Flat Solar Collector Research Articles

Influence of multiple internal reflection of transmitted solar radiation between interfaces on temperature regime of transparent flat solar collector casing covers

Analytical expressions are proposed to calculate the temperature regime of the transparent covers of flat solar collector casings. These expressions account for the influence of multiple internal reflection of transmitted solar radiation between the interfaces of the transparent covers. An example of the calculation of a practical implementation of the results is presented.

Hybrid Model Predictive Control of a Solar Air Conditioning Plant

This paper describes the development and experimental validation of a multi-layer hybrid controller for optimizing energy management in a solar air conditioning plant. The hybrid nature of the process is due to its multi-mode structure: the refrigeration circuit can be fed by flat solar collectors, a storage system, by an auxiliary gas heater, or by a combination of them. The selection of the operating mode is obtained by switching electrovalves, pumps, and three-way mixing valves. The proposed multi-layer hybrid controller consists of a high-level supervisor that decides on-line the optimal operating mode through a hybrid model predictive control strategy, a static lower-level controller defining proper set-points for the chosen mode, and existing standard low-level controllers that ensure robust tracking of such set-points. The overall controller was designed in Matlab/Simulink using the Hybrid Toolbox, and then tested experimentally a real process, showing the effectiveness of the approach.

Model development and validation of a solar cooling plant

This paper describes the dynamic model of a solar cooling plant that has been built for demonstration purposes using market-available technology and has been successfully operational since 2001. The plant uses hot water coming from a field of solar flat collectors which feed a single-effect absorption chiller of 35 kW nominal cooling capacity. The work includes model development based on first principles and model validation with a set of experiments carried out on the real plant. The simulation model has been done in a modular way, and can be adapted to other solar cooling-plants since the main modules (solar field, absorption machine, accumulators and auxiliary heater) can be easily replaced. This simulator is a powerful tool for solar cooling systems both during the design phase, when it can be used for component selection, and also for the development and testing of control strategies.

Comparing the operational characteristics of some types of solar collectors and water heating systems in the conditions of Uzbekistan

The criterion that includes the cost, the heat output, and the service life is used to compare the solar collectors and water heating systems. The characteristics of four types of flat solar collectors and two types of systems with flat-plate and evacuated tubular collectors are compared with the use of this criterion for their operation in the conditions of Uzbekistan.

Investigation and analysis on a cellular heat pipe flat solar heater

A new cellular heat pipe flat solar energy collector is introduced, and the thermal performance of the new solar heater comprised by water heat pipe or acetone heat pipe is tested. The results are compared with the performance of the evacuated glass tube solar heater. It is found that: the heat loss coefficient of the cellular heat pipe flat solar heater is 54% less than that of the evacuated glass tube solar heater, while the daily average efficiency of solar absorbency is 15% higher, when the water temperature of heating is lower than 65°C. In conclusion, the thermal performance of such new solar heater is better than that of evacuated glass tube solar heater or ordinary flat solar heater, both of which are still popular in China. This new solar energy application promises to be a prosperous technology.

Construction and performance of an assisted solar distiller

The design and construction of a new type of assisted solar distiller is presented. The device consists of a basin-type distiller, with the peculiarity that the basin liner is extended as an integrated solar collector accumulator with quite simple characteristics, recently developed at the National University of San Luis (Argentina). The covering is easy to remove for cleansing, and an improvement of the design for future tasks is being considered. The new distiller was compared with a common basin-type distiller and a commonplace basin-type distiller coupled with a flat solar collector. Daytime, nocturnal, weekly and hourly measurements showed that the daily production of the new assisted solar distiller always surpassed that of the basin-type distiller by approximately 70%, and that of the basin-type distiller coupled with a flat solar collector by approximately 20%. Results of 2 years of measuring are presented.

