Spherical Solar Collector Research Articles

Development of a spherical solar collector with a cylindrical receiver

Solar energy can be used for substitution of the depleting fossil fuels in thermal applications and electricity generation through thermal route. For medium and high temperature applications, a system for collecting solar energy at high temperatures was developed and built in this research work. The system, built at the center of development of renewable energy of the Algiers, consists of a 2=60°C included angle, R0=0.90 m diameter spherical reflector with a cylindrical receiver filled with water, tracking reflector which moves into the focus following the sun's movement. The system is capable of heating water or other fluids to temperatures above 350 °C, thus making it possible to obtain process heat for domestic use and to store solar energy in a compact and economical way. An analysis of the system's optical characteristics was performed to aid in the design of the spherical reflector and cylindrical receiver. The thermal performance of the system was analyzed. The effects of mirror reflection, concentration ratio, heat transfer to the fluid (water), incidence angle, size and form of the cylindrical receiver, environmental conditions (wind, ambient temperature), have been studied by means of thermal model. The performance of the spherical reflector was tested by the temperature of the water. Total efficiencies (solar to thermal) of = 60% - 70% were obtained for a wide range of temperatures up to 350 °C. The results of the present study show that it is possible to use the spherical reflector for systems requiring process heat and make possible substantial utilization of solar energy and considerable savings relative to fossil energy in the sunny countries of the world.

Study and Characterization of a Spherical Solar Collector. Part II: Comparative Analysis with Flat-Plate Devices

The paper analyses the performance of a spherical solar collector compared to the efficiency of a flat-plate solar collector, which is the type of solar collector that does not use a tracking system in collecting solar radiation for energy conversion. Spherical solar collector benefits from a constant value of the angle of incidence, which optimizes the solar radiation that strikes the absorber of the solar device and maximizes the energy collection. Besides, the spherical geometry has a larger area for equal dimensions, width, and length. The combined effect of a larger surface and a higher value of the effective solar radiation onto the surface of the absorber increases the energy collection and the performance of the solar device. We developed a theoretical analysis to obtain the algorithm to determine the collected solar energy, which increases when using the spherical solar collector. A simulation runs to calculate the predicted values. We developed experimental tests in a spherical solar collector of 1.05 m in diameter, and in a flat-plate solar collector of 1.94 m × 1.025 m. to validate the simulation. The comparative analysis shows that a spherical solar collector generates more energy than a flat-plate one of the same absorbing surface by a factor of 2.09, and 7.75 times more if the width and height of the flat-plate collector equals the diameter of the spherical one.

Study and Characterization of a Spherical Solar Collector. I. Efficiency and Thermal Losses Coefficient

This paper studies and characterizes a solar collector with spherical geometry to produce hot water for sanitary and domestic applications and other facilities. The new geometry enlarges the solar collector surface and allows full sun tracking during the day without needing a solar tracking system. Although this geometry has been in use for some time, its market penetration is low due to the lack of perfect knowledge of solar collector behavior and the benefits compared with conventional solar collectors. The studies carried out in the lab for small domestic application has shown that this new geometry has better efficiency than flat plate collectors because its particular structure maintains water temperature inside the hot water tank for longer, which allows better production and longer use. The carried-out tests have shown an increase of up to 38% in the collector’s efficiency at high-range operation and 13% at the low range. This increase is enlarged to 40% and 15% when dealing with the compact system (collector-storage tank). Global losses coefficient is also lower, around 50%, than for a flat plate solar collector of an equivalent cross-section.

Experimental study of an absorber coil in spherical solar collector with practical dimensions at different flow rates

The solar collectors’ shape is an essential parameter in the thermal performance of solar water heaters, and absorption of maximum radiation at different hours, regardless of the angle of the collector, is an important issue. A spherical solar water heater is experimentally investigated in practical dimensions. This solar water heater is a fixed, symmetrical collector with the ability to track the sun independent of the optimal placement angle. The heat transfer surface is also increased by designing the fluid passage bed as a spherical absorber coil. When the flow rate intensifies, the temperature difference between the input and output currents reduces. The maximum instantaneous and average daily thermal efficiencies are 87% and 69.7%, respectively, for a flow rate of 1.6 lit/min. In this case, the hot water required by 6.35 people is provided, then at higher flow rates, the thermal efficiency is reduced. At solar noon, the upper and lower semi-spheres absorb the maximum and minimum radiations, respectively. In general, the trend of changes in the absorption of the solar radiation has no absolute extremes, meaning proper tracking of the sun and stable performance during the day. This solar heater can be easily used in the facade of buildings.

An experimental study of a hemi-spherical solar collector under Egyptian climate

Traditional flat plate collectors have shown, under many investigations, low system operating efficiency, which prompted the idea of designing new solar collectors operating with higher efficiency. Such designs include spherical, hemi-spherical, cylindrical, or rhombic solar collectors. The current study experimentally investigates the performance of a stationary newly designed hemi-spherical solar collector in comparison with a flat plate solar collector with the same surface area and weather conditions. This target has been achieved through designing and manufacturing a hemi-spherical collector, followed by analyzing its performance under normal operating conditions of Egyptian climate. The Hemi-spherical solar collector showed a maximum efficiency of 69% compared to 42% for the flat plate solar collector. Additionally, the hemi-spherical collector resulted in an optical efficiency of 75% compared to 54% for the flat plate collector. Also, the flat plate collector achieved an average efficiency of 31%, compared to an average efficiency of 48.5% for the hemi-spherical collector. The hemi-spherical collector showed a more constant hourly efficiency distribution which makes the spherical solar collector a more reliable source of heating throughout the day, unlike the flat plate collector, where efficiency only peaks during midday, and drops significantly during the early morning and late afternoon.

