Active Solar Research Articles

Use of flat plate solar collectors and parabolic trough concentrators for greenhouse soil disinfestation

The aim of the present work was to investigate the use of low and medium temperature active solar energy systems for the disinfestation of greenhouse soils. Four flat plate solar collectors (low-temperature solar thermal energy devices) and six parabolic trough concentrators (medium-temperature solar thermal energy devices) were used to heat water, which, via a buried heat exchange system, was used to heat the soil of greenhouse plots. These treatments were compared to no solar (control) and solarized (using a 50 micro m-thick transparent polyethylene sheet) plots. Experiments performed in the summers of 2004 and 2005 showed that: 1) the temperatures reached and the energy accumulated in the soil - and therefore the disinfestation capacity - were greater with either of the active solar treatments (40-60 deg C and 10.222.438-18.102.054 J, respectively) than with solarization (< 40 deg C and 6.628.760 J, respectively) and 2) the temperatures reached using the parabolic trough concentrators (50-60 deg C) were higher than those achieved with the flat plate solar collectors (40-50 deg C). The soil temperatures reached suggest these systems could be used to disinfest greenhouse soils.

Parametric study of an active and passive solar distillation system: Energy and exergy analysis

This paper presents the parametric study of passive and active solar stills integrated with a flat plate collector based on the computer based thermal models. These models are developed based on mass and energy balance equations. The effect of inner and outer glass cover temperatures on the performance of the solar stills is studied which lacks in the present literature. Hence, this paper aims to compare the daily yield values from the thermal models based on both assumptions, (a) inner and outer glass cover temperatures are equal ( T gi = T go) and (b) inner and outer glass cover temperatures are not equal ( T gi ≠ T go). In this paper, the comparison is made between active and passive solar stills based on the hourly yield values for the two assumptions. The thermal performance of the active solar still is affected by design parameters like water depth, thickness of glass cover, insulation thickness, condensing cover material, type of solar collector, number of collectors, and also affected by a change in climatic parameters like ambient air temperature, solar intensity and wind velocity. The effect of design parameters and wind velocity on the daily yield of both passive and active solar stills is presented in this paper. The results of the thermal model of the active solar still integrated with a flat plate collector show that the daily yield values are 3.08 L and 2.85 L for the two conditions T gi = T go and T gi ≠ T go respectively. Similarly, in the case of the passive solar still, the daily yield values are 1.14 L and 1.09 L for T gi = T go and T gi ≠ T go respectively. The effect of the number of collectors and water depth on exergy and thermal efficiency of the active solar still is also obtained and presented. At the end, the comparison is made between the types of solar collectors and their effect on daily yield of the active solar still.

Thermal modelling, validation and exergetic analysis of a hybrid Photovoltaic/Thermal (PV/T) active solar still

This paper presents the thermal analysis of a self sustainable, new design of hybrid photovoltaic/thermal (PV/T) active solar distillation system. The experiments were conducted for 24 h (7am-7am) for the New Delhi (India) climatic conditions on typical days during the month of April 2006 for water at different depths (i.e., 0.05, 0.10, 0.15 m) in order to validate the experimental results, a thermal model was developed. The theoretical results obtained for basin water temperature and distillate yields are in fair agreement with experimental results. Further, the exergetic and energetic analysis of passive and hybrid active solar still inferred that the average annual exergy efficiency of hybrid active solar still is higher than passive solar still almost by 25%, while the energy efficiency is lower by 24%.

