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[en] This paper deals with a numerical and experimental investigation of a daily solar storage system conceived and built in Laboratoire de Maitrise des Technologies de l Energie (LMTE, Borj Cedria). This system consists mainly of the storage unit connected to a solar collector unit. The storage unit consists of a wooden case with dimension of 5 m3 (5 m x 1m x 1m) filed with fin sand. Inside the wooden case was buried a network of a polypropylene capillary heat exchanger with an aperture area equal to 5 m2. The heat collection unit consisted of 5 m2 of south-facing solar collector mounted at a 37 degree tilt angle. In order to evaluate the system efficiency during the charging period (during the day) and discharging period (during the night) an energy and exergy analyses were applied. Outdoor experiments were also carried out under varied environmental conditions for several consecutive days. Results showed that during the charging period, the average daily rates of thermal energy and exergy stored in the heat storage unit were 400 and 2.6 W, respectively. It was found that the net energy and exergy efficiencies in the charging period were 32 pour cent and 22 pour cent, respectively. During the discharging period, the average daily rates of the thermal energy and exergy recovered from the heat storage unit were 2 kW and 2.5 kW, respectively. The recovered heat from the heat storage unit was used for the air-heating of a tested room (4 m x 3 m x 3 m). The results showed that 30 pour cent of the total heating requirement of the tested room was obtained from the heat storage system during the whole night in cold seasons
[en] In order to increase energy security, production of renewable energies has been highly promoted by governments around the world in recent years. The typical base of various policy instruments used for this purpose is gross energy output of renewable energy. However, we show that basing policy instruments on gross energy output will result in problems associated with energy waste, economic inefficiency, and negative environmental effects. We recommend using net energy output as the base to apply price or quantity measures because it is net energy output, not gross energy output, which contributes to energy security. The promotion of gross energy output does not guarantee a positive amount of net energy output. By basing policy instruments on net energy output, energy security can be enhanced and the above mentioned problems can be avoided.
[en] A district space heating and cooling system using geothermal energy from bearing piles was designed in Shanghai and will be installed in two years before 2010. This paper describes the pile-foundation heat exchangers applied in an energy pile system for an actual architectural complex in Shanghai, 30% of whose cooling/heating load was designed to be provided by a ground-source heat pump (GSHP) system using the energy piles. In situ performance tests of heat transfer are carried out to figure out the most efficient type of energy pile and to specify the design of energy pile system. Numerical investigation is also performed to confirm the test results and to demonstrate the medium temperature variations along the pipes. The averaged heat resistance and heat injection rate of different types of energy piles are calculated from the test and numerical results. The effect of pile type, medium flow rate and inlet temperature on thermal performance is separately discussed. From the viewpoint of energy efficiency and adjustability, the W-shaped underground heat exchanger with moderate medium flow rate is finally adopted for the energy pile system
[en] The development of microsatellites requires the development of engines to modify their orbit. It is natural to use solar energy to drive such engines. For an unlimited energy source the optimal thruster must use a minimal amount of expendable material to minimize launch costs. This requires the ejected material to have the maximal velocity and, hence, the ejected atoms must be as light as possible and be ejected by as high an energy density source as possible. Such a propulsion can be induced by pulses from an ultra-short laser. The ultra-short laser provides the high-energy concentration and high-ejected velocity. We suggest a microthruster system comprised of an inflatable solar concentrator, a solar panel, and a diode-pumped fiber laser. We will describe the system design and give weight estimates.
[en] A novel nuclear astrophysics facility, CLAIRE (Center for Low Energy Astrophysics and Interdisciplinary REsearch), is being designed at Lawrence Berkeley National Laboratory to address the need for precise fusion cross section measurements at near-solar energies (∼20 keV). At these low energies, fusion cross sections decrease exponentially with energy and are expected to approach femtobarn levels or less. In order to measure such small cross sections, the CLAIRE facility will incorporate a versatile accelerator capable of transporting high current (>100 mA), low energy (50-300 keV) ion beams with a tight focus (<1 cm) to a cooled, dense gas-jet target. The conceptual design for this accelerator is discussed, and simulations of both beam extraction and transport are presented
[en] In today's electricity generation system, different resources make different contributions to the electricity grid. This fact sheet illustrates the roles of distributed and centralized renewable energy technologies, particularly solar power, and how they will contribute to the future electricity system. The advantages of a diversified mix of power generation systems are highlighted.
