Solar Collector Surface Research Articles

흑색 황산3가크롬을 이용한 태양열 흡열판 선택흡수막 도금기술

One of the most important factors that have a large influence on performance of the solar water heater system is performance of the solar collector, more detailedly, coating technology on the surface of the solar collector, which can provide high solar absorptance and low emittance. The core of the coating technology is to coat solar selective surfaces. In this study, various performance experiments are carried out using coating technology. Here, IGBT(Insulated Gate Bipolar Transistor) of 5000A-15V was used as the surface processing rectifier which can stably output power and also can control voltage and current. The plating solution mainly contains black chrome concentration, H-y Conductivity, N-u Complex, NF Additive and NC-2 Wetter. Before applying the black chrome coating on the copper plate, optimal conditions are provided by using various preprocessing methods such as removal of fat, activation, electrolytic polishing, nickel strike, copper sulfate plating and bright neckel plating, and then the automatic continuous coating experiment are performed according to plating time and cathode current density. In the experiment, after the removal of fat, chemical polishing, nickel strike and activation processes as the preprocessing methods, the black chrome coating was performed in a plate solution temperature of and a cathode current density of for 90 seconds. The thickness of chrome and nickel on the coated plate is , respectively. As a result of the coating experiment, it showed the most excellent performance having a high solar absorptance of 98% and a low emittance of when the black chrome surface had a thickness of .

Energy neutral districts in 2050 – the Dutch approach

For energy neutral district development in 2050, six innovative energy concepts have been elaborated for the Dutch situation and their potential for energy neutrality in 2020, 2035 and 2050 calculated. Three concepts are based on the idea of an energy hub - bio hub, geo hub and a solar hub. Other concepts are the all-electric, conventional and hydrogen concepts. Calculations show that implementation of each of the concepts can lead to energy neutral districts in 2050. When personal transport is included, energy neutrality in 2050 is not feasible. Based on the six general concepts, the most optimal energy concepts tailored for four Dutch cities have been elaborated as pilots, in close cooperation with municipality representatives. The EPG (Energy Pattern Generator) is applied for simulation of a virtual district with 1000 dwellings of various categories. The modelling of a solar hub shows that, assuming equal heat losses for the individual storages and the collective storage, an energy hub with collective heat storage can reduce the required storage capacity by 26%, and the total required solar collector surface by 30% at maximum. This shows the added value of energy hubs with exchange, central storage and conversion of energy on a district level and suggests that costs of an energy hub can be optimised, becoming financially more attractive than houses with individual seasonal heat storage. Energy hub concepts can contribute considerably to the energy neutral built environment in 2050. The effect can be intensified by an exchange of surplus sustainable energy with neighbouring districts and import of energy in case of a shortage.

Nomograph for rapid technical and economic assessment of solar thermal systems for DHW production

Different types of tools, software and empirical methods to size and assess the performance of solar thermal systems are available today. A quick and easy-to-use graphical tool is proposed here. It is based on a single diagram, called a nomograph, which embeds technical and economic information, allowing the optimisation of the size and performance of a solar thermal system starting from the main input parameters, such as the specific costs of the system and the auxiliary fuel. The optimal surfaces are calculated as a function of the fuel cost through several regressions made on data from the application of the F-Chart method for a set of system configurations. The authors have found good correlations among these two parameters for given collectors types, climates and fuel costs.Furthermore, the design information stemming from the use of the diagram considers the optimal area of the surface of solar collectors, the corresponding annual solar fraction, the annualised total cost of the solar system and the conventional systems meeting the same load, the annual savings achieved with the use of solar system and the corresponding payback time. Nomographs have been drawn for three Italian locations, representative of different South Europe climates, for a given demand of hot water and for two types of collectors. The methods and algorithms related to the construction of the diagrams are described in this paper. Additional nomographs can be produced through a standardised procedure based on Excel Macros. An analysis of the results obtained is then performed for a sample application.

