Efficiency in the disinfection of water for human consumption in rural communities using solar radiation

The efficiency of solar disinfection for the inactivation of Total Coliforms (TC) and Escherichia coli (EC) in drinking water was tested in rural communities of the Guachochi Municipality, in the Tarahumara Sierra, State of Chihuahua, Mexico.The study zone was selected mostly because it lacks formal water supply systems and the population is forced to consume untreated water directly from rivers and shallow or artesian wells without treatment.To determine the bacteriological quality of the water consumed by the population, the amount of TC and EC in the water supplies of 23 communities in the studied municipality was determined.The efficiency of the solar energy based water disinfection process was determined for several months of the humid and dry seasons with water from the most contaminated sources of the study zone. The performed tests consisted in studying the effect of disinfecting water by direct exposure to sunlight during the whole day, with and without solar concentrators, in plastic bottles of commercial beverages. The three types of bottles used were transparent, partially painted black (one half of the bottle, along the longitudinal axis), and totally black.The study shows that, in this geographic zone, the available water must be disinfected before consumption and disinfection efficiency can reach 100% through the use of solar radiation. It was found that, since more than 6 h of daily solar radiation are available during most of the year in this zone, no solar concentrators are really necessary to ensure the complete elimination of bacteria. A complete disinfection takes place by simply placing water bottles in the sunlight during the whole day.Nevertheless, the use of solar concentrators and bottles partially painted black increases the TC and EC inactivation efficiency, reducing the solar exposure time required for a total disinfection to just 2 h. With the use of solar concentrators and partially blackened bottles, the water temperature reached 65 °C, while only 50 °C were achieved when using the same concentrators and completely transparent bottles.     

Influence of reflectance from flat aluminum concentrators on energy efficiency of PV/Thermal collector

In this paper the results of the influence of reflectance from flat plate solar radiation concentrators made of Al sheet and Al foil on energy efficiency of PV/Thermal collector are presented. The total reflectance from concentrators made of Al sheet and Al foil is almost the same, but specular reflectance which is bigger in concentrators made of Al foil results in increase of solar radiation intensity concentration factor. With the increase of solar radiation intensity concentration factor, total daily thermal and electrical energy generated by PV/Thermal collector with concentrators increase. In this work also optimal position of solar radiation concentrators made of Al sheet and Al foil and appropriate thermal and electrical efficiency of PV/Thermal collector have been determined. Total energy generated by PV/Thermal collector with concentrators made of Al foil in optimal position is higher than total energy generated by PV/Thermal collector with concentrators made of Al sheet.     

Optimization of arrangement of photoelectric power plants with radiation concentrators in solar electric power plant design

A model is proposed for determining the energy generated by tracking photoelectric power modules (TPEM) with their partial shadowing. The model takes into account the direct solar radiation input, and also the dependence of the efficiency of the tracking photoelectric modules with multijunction solar cells and radiation concentrators on the atmospheric mass. The optimal variant of solar module arrangement for different locations is determined, and the ground area required by a single TPEM of given size is estimated.     

Reverse ray-tracing model for the performance evaluation of stationary solar concentrators

The yearly energy collection efficiency of stationary solar concentrators can be evaluated using reverse ray-tracing, and a solar radiation model. In reverse ray-tracing, rays originating at the receiver of the concentrator are traced towards the surrounding hemisphere. The method allows for the evaluation of the absolute energy collection: new concentrators may be optimized for location and tilt, requiring one-time ray-tracing. The tilt of existing concentrators is optimized. Only possible solar incidence is considered by our model. The method is fast and realistic; it can be modified for concentrators in tilt operation.     

Numerical simulation and experiment research of radiation performance in a dish solar collector system

The Monte Carlo ray-tracing method is applied and coupled with optical properties to predict the radiation performance of solar concentrator/cavity receiver systems. Several different cavity geometries are compared on the radiation performance. A flux density distribution measurement system for dish parabolic concentrators is developed. The contours of the flux distribution for target placements at different distances from the dish vertex of a solar concentrator are taken by using an indirect method with a Lambert and a charge coupled device (CCD) camera. Further, the measured flux distributions are compared with a Monte Carlo-predicted distribution. The results can be a valuable reference for the design and assemblage of the solar collector system.     