Green and Healthy Housing

The basic role of a house has not changed since humans lived in caves. It shelters us from the elements and provides a place to live, work, and play. With the exception of changes in designs and styles, that role remained unquestioned in the United States until the mid 1970s, when the Arab oil embargo highlighted energy inefficiencies in the residential sector. Initial responses from architects and engineers to that early crisis were to explore such alternative energy sources as active and passive solar heating systems. Years of experimentation followed until the premise of that direction was questioned. Instead of replacing the energy source, why not reduce the need for it? That question led to the development of what were called superinsulated homes, some of which required as little as 5% of the energy used by conventional homes at the time. But initial applications of this technology suffered serious problems with moisture generated from normal household activities and resulted in a focus on indoor air quality. That focus evolved beyond moisture and resulting biological contaminants to gradually include radon and other soil gases, volatile organic compounds VOCs , combustion pollutants, and other toxicants. The significance of this shift in focus is highlighted by findings that approximately 70% of people’s lives are typically spent inside the house. In recent years, house design and construction issues have broadened beyond energy efficiency and indoor environmental quality to include embodied energy content and durability of construction materials. Now called sustainable, regenerative, or green design, this view takes a systems approach to the design and construction of a house and the selection of its building materials. A green house is a high-performance home with respect to its energy use and a healthy home regarding its indoor environmental quality. Its small carbon footprint also makes it an earth-friendly

Effect of condensing cover material on yield of an active solar still: an experimental validation

An attempt has been made to evaluate inner and outer glass temperature and its effects on yield. Numerical computations have been performed for a typical day in the month of December, 2005, for the climatic condition of New Delhi (latitude: 28°35´ N; longitude: 77°12´ E and an altitude of 216 m above mean sea level). Higher yield was observed for an active solar distillation system as compared to the passive mode due to higher operating temperature differences between water and inner glass cover. The parametric study has also been performed to find out the effects of various parameters, namely thickness of condensing cover, collector absorbing surface, wind velocity and water depth of the still. It is observed that there is significant effect on daily yield due to change in the values of collector absorbing surface, wind velocity and water depth. For all the cases, the correlation of coefficients ( r) between predicted and experimental values have been verified and they showed fair agreement with 0.90 < r < 0.99 and root mean square percent deviation 3.22% < e < 22.64%. Effect of condensing cover materials, namely copper and polyvinyl chloride (PVC), on daily yield have also been investigated and compared.

Exergetic analysis of passive and active solar stills

This paper presents an exergetic analysis for passive and active solar distillation systems. The analysis is based on mass, energy and exergy balance equations, which has not been attempted in the past for active solar stills. In the present paper, it has been tried to compare the hourly exergy and thermal efficiency of passive and active solar stills. The values of hourly exergy and thermal efficiency of passive solar still are 0.1?0.8% and 2?17% while those for active solar still are in the range 0.1?1.1% and 3 15%, respectively. In case of active solar still, the effect of water depth and number of collectors on overall exergy and thermal efficiency have been obtained.

Daily solar irradiation estimation over a mountainous area using artificial neural networks

In order to design both active and passive solar energy systems, radiation data are needed for the studied location. The implementation of such renewable energy systems is especially important in places like natural parks, where acoustic and fossil fuel derived contamination has to be completely avoided. Measure of solar radiation is usually accomplished by means of radiometric station nets with a low spatial resolution. To estimate the radiation in sites located away from the stations, different interpolation/extrapolation techniques may be used. These methods are valid on places where the spatial variability of radiation is not significant, but becomes less accurate if complex terrain areas are present in between the radiometric stations. As an alternative, artificial intelligence techniques have been used in this work, along with a 20 m resolution digital model of terrain. The inputs to the network have been selected using the automatic relevance determination methodology. The data set contains 3 years’ data of daily global radiation measured at 12 different stations located in the north face of the Sierra Nevada National Park in the surroundings of Huéneja (Granada), a town located in the South East of Spain. The stations altitude varies from 1000 to 1700 m. The goal of this work has been to estimate daily global irradiation on stations located in a complex terrain, and the values estimated by the neural network model have been compared with the measured ones leading to a root mean square error (RMSE) of 6.0% and a mean bias error (MBE) of 0.2%, both expressed as a percentage of the mean value. Performance achieved individually for each of the stations lies in the range [5.0–7.5]% for the RMSE and [−1.2 to +2.1]% for the MBE. Results point out artificial neural networks as an efficient and easy methodology for calculating solar radiation levels over complex mountain terrains from only one radiometric station data. In addition, this methodology can be applied to other areas with a complex topography.