Solar Load Ratio and ISO 13790 methodologies: Indirect gains from sunspaces

This paper reviews and analyzes the compatibility of the simplified empirical method based on the dimensionless parameter of Solar Load Ratio (SLR) and the monthly procedure of the standard ISO 13790 for indirect gains, specifically for unconditioned zones adjacent to a conditioned zone, but separated from it by a partition wall (sunspaces).The main contribution of the work presented here is the new formulation to account SLR correlations in ISO 13790, obtained for sunspaces, but generalizable for other solar systems with known SLR functions.Simulation models are used to perform a sensitivity analysis of internal gains and heat transfer through solar collector surfaces, both issues that distinguishes ISO 13790 from Load Ratio methods. The analysis shows that internal gains can be added to the heat source term or subtracted to heat transfer term without influencing the utilization factor dependence with the gain-to-loss ratio. On the other hand, the SLR assumption that solar collector surfaces are neutral elements and, therefore, not added to the heat transfer term, results in large inconsistencies between SLR and ISO 13790 methods.The detailed monthly methodology of ISO 13790 fairly reproduces results obtained by simulation. However, predictions from the simplified monthly methodology of ISO 13790 fail in mid season months and coldest months.

White light interferometry for quantitative surface characterization in ion sputtering experiments

White light interferometry (WLI) can be used to obtain surface morphology information on dimensional scale of millimeters with lateral resolution as good as ∼1μm and depth resolution down to 1nm. By performing true three-dimensional imaging of sample surfaces, the WLI technique enables accurate quantitative characterization of the geometry of surface features and compares favorably to scanning electron and atomic force microscopies by avoiding some of their drawbacks.In this paper, results of using the WLI imaging technique to characterize the products of ion sputtering experiments are reported. With a few figures, several example applications of the WLI method are illustrated when used for (i) sputtering yield measurements and time-to-depth conversion, (ii) optimizing ion beam current density profiles, the shapes of sputtered craters, and multiple ion beam superposition and (iii) quantitative characterization of surfaces processed with ions.In particular, for sputter depth profiling experiments of 25Mg, 44Ca and 53Cr ion implants in Si (implantation energy of 1keV per nucleon), the depth calibration of the measured depth profile curves determined by the WLI method appeared to be self-consistent with TRIM simulations for such projectile-matrix systems. In addition, high depth resolution of the WLI method is demonstrated for a case of a Genesis solar wind Si collector surface processed by gas cluster ion beam: a 12.5nm layer was removed from the processed surface, while the transition length between the processed and untreated areas was 150μm.

The Optimal Slope Angle for Solar Collectors in Hot and Dry Parts of Iran

The performance of a solar collector is highly susceptible by its slope angle with the horizon. This is due to the fact that the solar radiation intensity over the solar collector surface changes with the slope angle. A well known mathematical model was used for estimating the total (global) solar radiation intensity on an inclined surface faced to the south, and to determine the optimum slope angle for the solar collectors in hot and dry parts of Iran based on experimental data for a horizontal surface. The monthly, seasonal, and yearly optimum slope angles were calculated. The slope angle was calculated for different intensities of total radiation on the collector surface and the corresponding values for maximum total radiation were specified as the optimum slope angles. The results showed that the yearly optimum slope angle for each city is close to the local latitude. The results also indicated that changing the monthly, seasonal, and yearly slope angles causes to achieve a significant yearly gain in solar radiation intensities when the gains are calculated with respect to a solar collector fixed at zero slope angle for the region under investigation.

Optimization of solar collector surface in solar desiccant wheel cycle

This work presents the optimization of a solar collector surface in solar desiccant wheel cycle which for cooling process with typical configuration naming desiccant wheel, heat exchanger and water spray evaporative cooler. In this cooling cycle the thermal solar energy has used to heat the regeneration air of desiccant wheel cycle. The optimum solar collector surface has determined by taking into account of design parameters such as velocity of air, wheel speed, thickness of the desiccant and hydraulic diameter of the desiccant wheel and also operating conditions such as outside temperature, outside relative humidity, regeneration air temperature and total solar irradiance. For this purpose, effect of desiccant wheel parameters has investigated on solar collector surface. After that, optimum design parameters and minimum solar collector surface has calculated. In this cooling process, a mathematical model has used that shows physical properties of air. The calculated values for design condition show that necessary solar collector surface has decreased about 45% in comparison of an empirical model in equal operating conditions. The results of this study show that necessary solar collector surface will be decreased by increasing inlet air temperature, inlet air humidity ratio and solar irradiance and will be increased by increasing the regeneration air temperature.

