviewed. In Part II, projects since 1950 with devices up to 100 kW output where the design philosophy was to use “conventional” modern technologies. In this paper, “unconventional” devices are reviewed, where the designers attempted to employ different technologies, often at the expense of performance, so as to provide devices suitable for construction and maintenance in less developed regions of the world. As in Part II, the size of devices reviewed has been limited to 100 kW, and they have been categorised by their proposed source temperature and working medium. Since solar power is most likely to be employed in remoter regions in both developed and developing countries, the devices have been reviewed in this light. At the end, the prospects of small solar engines are discussed.

In preceding centuries, a number of engines were built and tried to provide mechanical power from solar energy, and these were reviewed in Part I of this set of papers. Since 1950, the number of attempts to produce viable mechanical power from solar energy has increased enormously, their sizes ranging from a few watts to several megawatts and, because of their number, the size of devices reviewed has been limited to 100 kW. The design philosophies of the projects have been varied; some included technologies at the forefront of current developments to obtain maximum performance, while others attempted to employ simpler technologies at the expense of performance so as to provide devices suitable for construction and maintenance in less developed regions of the world. In this set of papers, the two philosophies have been distinguished as “conventional” (using modern technologies) and “unconventional” (using simpler technologies) in an attempt to examine each in an appropriate context. To assist those contemplating further investigations, the devices have also been categorised by their proposed source temperature and working medium. Since solar power is most likely to be employed in remoter regions in both developed and developing countries, the merits of devices have been reviewed in this light. This paper covers devices falling into the “conventional” category.

Much work has been done over the centuries to drive machines using thermal energy from the sun, and there is a danger of our failing to learn from this work. In this, the first of three papers reviewing this work, attempts of all kinds made before 1950 to produce mechanical energy from thermal solar power are reviewed chronologically. Early devices were effectively only proving the concept, which many did, but some of the later projects came quite close to viable and effective operation. The second and third Parts of this set of papers review the very many devices, rated up to 100 kW output, which have been developed since 1950.

This article implements an algorithm for the calculation of solar position that has a stated. and partially demonstrated, accuracy of 0.01 deg until the year 2050. The algorithm is taken from The Astronomical Almanac, which has published it as an addendum to their very accurate tabulations since 1984. It uses the same approach as an earlier paper by Walraven, but has a more simplified form. This subject of the calculation of the solar position is revisited because of the somewhat confusing sequence of notes and letters that followed Walraven's publication in this journal and because of a report challenging the accuracy claimed by him. The Almanac approximation is compared to exact values and to some commonly used approximations. An appendix contains an annotated subroutine in FORTRAN, which should be easily converted to other programming languages.

Detailed information on solar radiation characteristics on Mars are necessary for effective design of future planned solar energy systems operating on the surface of Mars. In this paper we present a procedure and solar radiation related data from which the daily variation of the global, direct beam, and diffuse insolation on Mars are calculated. Given the optical depth of the Mars atmosphere, the global radiation is calculated from the normalized net flux function based on multiple wavelength and multiple scattering of the solar radiation. The direct beam was derived from the optical depth using Beer's law, and the diffuse component was obtained from the difference of the global and the direct beam radiation. The optical depths of the Mars atmosphere were derived from images taken of the Sun with a special diode on the cameras used on the two Viking Landers.

A closed-loop solar thermochemical energy storage and transport system using the dissociation and synthesis reactions of ammonia has been investigated at the Australian National University (ANU). Work relating to the optimisation of the heat recovery part of the system is reported. Experimental investigation has shown a 1-kWchem laboratory-scale ammonia synthesis reactor to operate in a stable and repeatable manner. A two-dimensional pseudo-homogeneous packed-bed catalytic reactor model previously used successfully for ammonia dissociation reactors is also confirmed to be valid for ammonia synthesis. Experiments were carried out in a closed-loop configuration and involved pressures from 9.3 to 19 MPa with internal peak reactor temperatures of up to 524°C and a constant mass flow of 0.3 g s−1. A simple adjustment of intrinsic rate parameters was required to calibrate the model and reproduce the experimentally observed effects of the variation of reactor wall boundary condition and operating pressure. The investigation revealed that thermal output strongly depends on reactor wall temperature and linearly increases with operating pressure. It is now possible to predict with confidence the performance of future reactor designs. The calibrated model can also be used for detailed theoretical examination of operating strategics designed to maximise thermal and exergetic output from heat recovery reactors.