Comparative thermal performance evaluation of an active solar distillation system

In this paper, thermal models of all types of solar collector-integrated active solar stills are developed based on basic energy balance equations in terms of inner and outer glass temperatures. In this paper, hourly yield, hourly exergy efficiency, and hourly overall thermal efficiency of active solar stills are evaluated for 0.05 m water depth. All numerical computations had been performed for a typical day in the month of 07 December 2005 for the climatic conditions of New Delhi (28°35′N, 77°12′E, 216 m above MSL). The thermal model of flat-plate collector integrated with active solar still was validated using the experimental test set-up results. Total daily yield from active solar still integrated with evacuated tube collector with heat pipe is 4.24 kg m−2 day−1, maximum among all other types of active solar stills. Copyright © 2007 John Wiley & Sons, Ltd.

Design and construction possibilities for photovoltaic integration in envelopes of new and existing buildings

Sun is the renewable energy source whose usage exerts influence on architectural design. Facade concepts of energy efficient buildings are developed producing new facade structures and components. Photovoltaic systems, as elements of active solar systems are discussed in the paper and particular attention is paid to building integrated systems, as they influence building appearance. Classification and analyzes of PV systems - materials, supporting systems, coatings and design principles are presented in the paper. The purpose of this paper is discussion on design and construction possibilities for PV integration in envelopes of new and existing buildings. Possibilities for structural variability of envelopes with PV integrated systems are described in the paper. .

Energy software programs for educational use

A package of six fully interactive energy software programs was developed for educational use. The first three programs can be used to simulate energy systems, while the rest three can be used to calculate some characteristic values, which can be used separately or in conjunction with the first three programs. The first one is a multimedia program for an active solar hot water system. It accounts for a large number of parameters and can be used to investigate their effect on the thermal efficiency of the system. The second program is a transient simulation for thermal behavior of a building. It can be used to predict the temperature and relative humidity inside a building along with the heating/cooling load required to keep the temperature at a preset point. The third program has been developed for sizing solar thermal systems. The fourth program is a graphical representation of the apparent motion of the sun on the celestial vault. The fifth program calculates the thermophysical properties of a number of gases and liquids for a desired temperature. The sixth program represents graphically the psychrometric chart. The above-mentioned programs, are useful tools for education in energy, suitable for high school students and Universities. It can also be used for an extensive set of exercises in the tertiary education sector.

06/02250 Renewable energy for passive house heating. Model of the active solar heating system: Badescu, V. and Dan Staicovici, M. Energy and Buildings, 2006, 38, (2), 129–141.

06/02250 Renewable energy for passive house heating. Model of the active solar heating system: Badescu, V. and Dan Staicovici, M. Energy and Buildings, 2006, 38, (2), 129–141.

Experimental Investigations on Packed Bed Solar Air Heater

Solar collector is important component of active solar heating systems. It has been observed that the performance of flat plate collector improves appreciably by packing its duct with blackened wire screen matrices and this improvement is a strong function of bed and operating parameters. In this paper an experimental test setup is designed and fabricated. Performance evaluation of packed bed Solar air heater using wire mesh screen matrices and its comparison with conventional design has been done. Data collection at different mass flow rates for a number of configurations has been done. Further suitable recommendations have been made accordingly.

Thermal performances of the active and passive water heating systems based on annual operation

In this paper, the year round thermal performance evaluation of active and passive solar water heating systems for rural/urban area have been studied. Two types experiments are the normalized draw-off temperature profile and the normalized draw-off mixing profile conducted in the months of April 2003–March 2004. Effect of morning, mid-afternoon, evening draw-off and effect of water mixing in the morning and evening are also studied during the experiments. Thermal efficiency for the system and collection efficiency for the collectors were calculated during the experiments. The values of F R · ( τα) of the collectors used in active and passive water heating systems were found 0.69 and 0.61 respectively. Ethylene glycol has a 50/50 glycol-to-water ratio used as a heat transfer fluid (HTF) in the systems due to the cold climate in South Korea.