A comparison of solar absorption system configurations

Abstract Solar thermal driven cooling systems for residential applications are a promising alternative to electric compression chillers, although its market introduction still represents a challenge, mainly due to the higher investment costs. The most common system configuration is an absorption chiller driven by a solar thermal system, backed up by a secondary heating source, normally a gas boiler. Heat storage in the primary (solar) circuit is mandatory to stabilize and extend the operation of the chiller, whereas a cold storage tank is not so common. This paper deals with the selection of the most suitable configuration for residential cooling systems with solar energy. In Spain, where cooling needs are usually higher than heating needs, the interest of a reversible heat pump as auxiliary system and a secondary cooling storage are analyzed. A complete TRNSYS model has been developed to compare a configuration with just hot storage (of typical capacity 40 L/m 2 of solar collector surface) and a configuration with both, hot and cool storages. The most suitable configuration is very sensible to the solar collector area. As the collector area increases, the advantages of a cool storage vanish. Increasing the collector area tends to increase the temperature of the hot storage, leading to higher thermal losses in both the collector and the tank. When the storage volume is concentrated in one tank, these effects are mitigated. The effect of other variables on the optimal configuration are also analyzed: collector efficiency curve, COP of the absorption chiller, storage size, and temperature set-points of the chillers.

Comparative study of solar cooling systems with building-integrated solar collectors for use in sub-tropical regions like Hong Kong

The performance of solar cooling systems with building-integrated (BI) solar collectors was simulated and the results compared with those having the solar collectors installed conventionally on the roof based on the weather data in Hong Kong. Two types of solar collectors and the corresponding cooling systems, namely the flat-plate collectors for absorption refrigeration and the PV panels for DC-driven vapour compression refrigeration, were used in the analysis. It was found that in both cases, the adoption of BI solar collectors resulted in a lower solar fraction ( SF) and consequently a higher primary energy consumption even though the zone loads were reduced. The reduction in SF was more pronounced in the peak load season when the solar radiation was nearly parallel to the solar collector surfaces during the daytimes, especially for those facing the south direction. Indeed, there were no outputs from the BI flat-plate collectors facing the south direction between May and July. The more severe deterioration in the system performance with the BI flat-plate type collectors made them technically infeasible in terms of the energy-saving potential. It was concluded that the use of BI solar collectors in solar cooling systems should be restricted only to situations where the availability of the roof was limited or insufficient when applied in sub-tropical regions like Hong Kong.

Performance Characteristics of Four Solar Still Designs

Four solar still designs were evaluated based on their condensed water production and solar radiation absorption efficiency. The designs of the four distillation units were: (1) flat bottom reservoir with single inclined glass (SS1), (2) stair-step reservoir with single inclined glass and continuously fed (SS2), (3) flat bottom reservoir with woven wick material on an absorber plate and double inclined glass (SS3), and (4) flat bottom reservoir with woven wick material on an absorber plate, double inclined glass, and continuously fed (SS4). The water surface areas of solar stills SS1, SS3 and SS4 were 0.5 m2 and of SS2 was 1 m2. Water input and condensed water output were measured each day, as well as solar radiation absorbed. Solar energy conversion efficiency for water distillation was evaluated for the four designs. Condensed water production per square meter of the solar still was correlated to the solar energy received to determine if there was a statistically significant correlation. Results showed that all solar stills showed a s1 slope regression coefficient that was statistically different than zero, when determining a correlation between condensed water production and solar radiation. SS2 had an average distilled water production rate of 2.9 L/m2/day followed by SS1 and SS3 at 2.2 L/m2/day. SS4 had a distilled water production rate of 1.2 L/m2/day. The average energy conversion efficiency was 50% for SS2, 36% for SS3, 31% for SS1, and 21% for SS4. To generate 2 L of distilled water per day (the current daily per capita consumption in the United States), it would take less than 0.7 m2 of solar collector surface area. The yearly condensed water production rate, for a still utilizing the SS2 design and the developed prediction model, in Austin, Texas was estimated to be 1290 L of condensed water per square meter of still surface area (341 gal/m2/yr).