Pyrometallurgical and physical metallurgical research often require high temperatures, controlled atmospheres, and freedom from contamination. To obtain such conditions at the Kennecott Research Center, a high temperature solar furnace was constructed using the 60-in. rhodium-plated mirror from an Army surplus searchlight. For maximum flexibility in sample handling, a modified heliostat-type mounting with two auxiliary mirrors was used. A traversing mechanism for zone refining experiments and a totally enclosed sample chamber have been provided. The installation and its characteristics as well as some of its projected uses are described.

Among advanced oxidation processes (AOP), the photochemically enhanced Fenton reaction (photo-Fenton) may be particularly effective for the treatment of industrial waste water, and the possibility to use solar light is an additional advantage of this process. In the present work, a Fe3+-exchanged zeolite Y was tested as a heterogeneous photo-Fenton catalyst for the degradation of the model organic pollutant, 2,4-xylidine. The performance of the catalyst was investigated using a bench photochemical reactor as well as solar reactors. The incident solar radiant powers (determined by ferrioxalate actinometry) showed linear correlations with the outputs of a Si-photodiode and a bolometer mounted on the solar unit, and could therefore be easily estimated from the on-line observation of the sensor outputs. The experimental design methodology was used for planning the experiments under normalized conditions and for modeling the rates of 2,4-xylidine oxidation as a function of the concentrations of the additives (Fe3+-exchanged zeolite catalyst and hydrogen peroxide). Although a direct quantitative comparison between both reactors is difficult (different geometries and volumes, different spectral distribution of the radiation sources), the performance of the solar reactor appears to compare favorably with that of the bench photochemical reactor.

In life cycle assessment (LCA) of solar PV systems, energy pay back time (EPBT) is the commonly used indicator to justify its primary energy use. However, EPBT is a function of competing energy sources with which electricity from solar PV is compared, and amount of electricity generated from the solar PV system which varies with local irradiation and ambient conditions. Therefore, it is more appropriate to use site-specific EPBT for major decision-making in power generation planning. LCA and life cycle cost analysis are performed for a distributed 2.7 kWp grid-connected mono-crystalline solar PV system operating in Singapore. This paper presents various EPBT analyses of the solar PV system with reference to a fuel oil-fired steam turbine and their greenhouse gas (GHG) emissions and costs are also compared. The study reveals that GHG emission from electricity generation from the solar PV system is less than one-fourth that from an oil-fired steam turbine plant and one-half that from a gas-fired combined cycle plant. However, the cost of electricity is about five to seven times higher than that from the oil or gas fired power plant. The environmental uncertainties of the solar PV system are also critically reviewed and presented.

Between 1992 and 1994 a 200 kWp-rooftop programme to promote small grid-connected Photovoltaic (PV) systems was conducted in Austria. Within this programme about 100 PV systems with an average capacity of 2.28 kWp were installed. This paper investigates the socio-economic aspects of this programme and the prospects for a further dissemination of this technology. The major conclusions of this investigation are as follows: (1) The motives to invest in a PV system are: (i) environmental protection; (ii) an alternative to nuclear power; (iii) technical interest. Yet, it is also important that the public supports this purchase by means providing subsidies. (2) The purchase of a PV system leads to different changes in consumer behaviour. Consumers with low initial consumption increased their electricity demand slightly, while the majority of consumers with high initial electricity demand saved electricity. (3) The financial incentives in the programme were not optimally designed. With the same amount of total subsidies it would have been possible to promote more PV systems. (4) The key factors for a further dissemination of PV systems are: (i) financial incentives; (ii) a reduction of the investment costs; (iii) increase in reliability; (iv) distribution of information; (v) enhancement of environmental awareness.