Improvements in solar radiation models based on cloud data

Simple radiation estimation models using meteorologically observed input parameters are often used in the applications requiring rough estimations of solar horizontal radiation. One of the parameters employed, cloud cover, is widely available from multiple regional and national weather stations. Kasten and Czeplak, Muneer and Gul, and Lam and Li, have proposed cloud-based models for the estimation of global and diffuse horizontal irradiance. In the current study, three new cloud-based models have been proposed. To compare the validity of the above models, statistical indicators have been developed for assessing the accuracy of estimation of global, diffuse and beam horizontal irradiance. The slope of the best fit line and the coefficient of determination between measured and calculated values, mean bias error, and root mean square error were calculated. In addition, the kurtosis and skewness of error histograms were also obtained. These parameters were used to obtain accuracy indicators for the models under validation. It was concluded that the proposed models outperformed the Kasten / Czeplak, and Lam / Li models, in both their original and modified forms. Practical application: Solar radiation data is an essential part of designing passive and active solar systems in building services. However, the solar radiation data is not always measured at the desired location, but other meteorological data are more available, therefore, tools have been developed to estimate the solar radiation from other measured parameters such as cloud cover. The models that are proposed are more accurate than their predecessors are, and provide global, beam and diffuse horizontal irradiance estimations. List of symbols

Thermal modeling of passive and active solar stills for different depths of water by using the concept of solar fraction

This communication presents the thermal analysis of passive and active solar distillation system by using the concept of solar fraction inside the solar still with the help of AUTOCAD 2000 for given solar azimuth and altitude angle and latitude, longitude of the place. Experiments have been conducted for 24 h (9 am to 8 am) for New Delhi climatic conditions (latitude 28°35′N, longitude 77°12′E) during the months of November and December for different water depths in the basin (0.05, 0.1 and 0.15 m) for passive as well as active solar distillation system. Analytical expressions for water and glass cover temperatures and yield have been derived in terms of design and climatic parameters. It is observed that (i) the solar fraction plays a very important role at lower values of solar altitude angle; (ii) the internal convective heat transfer coefficient decreases with the increase of water depth in the basin due to decrease in water temperature; (iii) there is a fair agreement between the experimental observation and theoretical prediction during daytime as compared to that during the night.

Lithopanspermia in Star-Forming Clusters

This paper considers the lithopanspermia hypothesis in star-forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to action in the field) because of the close proximity of the systems and lower relative velocities. These effects more than compensate for the reduced time spent in such crowded environments. This paper uses approximately 300,000 Monte Carlo scattering calculations to determine the cross sections <sigma(cap)> for rocks to be captured by binaries and provides fitting formulae for other applications. We assess the odds of transfer as a function of the ejection speed v (eject) and number N(.) of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low, about 1:10(3)-10(6) over the expected range of ejection speeds and cluster sizes. Because the number of ejected rocks (with mass m > 10 kg) per system can be large, N (R) approximately 10(16), virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster. The number of ejected rocks that carry living microorganisms is much smaller and less certain, but we estimate that N (B) approximately 10(7) rocks can be ejected from a biologically active solar system. For typical birth environments, the capture of life-bearing rocks is expected to occur N (bio) asymptotically equal to 10-16,000 times (per cluster), depending on the ejection speeds. Only a small fraction (f (imp) approximately 10(4)) of the captured rocks impact the surfaces of terrestrial planets, so that N (lps) asymptotically equal to 10(3)-1.6 lithopanspermia events are expected per cluster (under favorable conditions). Finally, we discuss the question of internal versus external seeding of clusters and the possibility of Earth seeding young clusters over its biologically active lifetime.