Numerical simulation of phase change heat transfer of a solar flat-plate collector with energy storage

The technical feasibility of an innovative solar collector is studied in this paper. A phase change material (paraffin) is used in the solar collector to store solar energy. This type of system combines both collection and storage of thermal energy into a single unit. The major advantages of the phase change stores are their large heat storage capacity and isothermal behavior during the melting and solidifying processes. A negative aspect of paraffin is its low thermal conductivity which increases the melting and solidifying time for paraffin energy storage. In this paper, new aluminum foams infiltrated with paraffin are presented. It presents a two dimensional model describing the melting and solidifying processes of paraffin while accounting for both phase change heat transfer and natural convection. Apparent heat capacity method was used to simulate the melting and solidifying processes of paraffin. The simulation results show that the motion of the hot liquid paraffin plays an important role in increasing the heat transfer between paraffin and top surface of solar collector. The shape profile of the pure paraffin solid-liquid interface is determined by the synergistic relationship between its temperature and velocity field. Though aluminum foams impregnated with paraffin will limit motion of the hot liquid paraffin, the heat transfer ability is greatly improved. The distributions of the temperature in the paraffin with aluminum foams are more homogeneous compared with that of the paraffin without aluminum foams. Thus, use of aluminum foams infused with paraffin improves heat transfer and enhances paraffin’s melting and solidifying rates.

A SOLAR DRYER PERFORMANCE OF ONION SLICES UNDER FAYOUM CLIMATIC CONDITIONS

A solar drying unit was developed and constructed for drying onion slices under Fayoum conditions. The drying unit consists of a solar collector, which oriented and tilted with an optimum tilt angle and attached with drying chamber. The drying experiments were carried out to examine the effect of onion slice thicknesses (3, 6 and 10 mm) and airflow rate (2.4 and 1.6 m 3 .min -1 ) on the onion slices drying rate. The obtained results indicated that the daily average total solar radiation flux incident on the tilted solar collector surface (7.32kWh.m -2 .day -1 ) was greater than that incident on the horizontal surface (6.13kWh.m -2 .day -1 ) by 19.41%. The higher air temperatures were obtained at the lower airflow rate (1.6 m 3 .min. -1 ) whereas; the amount of heat gained to the air from the solar collector was relatively higher at the higher airflow rate as compared with the lower airflow rate. Consequently the higher efficiency of the solar collector was obtained at the higher airflow rate. The solar collector with the higher airflow rate increased the overall thermal efficiency by 12.56% as compared to the lower airflow rate. The moisture content of dried onion slices was strongly affected by the onion slices thickness and the airflow rate. The final moisture content of dried onion slices ranged from (6.8% to 7.7% dry-basis) depending on the drying temperature cycle. Effect of the individual variables (airflow rate, onion slice thickness, moisture removed, and their interactions) on the drying rate was statistically analyzed. A forward step-wise regression technique was applied to arrive at a reasonable good best set of independent variables. The coefficient of determination (R 2 ) was above 0.97 when

CONVECTION SUPPRESSION IN A TRIANGULAR-SHAPED ENCLOSURE

The use of convection suppression devices has been widely discussed in the literature as a means of reducing natural convection heat loss from the front surface of glazed solar collectors. In this study, the use of baffles in an attic-shaped enclosure was examined as a possible low-cost means of suppressing heat loss by natural convection from the rear surface of a roof-integrated solar collector. To determine the effect of baffles in the attic-shaped enclosure, a three-dimensional triangular cross-sectioned enclosure with a vertical aspect ratio of 0.5 and a horizontal aspect ratio of 3.3 was modeled. The flow patterns and heat transfer in the enclosure were determined for Grashof Numbers in the range of 106−107 using a commercially available finite volume CFD solver. It was found that the use of a single adiabatic baffle mounted vertically downward from the apex, and extending the length of the enclosure, would alter the flow such that the heat transfer due to natural convection was reduced as the length of the baffle was increased.

Three dimensional numerical and experimental study of forced convection heat transfer on solar collector surface

In this study, experimental and three dimensional numerical work was carried out to determine the average heat transfer coefficients for forced convection air flow over a rectangular flat plate. Three dimensional numerical simulations were obtained using a commercial finite volume based fluid dynamics code called Fluent 6.3. The experiments were performed for mass transfer using the naphthalene sublimation technique. The results were presented in terms of heat transfer parameters using the analogy between heat and mass transfer. All the experimental results are correlated within an accuracy of ± 12%.

Heat losses of large tray solar collectors with exposed evaporation surface

An analytic expression for determining the heat losses from the exposed surface of large tray solar water heating collectors via evaporation is proposed, and a numerical example of its practical implementation is presented.

