Hybrid solar and electrically controlled transmission of light filters

The investigations show that it is possible to develop hybrid light filters which could be switched by solar as well as by electrical energy. The light filters are based on thermotropic gels changing their transmission depending on the concentration of the cross-linker from 60% to 80% to 1% in the temperature range 29–36°C. Detailed investigations of the electrical switching process show that the switching times significantly decrease with increasing thickness of the tin-doped indium oxide (ITO) used as transparent electrodes. The switching times could be varied from 3 to over 50 min. Furthermore the required wattage for the switching process significantly decreases with increasing thickness of the ITO-layers. A gel layer having a thickness of 2 mm is quite enough to realize changes in the transmission from about 62% to 1%. Comparable results were obtained for light filters having a size of either 25 or 180 cm², respectively. Therefore, it should be possible to transfer these results to light filters having a size of 0.5-1 m².     

Design and analysis of low-reflection grating microstructures for a solar energy absorber

The problem of calculating the photo-induced current in an n⁺p junction solar cell with a microstructure grating on the top is formulated. For the case where useful absorption regions lie below the grating a closed solution of the problem is obtained, in which the carrier photo-generation rate is calculated using a full-vector electromagnetic simulation technique. Two structures: filled lamellae grating and overlayer, and filled V-groove grating and overlayer are considered. The first structure is optimized with respect to the integral photo-current and the second with respect to reflection loss. Both optimized structures are much less reflective and more efficient than an optimized flat-surface Si–SiO₂ layer cell.     

Effect of compact structure on the phase transition in the oxides derived Cu2ZnSnSe4 thin films

Cu₂ZnSnSe₄ (CZTSe) films were prepared by selenization of oxides nanoparticles. A novel densification method was performed to improve the grain size and morphology of the CZTSe films. From absorption spectroscopy measurement, it was also found that the compressed CZTSe films showed Kesterite structure with a band gap of 0.92 eV, while the untreated CZTSe films showed partially disordered Kesterite structure with a band gap of 0.86 eV. The phase transition during the selenization of oxides nanoparticles is affected significantly by the compact density. The nucleation and growth of Kesterite phase is considered to be facilitated by the mass transfer around the particle contacts. The different characterization techniques show that the dense CZTSe layer with very large grain size can be achieved by using compression method.     

Thermal utilisation of solar energy : Croatian National Energy Program SUNEN, 1998 – 2010

In the paper, thermal use of solar energy as well as prospects and problems of its utilisation in Croatia have been given. The National Solar Energy Program, SUNEN, has been established to stimulate the usage of solar energy. The main goals of the program are the assessment of technical and economically viable solar potential in order to define real objectives and tasks to provide use of exploitable indigenous clean and renewable energy potential. The Program addresses benefits, the most promising solar applications and solar potential. Much attention has been given to identification of obstacles and barriers in the process of solar technology dissemination. SUNEN is an initiative to increase solar energy use and to become more compatible with the present renewable energy sources policy in EU and Mediterranean countries. The program proposes twelve different types of thermal solar energy systems, which could be multiplied up to 28 000 installations until the year 2010 with annual heat recovery of approximately 1,5 TWh (5,4 PJ).     

Solar ICS systems with two cylindrical storage tanks

Two types of ICS solar water heaters designed, constructed and tested. The systems consist of two cylindrical storage tanks, which are connected in series and are horizontally incorporated in a stationary asymmetric CPC type mirror. The efficient operation of the system is due to the thermal losses suppression of the two inverted cylindrical surfaces and the effective use of the two tanks during sunshine period. Low cost and durable materials are used to construct the systems. The mean daily efficiency and the thermal performance of the hot water storage during night are calculated from outdoor experimental data. The results show that the proposed ICS systems are efficient and suitable for practical use as DHW systems.     

Theoretical study and practical application of the capillary film solar distiller

In the south of Algeria, to supply sufficient fresh water for the population, desalination is necessary because water resources (underground and geothermal) are brackish.This paper presents the theoretical study and the results of experiments carried out with a capillary film multi-effect distiller installed in the south of Algeria (in a village near Touggourt, where the temperature of the groundwater is about 65°C at the source). The name of this device is DIFICAP (stiller with a lm in illary motion).The aim of our study is to improve the efficiency of this distiller. The research and development of this desalination process is carried out under the following aspects: modelisation of heat and mass transfer, experimentation under direct solar radiation in South Algeria and technical development to aim to optimize the efficiency of this distiller.The theoretical and experimental results show that the efficiency of this distiller increases when the temperature of the brackish water, the intensity of the solar radiation and the number of stages increase.     

Formation of CuIn(S,Se)2 thin film by thermal diffusion of sulfur and selenium vapours into Cu–In alloy within a closed graphite container

The formation of CuIn(S,Se)₂ thin films by thermal diffusion of sulfur (S) and selenium (Se) vapours into co-sputtered Cu–In alloy within a closed-space graphite container is reported. All films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Four-point-probe and hot-probe measurements. Cu–In alloy films with composition varying from Cu-rich to In-rich were deposited. The synthesized In-rich films yielded CuIn₅(S,Se)₈ spinel compound which gradually transformed into a single phase CuIn(S,Se)₂ as the film composition approached the Cu-rich region. The morphology of the CuIn₅(S,Se)₈ was found to differ from the stoichiometric and Cu-rich CuIn(S,Se)₂ as observed from SEM. EDX composition analysis of the films showed a Cu/In ratio varying from 0.36 to 1.54 and a (S+Se)/(Cu+In) varying from 0.97 to 1.32. The amount of S incorporated in the films was found to differ with changes in the composition. The resistivity of the films ranged between 10⁻¹ and 10⁷ Ω cm and it strongly followed the change in the alloy film composition.     

Modeling and Testing of a Thermosiphon Solar Air-Heater

A flat-plate solar air-heater was analysed and tested. A model was proposed to predict air mass-flow rate and useful energy collection. The model snowed good agreement with the experimental data. The system performance was characterised with wide scatter of data and low efficiency. However, the low efficiency is tolerated for the sake of simplicity and economic considerations.     

Summary of the Closing Session

Plausible costs of photovoltaic power plants of concentration are presented. Costs are based as much as possible on the recent experience of solar thermal plants. Efficiencies, on the existing world experience of PV power plants. The result is that the costs of concentrating photovoltaic plants should be of 0.08 ECUs/ kWh, about 1/3 of that of flat module plants, and of the same order of magnitude, even lower, than those attributed to solar thermal plants of present technology.

For the future, high concentration systems based on Si or tandem cells seem to be the most promising, also in the range of costs of the advanced solar thermal plants.     

INSTANTANEOUS THERMAL LOSS EFFICIENCY FACTOR FOR SUMMER GREENHOUSE

In this technical note, an attempt has been made to develop an analytical expression for an instantaneous thermal loss efficiency factor for a summer greenhouse. The analysis is based on energy balance equations for each component of the greenhouse in a steady state condition. Effect of design and climatic parameters have also been taken into account. An ideal condition has been achieved analytically, for a best summer greenhouse. The nature of characteristic curve obtained by the present model has been compared with the experimental results obtained by others.