Flat Plate Collector System Research Articles

Use of R-114 as the working fluid in a flat-plate collector system for electric power generation

The use of flat-plate solar collectors for the generation of electric power is attracting the attention of engineers and scientists for its simplicity in construction and operation. The efficiency of collection is low due to the low operating temperatures of the flat-plate collectors. In the low temperature range applicable to flat-plate collectors, refrigerants can be used as working fluid. The cost of construction can be reduced by the suitable selection of collector and refrigerants. It has been shown that R-114 has suitable characteristics for use as a Rankine cycle working fluid. By using an aluminium tube-plate type collector with 0·005 m tube diameter, 10 risers per metre width of collector, it becomes light and cheap. When the emissivity of the collector is 0·1 and a single cover is used, the maximum efficiency condition is attained. Limited to a pressure drop of 2·5 bar in the collector, 16 collectors can be used in series and the overall efficiency can be as high as 7·8% under 1000 W/m 2 insolation conditions and for an outlet temperature of 380 K. Under these conditions 5600 collectors of 1·5 m × 1·5 m size will be required to produce 1000 kW of electricity.

Solar distillation : the solar-driven case

This paper considers distillation systems where all the plant's thermal energy requirements are provided by solar energy. Fairly small capacity plants are considered operating in remote arid regions. Such systems consist of solar collectors and thermal storage coupled to a distillation plant. Each of these aspects is considered as well as the type of control strategy to be used. Using a dynamic computer simulation model, two solar-driven systems are considered: one using flat-plate collectors and a 76°C MEE desalination plant, the other using evacuated tubular collectors and a 95°C MEE plant. Various combinations of collector area and thermal storage volume are considered, and optimal values determined for each case. For the particular example chosen (lOOm 3/day, located at 23 1 2 °S) the flat-plate collector system was superior at current prices, giving an overall water cost of $5.82/m 3 versus $7.34 for the second system. Both these costs are considerably less than water costs from conventional solar stills.

Studies on low-temperature salt-hydrate for thermal storage applications

A novel thermal-energy storage concept involving the use of salt-hydrates such as sodium thiosulphate pentahydrate, Na 2S 2O 3·5H 2O is under investigation. With fusion temperatures of many salts lying between 0 and 100°C, such substances may be considered as likely materials to be used in conjunction with solar energy flat-plate collector systems for domestic use. Phase change storage or latent heat storage is concluded to be a promising technique for storing solar energy. The solid-liquid transformation of salt-hydrates is actually a dehydration or hydration of salt, although this process resembles melting or freezing thermodynamically. Three types of behaviour can be identified: congruent, incrongruent, and semicongruent melting. None of the congruent melting salt-hydrates have been judged for use in thermal storage because of cost and safety considerations.

Critical analysis of a proposed solar assisted HTE desalination system [1

A solar assisted desalination system proposed by Gasparini . [1] is reviewed. The authors show that there are errors and misconceptions in the paper that render its conclusions invalid. Factors that should be considered in a rigorous analysis of the problem are outlined. Contrary to the original conclusions the current analysis shows that a flat plate collector system is a more attractive proposition than a concentrating option, and that the actual payback periods for the options proposed are unacceptably long at present fuel oil prices.

Evaluation of the flat-plate solar collector system for electric power generation

The simplest method of utilizing the energy of the sun to generate electric power is to use a flat-plate collector system. Flat-plate collectors have no tracking mechanism, make use of both direct and diffuse radiation, have no focusing arrangements and are less costly per square foot than parabolic trough collectors, paraboloid of revolution collectors or heliostats. The main disadvantage to the flat-plate collector system is the relatively low temperatures reached by the collector surface (∼ 300°F maximum). This evaluation of the flat-plate collector system was designed to determine the number of flat-plate collectors required to generate a given amount of electricity with optimum efficiency. Variable parameters are the temperature of the heat transport fluid, both to and from the collector field. In the analysis, the efficiency of the flat-plate collectors was coupled to the efficiency of the thermal cycle to calculate optimal overall system effeciencies. Overall system efficiencies for the system are on the order of 3·5 per cent or less. Over two million 4 ft by 4 ft collectors would be required to produce 100,000 kW(e). Based on the results of this analsis, it can be shown that the limiting factor in the use of the flat-plate collector system for electric power generation is the efficiency of the collectors. An increase in the overall system efficiency can occur only if the collector efficiency can be increased at the higher surface tempertures.