Comparison of solar concentrators

Even though most variations of solar concentrators have been studied or built at some time or other, an important class of concentrators has been overlooked until very recently. These novel concentrators have been called ideal because of their optical properties, and an example, the compound parabolic concentrator, is being tested at Argonne National Laboratory. Ideal concentrators differ radically from conventional instruments such as focussing parabolas. They act as radiation funnel and do not have a focus. For a given acceptance angle their concentration surpasses that of other solar concentrators by a factor of two to four, but a rather large reflector area is required. The number of reflections varies with angle of incidence, with an average value around one in most cases of interest. In order to help provide a rational basis for deciding which concentrator type is best suited for a particular application, we have compared a variety of solar concentrators in terms of their most important general characteristics, namely concentration, acceptance angle, sensitivity to mirror errors, size of reflector area and average number of reflections.The connection between concentration, acceptance angle and operating temperature of a solar collector is analysed in simple intuitive terms, leading to a straightforward recipe for designing collectors with maximal concentration (no radiation emitted by the absorber must be allowed to leave the concentrator outside its acceptance angle). We propose some new concentrators, including the use of compound parabolic concentrators as second stage concentrators for conventional parabolic or Fresnel mirrors. Such a combination approaches the performance of an ideal concentrator without demanding a large reflector; it may offer significant advantages for high temperature solar systems.     

Theoretical aspects for optimization of solar radiation concentrators with plane facets

The experience of the 25 years operation of two concentrators of solar energy (CSE) of 2.8 and 5.0 m diameter manufactured by gluing plane facets of thin glass onto metal radio antennae convincingly demonstrates their technical and economic efficiency. Besides (or in addition to) simplicity of manufacturing and the possibility to achieve temperatures up to 2000 K and more, there is one more undoubted advantage of such concentrators: it is possible to get a focal spot with rather uniform distribution of the irradiance. The problem of determining the plane facets’ optimum configuration and the structure of their arrangement on the CSE surface which guarantees forming a focal spot of the given dimension is solved by this work. Perfect geometric configuration of the facets and paraboloid is assumed. The working zone of the facets reflecting the incident solar radiation at the circular focal spot is approximately an ellipse. Trapezoid is an optimum configuration for the facets taking up a minimum area and ensuring the maximum use of CSE surface. A system of equations is obtained for calculation of a CSE structure with annular packing of the facets. The results of calculations for the 1.8 m and 15 m diameter concentrators are presented.     

Solar radiation concentration in parabolocylindrical system with focusing wedge

The problem of whether it is possible to increase the concentration of solar radiation in parabolocylindrical concentrators (PCC) with the help of a secondary concentrator of the “focusing wedge” (FW) (foclin) type has been examined. It is found that the foclin is able to increase the focal concentration of the PCC from 5 to 100 %, depending on the PCC aperture angle.     

Nontracking solar concentrators

We derive the theoretical upper limit for concentration of direct solar radiation at low latitudes with nontracking concentrators from the projected solid angle sampled by the apparent motion of the sun, for the case where the energy efficiency is referred to the energy incident on the entrance aperture. Based on the fact that the solar radiation is not uniformly distributed within this projected solid angle and that the apparent solar motion is known, we derive the optimal acceptance as a function of direction and time, which means rejecting the lower density radiation and switching off the device when losses would be higher than gains. Just as a device may gain concentration by rejecting radiation from certain directions, it can also gain by not operating at all, thus avoiding losses at certain times. Trough-type systems, which have translational symmetry, cannot be ideal nontracking concentrators, but for low losses they perform only slightly worse than general three-dimensional concentrators.     