Within the 10 year Programme “Solarthermie-2000” of the German Federal Ministry for Economics and Technology (BMWi), large-scale solar-assisted heating plants have been funded in Germany. Long-term monitoring programmes are carried out to prove the technical and economic feasibility of various solar system concepts with and without seasonal storage. The paper presents a summary and review of the present status and results of the activities in the Programme. Long-term monitoring programmes have shown that the design data of the solar plants can be achieved if realistic assumptions are made. The main obstacle for the implementation of the concepts on a broader scale without public subsidies is the high investment costs of the solar systems. The main goal of the Programme is the further improvement of the cost-effectiveness of the solar concepts.

A simulation algorithm is proposed that predicts the lighting energy performance of manually and automatically controlled electric lighting and blind systems in private and two-person offices. Algorithm inputs are annual profiles of user occupancy and work plane illuminances. These two inputs are combined with probabilistic switching patterns, which have been derived from field data, in order to predict the status of the electric lighting and blinds throughout the year. The model features four different user types to mimic variation in control behavior between different occupants.An example application in a private office with a southern facade yields that––depending on the user type––the electric lighting energy demand for a manually controlled electric lighting and blind system ranges from 10 to 39 kW h/m2 yr. The predicted mean energy savings of a switch-off occupancy sensor in the example office are 20%. Depending on how reliably occupants switch off a dimmed lighting system, mean electric lighting energy savings due to a daylight-linked photocell control range from 60% to zero.

Focal region characterisation of a 20 m2 point focus dish concentrator having approximately 2300 flat, 10 cm square mirror tiles as its reflecting surface has indicated a focal flux distribution having a flat-topped peak with approximately Gaussian limbs. A peak concentration of 970 suns was evident, while a dish optical efficiency of 74% was measured, which is a direct indication of the average dish reflectivity. Total integrated power of 14.8 kW was measured under the focal flux distribution. Predicted fluxes using a ray trace algorithm (COMPREC) developed at the Australian National University (ANU) and utilising 2.0 mrad surface slope error showed a good approximation to the measured distribution. The value of 2.0 mrad also compared well with a photogrammetrically predicted value of 1.8 mrad.

Collector thermal performance tests on a 22-year-old double-glazed black painted solar water heater indicate that the degradation in its performance is due mainly to glazing seal failure allowing moisture into the insulation. The effect of dirt on the covers does not appear to have adversely affected its thermal performance.

The three-zone salt gradient solar pond is analyzed as a steady-state flat-plate solar energy collector. The resultant efficiency equation is of the Hottel-Whillier-Bliss type commonly used for flat-plate collectors. The quantities that occur in this equation—the effective absorptivity-transmissivity product ατ, the loss factor UL, the heat removal factor FR, and the incident angle modifier θ(i)—are related to the physical properties and dimensions of the pond. For a given [(fluid inlet temperature—surface temperature)/insolation], the thickness of the nonconvective zone can be adjusted for maximum efficiency. UL and ατ are smaller than the equivalent quantities for flat-plate collectors, while θ(i) and FR are close to unity. As a consequence, steady-state salt-gradient solar ponds are less efficient than common flat-plate collectors at low , but they are more efficient at high .

Forecasting of solar irradiance is in general significant for planning the operations of power plants which convert renewable energies into electricity. In particular, the possibility to predict the solar irradiance (up to 24 h or even more) can became – with reference to the Grid Connected Photovoltaic Plants (GCPV) – fundamental in making power dispatching plans and – with reference to stand alone and hybrid systems – also a useful reference for improving the control algorithms of charge controllers. In this paper, a practical method for solar irradiance forecast using artificial neural network (ANN) is presented. The proposed Multilayer Perceptron MLP-model makes it possible to forecast the solar irradiance on a base of 24 h using the present values of the mean daily solar irradiance and air temperature. An experimental database of solar irradiance and air temperature data (from July 1st 2008 to May 23rd 2009 and from November 23rd 2009 to January 24th 2010) has been used. The database has been collected in Trieste (latitude 45°40′N, longitude 13°46′E), Italy. In order to check the generalization capability of the MLP-forecaster, a K-fold cross-validation was carried out. The results indicate that the proposed model performs well, while the correlation coefficient is in the range 98–99% for sunny days and 94–96% for cloudy days. As an application, the comparison between the forecasted one and the energy produced by the GCPV plant installed on the rooftop of the municipality of Trieste shows the goodness of the proposed model.

