Finding energy sources to satisfy the world's growing demand is one of society's foremost challenges for the next half-century. The challenge in converting sunlight to electricity via photovoltaic solar cells is dramatically reducing $/watt of delivered solar electricity. In this context the sun trackers are such devices for efficiency improvement. The diurnal and seasonal movement of earth affects the radiation intensity on the solar systems. Sun-trackers move the solar systems to compensate for these motions, keeping the best orientation relative to the sun. Although using sun-tracker is not essential, its use can boost the collected energy 10–100% in different periods of time and geographical conditions. However, it is not recommended to use tracking system for small solar panels because of high energy losses in the driving systems. It is found that the power consumption by tracking device is 2–3% of the increased energy. In this paper different types of sun-tracking systems are reviewed and their cons and pros are discussed. The most efficient and popular sun-tracking device was found to be in the form of polar-axis and azimuth/elevation types.

A review of principle and sun-tracking methods for maximizing solar systems output

Several simplified design procedures for solar energy systems require monthly average meteorological data. Monthly average daily totals of the solar radiation incident on a horizontal surface are available. However, radiation data on tilted surfaces, required by the design procedures, are generally not available. A simple method of estimating the average daily radiation for each calendar month on surfaces facing directly towards the equator has been presented by Liu and Jordan [1]. This method is verified with experimental measurements and extended to allow calculation of monthly average radiation on surfaces of a wide range of orientations.

Calculation of monthly average insolation on tilted surfaces

https://nanoptics.files.wordpress.com/2012/08/imenes-spectral-beam-splitting-technology-for-increased-conversion-efficiency-in-solar-concentrating-systems-a-review-semsc-2004.pdf

Spectral beam splitting technology for increased conversion efficiency in solar concentrating systems: a review

Solar radiation is a primary driver for many physical, chemical, and biological processes on the earth’s surface. Solar energy engineers, architects, agriculturists, hydrologists, etc. often require a reasonably accurate knowledge of the availability of the solar resource for their relevant applications at their local. In solar applications, one of the most important parameters needed is the long-term average daily global irradiation. For regions where no actual measured values are available, a common practice is to estimate average daily global solar radiation using appropriate empirical correlations based on the measured relevant data at those locations. These correlations estimate the values of global solar radiation for a region of interest from more readily available meteorological, climatological, and geographical parameters. The main objective of this study is to chronologically collect and review the extensive global solar radiation models available in the literature and to classify them into four categories, i.e., sunshine-based, cloud-based, temperature-based, and other meteorological parameter-based models, based on the employed meteorological parameters as model input.

Furthermore, in order to evaluate the accuracy and applicability of the models reported in this paper for computing the monthly average daily global solar radiation on a horizontal surface, the geographical and meteorological data of Yazd city, Iran was used. The developed models were then evaluated and compared on the basis of statistical error indices and the most accurate model was chosen in each category. Results revealed that all the proposed correlations have a good estimation of the monthly average daily global solar radiation on a horizontal surface in Yazd city, however, the El-Metwally sunshine-based model predicts the monthly averaged global solar radiation with a higher accuracy.

Empirical models for estimating global solar radiation: A review and case study

On 16 November 2005 a water sample was taken from an urban stream in a metropolitan area in the southern United States and tested for the presence of E. coli. Although water samples from this and other streams in the metropolitan area frequently registered over 15,000 colonies/100 ml, this particular sample is unique in that it registered a reading of 70,000 colonies/100 ml, 350 per cent greater than the 200 colonies/100 ml—the Environment Protection Agency’s standard for streams. The fetid fl oodwaters in New Orleans from Hurricane Katrina, which had a contamination level of 10,000 colonies/100 ml and attracted considerable public attention, were cleaner than this stream at the time of sampling. Although a number of factors can contribute to this high reading, the stream consistently failed to meet water quality standards throughout the year. In addition, children from the local neighbourhood often played in the stream. Yet, presentations on water quality issues and potential health hazards did not raise any concerns among the citizenry, news outlets, and policy-makers. Obviously, there appears to be a disconnection between social and ecological systems as refl ected by the lack of concern by residents, natural resource managers, and decision-makers to the degraded stream conditions. This disconnection suggests the following question: How are social and ecological systems linked in urban landscapes and how does one begin to examine that linkage? In this chapter, we explore the linkage between the ecological and social systems of urban landscapes. First, we examine two metrics—sense of place and land cover—that have been used to integrate social and ecological systems. Second, we examine how system models have been used to link ecological systems with social systems. Third, we introduce the concept of complex adaptive systems (Gunderson & Holling 2002), as it may apply to urban landscapes, and fi nally we present a socio-ecological model ( Morse 2007 ), based on complex adaptive systems and structuration theory ( Stones 2005 ), as a means to link social systems with ecological systems.