Modeling Spatio-Temporal Dynamics of Optimum Tilt Angles for Solar Collectors in Turkey.

Quantifying spatial and temporal variations in optimal tilt angle of a solar collector relative to a horizontal position assists in maximizing its performance for energy collection depending on changes in time and space. In this study, optimal tilt angles were quantified for solar collectors based on the monthly global and diffuse solar radiation on a horizontal surface across Turkey. The dataset of monthly average daily global solar radiation was obtained from 158 places, and monthly diffuse radiation data were estimated using an empirical model in the related literature. Our results showed that high tilt angles during the autumn (September to November) and winter (December to February) and low tilt angles during the summer (March to August) enabled the solar collector surface to absorb the maximum amount of solar radiation. Monthly optimum tilt angles were estimated devising a sinusoidal function of latitude and day of the year, and their validation resulted in a high R2 value of 98.8%, with root mean square error (RMSE) of 2.06°.

Natural and semi-natural field exposure testing and analysis, on optical degradation of a building integrated unglazed solar collector surface

Durability is of great importance when considering sustainable energy systems. In turn it lays emphasis on assessing performance over time of energy systems and components. This paper presents a study on optical degradation of a building-integrated Unglazed Solar Collector (USC) surface, by exposing USC specimens to a natural and semi-natural field exposure test. Particular interest is devoted to the semi-natural field exposure test method evaluation, and the degradation of optical properties. The study showed that about 11 months of field exposure testing did not cause any significant optical (total solar absorptance and IR emittance) or material (surface coating) degradation; although measurements revealed a decrease in specular reflectance as diffuse increased. It was likely due to surface pollution that predominantly consisted of quartz. The study also showed that it is possible to achieve a considerable increased moisture exposure on test surfaces (semi-natural field exposure test), through a relatively simple cooling device (Direct-Air Peltier-Element) and rough control strategy.

Air humidification–dehumidification for a water desalination system using solar energy

This paper presents a theoretical study of a solar desalination system with humidification–dehumidification which is a promising technique of production of fresh water at small scale (few m 3/d). A general model based on heat and mass transfer balances in each component of the system was developed and used to optimize the system's non-dimensional characteristics. The daily production of fresh water depends on the ratio between the salt water and the air mass flow rates. It was shown that, if this ratio is continuously adjusted for optimum performance, it is possible to produce more than 40 L of fresh water daily per square meter of solar collector surface on a typical July day in Tunisia. Annual performances for open and closed air loop systems are also presented.

Optimum Tilt Angle for Solar Collectors

A solar collector is required to absorb solar radiation and transfer the absorbed energy into a heat transfer fluid with a minimum of heat loss. In assessing the performance of a collector, it is therefore important not only to determine its ability to absorb solar radiation but also to characterize its heat losses. The ability of a collector to absorb solar radiation is largely determined by its optical and geometric properties. One of the important parameters that affect the performance of a solar collector is its tilt angle with the horizontal. This is due to the fact that the variation in tilt angle affects the amount of solar radiation reaching the collector surface. In this study, a mathematical model is used to estimate the total (global) solar radiation on a tilted surface and to determine the optimum tilt angle for a solar collector in Izmir, Turkey. Total solar radiation on the solar collector surface with an optimum tilt angle is computed for specific periods. It is found that the optimum tilt angle changes between 0° (June) and 61° (December) throughout the year. In winter (December, January, and February) the tilt should be 55.7°, in spring (March, April, and May) 18.3°, in summer (June, July, and August) 4.3°, and in autumn (September, October, and November) 43°. The yearly average of this value was found to be 30.3° and this would be the optimum fixed tilt throughout the year.

Derivation of the solar geometric relationships using vector analysis

The standard mathematical approach used in deriving equations to describe the apparent motion and position of the Sun is spherical trigonometry. Additionally, the derivation of the equations for the intensity of the direct beam radiation, incident on the surface of a solar collector or architectural surface, also generally relies on the same approach. An alternative approach utilizing vector analysis is used to derive all of these equations. The technique greatly simplifies the derivation of equations for quantities such as the declination, altitude and azimuth of the Sun, and the intensity of the direct beam radiation on a tilted panel with an arbitrary orientation. Additionally, it allows a simple derivation of the equations needed to accurately describe the Equation of Time and the right ascension.