A statistical model which captures the main features of hourly exposure series of global radiation is proposed. This model is used to obtain a procedure to generate radiation series without imposing, a priori, any restriction on the form of the probability distribution function of the series. The statistical model was taken from the stationary stochastic processes theory. Data were obtained from ten different Spanish locations. As monthly hourly exposure series of global radiation are not stationary, they are modified in order to remove the observed trends. A multiplicative autoregressive moving average model with regular and seasonal components was used. It is statistically accepted that this is the true model which generates most of the analyzed sequences. However, the underlying parameters of the model vary from one location to another and from one month to another. Therefore, it is necessary to examine further the relationship between the parameters of the model and the available data from most locations.

An angle in solar geometry termed the EWV altitude is defined, and its variation with time and season is shown. This variation indicates the necessary acceptance angle of a stationary mirror system for solar collectors. It is shown that a completely stationary mirror cannot give any useful concentration, but that if the tilt is varied with the seasons, an eastwest cylindrical parabolic mirror without diurnal movement can yield a concentration of approximately three. This may be increased to about four with the aid of a small auxiliary (fixed) mirror to provide a second stage of optical concentration.

The results of a detailed optical analysis of parabolic trough solar collectors are summarized by a few universal graphs and curve fits. These graphs enable the designer of parabolic trough collectors to calculate the performance and optimize the design with a simple hand calculator. The method is illustrated by specific examples that are typical of practical applications. The sensitivity of the optimization to changes in collector parameters and operating conditions is evaluated.

Intensity variations of global daily ultraviolet (UV) radiation throughout the year and the effect of dust on daily total UV radiation were investigated. It was found that the highest UV radiation levels are received during July and August and that the daily total UV is approximately lower by 44% during dusty days. From measurements carried out, it was found that, on average, 4.62% of the monthly-daily global radiation received is UV radiation. Over a two-year period, the measured yearly-monthly-daily mean of global UV radiation was 260 WH/m2.

Evacuated CPC (compound parabolic concentrator) collectors with non-tracking reflectors are compared with two novel tracking collectors: a parabolic trough and an evacuated tube collector with integrated tracking reflector. Non-tracking low concentrating CPC collectors are mostly mounted in east–west direction with a latitude dependent slope angle. They are suitable at most for working temperatures up to 200–250 °C. We present a tracking evacuated tube-collector with a trough-like concentrating mirror. Single-axis tracking of the mirror is realized with a magnetic mechanism. The mirror is mounted inside the evacuated tube and hence protected from environmental influences. One axis tracking in combination with a small acceptance angle allows for higher concentration as compared to non-tracking concentrating collectors. Ray-tracing analysis shows a half acceptance angle of about 5.7° at geometrical concentration ratio of 3.2. Losses of well constructed evacuated tube collectors (heat conductivity through the manifolds inside the thermally insulated terminating housing are low) are dominated by radiation losses of the absorber. Hence, reducing the absorber size can lead to higher efficiencies at high operating temperature levels. With the presented collector we aim for operating temperatures up to 350 °C. At temperatures of 300 °C we expect with anti-reflective coating of the glass tube and a selective absorber coating efficiencies of 0.65. This allows for application in industrial process heat generation, high efficient solar cooling and power generation. A first prototype, equipped with a standard glass tube and a black paint absorber coating, was tested at ZAE Bayern. The optical efficiency was measured to be 0.71. This tube-collector is compared by ray-tracing with non-tracking market available tube-collectors with geometrical concentration ratios up to 1.1 and with a low cost parabolic trough collector of Industrial Solar Technology (IST) with an acceptance half angle about 1.5°, a geometrical concentration ratio of 14.4 and a measured optical efficiency of 0.69.

