Active Solar Research Articles

An active indirect solar system for food products drying

Abstract An energy independent active indirect solar drying system for the study of food products drying at specific climate conditions was developed and tested. As a model material, sliced tomato was selected because of its short shelf live, high humidity and potential to be a high value dried product. Indirect solar dryer enabled complete protection of the dried material against sunlight, birds, insects, rain and dust during the drying process. The solar dryer system design includes a rectangular section (1000 × 600 × 400) mm chamber and a flat solar collector (1500 × 600 × 100) mm with the surface area of 0.9 m2. Air flow was induced by a fan installed at the inlet of the collector and powered by a photovoltaic solar panel and a battery system. Temperature and humidity of air were monitored at the collector inlet, collector outlet and the drying chamber outlet. The key element of the collector is a 10.5 m long rectangular section aluminum pipe (55 × 35) mm coated with an absorption layer. The maximum dryer capacity is around 3 kg of wet material (sliced tomato) per batch. Average air temperature increase in the collector was measured to be 30 °C during the winter season. Air relative humidity decreased from 21 % to 15 % after passing through the collector. The moisture of tomato slices decreased from the initial value of 92 % down to 22 % during the time of the experiment (30 h). Quality of tomatoes dried using the designed solar dryer differed significantly in color as well as in texture from those dried by the commonly used methods, like an open sun drying system. Equilibrium moisture content of the product was reached after 30 h in December when the maximum outside temperature was 17.6 °C. The tomato mass decreased from 333 g to 33.15 g; the mass loss being approximately 90 %. The heated air temperature and humidity at the dryer inlet and outlet were influenced by the change of the ambient temperature and humidity during the day. Variation of the drying rate with the change of the ambient temperature and humidity was observed. During summer, when the sun radiation increases, the drying time for sliced tomato with 9 mm thickness decreased from 25 h to 15 h. The sample thickness also has an impact on the drying process. When the sample thickness increased from 9 mm to 12 mm, the drying time increased from 15 h to 20 h of active device time.

Modified active solar distillation system employing directly absorbing Therminol 55–Al2O3 nano heat transfer fluid and Fresnel lens concentrator

This paper reports the design and construction of a modified active solar distillation system (MSDS) and comparison of its performance parameters with that of a conventional solar still (CSS). MSDS consists of a solar still, a Fresnel lens concentrator with an evacuated receiver tube and a serpentine loop type heat exchanger. Al2O3–Therminol-55 nanofluid (nHTF) is used as the heat transfer fluid in the solar collector loop. Various performance parameters of MSDS and CSS such as saline water temperature, hourly yield and total yield have been compared under the ambient and solar conditions prevailing at Trichy. The experimental results indicate the hourly yield of MSDS with 0.1% nHTF is 45–250.27% more than CSS, and the total yield of MSDS with 0.1% nHTF is 12.190 L/m2 day compared to 3.48 L/m2 day for CSS. The daily efficiency of MSDS is found to vary with volumetric concentration of nanofluid, and maximum efficiency of 53.55% is obtained for 0.1% nHTF. Estimated cost for production of one litre-distilled water is approximately 1.54 INR for CSS and 1.41 INR for MSDS. MSDS developed in this study is found to be a better alternative to the CSS still due to its high productivity and cost-effectiveness.

Thermal performance evaluation of isolation and two active solar heating systems for an experimental module: A rural Peruvian case at 3700 masl

Evaluation results of the thermal performance of an experimental housing module (EHM) are presented with considerations for the level of insulation and the installation of two active heaters powered by solar energy. The EHM is located in a high Andean rural area in southern Peru (latitude: 13° 45’40” S, longitude: 73° 51’26” W, and elevation: 3700 masl), where in situ measurements were made. The design and implementation of the EHM was based on the application of bioclimatic strategies and techniques. For the thermal evaluation of the EHM, 43 temperature sensors connected to dataloggers were used. The results show that the temperature inside the EHM increased more than 12 °C with respect to the outside temperature in the critical hours of extreme cold and frost when the isolation and the proposed radiative systems are used. Finally, the thermal behavior of the EHM was simulated using the EnergyPlus 8.4 program, which showed that there was an average difference of 0.5 °C between the measured interior temperature and the corresponding simulated temperature.

