Showing papers on "Solar power published in 2008"

Advanced Material Concepts for Luminescent Solar Concentrators

Abstract: Sunlight that is incident on the front surface of a luminescent solar concentrator (LSC) is absorbed and subsequently re-emitted by luminescent materials. The resulting luminescence is transported to the edge of the LSC sheet and concentrated onto photovoltaic devices. Despite its potential for generating low-cost solar power, LSC development faces numerous challenges, the majority of which are related to the luminescent materials used in their design. Earlier LSC research focused on organic dyes, and while several of the shortcomings with these materials have been solved over time, some major challenges remain. This paper outlines the loss mechanisms that limit conversion efficiency of the LSC and highlights the role that advanced materials can play. Losses include nonunity fluorescence quantum yield (FQY), reabsorption losses, incomplete utilization of the solar spectrum, and escape cone losses. Long-term photostability is also discussed as it is essential for commercial feasibility of any solar technology. Past and current techniques, designed to reduce these losses, are described and their experimental achievements are discussed.

Direct Growth of Highly Mismatched Type II ZnO/ZnSe Core/Shell Nanowire Arrays on Transparent Conducting Oxide Substrates for Solar Cell Applications

Abstract: A number of nanometer-scale photovoltaic (PV) concepts based on semiconductor nanowires have been developed or proposed in recent years, with either inorganic/organic hybrid or all-inorganic approaches. The quasi-one-dimensional (quasi-1D) structure is perhaps the optimized choice for optoelectronic devices such as solar cells and photodetectors, because it allows for maximal advantage to be taken of reduced dimensionality whilst retaining the last and only needed conduction channel. Besides the possibility of exploring quantum effects at the nanoscopic scale, the quasi-1D system could be superior to the bulk material even at the mesoscopic scale, where the lateral size falls below the carrier diffusion length, for instance, by reducing the nonradiative recombination and carrier scattering loss through elimination of the unnecessary lateral transport and the resulting recombination loss. Additionally, a nanowire array constitutes a natural architecture, such as a photonic crystal, for light trapping. The charge separation of the electron and hole is a key step in the generation of solar power in a PV device. In a conventional solar cell, it is typically achieved by a planar p–n homojunction along the path of the current flow or longitudinally. In nanometer-architecture PV devices, however, the charge separation is often facilitated by a type II or staggered energy alignment of a heterojunction, constructed from two materials for which both the valance and conduction bands of one component lie lower in energy than the corresponding bands of the other component. Such heterojunctions have been intensively investigated for solar cell applications, including dyesensitized solar cells (DSSCs), quantum-dot-sensitized solar

Schottky-quantum dot photovoltaics for efficient infrared power conversion

Abstract: Planar Schottky photovoltaic devices were prepared from solution-processed PbS nanocrystal quantum dot films with aluminum and indium tin oxide contacts. These devices exhibited up to 4.2% infrared power conversion efficiency, which is a threefold improvement over previous results. Solar power conversion efficiency reached 1.8%. The simple, optimized architecture allows for direct implementation in multijunction photovoltaic device configurations.

Design, Modeling, and Capacity Planning for Micro-solar Power Sensor Networks

Abstract: This paper describes a systematic approach to building micro-solar power subsystems for wireless sensor network nodes. Our approach composes models of the basic pieces - solar panels, regulators, energy storage elements, and application loads - to appropriately select and size the components. We demonstrate our approach in the context of a microclimate monitoring project through the design of the node, micro-solar subsystem, and network, which is deployed in a challenging, deep forest setting. We evaluate our deployment by analyzing the effects of the range of solar profiles experienced across the network.

Solar Cells, Photodetectors, and Optical Sources from Infrared Colloidal Quantum Dots

Abstract: Optoelectronic devices made via spin-coating of soft materials onto an arbitrary substrate enable ready integration, low cost, and physical flexibility. The use of solution-processed colloidal quantum dots offers the added advantage of quantum-size-effect tuning of material bandgap. Tuning across the near- and short-wavelength infrared (SWIR) spectral regions enables applications in fiber-optic communications, night vision and biomedical imaging, and efficient solar energy collection. Here we review progress in infrared solar cells, light sensors, and optical sources based on solution-processed materials. The latest solution-processed photovoltaics now provide 4.2% power conversion efficiencies in the infrared, placing them a factor of three away from enabling a doubling in overall solar power conversion efficiency of visible-wavelength solution-processed photovoltaics. The best solution-processed photodetectors now provide sensitivities of 1013 Jones D* (normalized detectivity), exceeding the sensitivity of the best epitaxially grown SWIR photodetectors. Infrared optical sources, both broadband light-emitting diodes and, more recently, lasers, have now also been reported at 1.5 µm.