Economic operation of high-efficiency concentrator solar cells requires solar concentration ratios which up to now can only be achieved with two-axis tracking. In this paper we present a two-stage concentrator approaching concentration ratios up to 300X while being tracked around only one polar axis. Its principle is as follows: a parabolic trough focuses the direct solar radiation onto a line parallel to the polar tracking axis. The half rim angle of this first concentrating stage is chosen to be equal to the sun's maximum declination of 23.5°. The second stage consists of a row of dielectric, nonimaging 3-D-concentrators, which couple the concentrated light directly into square solar cells. In contrast to linear secondaries the 3-D-secondaries make use of the limited divergence of ± 23.5° in the NS-direction to achieve additional concentration. The performance of the system depends sensitively on how well the angular acceptance characteristic of the second stage matches with the square-shaped angular irradiance distribution in the focal line of the parabolic trough. A new concentrator profile has been found that exhibits an almost ideal square acceptance characteristic with a very sharp cut-off. A prototype two-stage concentrator has been constructed with a total geometrical concentration of 214X. In outdoor measurements a total optical efficiency of 77.5% was obtained.

A linear correlation between UV-A and 380 nm was developed by means of the TUV 4.1 radiative transfer model. The prediction error of the correlation was evaluated with data from Buenos Aires, Argentina, 2001, and from 2006, Almería, Spain. Percent random mean square error (RMSE%) was calculated for intervals of 10° of solar zenith angles, ranging 4.75% at 20° to 37.70% at 90° in clear days and 22.16% at 20° to 26.17% at 90° for cloudy days in Buenos Aires Argentina, and 1.27% at 20° to 11.27% at 90° for clear days in Almeria, Spain. Clouded days were not assessed with the data from Spain. In Argentina, the UV-A radiometer is located in a rural area and the 380 nm radiometer is located in an urban area 6 km away. Hence the real error of the proposed model is closer to that found in Spain were both measurements were performed at the same site. The objective of the work is to achieve a simple and precise method to assess UV-A availability for environmental applications of solar energy, particularly for solar water treatment, at any desired latitude.

As a passive cooling strategy aimed at controlling increased surface temperatures and creating cooler urban environments, the authors have developed a passive cooling wall (PCW) constructed of moist void bricks that are capable of absorbing water and which allow wind penetration, thus reducing their surface temperatures by means of water evaporation. Passive cooling effects, such as solar shading, radiation cooling and ventilation cooling can be enhanced by incorporating PCWs into the design of outdoor or semi-enclosed spaces in parks, pedestrian areas and residential courtyards. The purpose of the present paper is to detail the development of a 3D CAD-based simulation tool that can be used to predict and evaluate the thermal improvement effect in urban locations where PCW installation is under consideration. Measurement results for the surface reduction effect of a PCW are introduced in the first part of the paper. In the second part, thermal modeling of a PCW is proposed based on analysis results of experimental data. Following that, a comparison study that integrates the proposed thermal modeling was conducted to validate the simulation method. In order to demonstrate the applicability of the developed simulation tool, a case study was then performed to predict and evaluate the thermal improvement effect at an actual urban location where PCWs were installed. Simulations were performed by modeling the construction location in two scenarios; one where the PCWs were composed of dry bricks, and another where the bricks were wet. The results show that, in terms of surface temperature and mean radiant temperature (MRT), this simulation tool can provide quantitative predictions and evaluations of thermal improvements resulting from the installation of PCWs.

The Australian National University (ANU) has worked for many years on paraboloidal dish solar concentrators and demonstrated a 400 m2 system in 1994. The commercialization of this technology has involved a re-design of the Big Dish concept for mass production. The new design is a 500 m2 concentrator with 13.4 m focal length and altitude–azimuth tracking. It uses 380 identical spherical 1.17 m × 1.17 m mirror panels, which incorporate the Glass-on-Metal Laminate mirrors. Construction of a first prototype on the ANU campus began in the first quarter of 2008. The first on sun test was carried out on 29 June 2009.