Practical performance of a small PTC solar heating system in winter

The active solar house-heating in winter is a novel technology that is eco-friendly and economical. The performance of a small solar heating system composed of parabolic trough collector (PTC) and ventilation pipelines has been experimentally investigated in the current study. With an automatic solar-tracking device, the system adopted a PTC device of aperture area 2.407 m2. The air stream was heated in the tube collector and then driven into the test room. By examining the heat gain of the air stream passing through the PTC as well as the temperature distribution of the indoor air, the working characteristic of the solar-heating system in winter was evaluated practically. The experimental results showed that for the generally-insulated room that was located in 39.87°N latitude, the daily solar heating time reached to 6–7 h, and the thermal efficiency of the PTC device was above 60%. Supposing the heat loss is reduced effectively along the outdoor pipelines in the future, such active solar heating system will be a promising heating technology in regions that are not far north on the earth.

Siting and building-massing considerations for the urban integration of active solar energy systems

This paper aims to determine the optimum geometry of the building blocks in order to ensure the viable building integration of active solar energy systems in the urban fabric. Through literature review, similar research objectives are reported and analysed, whilst the building integration of active solar systems in urban areas is explored. The motivation for the proposed research emanates for a need for an analysis at the scale of urban blocks and of building massing configurations at the scale of a cluster of buildings rather than that of an individual building. These sets of physical characteristics are examined to arrive at simplified archetypes, while at the same time the habitation density is held constant.A set of twelve simplified building block configurations is created, whereby the geometrical parameters examined include the width of the streets separating the building blocks, the height of existing and proposed buildings and the massing configurations of the buildings that can be accommodated in the proposed building blocks. These parameters are manipulated to effect changes in collective building massing and siting decisions that result in the optimal integration of active solar energy systems that may be integrated on a building cluster’s facades and roofs. Subsequently, the energy production potential of the buildings’ integrated systems was calculated for each case so that the twelve simplified massing and siting configurations could be compared and contrasted, so as provide architectural designers as well as planning authorities a way of quantifying solar planning decisions at the neighbourhood scale.

Saving Energy by Reducing Cooling Load of Rural Houses with using Passive Solar System and Well Water

Saving energy helps in reducing the effect of the environmental contamination. This could be obtained by decreasing the cooling load of rural houses and small buildings by using passive and active solar systems. The big temperature differences between the well water and the ambient temperatures is also utilizing for the purpose of air conditioning. This is done by adding heat exchanger (Fan-Coil) inside the house, which is operated by external photoelectric cells to reduce the cooling load of the house. The passive systems have also been studied like the directions and areas of the windows. Its significance comes from the importance of passive system applications to reduce the cooling load of houses in summer. Energy balance is done to get the governing equation that is necessary to calculate the variation in cooling load along the day for different parameters design, then to find out the optimum values of these parameters in order to reduce the houses’ cooling load through the day hours. The results have shown that the use of well water to cool the house would help to reduce the cooling load by 30%. Also the best orientation of windows in the south direction with suitable length of overhang, which prevent the direct solar radiation through the windows is investigated .This results in a reduction by 6% in cooling load during the summer season. The use of the passive system and well water in house cooling decreases the cooling load of the house by 36%.

Characterization of a Water Heating System Using Solar Collector With Conical Concentrator

This study aimed to evaluate a solar water heating system for using on residences, using a solar collector with conical concentrator. The principle of light concentration in a solar collector with conical concentrator is the capture and reflection of solar radiation in the center of a tapered concentrator with internal reflective faces. The area of concentration of solar energy is occupied by a receiver with material of high thermal conductivity, properly isolated by transparent surfaces, to form the greenhouse effect, where the thermal energy is transferred to a working fluid. The characterization of the system was done through field tests to determine the efficiency in the water heating. The tests were performed considering different scenarios, which varied according to the heating system (passive and active with different water flow) and solar tracking (manual adjustment and stationary). The results showed that the scenarios with solar tracking presented an average efficiency of 12.63%, which was more efficient than those presented by the fixed orientation, which was 11.44%. Besides that, it was verified that the active solar heating systems were more efficient than the passive ones.