[en] The adoption of an innovation is partly dependent on the consumers' perception of the product attributes, starting with the 'relative advantage' a product may have over another existing product, and also include issues of compatibility, complexity, observability and trialability. Using diffusion of innovations theory as a conceptual framework, this paper describes a case study that investigated the innovation adoption process that a group of identified potential adopters of domestic solar thermal systems stated they would follow. Data was generated from the results of a postal survey to a group of 43 defined innovators and a group of 350 assumed 'early majority', pragmatic consumers. The survey results showed that while the pragmatic customers did follow the process as theorised in diffusion theory, the innovators disregarded the observability attributes of the innovation and went ahead with implementation without having seen the products beforehand. The group of innovators was also split in their opinion that 'complexity' may be a limiting factor. There were differences in the pragmatic group between certain demographic sub groups. Conclusions are drawn on how the findings may impact marketing activities
[en] This paper discusses some energy scenarios for photovoltaic applications in Brazil engendered by using SWERA database in order to demonstrate its potential for feasibility analysis and application in the energy planning for electricity generation. It discusses two major different markets: hybrid PV-Diesel installations in mini-grids of the off-grid Brazilian electricity system in the Amazon region, and grid-connected PV in urban areas of the interconnected Brazilian electricity system. The potential for using PV is huge, and can be estimated in tens to hundreds of MWp in the Amazon region alone, even if only a fraction of the existing Diesel-fired plants with a total installed capacity of over 620 MVA would fit to run in an optimum Diesel/PV mix. Most of the major cities in Brazil present greater electricity demand in summertime with the demand peak happening in the daytime period. This energy profile match the actual solar resource assessment provided by SWERA Data Archive, enabling grid-connected PV systems to provide an important contribution to the utility's capacity
[en] The North Africa climate is dry and warm with annual mean temperature from 15 degree centigrade to 25 degree centigrade, with a temperature difference of 20 degree centigrade between the coldest and warmest month. Heating is needed during the short winter and there is a large cooling demand during the long summer. Since the undisturbed ground temperature is equal to the annual mean air temperature, the ground is warmer than the air during the winter and colder than air during summer. This is what is required for the direct use of the ground for heating and cooling. In such systems, ground coupled heating and cooling systems, and also in storage systems, Underground Thermal Energy Storage (UTES), some kind of underground duct (PIPE) system is used to inject or extract heat from the ground. Thermal energy is then stored and recovered by heating and cooling of the ground, while the ducts are the heat exchangers with the system. The duct system could be placed horizontally or vertically (e.g. in boreholes) in the ground. In many cases heat pumps or cooling machines are included in the systems but in favourable cases, such as in the North African climate, the ground can be used directly for heating and cooling. then, only a circulation pump is used to pump water through the underground duct system with high efficiencies. Such systems can also be used for thermal energy storage, during shorter periods (diurnal) or even between the seasons. In September 2005 Sebha University and Luleu University of Technology started a Libyan Swedish collaboration to develop and implement these systems for the North African climate. Sweden has considerable experience in ground coupled systems, theoretically and practically, and there are presently more than 300.000 systems in operation in Sweden, mainly for heating. Most of these are small-scale heating systems for singe-family houses but during the last decade several hundred large-scale systems have been built for heating and cooling of commercial buildings. The ongoing collaboration will consider local traditions and systems for cooling and the aim is to combine such old methods with ground coupled heating and cooling systems. This PhD work includes simulation, testing, and the design of this system for Libya. Planned ongoing work is outlined in this paper.(Author)