An efficient solar energy harvester for wireless sensor nodes

Abstract: Solar harvesting circuits have been recently proposed to increase the autonomy of embedded systems. One key design challenge is how to optimize the efficiency of solar energy collection under non stationary light conditions. This paper proposes a scavenger that exploits miniaturized photovoltaic modules to perform automatic maximum power point tracking at a minimum energy cost. The system adjusts dynamically to the light intensity variations and its measured power consumption is less than 1 mW. Experimental results show increments of global efficiency up to 80%, diverging from ideal situation by less than 10%, and demonstrate the flexibility and the robustness of our approach.

Solar Tracking System: More Efficient Use of Solar Panels

Abstract: This paper shows the potential system benefits of simple tracking solar system using a stepper motor and light sensor. This method is increasing power collection efficiency by developing a device that tracks the sun to keep the panel at a right angle to its rays. A solar tracking system is designed, implemented and experimentally tested. The design details and the experimental results are shown. XTRACTING useable electricity from the sun was made possible by the discovery of the photoelectric mechanism and subsequent development of the solar cell - a semi- conductive material that converts visible light into a direct current. By using solar arrays, a series of solar cells electrically connected, a DC voltage is generated which can be physically used on a load. Solar arrays or panels are being used increasingly as efficiencies reach higher levels, and are especially popular in remote areas where placement of electricity lines is not economically viable. This alternative power source is continuously achieving greater popularity especially since the realisation of fossil fuel's shortcomings. Renewable energy in the form of electricity has been in use to some degree as long as 75 or 100 years ago. Sources such as Solar, Wind, Hydro and Geo- thermal have all been utilised with varying levels of success. The most widely used are hydro and wind power, with solar power being moderately used worldwide. This can be attributed to the relatively high cost of solar cells and their low conversion efficiency. Solar power is being heavily researched, and solar energy costs have now reached within a few cents per kW/h of other forms of electricity generation, and will drop further with new technologies such as titanium- oxide cells. With a peak laboratory efficiency of 32% and average efficiency of 15-20% (1-4) , it is necessary to recover as much energy as possible from a solar power system. This includes reducing inverter losses, storage losses, and light gathering losses. Light gathering is dependent on the angle of incidence of the light source providing power (i.e. the sun) to the solar cell's surface, and the closer to perpendicular, the greater the power (1-7). If a flat solar panel is mounted on

Solar Advisor Model User Guide for Version 2.0

Abstract: The Solar Advisor Model (SAM) provides a consistent framework for analyzing and comparing power system costs and performance across the range of solar technologies and markets, from photovoltaic systems for residential and commercial markets to concentrating solar power and large photovoltaic systems for utility markets. This manual describes Version 2.0 of the software, which can model photovoltaic and concentrating solar power technologies for electric applications for several markets. The current version of the Solar Advisor Model does not model solar heating and lighting technologies.

Prospect of concentrating solar power in China : the sustainable future

Abstract: Limited fossil resources and severe environmental problems require new sustainable electricity generation options, which utilize renewable energies and are economical in the meantime. Concentrating solar power (CSP) generation is a proven renewable energy technology and has the potential to become cost-effective in the future, for it produces electricity from the solar radiation. In China, the electricity demand is rapidly increasing, while the solar resources and large wasteland areas are widely available in the western and northern part of China. To change the energy-intensive and environment-burdensome economical development way, Chinese government supports the development of this technology strongly. These factors altogether make China a suitable country for utilizing CSP technology. In this paper, the potential of CSP in China was studied and strategies to promote development of this technology were given.

