Optical geometry approach for elliptical Fresnel lens design and chromatic aberration

This research formulates an elliptical-based Fresnel lens concentrator system using optical geometry and ray tracing technique. The author incorporates solar spectrum with the refractive indices of lens materials to form different color mixes on the target plane. The model illustrates the solar spectrum distributions under the Fresnel lens. It can be used to investigate each spectral segment's distribution patterns and helps to match the concentration patterns of different wavelengths to different solar energy applications.     

Design of pressure vessels taking plastic reserve into account

Stress-collecting cross-sections of pressure vessels and process equipment, lying close to sudden curvatures or cross-section changes, openings and joints, etc., can also be loaded by pressures even greater than their elastic load-carrying capacity because these cross-sections have a considerable plastic reserve due to the stress rearrangement occurring after the first loading (test pressure) as stress reserves. The elastic-plastic state of the stress-collecting cross-sections can be analyzed by the finite element method (FEM), while plastic reserves and stress reserves can be explored by a numerical method. When designing, these reserves can easily be taken into account by limiting the residual deformations after the first loading.     

Design of one-axis tracked linear Fresnel lenses

The most frequently used criterion in the design of linear Fresnel lenses consists of minimizing the radiation spread at the collector when the lens is illuminated by rays that are contained in the full lens acceptance angle and are incident on the lens in the plane perpendicular to the lens axis. This paper analyzes this topic and concludes that when the lenses are one-axis-tracked this criterion can be improved by replacing the perpendicular plane with another forming a certain angle to it. When calculated for a specific lens, at the location of Madrid, the new criterion was found to yield an increase of more than 7% in the total annual energy collected.     

Analysis of point-focused,non-imaging Fresnel lenses' concentration profile and manufacture parameters

The purpose of this study is to develop a mechanism of a curve-based, point-focused Fresnel lens concentrator system and use it to examine each spectral segment's distribution patterns on the lens' focal area. The mechanism incorporates optical geometry and ray tracing technique with the components of solar spectrum, refractive index information of lens materials, and the formulation for quantifying the concentrator systems' transmittance loss and prism-tip dispersion loss. In addition to the facet angles' role in refracting the incoming radiation, this research has addressed spectrum-filtering role of the side angle, the angle between the entry face and the side face of each facet on the lens. The theoretical aspect has been elaborated on the basis of the lens' design wavelength. A computerized model has been developed and the simulated outcome compared to the measured data from a previous research. The result of this study provides the information of illumination patterns under a circular lens, which will help to match up various spectrum distributions to their suitable solar applications.     

The GHG balance of biofuels taking into account land use change

The contribution of biofuels to the saving of greenhouse gas (GHG) emissions has recently been questioned because of emissions resulting from land use change (LUC) for bioenergy feedstock production. We investigate how the inclusion of the carbon effect of LUC into the carbon accounting framework, as scheduled by the European Commission, impacts on land use choices for an expanding biofuel feedstock production. We first illustrate the change in the carbon balances of various biofuels, using methodology and data from the IPCC Guidelines for National Greenhouse Gas Inventories. It becomes apparent that the conversion of natural land, apart from grassy savannahs, impedes meeting the EU's 35% minimum emissions reduction target for biofuels. We show that the current accounting method mainly promotes biofuel feedstock production on former cropland, thus increasing the competition between food and fuel production on the currently available cropland area. We further discuss whether it is profitable to use degraded land for commercial bioenergy production as requested by the European Commission to avoid undesirable LUC and conclude that the current regulation provides little incentive to use such land. The exclusive consideration of LUC for bioenergy production minimizes direct LUC at the expense of increasing indirect LUC.     

Structural behavior during a PTS transient taking into account the WPS effect

The Reactor Pressure Vessel (RPV) is an essential component liable to limit the life duration of PWR's. Its behavior in service is limited in time due to the embrittling effects of irradiation. The structural integrity of the RPV is assessed by conventional fracture mechanical studies, where it is assumed that the failure of a flawed structure occurs when the stress intensity factor at the crack tip reaches the toughness value of the structure material. Toughness curves of materials are obtained from monotonously increasing and isothermal loading. On the other hand, RPV integrity assessment involves loading conditions with coupled cooling, heating, increasing and decreasing load.The safety analyses made at the European level study, the behavior of defects in the vessel subjected to loading resulting from thermal transients. These analyses usually do not take into account the effect of load history/warm pre-stressing (WPS) of the defects, which is observed in a wide range of experimental studies. The non-consideration of the beneficial effect of this physical phenomenon has two major consequences:

• •a poor knowledge of the real margins associated with the transients to which the vessel is subjected,
• •an economical penalty due to large under-estimation of the life duration of the vessel.