The effect of absorber packing height on the performance of a hybrid liquid desiccant system

A hybrid system consisting of vapour compression unit, a liquid desiccant system, and a flat solar hot water collector were designed, fabricated and tested. This combination allowed for a separate control of humidity and temperature without energy penalty. Various packing heights of the absorber component were tested to determine the optimal performance of the combined unit. A 1000 mm packing height with cross-sectional area of 600×600 mm, proved to be the best height that gives promising improvements in the coefficient of performance of the vapour compression unit.

Theoretical and Experimental Investigation of a Novel Hybrid Heat-Pipe Solar Collector

This article describes a novel flat plate heat-pipe solar collector, namely, the hybrid heat-pipe solar collector. An analytical model has been developed to calculate the collector efficiency as well as simulate the heat transfer processes occurring in the collector. The effects of heat pipes/absorber, top cover, flue gas channel geometry, and flue gas temperature and flow rate, on the collector efficiency were investigated based on three modes of operation, i.e., solar only operation, solar/exhaust gas combined, and solar, exhaust gas and boiler combined. Experimental testing of the collector was also carried out for each of these modes of operation under real climatic conditions. The results were used to estimate the efficiency of the collector and determine the relation between the efficiency and general external parameter. The modeling and experimental results were compared and a correlation factor was used to modify the theoretical predictions. It was found that the efficiency of the collector was increased by about 20–30% compared to a conventional flat-plate heat pipe solar collector.

Determination of the optimal operation mode of a flat solar collector by exergetic analysis and numerical simulation

It is common knowledge that the solar-thermal energy efficiency increases without extremum points with the flow rate, and similarly the fluid outlet temperature increases with the collecting area. The absence of maximum points for the functions η en = f ( m ˙ ) and T f,o= f( A C) has created difficulties in the design of flat solar collectors. The exergy efficiency of a flat-plate solar collector, η ex = f ( m ˙ , A C ) presents points of local maxima and a point of global maximum. In order to eliminate the drawbacks arising from the random variation of T f,i, the paper proposes an exergy analysis of a flat-plate solar collector based on the assumption that T f,i= T e=const. ( T e—environment temperature). The method has proven valuable in the design of solar collectors for the specific climatic and insulation conditions of a certain region.

The impact of optical and thermal properties on the performance of flat solar collectors : Hellstrom, B. et al. Renewable Energy, 2003, 28, (3), 331–344

The impact of optical and thermal properties on the performance of flat solar collectors : Hellstrom, B. et al. Renewable Energy, 2003, 28, (3), 331–344

Capillary pumping systems for solar heating application

Capillary pumping two-phase loops have been continuously investigated for electronic cooling systems, satellite thermal control and other space applications. Most tests were performed in capillary evaporators using plastic or metallic porous wick as capillary structure and anhydrous ammonia as the working fluid. In this work, capillary pumping system assisting flat solar collectors is proposed as an alternative to residential and commercial water heating systems, using fine circumferential grooves as capillary structure and acetone as the working fluid. The experimental results are obtained for a small-scale solar heating system, using one capillary pump attached to a flat copper plate of 46 cm in length and 6 cm in width. The capillary pump consists of a 19 mm OD and 500 mm long aluminium tube, with fine internal circumferential groves as the capillary structure. The working fluid is pumped from a condenser designed to delivery heat to the water storage. Heat inputs up to 14 W (507 W/m 2) were estimated for heating purpose. The system presented reliable start-ups and good performance in continuous operation. The measurements were found to be in good agreement with theoretical results for the temperature field and solar power absorbed by the system.

Market development of the solar crops drying technologies in Poland and Europe

The research results and practical experiments obtained in the past twenty years in Europe show that the use of flat solar collectors in the drying processes has a large potential and enables to achieve a reduction of fuel consumption. Constructing solar dryers brings also a number of advantages to farmers themselves and to the agricultural sector, rural communities and natural environment. Therefore, the stimulators of the market development are not only the direct economic advantages but also the social needs defined on the local level.

