Showing papers on "Solar energy published in 2003"

A stable quasi-solid-state dye-sensitized solar cell with an amphiphilic ruthenium sensitizer and polymer gel electrolyte.

Abstract: Dye-sensitized nanocrystalline solar cells (DSC) have received considerable attention as a cost-effective alternative to conventional solar cells. One of the main factors that has hampered widespread practical use of DSC is the poor thermostability encountered so far with these devices. Here we show a DSC with unprecedented stable performance under both thermal stress and soaking with light, matching the durability criteria applied to silicon solar cells for outdoor applications. The cell uses the amphiphilic ruthenium sensitizer cis-RuLL'(SCN)(2) (L = 4,4'-dicarboxylic acid-2,2'-bipyridine, L' = 4,4'-dinonyl-2,2'-bipyridine) in conjunction with a quasi-solid-state polymer gel electrolyte, reaching an efficiency of >6% in full sunlight (air mass 1.5, 100 mW cm(-2)). A convenient and versatile new route is reported for the synthesis of the heteroleptic ruthenium complex, which plays a key role in achieving the high-temperature stability. Ultramicroelectrode voltammetric measurements show that the triiodide/iodide couple can perform charge transport freely in the polymer gel. The cell sustained heating for 1,000 h at 80 degrees C, maintaining 94% of its initial performance. The device also showed excellent stability under light soaking at 55 degrees C for 1,000 h in a solar simulator (100 mW cm(-2)) equipped with a ultraviolet filter. The present findings should foster widespread practical application of dye-sensitized solar cells.

Heat Transfer Analysis and Modeling of a Parabolic Trough Solar Receiver Implemented in Engineering Equation Solver

Abstract: This report describes the development, validation, and use of a heat transfer model implemented in Engineering Equation Solver. The model determines the performance of a parabolic trough solar collector's linear receiver, also called a heat collector element. All heat transfer and thermodynamic equations, optical properties, and parameters used in the model are discussed. The modeling assumptions and limitations are also discussed, along with recommendations for model improvement.

Superior radiation resistance of In1-xGaxN alloys: Full-solar-spectrum photovoltaic material system

Abstract: High-efficiency multijunction or tandem solar cells based on group III–V semiconductor alloys are applied in a rapidly expanding range of space and terrestrial programs. Resistance to high-energy radiation damage is an essential feature of such cells as they power most satellites, including those used for communications, defense, and scientific research. Recently we have shown that the energy gap of In1−xGaxN alloys potentially can be continuously varied from 0.7 to 3.4 eV, providing a full-solar-spectrum material system for multijunction solar cells. We find that the optical and electronic properties of these alloys exhibit a much higher resistance to high-energy (2 MeV) proton irradiation than the standard currently used photovoltaic materials such as GaAs and GaInP, and therefore offer great potential for radiation-hard high-efficiency solar cells for space applications. The observed insensitivity of the semiconductor characteristics to the radiation damage is explained by the location of the band edge...

Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field

Abstract: An evaluation was carried out to investigate the feasibility of utilizing a molten salt as the heat transfer fluid (HTF) and for thermal storage in a parabolic trough solar field to improve system performance and to reduce the levelized electricity cost. The operating SEGS (Solar Electric Generating Systems located in Mojave Desert, California) plants currently use a high temperature synthetic oil consisting of a eutectic mixture of biphenyl/ diphenyl oxide. The scope of this investigation included examination of known critical issues, postulating solutions or possible approaches where potential problems exist, and the quantification of performance and electricity cost using preliminary cost inputs. The two leading candidates were the so-called solar salt (a binary salt consisting of 60% NaNO 3 and 40% KNO 3 ) and a salt sold commercially as HitecXL (a ternary salt consisting of 48% Ca(NO 3 ) 2 , 7% NaNO 3 , and 45% KNO 3 ). Assuming a two-tank storage system and a maximum operation temperature of 450°C, the evaluation showed that the levelized electricity cost can be reduced by 14.2% compared to a state-of-the-art parabolic trough plant such as the SEGS plants. If higher temperatures are possible, the improvement may be as high as 17.6%. Thermocline salt storage systems offer even greater benefits.

