Evaluation of solar fraction (Fn) for quonset type empty greenhouse: an experimental validation

In this study, the experiments were conducted from December 2000 to November 2001 to evaluate solar fraction (F_n) for quonset type empty greenhouse. Solar radiation was measured at different points inside and outside the greenhouse weekly once. The model based on Auto-CAD 2000 has been used for a given solar altitude and azimuth angles. Calculations have also been carried out for a typical day of each month of the year. It is observed that the solar fraction obtained by using Auto-CAD 2000 are very close to the value determined by using experimental observations and its value is more during winter months. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of thermal storage on the performance of greenhouse

In this communication, thermal model of a greenhouse has been developed by incorporating the effect of water wall in the north side. Various temperatures, namely plant, water wall and room temperatures as a function of climatic and design parameters have been obtained by solving coupled single-order differential equation using Runge–Kutta method. Numerical methods have been carried out for a typical day of winter for Delhi condition. It has been observed that there is significant effect in the plant, room air and water temperatures due to change in fraction of solar radiation incident on north wall (F_n) and heat capacity of water wall. Experimental validation of the proposed model for a greenhouse with brick north wall has also been carried out. It has been observed that there is a fair agreement between experimental and theoretical values. Copyright © 2002 John Wiley & Sons, Ltd.     

Testing of box-type solar cooker: Second figure of merit F2 and its variation with load and number of pots

The performance of a box-type solar cooker can be represented in terms of two figures of merit, F₁ and F₂. The second figure F₂ is a controlling factor in the sensible heating of a load. The present work validates F₂ by computing this figure from experimental data by two different procedures and comparing the results. An attempt has also been made to provide some guidelines for selecting a suitable temperature interval for determination of F₂. The results of some experiments to study the effect of number of pots and the load on F₂ have also been presented. It is recommended that for standardization tests should be conducted at full load.     

Novel solar cookers: suitable for small families

This paper presents the fabrication details and on-field experimental studies of two novel solar cookers, suitable for cooking requirements of small families; these are named as small family solar cookers (SFSC-1 and SFSC-2). Small size, good thermal performance, light weight, low-cost and short payback periods are some important features of these cookers. The values of some essential thermal performance parameters, first figure of merit (F₁), second figure of merit (F₂) and standard cooking power suggested by Bureau of Indian Standards and International Standard for box-type solar cookers, have been evaluated by experimental studies and found to be 0.116°C m²/W, 0.466, 30 W and 0.118°C m²/W, 0.488, 50 W for SFSC-1 and SFSC-2, respectively. A comparative analysis of the thermal performances of SFSCs with the solar cookers, developed by many authors, has also been presented here. The payback periods with respect to different cooking fuels for SFSCs have been found to be reasonably short.     

Energy‐efficient design of greenhouse for Canadian Prairies using a heating simulation model

Greenhouses in northern climates require a large amount of supplemental heating for growing crops in winter seasons, so energy‐efficient design of greenhouses based on local climate is important to minimize the heating demand. In this study, greenhouse design parameters including shape, orientation, the angle of the roof, and width of the span have been studied for the conceptual design of conventional greenhouses for Canadian Prairies using a heating simulation model. Five different shapes of greenhouses including even‐span, uneven‐span, modified arch, vinery, and quonset shape have been selected for the study. The simulation results proved that the uneven‐span gable roof shape receives the highest solar radiation, whereas the quonset shape receives the lowest solar radiation. However, the quonset shape greenhouse requires about 7.6% less annual heating as compared to the gable roof greenhouse, but the quonset would not be adopted as multispan greenhouses. Therefore, the gable roof greenhouse is considered as energy efficient for the multispan gutter connected greenhouses whereas quonset shape as a free‐standing single‐span greenhouses. In high northern latitudes, the greenhouse with east‐west orientation is more energy efficient from heating and cooling point of view when the length‐width ratio of the greenhouse is more than 1. The heating energy saving potential of the large span width in single‐span greenhouses is relatively higher as compared to the multispan greenhouses.     