Evaluation of the Feasibility of Alternative Energy Sources for Greenhouse Heating

Abstract Four greenhouse heating systems were compared by computer simulation in seven European locations: a conventional fossil-fuel system and three hybrid systems, in which part of the heating demand was covered by solar collectors, a heat pump and a cogeneration system, respectively. Flat solar collectors were found to be of no interest for greenhouse heating. There were possibilities of economic feasibility for heat pumps in northern European countries with electricity/fuel-price ratios (when buying electricity from the grid) of between 2·1 and 3·0 (or lower). Cogeneration systems were found to have the best possibilities, especially in northern European countries with electricity/fuel-price ratios (when selling electricity to the grid) of between 2·3 and 3 (or higher). Heat storage improved the economical performance of the cogeneration systems: life-cycle costs decreased by about 4%. The electricity/fuel-price ratios are calculated with the prices of electricity and fuel which give the same amount of energy.

Solar distillation in forced convection. Simulation and experience

Scarcity of water and fossil energies in the canary Islands leads to an interest in a study on solar assisted desalination. A forced convection humidification-dehumidification process is analysed, where air is forced into an evaporation channel while saline water flows along the bottom, so that a fraction will evaporate to be absorbed by air. Two simulation models are developed for the proposed system. Their output in terms of temperature and humidity are discussed. Evaluation of different alternatives of operation is carried out in terms of exergy efficiency as the basic criterion. Simulation results are also compared with data obtained at a pilot plant. Data measured as well as the efficiencies are similar to those obtained for flat solar collectors.

Desinfestação de substratos com a utilização de coletor solar

Coletores solares planos constituídos de caixas de madeira com canaletas de chapa de alumínio, onde se coloca o substrato e se cobre com plástico transparente, foram testados quanto ao controle de Sclerotium rolfsii, Rhizoctonia solani, Verticillium sp., Meloidogyne arenaria e Cyperus rotundus (tiririca). Dependendo da intensidade de radiação solar, é necessário um dia para desinfestação do substrato com S. rolfsii e dois dias para R. solani, Verticillium sp. e M. arenaria.

Photochemically assisted solar energy storage using eriochrome black-T in solar flat collector

The criteria for cis-trans photoisomerization of eriochrome black-T (EBT) in the flat-plate collector system, which consists of endoergic photochemical reaction, has been investigated. The efficiencies of this collector in both summer and winter have been compared with blank (distilled water only) and colored liquid (non-isomer-dye-absorbing in the same wavelength range). The photochemical storage efficiency was found to be higher in winter than in summer. The optimum efficiency for this photoisomerization-thermal reversion cycle was found by varying with the pumping rate of the liquid to match the value of rate constant of cis to trans reaction. The stability of (EBT) has been studied under different environmental conditions.

Heat exchange in a flat solar collector with heat pipes and honeycombed fill

A flat solar collector with honeycombed fill and a system of heat pipes has been developed.

Solar flat collector technology

Abstract A survey of the present status is given for solar water and air heaters. Emphasis is put on the necessity of carefully selecting the most economic collector types for given climatological conditions and working temperatures. The potentials and limitations of standard flat collectors, tubular vacuum and plastic collectors are discussed in some detail.

Steady wind pressures on solar collectors on flat-roofed buildings

Tests carried out in the boundary layer wind tunnel of the Civil Engineering Department in Iassy investigated the characteristics of steady-state wind loads affecting rectangular flat solar collectors of two different sizes mounted in clusters on the flat roofs of five-story buildings. A key conclusion of the study was that, in comparison with isolated flat plates, the wind loads on solar collectors are significantly reduced by the sheltering effects of the first row of collectors and of the building itself.

Optimization of flat-plate solar energy heat pipe collector parameters

Performance characteristics of flat solar energy collectors with heat pipes have been analysed with regard to various parameters. Their advantages are discussed. The use of heat pipes in solar energy collectors is proved to be efficient.