Solar technologies for buildings

Abstract: Preface. Abbreviations in the Text. 1. Solar energy use in buildings. Energy consumption of buildings. Meeting requirements by active and passive solar energy use. 2. Solar irradiance. Extraterrestrial solar irradiance. The passage of rays through the atmosphere. Statistical production of hourly irradiance data records. Global irradiance and irradiance on inclined surfaces. Shading. 3. Solar thermal energy. Solar-thermal water collectors. Solar air collectors. 4. Solar cooling. Open cycle desiccant cooling. Closed cycle adsorption cooling. Absorption cooling technology. 5. Grid connected photovoltaic systems. Structure of grid connected systems. Solar cell technologies. Module technology. Building integration and costs. Energy production and the performance ratio of PV systems. Physical fundamentals of solar electricity production. Current-voltage characteristics. PV performance with shading. Simple temperature model for PV models. System engineering. 6. Thermal analysis of building-integrated solar components. Empirical thermal model of building-integrated photovoltaics. Energy balance and stationary thermal model of ventilated double facades. Building-integrated solar components (U- and g-values). Warm-air generation by photovoltaic facades. 7. Passive solar energy. Passive solar use by glazings. Transparent themal insulation. Heat storage by interior building elements. 8. Lighting technology and daylight use. Introduction to lighting and daylighting technology. Solar irradiance and light flux. Luminance and illuminance. Sky luminance intensity models. Light measurements. Daylight distribution in interior spaces. References. Index.

Concentrating solar energy receiver

Abstract: There is disclosed herein a concentrating solar energy receiver comprising a primary parabolic reflector having a center and a high reflectivity surface on a concave side of the reflector and having a focal axis extending from the concave side of the reflector and passing through a focal point of the primary parabolic reflector, and a conversion module having a reception surface wherein the reception surface is spaced from the focal point by a predetermined distance and disposed to receive a predetermined cross section of radiant solar energy reflected from the concave side of the primary parabolic reflector for conversion to electrical energy in the conversion module. In one aspect, the conversion module includes a reception surface comprising a planar array of at least one photovoltaic solar cell. In another aspect, the conversion module includes a reception surface coupled to a thermal cycle engine. The mechanical output of the thermal cycle engine drives an electric generator.

PCM-module to improve hot water heat stores with stratification: first tests in a complete solar system

Abstract: The final goal of this work was to bring the idea to improve hot water heat stores with stratification by inserting PCM-modules at the top closer to application in the market. Therefore, in contrast to previous work, tests were performed under real operating conditions in a complete solar heating system that has been constructed at the University of Lleida, Spain. Furtheron, a new PCM graphite compound with optimized thermal properties was used. The results of this work show that only 3 kg of the PCM compound in a 146 liter storage tank are enough to compensate for a heat loss of 3-4oC in 32 liters of water in the top of the storage. This is equivalent to the cool down in the storage without PCM module over a period of about 10 hours. Reheating of cold water after a fast cool down (unloading) of the storage was in 10-15 minutes. This is considered to be fast enough for most applications. 1. INTRODUCTION Thermally stratified storage tanks are an effective heat storage technique that is widely used in energy conservation, for example solar energy systems, and load management applications. If water of different temperatures is contained in a tank, thermal stratification arises because a temperature variation in the water leads to a density variation and warm and cold water are separated by means of gravitational effect, hot on top, cold at the bottom. The stratification phenomena can be employed to improve the efficiency of storage tanks. Heat at an intermediate temperature, not high enough to heat the top layer, can still be used to heat the lower, colder layer. In ordinary hot water heat stores the water mixes and supply of water at an intermediate temperature can lower the maximum temperature to a level not useful any more. In contrast, the temperature change in the top layer of a hot water heat store with stratification is usually small as mixing is avoided, and is held as close as possible at or above the temperature for usage. The temperature change at the bottom however can be large. Latent heat storage with phase change materials (PCM) gives a high heat storage density at small temperature difference, as it is the case in the top layer of a hot water heat store with stratification. This allows a favorable combination of both technologies. The low price and high power by direct discharge of the water as storage medium remain, while small amounts of PCM significantly increase the storage capacity of the top layer and improve performance of the storage for special load profiles.