Simulation and multi‐objective optimization of a fixed bed catalytic reactor to produce hydrogen using ethanol steam reforming

A mathematical model is developed for a fixed bed catalytic reactor to produce hydrogen using ethanol steam reforming in the presence of a Ni (II)‐Al (III)‐LDH catalyst. The simulation of the reactor has been carried out using the ode23s module of MATLAB (version 2010a) based on a mechanistic kinetic model (Langmuir‐Hinshelwood approach) with proven reaction kinetics. There is a confusion regarding the values of the kinetic parameters even though earlier workers have used the same experimental data and the same model equations. The values of the model parameters obtained using two different curve‐fitting techniques, the generalized reduced gradient (GRG) algorithm and a derivative‐free approach based on the simplex method, were different. This leads to differences in the agreement of model predictions vs experimental results. A more powerful and recent technique, genetic algorithm (GA), has been used to resolve this problem by minimizing a sum‐of‐square errors (SSE). Our tuned model parameters gave good agreement with experimental data. An SSE value of the order of 10^?4 is obtained in the present study over the SSE values of the order of 10^?2 obtained from earlier studies. Using this tuned model, multi‐objective optimization (MOO) of an isothermal fixed bed ESR reactor has been carried out using NSGA‐II to achieve the maximum hydrogen mole fraction in the product gas while simultaneously minimizing the mole fractions of the greenhouse gases, CO + CO₂. The maximum theoretical mole fraction of hydrogen obtained is 0.088 at 911.86 K vs 0.080 at 923 K, as observed experimentally. The more recent jumping gene adaptation of NSGA‐II, namely, NSGA‐II‐JG, was also tried to check if it can give more rapid convergence to the Pareto set. It is found that the present problem is far too simple, and the advantage of the JG adaptation is small.     

Thermal performance of artificially roughened solar air heaters

Artificially roughened solar air heaters have been analysed (Prasad and Saini, 1988) for fully developed turbulent flow and found to perform better both quantitatively and qualitatively compared to the smooth ones under the same operating conditions. Optimal thermo-hydraulic performance of such solar air heaters has been analysed (Prasad and Saini, 1991) and investigated (Prasad and Verma, 2000) for the maximum heat transfer and minimum pressure drop.This paper represents the experimental results on heat transfer and thereby thermal performance of artificially roughened solar air heaters for fully developed turbulent flow data collected under actual outdoor conditions. Such solar air heaters have been found to give considerably high value of collector heat removal factor (F_R), collector efficiency factor (F′) and thermal efficiency (η_th) as compared to the corresponding values of those of smooth collectors. In the range of the operating parameters investigated, the ratio of the respective values of the parameters F_R, F′ and η_th for the roughened collectors to the smooth collectors have been found to be 1.786, 1.806 and 1.842 respectively.     

Estimation of design parameters for thermal performance evaluation of box-type solar cooker

The paper presents a simple test procedure for determination of design parameters to predict the thermal performance of a box-type solar cooker. A series of out-door experiments were performed on the double-glazed solar cooker of aperture area 0.245 m² with a fibre body to obtain two figures of merit, F₁ and F₂. The necessary design parameters—optical efficiency, F′η_o and heat capacity, (MC)′ of the cooker are calculated using the linear regression analysis of experimental F₂ data for different load of water. Based on the experimental results, a correlation for F₂ as a function of quantity of water (load) is proposed. The close agreement between experimental and calculated F₂ indicates the validity of the correlation. The proposed procedure is then applied to predict the heating characteristic curves of the solar cooker for different load of water. The predicted heating characteristic curves are validated by comparing with the experimental data from a series of cooker testing experiments. The results of present study reveal that F′η_o and (MC)′ are the critical design parameters required for the prediction of thermal performance of the solar cooker.     

Simultaneous optical losses and current measurements in photovoltaic devices at variable angle of the incident light

In this work, the apparatus and the method for a simultaneous measurement of the optical losses and short-circuit current in a solar cell, at variable incidence angle of the light, is presented. The method has been applied to an n⁺/p c-Si cell with a polished surface. The investigation has been performed over an angular range from 8° to 80°, using a linearly polarized laser beam, either normally or parallelly polarized with respect to the incidence plane. The experimental curves of reflectance seem to be in a good agreement with the theoretical ones derived from the Fresnel equations. Since the measurements are performed inside an integrating sphere, a procedure has been developed to derive, from the total current I^tot, the calculated direct one, I_dirCal excluding contributions from the incoming light back-diffused to the cell under investigation; the results are compared with real direct-current measurement. Since with the proposed method both reflectance and current are measured for the same surface region and under identical illumination conditions, the results have been combined to get the internal spectral response of the n⁺/p c-Si polished surface solar cell.     

Effect of selective surface degradation on the performance of solar water heating systems

Selective surface often degrade in the field. Their solar absorptivity α_s and thermal emittance change with time in service by some amount, say Δα_s and Δ, from their starting values. It is important to quantify the effect this degradation has on the annual fraction solar F_s. A given relative change in F_s can be caused by different combinations of Δα_s, and Δ. In this paper we use computer simulation of solar domestic hot water systems to graph these combinations, in a plot of Δα_s versus Δ, for relative changes in F_s, of 10% and 5%. The slope and intercepts of this plot, which is found to be linear, are studied for their dependence on a wide range of solar system parameters, such as geographical location, collector area, and set point temperature. We find that the slope, and - for starting values of F_s less than about 0.5 - the intercepts, are relatively insensitive to the system parameters. We show that this result is consistent with a simple model. For F_s 0.5, the intercepts rise sharply with F_s, in a way that is strongly (and to some extent, only) dependent on the geographical latitude of location. These results have direct application to projecting the useful service life of a selective surface.     