Comparison of Fresnel concentrators for building integrated photovoltaics

To develop concentrating photovoltaic systems for building integration applications, two optical devices are proposed. The concentrators are based in stationary linear Fresnel lenses and secondary CPC. The moving focal area is ten times smaller than the Fresnel lens aperture. Concentrator characteristics are studied in detail: shadowing effect, placement of the focal area and optical concentration efficiency. The main contribution of this paper is the three-dimensional optical analysis of the non-imaging concentrating systems. In terms of solar radiation, photovoltaic moving modules placed in the focal area of stationary concentrators are compared with simply fixed photovoltaic modules. In favourable weather locations, the beam radiation incident on the concentrating modules would be a large percentage, more than 50%, of the global radiation received by the fixed photovoltaic devices.     

Analysis of terrestrial solar radiation exergy

Based on Candau’s definition of radiative exergy, the exergy of the extraterrestrial and the terrestrial solar radiation are computed and compared by using the solar spectral radiation databank developed by Gueymard. The results show that within the spectrum region from 0.28 to 4.0 μm, the total energy quality factor (i.e., the exergy-to-energy ratio) of extraterrestrial solar radiation is about 0.9292, and that of the global terrestrial solar radiation is about 0.9171 under US standard atmosphere condition and zero solar zenith angle. The terrestrial solar spectral radiation exergy flux is large in the near ultraviolet and the visible light region. The reference radiation exergy spectra are obtained under atmospheric conditions consistent with ASTM standard G173-03. The effect of tilt angle on the terrestrial solar radiative exergy for inclined surface, and the effect of air mass on total energy quality factor of the terrestrial solar radiation for horizontal surface are analyzed. With the increase of tilt angle, the terrestrial solar spectral radiation exergy flux initially increases and then decreases, the total energy quality factor of the diffuse part decreases monotonically, while that of the direct part is invariant. The total energy quality factor of the direct, the diffuse and the global terrestrial solar radiation all decrease with the increase of air mass.     

Optical performance of CPCs for concentrating solar radiation on flat receivers with a restricted incidence angle

In some applications of compound parabolic concentrators (CPCs), the incidence angle of solar rays on the absorber is restricted and must be less than a specified value (θ_e) for efficient energy conversion or transfer. For a flat receiver with a restricted incidence angle (RWARIA, in short), two ideal concentrators designed based on one-sided flat absorber can be employed for radiation concentration: one is the CPC without exit angle restriction (CPC-1), and another is the CPC with a restricted exit angle (CPC-2). In this work, the angular dependence of optical efficiency factor of both CPC-1 and CPC-2 for concentrating radiation on the RWARIA was derived, and a mathematical procedure to estimate daily radiation accepted by the RWARIA by using east-west oriented CPC-1 and CPC-2 was suggested based on the solar geometry and monthly horizontal radiation. Results by numerical calculations show that, for fixed full CPC-1 and CPC-2 with identical acceptance half-angle (θ_a), the CPC-2 is slightly more efficient than CPC-1 for concentration radiation on the RWARIA except periods of about 30 days before and after both equinoxes; whereas for fixed truncated CPC-1 and CPC-2 with identical geometric concentration factor (C_t) and θ_a, the CPC-2 is always more efficient. Results also indicate that, for the case of the tilt-angle of the aperture of CPCs being yearly adjusted four times at three tilts, full CPC-2 is less but truncated CPC-2 is more efficient than CPC-1 for concentrating radiation. In practical applications, CPCs are usually truncated due to less efficient of top portion of a CPC reflector for radiation concentration and less reflector material use, therefore, the CPC-2 is more favorable and advisable for concentrating radiation on the RWARIA.     

Projected beam irradiation at low latitudes using Meteonorm database

The quantitative analysis of beam radiation received on a solar concentrator may be understood by evaluating the projected solar height angle or profile angle along the north–south vertical plane. This means that all the sunrays projected along the north–south vertical plane will be intercepted by a collector provided the projection angle lies within the acceptance angle. The Meteonorm method of calculating solar radiation on any arbitrary oriented surface uses the globally simulated meteorological databases. Meteonorm has become a valuable tool for estimating solar radiation where measured solar radiation data is missing or irregular. In this paper we present the projected beam solar radiation at low latitudes based on the standard Meteonorm calculations. The conclusion is that there is potential in using solar concentrators at these latitudes since the projected beam radiation is more during winter periods than in summer months. This conclusion is in conformity with the design principle of solar collectors for worst case conditions.     