Systems for highly efficient solar power

Abstract: Different systems to achieve solar power conversion are provided in at least three different general aspects, with circuitry that can be used to harvest maximum power from a solar source (1) or strings of panels (11) for DC or AC use, perhaps for transfer to a power grid (10) three aspects can exist perhaps independently and relate to: 1) electrical power conversion in a multimodal manner, 2) alternating between differing processes such as by an alternative mode photovoltaic power converter functionality control (27), and 3) systems that can achieve efficiencies in conversion that are extraordinarily high compared to traditional through substantially power isomorphic photovoltaic DC-DC power conversion capability that can achieve 99.2% efficiency or even only wire transmission losses. Switchmode impedance conversion circuits may have pairs of photovoltaic power series switch elements (24) and pairs of photovoltaic power shunt switch elements (25).

Defossiling fuel: how synthetic biology can transform biofuel production.

Abstract: A lthough crude oil production is predicted to peak soon, it is reasonable to assume that unconventional fossil fuel sources can continue to meet society’s increasing energy demands for many decades to come (1). The real challenge is sustainability: stabilizing and reversing global climate change, minimizing political and economic energy volatility, and smoothing the transition from fossil fuels in the distant future. In response to this challenge, many are looking to biotechnology to develop biofuels, such as ethanol, butanol, biodiesel, and hydrogen (H2), in which the energy ultimately derives from photosynthetic capture of sunlight. A fundamental issue with biofuels is efficiency. The pathway from sunlight through natural intermediates to final molecule is long, and biofuel production is perhaps the ultimate metabolic engineering problem (2). This challenge is made even greater by its inherent systems complexity, because any solutionmust be implemented in the context of an energy infrastructure with challenging engineering, economic, political, and environmental realities. Are biofuels sustainable? Consider U.S. transportation fuels, a market poised for impact. Biofuels derive their stored chemical energy from the sun viaphotosynthesis. Biofuel use is therefore a closed carbon cycle, as carbon released during combustion is sequestered during photosynthesis. Solar radiation is clearly a sustainable energy source on human time scales, and U.S. incident solar power ( 2300 TW) (3) greatly exceeds our transportation fuel usage ( 1.0 TW) (Table 1) (4). The reactions of photosynthesis impose a maximal efficiency of 12%, but final yields are significantly lower (2). Terrestrial plant efficiencies for solar to biomass conversion is maximally 2% (e.g., for the rapidly growingMiscanthus (5)), and the subsequent conversion into biofuels is 50% efficient (6). It would therefore require 4.3% of the U.S. land area to meet our transportation energy demands, which corresponds to 22% of current cropland. Thus, in an optimistic approximation (and ignoring social, political, and economic complexities), we can say biofuel production could be sustainable, albeit with significant challenges. These calculations suggest that a biofuelbased energy economy is feasible but that enhancements in the efficiency of any step in energy production would be favorable fromaneconomic and environmental standpoint. The upper bound on efficiency is set by photosynthesis—the challenge is therefore to come as close to this bound as possible. Put another way, how can one optimizemetabolism todirectmaximal flux from one set of metabolites to another, while still maintaining, at least partially, host fitness? Traditional industrial approaches have given us many such successes (e.g., beer) andwill play amajor role, but the tools of systems and synthetic biology promise to deliver a degree of optimization not previously attainable (7). A synthetic-biological redesign of the organisms that produce biofuels has the potential to significantly increase efficiency, *Corresponding author, pamela_silver@hms.harvard.edu.

Case Studies on the Use of Solar Irradiance Forecast for Optimized Operation Strategies of Solar Thermal Power Plants

Abstract: The Spanish Royal Decree 661/2007 for the regulation of renewable energy allows operators of power plants to participate directly on the electricity market instead of reverting to flat-rate prices. The premium tariff option motivates operators of renewable energy plants to increasingly act like managers of conventional plants, selling electricity at the liberalized market. Just like a normal market participant, the operator places bids in advance on the day-ahead market and is obliged to fulfill them. Thus, there is the need for operators of renewable energy plants to be able to provide predictable and dispatchable energy in the profitable premium tariff. This legal setting motivates the following analysis on the value of irradiance forecasts for determining optimal operation strategies of solar power plants. The scientific background of this study are ongoing research activities on the use of satellite-based now casting of solar irradiance using cloud motion vector techniques and on data assimilation of aerosols into air quality models as a basis for day-ahead irradiance forecasts. The influence of a schedule based on imperfect forecasts on the daily revenue for a solar thermal power plant is assessed. Three typical weather situations are analyzed: clear-sky, overcast, and aerosol-charged situations. This paper shows the economic potential of the participation at the premium tariff with optimized operation strategies using direct solar irradiance forecasts based on Earth observation techniques.