Solar energy materials

Abstract: This paper introduces materials for energy efficiency and solar energy utilization and discusses some current trends for basic research and development. Most of the materials involve thin surface coatings. Overviews are given for solar absorber surfaces, transparent infrared reflectors and transparent conductors, large-area chromogenics for transmittance control in “smart windows”, and transparent convection-suppressing materials, whereas solar cell materials are not included. The paper also treats a few examples of specific coatings that are presently being investigated; data are given for angular-selective transmittance through porous Cr films with oblique columnar microstructure, transparent and conducting non-stoichiometric SnO2 films, and chromogenic effects in Li-intercalated VO2 films.

System and method for generation of electricity and power from waste heat and solar sources

Abstract: Recovery of electric power from low-grade waste heat/solar energy, comprising a closed-cycle charged refrigerant loop. Pressurized refrigerant fluid is pumped at ambient temperature through a heat exchanger connected to a waste heat/solar source to extract heat energy during conversion to a high pressure gas. Heated/pressurized refrigerant gas is inlet into an expander to power an output shaft during the expansion of the fluid to a cooled gas at approximately 0 psig. Cooled gaseous refrigerant is condensed to a liquid at low pressure and ambient temperature, and recycled under pressure to the heat exchanger. The expander is a reverse-plumbed gas compressor; the pressurized, hot refrigerant gas is inlet at what is ordinarily its outlet, and the normal inlet becomes the expander end. The refrigerant gas mass flow pressure/temperature drop spins the expander shaft for direct mechanical power take-off, or coupling to a synchronous or inductive generator to produce electricity.

Solar collector and method

Abstract: An apparatus and method for collecting solar energy are provided. The apparatus is a trough-type solar collector having one or more mirrors and lenses for directing solar radiation toward a receiver configured to receive a heat transfer fluid therein. The amount of solar radiation directed toward the receiver can be controlled by adjusting one or more of the mirrors and/or lenses or by adjusting a shade. Thus, the collector can direct different amounts or solar radiation toward the receiver, thereby selectively heating the receiver at different rates, e.g., to preheat the receiver, to heat fluid in the receiver for power generation, or to thaw solidified fluid in the receiver. Subsequently, the heated fluid can be used to generate steam and/or electricity.

Burning Buried Sunshine: Human Consumption of Ancient Solar Energy

Abstract: Fossil fuels developed from ancient deposits of organic material, and thus can be thought of as a vast store of solar energy from which society meets >80% of its current energy needs. Here, using published biological, geochemical, and industrial data, I estimate the amount of photosyntheti- callyfixed and stored carbon that was required to form the coal, oil, and gas that we are burning today. Today's average U.S. Gallon (3.8 L) of gasoline required approximately 90 metric tons of ancient plant matter as precursor material. The fossil fuels burned in 1997 were created from organic matter containing 44 × 10 18 gC , which is>400 times the net primary productivity (NPP) of the planet's current biota. As stores of ancient solar energy decline, humans are likely to use an increasing share of modern solar resources. I conservatively estimate that replacing the energy humans derive from fossil fuels with energy from modern biomass would require 22% of terrestrial NPP, increasing the human appropriation of this resource by ∼50%.

Status and outlook of solar energy use in Pakistan

Abstract: Pakistan is an energy deficient country, where a large fraction of the population still does not have access to modern day energy services such as electricity. This is due to very limited fossil fuel resources and poor economy, which restrains the import of fossil fuels on a large scale. To overcome energy shortage, Pakistan needs to develop its indigenous energy resources like hydropower, solar and wind. Pakistan lies in an area of one of the highest solar insolation in the world. This vast potential can be exploited to produce electricity, which could be provided to off-grid communities in the northern hilly areas and the southern and western deserts. Applications other than electricity production such as solar water heaters and solar cookers also have vast applications. All this will help in both reducing the import of fossil fuels and dependency of people on fuel wood, which in turn will provide some respite for the dwindling forest reserves of Pakistan. Accordingly, the status and outlook of solar energy use in Pakistan is discussed in this paper. In addition, the role of R&D organizations in the promotion of solar energy technologies in Pakistan is also presented including a description of some proposed projects. It is concluded that the current infrastructure has not been able to advance the status of solar energy of Pakistan. Significant efforts are needed to effectively utilize this cheap renewable energy source.