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Linking social and ecological systems

Correlation of global solar radiation with meteorological parameters over Egypt

Were the temples of the ancient Egyptian civilization astronomically orientated? This is a very important question and one that, as the above quotation stresses, is far from being solved. Recently, Richard Wilkinson, in his useful The complete temples of Ancient Egypt, clearly stated that “most commonly temples built along the Nile were oriented on an east–west axis, according to local cardinal directions as determined by the river”, and if so local topography would be the commanding reason for temple orientation. However, he also pointed out that “on occasions, orientation towards the Sun or important stars was defi nitely the priority, and this principle may be more important than is often recognized”. As we have explained elsewhere, the ground plan of a temple (or at least its four corners), including the orientation of its main axes, was normally established in a ceremony known as the “stretching of the cord”, records of which exist as early as the 1st Dynasty. The fi rst depiction of the ritual dates from the reign of Khasekhemuy, last king of the 2nd Dynasty (c. 2750 B.C.). The ceremony is represented on several occasions throughout Egyptian history but only in the Graeco-Roman period do the associated inscriptions refer to the way in which the axis was placed. As shown in Figure 1, the earliest inscriptions are written on the walls of Horus’s temple in Edfu, whose foundations were settled in 237 B.C. The texts are unanimous: the King was looking at Meskhet(yu), the Bull’s Thigh or Foreleg, the asterism of the Plough. So, for the Egyptians, at least of later epochs, the orientation was astronomical, in apparent contradiction with the opinion of most specialists. This fact has been well known since the nineteenth century when the inscriptions at Edfu were fi rst translated, and one would have expected that a close collaboration between (archaeo)astronomers and Egyptologists would have been resulted. However, this potentially productive synergy never occurred. We could raise the question of why and the answer, or the blame, could probably be attributed to a book, The dawn of astronomy, published at the end of that century by an otherwise reputable astronomer. This volume was written by Sir Norman Lockyer, the fi rst editor of the JHA, xxxvi (2005)

/pdf/on-the-orientation-of-ancient-egyptian-temples-1-upper-egypt-44bly9krv8.pdf

On the Orientation of Ancient Egyptian Temples: (1) Upper Egypt and Lower Nubia:

Typical solar radiation year for Egypt

Solar cell overheating due to high irradiation levels is a significant problem facing concentrator systems. Some form of cooling is needed to maintain the highest possible performance of such systems. Liquid filters may be used to inhibit unwanted solar radiation from reaching the cell and thus limit cell-operating temperatures. The performance of the cooling will depend on the optical properties of the liquid filter applied, as illustrated in this paper, on the basis of different filters. An ideal filter is identified and its effects on the systems are described. It is shown, on the basis of system modeling calculations, that cell performance could be increased by up to 25% using an ideal filter. Such a system can reach an efficiency of 22% in a realistic working environment compared to a STC value of 16%. The absorbed part of the incident radiation can be used as a heat source, so adding to the potential value of the system.

/pdf/optical-filtering-of-solar-radiation-to-increase-performance-36oahftewj.pdf

M.A. Mosalam Shaltout

Papers

Correlation of global solar radiation with meteorological parameters over Egypt

On the Orientation of Ancient Egyptian Temples: (1) Upper Egypt and Lower Nubia:

Typical solar radiation year for Egypt

Optical filtering of solar radiation to increase performance of concentrator systems

V-trough concentrator on a photovoltaic full tracking system in a hot desert climate