Impact of load profile and collector technology on the fractional savings of solar domestic water heaters under various climatic conditions

This paper investigates the influence of the domestic hot water load profiles and the collector's technology (Flat Plate FPC, Evacuated Tube ETC and Compound Parabolic CPC) on the performance of forced circulation solar water heaters operating under various climatic conditions. For this end, a typical single family house composed of five occupants located in Morocco was considered. It is found that, the solar fraction can reach annual average values of 80% especially in areas with high solar energy potential. For a fixed consumption profile, the simulations showed that the installations with FPC, ETC and CPC can consume about 1644, 1199 and 1481 kWh/year of auxiliary energy, respectively. Moreover, it is found that, adapting the consumption profile, can save approximately 43 kWh/year for FPC, 13 kWh/year for ETC and about 29 kWh/year for CPC of energy.     

Exergy based performance evaluation of latent heat thermal storage system: A review

Phase change material (PCM) based latent heat thermal storage (LHTS) systems provide an attractive solution to bridge the gap between energy source and demand, if source is intermittent and time dependent. The optimization of LHTS systems is not necessarily on the basis of performance study through energy analysis, but on the basis of exergy based performance study. The exergy based performance evaluation and subsequent optimization of LHTS units have been a growing interest among the researchers in recent years. This can be seen through the various works reported in the literature. This paper reviews the various procedures adopted for the exergy based performance evaluation of LHTS units. The influence of operating and design parameters on the exergy stored/retrieved and thus, on the optimization is addressed as a main aspect. The need of exergy analysis for the comparative evaluation of LHTS systems with performance enhancement techniques is emphasized. Thermoeconomics methods applicable to LHTS systems are also presented in this paper.     

Multi-objective optimization of a grid-connected PV system for a public building: Faculty of Sciences and Technology at Pau

Clean Technologies and Environmental Policy - In this paper, an optimal sizing of a grid-connected PV system to accommodate the load demands of a public building (i.e., Faculty of Sciences and...     

Prototype Combined Heater/Thermoelectric Power Generator for Remote Applications

This study presents a prototype thermoelectric generator (TEG) developed for remote applications in villages that are not connected to the electrical power grid. For ecological and economic reasons, there is growing interest in harvesting waste heat from biomass stoves to produce some electricity. Because regular maintenance is not required, TEGs are an attractive choice for small-scale power generation in inaccessible areas. The prototype developed in our laboratory is especially designed to be implemented in stoves that are also used for domestic hot water heating. The aim of this system is to provide a few watts to householders, so they have the ability to charge cellular phones and radios, and to get some light at night. A complete prototype TEG using commercial (bismuth telluride) thermoelectric modules has been built, including system integration with an electric DC/DC converter. The DC/DC converter has a maximum power point tracker (MPPT) driven by an MC9SO8 microcontroller, which optimizes the electrical energy stored in a valve-regulated lead–acid battery. Physical models were used to study the behavior of the thermoelectric system and to optimize the performance of the MPPT. Experiments using a hot gas generator to simulate the exhaust of the combustion chamber of a stove are used to evaluate the system. Additionally, potential uses of such generators are presented.     

Second law analysis of latent thermal storage for solar system

A theoretical model has been developed for analysis and optimization of the solar system using phase change material (PCM). The later consists of a solar air heating collector coupled with a cylindrical storage tank which contains spherical capsules filled with a PCM. Energy and exergy analyses are carried out to understand the behavior of the system using single PCM or multiple PCMs. Numerical results show that the performance of the latent thermal storage system can be ameliored by the judicious choice of the melting temperature of the PCM.     

Numerical study of thermoelectric power generation for an helicopter conical nozzle

This paper investigates the electric power extractable from an helicopter conical nozzle equipped with thermoelectrical modules. The thermoelectric nozzle is heated by the final exhaust gas from helicopter turbine and cooled by oil. A computer model has been developed to simulate the performance of the thermoelectric system. Results were obtained for various operating conditions showing that the electrical power produced in real operating conditions is significant but currently insufficient if we consider the weight-to-power ratio. The numerical model is also used to optimize the electric power showing a good potential for the future.     

Crystallization of PCMs inside an emulsion: Supercooling phenomenon

Heat transfer characteristics during crystallization and melting of the phase change material (PCM) dispersed inside an emulsion are investigated theoretically and experimentally. The dispersed PCMs are hexadecane, octadecane and water. The crystallization and melting processes are not symmetrical because of the supercooling phenomenon induced by the smallness of the emulsion droplet sizes. Nucleation laws are used to simulate the supercooling phenomenon. Energy analysis is carried out to understand the behavior of the emulsion using two paraffins (octadecane and hexadecane). The effects of different parameters such as the mass fraction of PCM and the stabilization temperature on thermal behavior of emulsion are also analyzed.     

PCM storage for solar DHW: From an unfulfilled promise to a real benefit

The present numerical study is concerned with the use of phase change materials (PCMs) in solar-based domestic hot water (DHW) systems. During the last decade, the majority of the studies related to that issue concluded that the recourse to PCMs-based storage units was quite promising in order to enhance the overall performances of solar-based DHW systems. One recently interesting published numerical study (Talmatsky and Kribus, 2008), suggested though that this beneficial impact is not guaranteed since the gains observed over the day period brought by the presence of PCMs to store the solar energy were compensated by the losses undergone by the storage tank during the night. The origin of this absence of any beneficial impact of the use of PCMs in a DHW system has to be clearly understood in order to reconcile studies which indicated apparently contradictory findings. In that framework, the goal of the present contribution is to analyze the conditions under which such an absence of advantage of the use of PCMs in a DHW system were obtained in order to propose some possibilities of improvement for demonstrating the interest in using PCMs in solar-based DHW systems. Thus, the mathematical model based on the one reported in Talmatsky and Kribus (2008) is considered. This model describes the heat storage tank with PCM, collector, pump, controller and auxiliary heater. Realistic environmental conditions and typical end-user requirements are imposed.     

Study of a TE (thermoelectric) generator incorporated in a multifunction wood stove

Replacing traditional open fire stoves, characterized by low efficiency, with improved ones is an important challenge for developing countries. Adding TE (thermoelectric) generators can provide electricity that permits not only the use of an electric fan increasing the ratio air to fuel to achieve a complete combustion in the stoves but also the satisfaction of basic needs: light, phones and other electronic devices. A review of existing TE generators for stoves is presented. To test the TE modules, an experimental device has been carried out in our laboratory where a gas heater simulates the stove. The generator set-up is described including the switching electric regulator that stabilizes the fluctuating voltage from the modules and stores the energy in a battery. The performance of the generator mostly depends on the heat transfer through the modules and especially on the thermal contact resistances. First experiments show the influence of the pressure on these resistances. Then a study of temperatures and electrical power measurements is compared to a theoretical analysis using TE and heat transfer equations. The very reasonable value of the obtained contact resistances shows that the mechanical design of the generator is almost optimized. The TE generator has produced up to 9.5 W.