Simulation of an efficient silicon heterostructure solar cell concept featuring molybdenum oxide carrier‐selective contact

Transition metal oxides/silicon heterocontact solar cells are the subject of intense research efforts owing to their simpler processing steps and reduced parasitic absorption as compared with the traditional silicon heterostructure counterparts. Recently, molybdenum oxide (MoO_x, x < 3) has emerged as an integral transition metal oxide for crystalline silicon (cSi)‐based solar cell based on carrier‐selective contacts (CSCs). In this paper, we physically modelled the CSC‐based cSi solar cell featuring MoO_x/intrinsic a‐Si:H/n‐type cSi/intrinsic a‐Si:H/n⁺‐type a‐Si:H for the first time using Silvaco technology computer‐aided design simulator. To analyse the optical and electrical properties of the proposed solar cell, several technological parameters such as work function and thickness of MoO_x contact layer, intrinsic a‐Si:H band gap, interface recombination, series resistance, and temperature coefficient have been evaluated. It has been shown that higher work function of MoO _x induces the formation of a favourable Schottky barrier height as well as an inversion at the front interface, stimulating least resistive path for holes. Utilising thinner MoO_x layer implies reduced tunnelling of minority charge carriers, thus enabling the device to numerically attain 25.33% efficiency. With an optimised interface recombination velocity and reduced parasitic absorption, the proposed device exhibited higher V_oc of 752 mV, J_sc of 38.8 mA/cm², fill‐factor of 79.0%, and an efficiency of 25.6%, which can be termed as the harbinger for industrial production of next‐generation efficient solar cell technology.     

Effects of auxiliary heater on annual performance of thermosyphon solar water heater simulated under variable operating conditions

A thermosyphon solar water heating system with electric auxiliary heater was simulated using the TRNSYS simulation program. Location of the auxiliary heater, inside the storage tank or connected in series between the system and the user, was studied using the TMY meteorological data for Los Angeles, California. Simulations were performed for two different water load temperatures (60 and 80°C) and for two types of daily hot water volumes (250 and 150 l). Four types of daily hot water consumption profiles were used in the present study, namely; the widely used Rand profile, continuous, evening and morning profiles. Also, the simulation is extended to cover the effects of thermal and optical properties of the flatplate collector and the volume of the storage tank. The results show that if water is drawn on a schedule corresponding to the Rand draw profile, the system operates with higher efficiency when the auxiliary heater is located in the storage tank than when the auxiliary heater is outside the storage tank. When operated with each of the other three draw schedules, however, better performance is achieved by locating the auxiliary heater outside the tank. The increase in solar fraction depends on the load profile and volume, temperature setting, as well as the quality of the collector and the storage tank volume. When the values of the parameters F_R(τα)_n and F_RU_L are changed from 0.8 and 16 kJ/h m²°C to 0.6 and 30 kJ/h m²°C, the solar fraction decreases by approximately 40–50%.     

Performance test of a box‐type solar cooker: effect of load on the second figure of merit

In this paper thermal performance test experiments for first figure of merit (without load) and second figure of merit (with load) of a box‐type solar cooker were conducted as per Bureau of Indian Standards. The values of second figure of merit (F₂) were determined for different loads of water and the results show that F₂ depends on the quantity of water loaded in a solar cooker. Therefore, it is recommended that the performance test method should specify the amount of water which is to be taken. Copyright © 1999 John Wiley & Sons, Ltd.     

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.

An investigation of optimum PV and wind energy system capacities for alternate short and long‐term energy storage sizing methodologies

The goal of this study is to find the optimal sizes of renewable energy systems (RES) based on photovoltaic (PV) and/or wind systems for three energy storage system (ESS) scenarios in a micro‐grid; (1) with pumped hydro storage (PHS) as a long‐term ESS, (2) with batteries as a short‐term ESS, and (3) without ESS. The PV and wind sizes are optimally determined to accomplish the maximum annual RES fraction (F_RES ) with electricity cost lower than or equal to the utility tariff. Furthermore, the effect of the use of battery and PHS on the electricity cost and F_RES are studied. A university campus on a Mediterranean island is selected as a case study. The results show that PV‐wind hybrid system of 8 MW wind and 4.2 MW PV with 89.5 MWh PHS has the highest F_RES of 88.0%, and the highest demand supply fraction as 42.6%. Moreover, the results indicate that the economic and technical parameters of RESs are affected significantly by the use of ESSs depending on the type and the capacity of both the RES and the ESS.     