Experimental investigation on the performance of spherical solar collector for water heating

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Experimental Study on the Sun Tracking Ability of a Spherical Solar Collector

The present paper describes an experimental investigation on a spherical shape and flat plate absorber exposed to sun without cover. The temperature of both absorbing surface has been measured during the test day, from sunrise to sunset. Temperature distribution has been analyzed using a thermal camera. Experimental results show a good correlation between measured temperatures on the absorbing surfaces and values of the incident solar radiation measured with a fixed and a sun tracking pyranometer. The spherical absorbing surface is behaving like a sun tracking surface, during the day a hemisphere is exposed to sun and the other hemisphere is shaded. The overall daily average temperature on the spherical absorber is smaller than on the flat plate absorber, suggesting that the spherical absorber is not efficient as a solar radiation capturing surface.

Development of a Spherical Solar Collector with a Cylindrical Receiver

Solar energy can be used for substitution of the depleting fossil fuels in thermal applications and electricity generation through thermal route. For medium and high temperature applications, a system for collecting solar energy at high temperatures was developed and built in this research work. The system, built at the center of development of renewable energy of the Algiers, consists of a 2θm= 60o included angle, R0 = 0.90 m diameter spherical reflector with a cylindrical receiver filled with water, tracking reflector which moves into the focus following the sun's movement. The system is capable of heating water or other fluids to temperatures above 350oC, thus making it possible to obtain process heat for domestic use and to store solar energy in a compact and economical way. An analysis of the system's optical characteristics was performed to aid in the design of the spherical reflector and cylindrical receiver. The thermal performance of the system was analyzed. The effects of mirror reflection, concentration ratio, heat transfer to the fluid (water), incidence angle, size and form of the cylindrical receiver, environmental conditions (wind, ambient temperature), have been studied by means of thermal model.The performance of the spherical reflector was tested by the temperature of the water. Total efficiencies (solar to thermal) of ηth= 60% -70% were obtained for a wide range of temperatures up to 350oC. The results of the present study show that it is possible to use the spherical reflector for systems requiring process heat and make possible substantial utilization of solar energy and considerable savings relative to fossil energy in the sunny countries of the world.

Evaluation of Global Solar Radiation Received by a Spherical Solar Collector

In the paper the global solar radiation incident on a fixed spherical solar collector is evaluated and compared to a south oriented with 46 grade tilt angle fixed flat plate solar collector. Mean daily and hourly solar radiation are calculated from existing data for Cluj-Napoca, Romania. The results show that depending on the equivalent absorbing surface area taken into account, spherical collectors can be more efficient in receiving solar radiation than flat plate collectors.

Estimation of incident radiation on a novel spherical solar collector

Most solar collectors commonly used are of the flat-plate type. In the present work, a novel type of solar collector, namely, spherical collector, is proposed. It consists of a stationary spherical body with a cover and an absorbing surface. The receiving hemisphere, normal to the incident beam radiation, keeps on shifting with the apparent position of the sun. The main advantage of this type of collector is its ability to effectively track the sun, without any actual mechanical movement. Both daily and hourly variations of incident radiation on such a spherical solar collector are calculated on the basis of available data. The results are compared with that on an equivalent flat-plate collector for different angles of tilt and latitude. From the results, the spherical collectors are found to be more effective in receiving solar radiation over equivalent flat-plate counterparts throughout the year.

Optical simulation for a fixed spherical solar collector

To calculate the absorber dimensions for a fixed spherical solar collector, an optical simulation of the raytracing type is proposed. The physical quantities, which have an effect upon these dimensions, are described as well as the measurement methods. Once the dimensions are determined, the incident flux on the absorber surface can be calculated by the same program in terms of different zenith distances. These calculations can be checked by comparing the calculated flux on the surface of the absorber with the measured flux at different points along the absorber aimed at the full moon instead of at the sun. Through the data obtained from the measurements, fluctuating points of high flux and permanent zones which receive double and triple reflection rays have been studied.

Enhanced Power Generation of GSS4PS by Optical Solar Reflectors

A novel arrangement is proposed to enhance the power generation capabilities of a gravitationally stabilized solid-state-satellite solar-power station (GSS4PS) spherical solar collector. The unilluminated portion of a GSS4PS is illuminated by employing optical solar reflectors. The different mechanisms required for implementation of this arrangement are already space proven. The detailed study of this arrangement made by the authors reveals that practical realization of this concept will enhance the power generation capability of the GSS4PS and simultaneously reduce the weight per unit power and cost per unit power in GSS4PS spherical solar collectors.

Optical study of fixed spherical solar collectors

Study of the geometrical optics of a spherical solar collector permits a graphical determination of the radiation incident along the sagittal line. In tropical regions, the addition of a mobile mirror element (visor) considerably increases the intercepted radiation.