Prediction of hourly diffuse solar radiation from measured hourly global radiation on a horizontal surface

A statistical procedure has been employed to develop correlations between the hourly global horizontal radiation and its diffuse component. Several years', hourly radiation data from three Canadian stations and two French stations have been employed for this purpose. The relationships have been developed in dimensionless form which predict for particular solar altitudes when is given.Under heavily cloudy conditions or when the sky is completely covered ( ), diffuse radiation increases linearly with the global radiation. In this region, solar altitude has no bearing on the fraction of diffuse radiation.As goes beyond 0.35, the effect of solar altitude begins to appear and the region immediately following this may be considered as partly-cloudy-skies conditions. In the beginning of this region, the diffuse component increases briefly with the increase in global radiation and then begins to decrease as the partly cloudy skies become clearer. At particular solar altitudes, a minimum value of the diffuse radiation is reached. The value of where reaches its minimum value varies with solar altitude.The region beyond which a minimum value of is reached may be considered as mainly-clear-sky conditions. In this region, increases again with , lower solar altitudes giving a higher percentage of diffuse radiation.Under partly cloudy skies and under clear skies, solar altitudes lower than 30° had a marked effect on the fraction of diffuse radiation. However, solar altitudes greater than 30° had minimal influence on the fraction of diffuse radiation.     

On the influence of real operating conditions on the energetic parameters of different types of solar photoelectric facilities

Results are presented of comparison of tracking solar photoelectric facilities (SPEF) with multitransition photoconverters (PEC) and solar radiation (SR) concentrators and fixed planar SPEFs with silicon PECs regarding their specific energy production. Relations to determine the real SPEF efficiencies as a function of the atmospheric mass value are presented. The annual sums are calculated of the specific electric energy transferred from the SPEF to the mains network.     

The effect of circumsolar radiation on a solar concentrating system

Empirical models for the energy distribution of the sun, as seen after atmospheric scattering, show a strong correlation on an annual or month-by-month basis to observed data. When applied to cases where the requirement is for a real-time solar energy distribution, such as in the optimisation of the flux distributions in imaging concentrators, these models prove insufficient. In this paper we present results illustrating trends in observed solar profiles that are invariant to changes in location that lay the framework to a definitive solar model. We show how using this information, a more complete understanding of the effect of a change in the spatial energy distributions of the sun can have on the size of the spatial energy distribution in the absorber plane of a (linear Fresnel) concentrating collector.     

Enhancing of solar pumped liquid laser efficiency

The neodymium-containing phosphorus oxychloride liquid laser material is studied as an active medium for pumping by concentrated solar radiation at the focus of small-size parabolic-dish concentrators. The possibility of increase its efficiency by means of frequency-down-shifting elements of solar spectrum is examined by simulation calculations by Monte-Carlo and ray-tracing methods using. More than 40% efficiency increase is obtained.     

Mathematical analysis of the performance of cylindrical-parabolic solar concentrators

Attention is devoted to the application of cylindrical-parabolic solar concentrators in the intermediate temperature range for which wide receivers are used. Suitable indices that describe the performance of the concentrator are defined and evaluated. The effect of each individual parameter on total concentrator performance is investigated. The results of the analysis are presented as a set of graphs which can be used easily when designing parabolic concentrators.     

On the effects of solar radiation variations on solar heating system performances

The effect of solar radiation availability on the performance of different solar heating systems has been studied. The systems include a solar water heater, passive solar houses and district solar heating systems with seasonal heat storage. Also, different collector orientations and collector types have been investigated. The hourly radiation data were generated by a simple computational simulation procedure. It was found that district solar heating systems with concentrating collectors and passive solar houses showed the largest variations for the given conditions.     

Calculated characteristics of the solar pumped solid-state laser

Results of an analytical study aimed at determination of optimal and limiting temperature and power characteristics of a solid-state laser under pumped by a concentrated flow of solar radiation in the focus of large concentrators of near megawatt power are presented.