High Flux Central Receivers of Molten Salts for the New Generation of Commercial Stand-Alone Solar Power Plants

Abstract: Molten salt technology represents nowadays the most cost-effective technology for electricity generation for stand-alone solar power plants. Although this technology can be applied to both concentrating technologies, parabolic through and central receiver systems (CRSs), CRS technology can take advantages from its higher concentration, allowing to work at higher temperatures and therefore with a reduction in the size and cost of the storage system. The receiver system is the "door" for which the energy passes from the field collector to the thermal-electric cycle; it represents, therefore, the core of the CRS and its performance directly affects plant production. Starting from the published lessons from SOLAR TWO receiver technology, the validation of an improved receiver for molten salt technology was assumed as part of the SOLAR TRES solar thermal power commercial plant development. Main challenges for the new receiver were to increase its allowable peak flux up to 1 MW/m 2 in order to maximize the thermal efficiency of the CRS solar power plant, and to improve its safe life without limiting the incident fluxes that the field of heliostats is able to deliver with an optimized pointing strategy. Several advanced features in geometric and thermodynamic aspects and in its material selection have been implemented on the receiver With the results of a sensitivity analysis carried out with an own code developed by SENER (SENREC), a prototype receiver panel was designed, fabricated, and installed in a proper test bed at the PSA. Test validation on this panel was carried out in 2007. The initial test results show a very good behavior of the prototype receiver, which allows to anticipate that the objectives of its design can be fulfilled. SENER and CIEMAT have joined forces to face up the challenge of sizing and designing a new molten salt receiver of high thermal efficiency, able to operate at high fluxes without compromising its durability (at least 25 years). Main challenges for the new receiver design were to optimize the receiver dimensions and receiver tube sizes and material selection to surpass the operating conditions in the new plants with respect to SOLAR TWO.

Solar-Terrestrial Coupling Evidenced by Periodic Behavior in Geomagnetic Indexes and the Infrared Energy Budget of the Thermosphere

Abstract: We examine time series of the daily global power (W) radiated by carbon dioxide (at 15 microns) and by nitric oxide (at 5.3 microns) from the Earth s thermosphere between 100 km and 200 km altitude. Also examined is a time series of the daily absorbed solar ultraviolet power in the same altitude region in the wavelength span 0 to 175 nm. The infrared data are derived from the SABER instrument and the solar data are derived from the SEE instrument, both on the NASA TIMED satellite. The time series cover nearly 5 years from 2002 through 2006. The infrared and solar time series exhibit a decrease in radiated and absorbed power consistent with the declining phase of the current 11-year solar cycle. The infrared time series also exhibits high frequency variations that are not evident in the solar power time series. Spectral analysis shows a statistically significant 9-day periodicity in the infrared data but not in the solar data. A very strong 9-day periodicity is also found to exist in the time series of daily A(sub p) and K(sub p) geomagnetic indexes. These 9-day periodicities are linked to the recurrence of coronal holes on the Sun. These results demonstrate a direct coupling between the upper atmosphere of the Sun and the infrared energy budget of the thermosphere.

Solar steam reforming of natural gas for hydrogen production using molten salt heat carriers

Abstract: The utilization of concentrated solar energy as external heat source for methane steam reforming has been investigated. Molten salts at temperatures up to 550°C can be used as solar heat carrier and storage system, and hydrogen selective membranes can be used to drive reforming reaction at lower temperatures than conventional (<550°C), with hydrogen purification achieved thereby. The combination of new technologies such as membranes and membrane reactors, concentrating solar power (CSP) systems, and molten salt heat carriers, allows a partial decarbonation of the fossil fuel together with the possibility to carry solar energy in the current natural gas grid. Different plant configurations and operating conditions have been analyzed using a mathematical model and AspenPlus simulator. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Reaching Consensus in the Definition of Photovoltaics Capacity Credit in the USA: A Practical Application of Satellite-Derived Solar Resource Data

Abstract: This paper describes an ongoing effort to reach consensus on the notion of capacity credit for solar power electrical generation. The paper presents different methodologies quantifying capacity credit and reports on their intercomparison through experimental case studies for three diverse electric utility companies. Satellite-derived solar resource data are used to simulate the site/time specific PV output injected in the selected power grids. The paper concludes by reporting the initial results of a consensus-building effort involving the utility industry, the solar industry, and government.