A 100 kWe/700 kWth distributed receiver, solar-thermal power plant was installed in remote desertlocation 35 km southwest of Kuwait City in the country of Kuwait. The co-generation solar power plant is designed to supply the electric power and fresh water, needs of a small agricultural desert settlement. The power plane utilizes 56 point-focusing, parabolic collectors, each five meters in diameter and equipped with a two-axis tracking system. A synthetic fluid is circulated in the collector field via a pipeline network, where it is heated to 400°C. In the energy conversion system, the heat-transfer fluid enters a series of heat exchangers where it heats and vaporizes another organic fluid (Toluene). The vapor, under high pressure, operates a radial flow turbine, producing mechanical and, subsequently, electric energy. The rejected heat is ultimately to be used for powering of a multistage flash desalination system to provide the fresh water needs for the integrated food-water-power complex which also includes desert greehouses and outdoor irrigation system.

Underground water is, by capillary action, sucked up to the surface of the earth through tiny crevices in the soil. When the ground surface is heated by the sun, this water dissipates in aqueous vapor. To collect such moisture in the form of droplets, the author installed on the ground a quadrilateral frame with a sloping lid made of glass, or plastic material with its inner surface chemically treated. The resulting structure resembled a small hothouse. As the temperature of the earth's surface rises over that of the glass (or plastic) lid while the sunshine strikes through the lid onto the earth, the moisture adheres to the inner surface of the lid in the form of droplets. Pure water can be obtained by collecting these droplets. It is possible for the device to collect water in considerably arid areas, yielding about 1000 cu cm per sq meter per day. The author conducted experiments in the suburbs of Tokyo, in the desert area at the top of Mt. Mihara, a volcano on Oshima Island, and in the desert in Pakistan, not only to substantiate the above principle but also to effect any possible improvements in the efficiency of water collection. Water obtained through the use of the device is suitable for chemical and medical use, for human consumption, etc., and is not radioactive.

Solar photodegradation of two commercial surfactants, SDS and DBS, has been studied in this work. Laboratory scale experiments showed that photo-Fenton reaction was the most effective method, although results were also very satisfactory using titanium dioxide as photocatalyst. In the photo-Fenton process, it was possible to use Fe(II) and Fe(III) cations, as well as Cr(III); the last possibility could be interesting in the case of wastewaters containing chromium, e.g., those produced by leather related industry. In all cases, it was easier to degrade DBS than SDS. Pilot plant experiments were carried out, and degradation yields higher than 80% were obtained in most of the cases in less than 3 h of exposure to sunlight. The best results were obtained again using iron salts as photocatalysts (photo-Fenton).

A systematic investigation is attempted in this paper of the intermittent vapour absorption refrigeration cycle employing the refrigerant-absorbent combinations of ammonia water and ammonialithium nitrate. A description is given of the actual cycle, and the differences between the actual and theoretical cycles are traced together with the effects of these differences on the values of the coefficient of performance and the effective cooling per 1b of initial mass of the solution. A simplified approximate expression is given for the theoretical coefficient of performance of the ammonia-water system, as also expressions for the theoretical coefficient of performance of the ammonialithium nitrate system suitable for use with the corresponding data charts. Some comments are made regarding condenser performance and evaporator design.

The efficiencies of solar thermal collectors are degraded if there are appreciable temperature differences between the solar absorbing surface and the heat extraction fluid. This problem has been well researched for flat plate collectors, but little has been done on the many possible heat extraction methods for all-glass tubular evacuated collectors. Measurements are reported here for assorted heat removal schemes in single-ended glass tubes with the non-uniform solar input around the tube simulated electrically. The results for two schemes with the flowing water in direct contact with the inside of the glass tube are consistent with a simple laminar flow model, with the heat input assumed to be uniform around the tube. Results for more complex schemes where the water is contained in a metal pipe are also given, and some are shown to possess unacceptably high temperature penalties. It is also shown that a simple fluid-in-glass scheme where the natural buoyancy forces alone keep the cold ingoing and hot outgoing streams apart should give acceptable performance.