Renewable energy for passive house heating: Model of the active solar heating system

The large windows on the south-oriented façade of a passive house strongly contribute to building space heating. These windows constitute the passive solar heating system. This paper studies the active heating system of a passive house, which includes the following sub-systems: (1) solar thermal collectors, (2) a water storage tank, (3) a secondary water circuit, (4) a domestic hot water preparation system and (5) an air ventilation and heating system. Models for all sub-systems are presented. The integrated model was implemented to Pirmasens Passive House (Rhineland Palatinate, Germany). The active solar heating system provides a smaller amount of heat than the heat provided by the passive solar heating system. Almost all the solar energy collected is not used for space heating but to domestic hot water (DHW) preparation. However, there is still a need for the classical water heater to operate all over the year. Almost all space heating thermal load is covered by using the classical air heater that operates mainly during the nights from November to April. The solar fraction lies between 0.180 in February and 0.679 in October, with a yearly average of 0.446. The study reveals that on a yearly basis it is more advantageous to use vertical south-oriented solar collectors instead of roof placed collectors.

Thermal Performance of a Solar Heat Storage Accumulator Used For Greenhouses Conditioning

The use of solar energy for greenhouse heating has gained an increasing acceptance during the last years. Active solar systems applied to greenhouses can supply a significant part of the heating requirements. However, there are some problems related to the cost of the heat collection unit and the heat storage methods. In this context several techniques were born. The most famous of these techniques is the seasonal storage of thermal heat in soil. The objective of our work is to study a system of thermal energy storage conceived in our Laboratory (LEPT, Tunisia). The system is composed of a vat having a large dimension (6 m 3 ) filled with fin sand. Inside the vat three batteries of capillary exchangers are buried at three different levels. To heat the accumulator soil, we use a solar collector with a surface equal to 6 m 2 . In order to size the heat accumulating system, a numerical study is started. It allows evaluating the soil temperature as well as the energy cumulated inside the accumulator during the charging and the discharging period.

Simulation analysis for the active solar heating system of a passive house

The active solar heating system consists of the following sub-systems: (1) a solar thermal collector area, (2) a water storage tank, (3) a secondary water circuit, (4) a domestic hot water (DHW) preparation system and (5) an air ventilation/heating system. An improved model for the secondary water circuit is proposed and two interconnection schemes for sub-systems (4) and (5) are analyzed. The integrated model was implemented to Pirmasens passive house (Rhineland Palatinate, Germany). Both interconnection schemes show that (almost all) the solar energy collected is not used for space heating but for domestic hot water preparation. The classical water heater operates all over the year and the classical air heater operates mainly during the nights from November to April. The yearly amount of heat required by the DHW preparation system is about 77% of the yearly total heat demand of the passive house and the classical water heater provides about 20% of the yearly heat required by the DHW preparation system. The solar fraction lies between 0.247 in January and 0.930 in August, with a yearly average of 0.597.

Effect of water depth on internal heat and mass transfer for active solar distillation

In this communication, an attempt has been made to find out the convective heat transfer coefficient for active solar distillation system. It is a well-known fact that the distillate output (the yield) decreases significantly with the increase of water depth in the basin of the solar still. It is also known that more yield is obtained in case of active solar distillation system as compared to passive solar still due to higher temperature difference between the water and inner glass cover temperatures in the active mode. For the present study, experiments have been conducted for 24 hours during winter months for different water depths in the basin (0.05, 0.1 and 0.15 m) for passive as well as active solar distillation system. The objective of the present paper is to study the effect of different water depths in the basin on the heat and mass transfer coefficients. It is inferred that the convective heat transfer coefficient between water and inner condensing cover depends significantly on the water depth in the basin. It is also observed that more yield is obtained during the off shine hours as compared to daytime for higher water depths in solar still (0.10 m and 0.15 m) due to storage effect.