100 W-class solar pumped laser for sustainable magnesium-hydrogen energy cycle

Abstract: A solar pumped laser system with 7%–9% slope efficiencies has been developed. A Fresnel lens (2×2 m, f=2000 mm) is mounted on a two-axis sun tracker platform and focuses solar radiation toward laser cavity, which embraces Cr:Nd:yttrium aluminum garnet ceramic rod. The maximum emitted laser power is 80 W corresponding to maximum total area performance of 20 W/m2 for the Fresnel lens area. This solar laser system would be used as a section of power plant in a magnesium energy cycle as a cost-efficient solar energy converter. Using direct solar radiation into laser, 4.3% net conversion efficiency has been achieved.

Desert Power: The Economics of Solar Thermal Electricity for Europe, North Africa, and the Middle East

Abstract: A climate crisis is inevitable unless developing countries limit carbon emissions from the power sector in the near future. This will happen only if the costs of low carbon power production become competitive with fossil fuel power. We focus on a leading candidate for investment: solar thermal or concentrating solar power (CSP), a commercially available technology that uses direct sunlight and mirrors to boil water and drive conventional steam turbines. Solar thermal power production in North Africa and the Middle East could provide enough power to Europe to meet the needs of 35 million people by 2020. We compute the subsidies needed to bring CSP to financial parity with fossil-fuel alternatives. We conclude that large-scale deployment of CSP is attainable with subsidy levels that are modest, given the planetary stakes. By the end of the program, unsubsidized CSP projects are likely to be competitive with coal- and gas-based power production in Europe. The question is not whether CSP is feasible but whether programs using CSP technology will be operational in time to prevent catastrophic climate change. For such programs to spur the clean energy revolution, efforts to arrange financing should begin right away, with site acquisition and construction to follow within a year.

The Economics of Solar Power

Abstract: Don’t be fooled by technological uncertainty and the continued importance of regulation; solar will become more economically attractive

Design and analysis of micro-solar power systems for Wireless Sensor Networks

Abstract: Wireless sensor networks are fundamentally limited by their energy storage resources and the power they obtain from their environment. Several micro-solar powered designs have been developed to address this important problem but little analysis is available on key design trade-offs. We develop a taxonomy of the micro-solar design space identifying key components, design choices, interactions, challenges, and trade-offs. Based on this taxonomy, we provide an empirical and mathematical analysis of two prominent designs of micro-solar power systems (Heliomote and Trio), and interpret the results to propose design guidelines for micro-solar power systems.

Short term forecasting of solar radiation

Abstract: Variations of solar irradiance are known to have a significant influence on electric power generation by solar energy systems. With high connection densities of PV system in the low voltage (LV) network, this might cause to degrade electric power quality. The present study describes a multiplicative ARMA models to generate instantaneous series of global irradiation. The data set used in this work corresponding to five minutes global irradiance data were recorded in a radiometric station located in south Spain (Cordoba) during a for years period (1994-1997). The development of these models is based on removing the annual periodicity and seasonal variation of solar radiation. The method proposed considers fitting an AR model to the data. The selection of the order of the model has been made on the basis of seven different criteria. The predicted values of solar radiation are compared with the observed data series and it was found that this approach leads to optimal predictions.

Reactive power compensation in solar power system

Abstract: A method of providing reactive power support is proposed. The method includes detecting at least one of a plurality of network parameters in a distributed solar power generation system. The generation system includes a plurality of photovoltaic modules coupled to a grid via inverters. The method further includes sensing a state of the photovoltaic modules coupled to the distributed solar power generation system and determining a reactive power measure based upon the sensed state and the detected network parameters. The reactive power measure is used to generate a reactive power command. The reactive power command is further used to compensate reactive power in the distributed solar power generation system.