Impact of solar energy on greenhouse climate and crop production

A 3-year research project was conducted to assess the effect of passive solar energy gains on two differently designed greenhouses, and to determine differences in heating cost. The two greenhouses (PS1 and PS2) were passive solar greenhouses with different design technology. The test crop was tomato (Solanum lycopersicum L. ‘Mountain Magic’). Solar energy data along with tomato fruit yield and plant growth characteristics were recorded from November to April in both greenhouses. Greenhouse PS2 maintained significantly (p<0.05) higher interior temperature and photosynthetically active radiation compared with greenhouse PS1. Outdoor heating and light effect on temperature required to heat the two greenhouses was significantly (p<0.05) higher in April compared with the other months. A non-significant difference was recorded between the months of November, December and January for outdoor heating effect. Similarly, non-significant difference between December and January and between March and April were recorded for outdoor light effect on temperature required to heat PS1 and PS2. Higher marketable fruit yield was harvested in PS2, with lower temperature required for heating. This study showed that a PS2-type greenhouse design, with a concrete in-floor active solar heating system, will provide a better crop production environment with reduced heating cost compared with PS1, with a gravel floor.

Review on Solar Space Heating - Cooling in Libyan Residential Buildings

This review paper focuses on documenting and studying published papers and works in the field of solar heating and cooling air space in residential buildings. The goal of this survey and documentation is to find out the most important flushing results and conclusions specifically in the fields of using solar energy for space heating, cooling, and ventilation of local residential buildings in Libya. This covers using active and passive solar systems in, achieving thermal human comfort in such buildings leading to reduce electrical energy consumption. This paper also concentrates on applying energy efficiency measures in buildings; planning, design, and construction stages with the use of the principles of energy conservation in buildings. There are several studies comparing traditional with modern house designs in several local cities including both famous old cities of “Ghadames” and “Gharyan”. Several conclusions and recommendations are summarized within the text of this paper.

Development of characteristic equations for PVT-CPC active solar distillation system

This paper deals with the development of analytical characteristic equation for N identical fully covered photovoltaic thermal (PVT) compound parabolic concentrator collector (CPC) integrated solar distillation system which is similar to Hottel-Whillier-Bliss equation of flat plate collector (FPC). The partially covered PVT has disadvantages like (a) thermal performance is lower due to higher top loss coefficient, (b) maintenance is higher and (c) fabrication is expensive. These problems are fully addressed in the case of fully covered PVT for the same watt peak. The development of analytical characteristic equation for the proposed system consists of writing energy balance equations for its various components. The results of proposed N-PVT-CPC integrated active solar distillation system [case (i)] has been compared with fully covered N identical PVT-FPC integrated solar distillation system [case (ii)] and conventional N identical FPC active solar distillation system [case (iii)]. It has been observed that average instantaneous efficiency of case (i) is higher than case (ii) by 10.60%, but lower than case (iii) by 20.74%.

Improvement of passive behaviour of existing buildings through the integration of active solar energy systems

This study aims at making an environmental assessment of the integration of active solar energy systems on building envelopes in southern Europe. More specifically, it focuses on energy production of active solar systems, as well as on the investigation of shading and insolation of indoor spaces in relation to the energy requirements and the visual comfort of inhabitants. For the needs of the present research, five active solar systems and three representative space typologies were selected for in-depth investigation. Autodesk Ecotect Analysis software v.5.2, Desktop Radiance v2.0 Beta and Clean Energy Project Analysis Software Retscreen4 were used for the simulations. The simulation results are presented and discussed comparatively. The findings indicate that the integration of active solar systems contributes to the reduction of the cooling and heating loads. In terms of natural lighting, the integration of active solar systems enables high levels of natural lighting while it minimizes glare issues for the majority of systems. The research highlights the role of building integrated active solar systems, both in the indoor built environment and in energy performance, introducing a comprehensive environmental approach. Moreover, it highlights the importance of an integrated architectural design approach in the built environment.

Life Cycle Assessment of solar energy conversion systems in energetic retrofitted buildings

This paper investigates the impact of solar energy conversion systems in a pre-existing detached single-family house in Greece on resources and the environment, and compares it to that of conventional fossil fuels, which such systems substitute. The solar energy conversion systems used cover 100% of its energy requirements turning the house into a Net Zero Energy Building (NZEB). To that purpose, a cradle to grave Life Cycle Assessment (LCA) of active solar conversion systems is conducted over their useful life of 25 years based on two scenarios. The case study employs the dynamic energy simulation for the energy analysis, whereas SimaPro software and the Ecoinvent database were used for the LCA. The LCA shows that the retrofitted building can cover 100% of its energy needs, while also breaking even, in terms of emissions, in less than 2 years in the worst case scenario examined.