Experimental study on conventional solar still integrated with inclined solar still under different water depth

This study primarily focuses on comparative experimental analysis on standalone conventional solar still (CSS), inclined solar still (ISS), and integrated conventional and inclined solar still (CSS‐ISS) for different parameters that affect the freshwater yield. For enhancing the freshwater yield only a few studies are available on still‐still integration. The present novel study provides a greater improvement in improving the freshwater yield by integrating ISS with CSS. This experimental work mainly concentrates on the importance of water depth (d _w) and mass flow rate of water ( m _w) in the solar still. Water depth inside the conventional still varied from 0.02 to 0.06 m whereas, water is constantly flown with a mass flow rate of 8.33 kg/hour in an ISS with baffles. The experimental result shows that the accumulated freshwater yield from CSS‐ISS, ISS, and CSS were 6.2, 5.04, and 4.24 kg, respectively. CSS‐ISS and ISS produced 46.23% and 18.87% higher productivity than the CSS. From the experimental investigation, it is also identified that the water temperature is significantly improved by 20% using integration as compared with CSS without integration under the same water depth of d _w = 0.02 m. The overall improvement in yield was higher in the case of CSS‐ISS. The deviations between experimental and theoretical values of yield from the conventional and modified solar still were in the range of ±7%.     

Construction and testing of a large-area CPC-collector and comparison with a flat plate collector

A 13.6 m² east-west aligned CPC-collector (compound parabolic concentrator) with flat absorbers, proposed for use in large-area applications, has been built and tested and compared with a flat plate collector. The performance of the CPC at a working temperature of 50°C over ambient can be described by F′η_O = 0.75 and F′U_L = 2.5 W m⁻² K⁻¹ while the flat plate collector is described by F′η_O = 0.80, and F′U_L = 3.3 W m⁻² K⁻¹. The large difference in heat loss coefficient is to a large degree explained by absorption of solar radiation in the reflectors in the CPC-collector. The incidence angle dependence of the optical performance of the two collectors showed a similar appearance. Both collector constructions are based on the LGB (long ground based) technology, which allows them to be built in large modules up to 170 m².     

Spray pyrolised thin film CdS homojunction solar cell with improved performance

CdS homojunction solar cell having an improved efficiency of 3% has been fabricated. This is achieved by the uniform distribution of copper into the n-CdS film by repeated thermal annealing of copper coated on the n-CdS. The ESCA analysis (Electron Spectroscopy for Chemical Analysis) gives the idea that no copper compounds like Cu_xS has not been formed. The depth profile of the sample showed that the copper distribution on the top layer of the CdS is uniform and there existed n-CdS layer below the p-CdS:Cu layer, free of copper atoms. The optical absorption studies on the sample revealed that there is a slight modification of optical band gap, for the copper diffused p-CdS. The spectral response curve for the cell has also been drawn.     

Investigation of thermal performance of solar air heater having roughness elements as a combination of inclined and transverse ribs on the absorber plate

An experimental investigation has been carried out to study the heat transfer and friction characteristics by using a combination of inclined as well as transverse ribs on the absorber plate of a solar air heater. The experimental investigation encompassed the Reynolds number (Re) ranges from 2000 to 14 000, relative roughness pitch (p/e) 3–8 and relative roughness height (e/D_h) 0.030. The effect of these parameters on the heat transfer coefficient and friction factor has been discussed in the present paper and correlations for Nusselt number and friction factor has been developed within the reasonable limits. A procedure to compute the thermal efficiency based on heat transfer processes in the system is also given and the effect of these parameters on thermal efficiency has been discussed.     

Heat transfer and friction characteristics of an equilateral triangular solar air heater duct using inclined continuous ribs as roughness element on the absorber plate

An experimental study has been carried out to determine the effect on the heat transfer and friction characteristics of an equilateral triangular solar air heater duct using inclined continuous ribs as roughness element on the absorber plate. The experimental study encompasses the range of Reynolds numbers from 5600 to 28,000, relative roughness height (e/D_h) 0.021–0.043, relative roughness pitch (p/e) 8–16 and angle of attack (α ) 30–60°. The duct has an aspect ratio (W/H) of 1.15. The effect of flow parameters and roughness parameters on heat transfer and friction factor is discussed. The thermohydraulic performance parameter has been determined for the given range of flow parameters and roughness parameters.