An experimental investigation has been carried out for a range of system and operating parameters in order to analyse effect of artificial roughness on heat transfer and friction in solar air heater duct having protrusions as roughness geometry. An increase in heat transfer and friction loss has been observed for duct having roughened absorber plate. Experimental data have been used to develop Nusselt number and friction factor correlations as function of system and operating parameters for predicting performance of the system having investigated type of roughness geometry.

In this study, black chrome (ChromeOnyx) was electrodeposited onto mechanically roughened, mechanically polished and electrochemically polished copper plates in order to investigate the influence of substrate surface preparation on the optical properties of the coating. The spectral reflectances of the uncoated and coated surfaces were measured. In addition, the total normal emittance of the coated surfaces and the directional solar absorptance of the coated roughened surfaces are reported. The spectral reflectance of black chrome in the visible spectrum was found to be unaffected by the substrate surface preparations considered in this study. However, the near infrared reflectance was dependent upon the surface preparation. Black chrome on electropolished and mechanically polished substrates has higher near-infrared absorptance than black chrome on fine ground (rough) substrates. Scanning electron micrographs revealed that the average size of the surface particles of the coating was largest for the mechanically polished and smallest for the electrochemically polished substrates, with that of the mechanically roughened substrates falling in between. The results suggest that the variations in near-infrared absorptance are a consequence of differences in the structure and composition of the films resulting from substrate preparation.

Long-term analyses are presented to predict the optimum tilt angle of an absorber plate at any surface azimuth angle γ. The analyses include the effects of number of glass covers, latitude angle, monthly average clearness index, month, and ground reflectivity. The effects of each of these parameters on the optimum tilt of a south-facing surface are studied. Two numerical correlations, for ground reflectivity equal 0.2 and 0.7, are developed to predict the monthly optimum tilt of a surface. The two correlations are used to predict the optimum tilt of a surface over any specified period of time that extends from one month up to several months or a year. The analyses are also extended to predict the optimum tilt angle and azimuth angles of surfaces exposed to shading by surrounding objects. Illustrative examples are presented to demonstrate the application of the analyses.

Periodically adjusted parabolic mirror/evacuated tube absorber combinations are evaluated using computer simulation methods. The results show that a 4–6X reflector adjusted 10–15 times per year, operating at 150°C, competes favourably in cost-effective terms with a fixed reflector CPC collector operating at 50°C. Periodically adjusted collectors are advocated for medium temperature industrial applications below 200°C.

The temperature distribution on solar trough absorber tubes determines thermal losses and hotspots can lead to material stress and limit absorber tube lifetime. The concentrated solar radiation, however, makes it difficult to determine the temperature on solar absorbers. Temperature sensors that require contact to the measurement object are not appropriate and even pyrometry fails, when external light sources interfere. Only solar-blind pyrometry offers reliable temperature readings without perturbation through reflected solar radiation. This paper presents two concepts for a pyrometric solar-blind measurement on solar trough absorber tubes. One solar-blind approach is a spectral measurement range in regions, where the solar spectrum shows gaps due to the discrete absorption of the atmosphere. Another possibility for a solar-blind pyrometric temperature measurement results from the optical behavior, i.e. the distinct angle dependence of the directional reflectance and emittance of a typical selective trough absorber coating. First experimental results are shown and the accuracy and performance advantages and disadvantages of the setups are reported and discussed.

A polymer solar heat collector was combined with single-crystal silicon PV cells in a hybrid energy-generating unit that simultaneously produced low temperature heat and electricity. The PV/T unit was tested experimentally to determine its thermal and photovoltaic performance, in addition to the interaction mechanisms between the PV and thermal energy systems. Thermal efficiency measurements for different collector configurations are compared, and PV performance and temperature readings are presented and discussed. An analytical model for the PV/T system simulated the temperature development and the performance of both the thermal and photovoltaic units.

Solar collectors having “tube-and-fin” absorber plates have traditionally used rectangular fins. The introduction of a “step-change” in fin thickness, so that the fin is thinner far from the tube, permits a savings in material content. Through heat transfer analysis, this paper derives an expression for the efficiency of a fin of this step-change shape, and applies it to the problem of finding the savings in material this shape permits. The results indicate that roughly a 20% reduction in fin material is possible.