A concise review on the role of nanoparticles upon the productivity of solar desalination systems

In recent years, nanofluids have been widely used to improve the performance of various energy systems due to their favourable thermo-physical and optical characteristics. In particular, solar distillation, as an affordable and reliable technique to provide freshwater, has benefited from nanofluid technology. This article performs a review of the literature on the implementation of nanofluid technology in active and passive solar distillation systems. The progress made and the existing challenges are discussed, and some conclusions and suggestions are made for future research. The review indicates that the daily productivities of solar distillation systems enhance by using nanofluid and increasing the volume fraction of nanoparticles. However, long-term operational stability and life cycle assessment remain critical issues. These factors should be considered for future research in this field.

HEAT FLUX IN A PASSIVE MULTI-LAYERED SOLAR PANEL

The paper deals with the question concerning the increase in buildings and structures energy efficiency and environmental safety at the construction and installation of engineering systems with financial constraints. We suggest solving this problem with low-cost method of solar radiation utilization which implies the passive thermal energy transformation into external fencing structures. In spite of the economic expedience of such heating systems, there is an opinion that they are suitable only for climatic conditions characterized by a mild heating period due to low efficiency indicators in comparison with the active solar power plant. As regards this, the paper analyzes the well-known and new building translucent, absorbing, accumulating and insulating materials along with the possibilities to create the multifunctional external fences that can expand the geography of the use of passive systems. We have studied the nonstationary thermal processes arising in multilayer external fences of buildings in order to solve the problems of effective solar radiation utilization by facade integrated panels. The analysis of mathematical methods has shown that theory of thermal waves should be used to describe the diurnal temperature changes inside building structures. The principle of temperature frequency superposition principle has made it possible to calculate the heat transfer in multilayer external panes. In Voronezh region climatic conditions (52º), we have evaluated the solar radiation effect on a two-layer and a four-layer structure consisting of a glass unit, an air layer, reinforced concrete and heater, protected from the outside by double-glass unit. In January at temperature -24 °C of the coldest fiveday period, the average daily heat losses through the surface area of 1 m2 of the two-layer outer wall are 6 W / m2 , and under the same weather conditions an average heat flux through the surface area of 1 m2 of the four-layer solar panel is of 36.3 W / m2 ; the maximum values of the heat flux are achieved in 18 hours. The presented data confirm the expedience of passive solar panels use in case of low temperatures during the cold period of a year. Moreover, considering the facade glazing trends and low cost of the passive solar panels in contrast with the active solar systems, we concluded that they should be used for increase in energy efficient of buildings.

Experimental Investigation of Using a Novel Insulation Material on the Functioning of a Solar Thermal Collector

This research document presents a new insulation material for solar thermal collectors. Tests were carried out in the laboratory, on an active solar energy demonstration system (ET 200), illuminated with a halogen lamp instead of sun. In this paper, the polystyrene used as insulation in the ET 200 flat plate solar collector was replaced by the cheaper natural material based on clay and straw. The polystyrene in the experimental device is placed under the absorber plate and along the edges of the casing containing the components of the solar collector. In this work, only the polystyrene of the four similar edges was replaced by the composite material. The use of the clay and straw as insulation material instead of polystyrene increased temperature difference (T2 − T1) between the inlet and the outlet of the absorber by 0.9±0.14 °C (p &lt; 0.05); thus, increasing the useful power transmitted to water in the solar collector. Compared to polystyrene, tank water was well heated using the proposed material (p &lt; 0.05). This latter also improved the performance of the solar collector by 5.77%. So, it is recommended to use the cheapest nonpolluting material based on clay and straw instead of synthetic insulation to improve the performance of the solar collector.

Improved Model for Calculating Instantaneous Efficiency of Flat-Plate Solar Thermal Collector

The performance of a flat-plate solar collector is usually assessed by its efficiency. This efficiency is normally defined on a steady-state basis, which makes it difficult to correctly track the instantaneous performance of the collector in various case-studies. Accordingly, this paper proposes an improved definition of instantaneous efficiency of a flat-plate solar collector used as a part of a solar water heating system. Using a predeveloped model by the authors for such a system, the proposed efficiency-definition is examined and compared with the conventional one for specific case studies. The results show that the improved definition of efficiency records reasonable values, i.e., no over-range values are observed contrast to the case of conventional efficiency-definition. Furthermore, this suggested efficiency approximately coincides with the conventional one at a wide range of time, as long as the system is operating in the so-called trans-steady-state phase or when the system is off-operational provided that the instantaneous rate of heat stored in the heat transfer fluid (HTF) is less than or equal to zero. As a result, the improved efficiency-definition yields more realistic results in reflecting the performance of a flat-plate collector in an active solar water heating system and is recommended to be used.

Development and performance evaluation of an active solar distillation system integrated with a vacuum-type heat exchanger

Industrialization and growth in the world's population have increased the demand for fresh water. Solar desalination systems are energy consuming and therefore using solar stills in the remote locations is more feasible and affordable. In the present study, a solar distillation system integrated with a solar parabolic trough concentrator and a vacuum-type heat exchanger with falling film technique has been developed and experimentally evaluated during five sunny days in October 2015 between 10am to 2.30pm. During the evaluation period, the environmental parameters of solar radiation, air temperature, and wind speed were recorded in every 15min. Then, the effect of these environmental parameters on the daily productivity of the distillation system through the performance evaluation of both solar concentrator and heat exchanger. Then, the energy and exergy efficiencies of the heat exchanger, as the central part of the system, were calculated based on the recorded environmental and operational parameters during the experiments. The obtained results showed that the solar radiation has the dominant effect on the thermal performance of the concentrator which delivers hot oil to the heat exchanger. Moreover, it has been investigated that the vacuum pressure of the heat exchanger has a significant effect on the vapor productivity of the system. The maximum distillate production of the distillation device was recorded to be 1.5kg/m2/day with the average solar radiation of 1227.68W/m2 under the heat exchanger vacuum pressure of 0.5bar. According to the results obtained from the energy and exergy analysis, the highest energy and exergy efficiencies were obtained as 60.98% and 56.80% respectively.

Thermal behavior of asphalt pavement as an active solar collector under Malaysia climate condition using rubber tube

Thermal behavior of asphalt pavement as an active solar collector under Malaysia climate condition using rubber tube

Designing a combinational solar water desalination system and investigation of solving sedimentation of minerals with water input from the Persian Gulf

In this research, an active combinational solar water desalination system was designed and investigated. Sea water was guided towards a solar collector and was evaporated in a glass chamber where the produced vapor was conducted towards a water cooled condenser using a compressor, thereby resulting in the production of distilled water. In the first experiment, the corrosion test was performed to investigate the occurrence of corrosion in the solar collector and the floor of the glass chamber. According to the corrosion test performed in the first experiment, the corrosion rate of copper, the galvanized sheet, and stainless steel was measured to be 21.874, 24.356, and 17.595 mm/year, respectively. In order to reduce corrosion in the system, a descaling solution (acetic acid) was used, where the results of the corrosion test for copper and the galvanized sheet in the presence of the descaling solution were measured to be 14.759 and 14.795 mm/year, respectively. Considering the closeness of the corrosion rate of the galvanized sheet and the stainless steel sheet, as well as the finished price of the sheet employed in the floor of the glass chamber, the application of the galvanized sheet is more economical than the use of the stainless steel sheet.

A feasibility study on active solar space heating technology for office buildings in Greece

Este artigo explora a viabilidade de utilizar coletores solares termicos com capacidade de armazenamento e radiadores convencionais para aquecimento de edificios de escritorios na Grecia. Um modelo dinâmico de simulacao na ferramenta ESP-r e utilizado para analisar o desempenho do sistema de coleta solar integrado ao edificio para diferentes perfis de demanda em todas as zonas climaticas da Grecia. O impacto da capacidade do sistema de armazenamento, a area do coletor e o ângulo de inclinacao sao investigados quanto ao desempenho geral do sistema. Os escritorios na Grecia se enquadram em varios cenarios de demanda anual, determinados pela orientacao do edificio, a localizacao e a exposicao ao ambiente externo. Finalmente, uma tentativa e feita para extrapolar as descobertas para todo o estoque de escritorios da Grecia. A partir desse ponto, utilizando o sistema de aquecimento de energia solar ativo proposto, a economia de energia termica alcancaria 29% no total devido a cobertura solar.