This paper presents the results of two independent programs.The first dealing with four WPS tests performed at CEA in France on CT specimens manufactured of ferritic 18MND5 steel undergoing different types of loading during the cooling phase as follow:

• •Load Cool Fracture (LCF)
• •Loading Maintained CMOD Cooling Fracture (LM2CF)

WPS effect is observed in the first case, while curve in the second case the failure occurs during the crossing of the transition because of the monotonous increase of the force due to constant CMOD (Crack Mouth Opening Displacement).The second program deals with tests performed at MPA in Germany in collaboration with EDF on CT25 and CT50 specimens using the same material with five types of WPS cycles:

• •LCF
• •Load Unload Cool Fracture (LUCF)
• •Load Transient Fracture (LTF)
• •Load Oscillation Cool Fracture (LOCF)
• •Load Oscillation Transient Fracture (LOTF)

In all these cases, WPS effect is demonstrated.For both the programs, numerical analyses were performed at MPA using Weibull [Metall Trans A, 14A (1987) 2277] and Chell [Fourth Int Conf Pressure Vessel Technol, Inst Mech Engng, 1980, Paper C22/80, London, U.K., 117] models to predict the WPS effect, details of which are presented here.     

The solution of some two-dimensional problems of thermoelasticity taking into account the microtemperature

In this work we consider the two-dimensional system of the differential equations describing the plane statical thermoelastic balance of homogenous isotropic elastic bodies, the microelements of which have microtemperature in addition to the classical displacement and a temperature field. It is construed the general solution of this system of the equations by means of analytic functions of complex variable and solutions of the equation of Helmholtz. The general representation of the solution obtained gives the opportunity to construct the analytical solutions of a number of plane boundary value problems of microthermoelasticity. As an example we consider the boundary value problem for a concentric circular ring.     

Analysis of spectrum distribution and optical losses under Fresnel lenses

During late 1970s and early 1980s, Fresnel lenses have received more attention in the field of solar energy application. This paper briefly examines the Fresnel lens development since 1970s and investigates the losses inherent in the linear Fresnel lenses. The research develops the formulation that helps to quantify the linear lens’ transmittance loss and prism-tip scattering loss and then derive a realistic model to simulate the measured data. In addition, the research has identified an elliptical-based lens that comes closest to the condition of minimum deviation. Such lens closely duplicates the curvature needed for maximum transmission. The researcher applies different design wavelengths to study the contribution of each wavelength interval on the receiving plane.     

Cost effectiveness of decentralized energy supply systems taking solar and wind utilization plants into account

In this article, results are presented of annual simulations of a decentralized (regional) plant for the power and heat supply of a residential complex. This complex consists of four houses with 40 flats all in all. The annual power consumption of the complex is 157 MWh and the heat requirement is 325 MWh. The concrete dynamics of the energy demands over the year is taken into consideration. The energy supply system is composed of a power-controlled combined heat and power (CHP) plant (55 kW), a photovoltaic plant (PV array or PV plant) array for power generation as well as a field of solar thermal collectors with a short-term accumulator for water heating and a long-term accumulator for supplying heat for domestic heating purposes. Simulation results demonstrate that synergetic effects result from the combination of a CHP plant with wind power and PV plants of varying sizes, which have an effect on the cost effectiveness of the plant as a whole with the different dynamics of energy sources (wind and solar energies) and of the consumption of power and heat being the decisive factors. The power deficits of wind power and PV plants are compensated through the application of a natural gas-operated CHP plant. In almost all variants, the demand for fossil energy carriers is distinctly less than in conventional energy supply plants.     

Thermal analysis of an electrical machine taking into account theiron losses and the deep-bar effect

The temperature distribution over the cross-section of an asynchronous squirrel cage machine is calculated by taking into account the copper losses and the iron losses at the steady-state condition. Under transient conditions, the deep-bar effect in the rotor is taken into account. Due to the deep bar effect, the current densities and thermal sources in the bar change and as a consequence the resistances, the leakage reactances, the currents and the thermal sources in the stator copper are also altered. Resistances depend upon temperatures     

Electricity demand response to price changes: The Portuguese case taking into account income differences

In this paper we study the behavior of electricity use in Portuguese households using microdata from five independent surveys. Our sample covers the period from 1989 to 2010, which was characterized by major changes in the country. We adopt the pseudo-panel methodology creating 350 cohorts based on the size of the household, the type of location (rural or urban), the region, and the income quintile. Our results show relatively high medium/long-run own price elasticities indicating that an increase in the electricity price due to, for instance, policy intervention would, in fact, decrease electricity use. Cross price elasticities indicate that electricity and gas are substitutes. Additionally, the income quintiles analysis shows significant differences in the elasticities depending on the income group. Hence, political interventions in the electricity sector may have important redistributive effects.     

考虑可再生性的全生命周期净能源成本评估方法研究

提出了一个新的考虑燃料可再生性的净能源成本指标。这一指标将燃料的净能源产出、气态污染物排放外部成本、生命周期成本和能源可再生性综合成一个统一的指标，燃料指标值越低表明燃料的总体表现越好。运用该指标对木薯乙醇——汽油混合燃料和传统汽油燃料分别进行了评估。结果表明与分别评价燃料的净能源产出、生命周期成本、排放和可再生性指标比较，为考虑燃料的可再生性的全生命周期净能源成本指标提供了一个区别燃料优劣的有力手段。     

Design method of non-imaging secondary (NIS) for CPV usage

Analytical method is used to obtain the geometrical shape for non-imaging secondary (NIS) mirror in the application of concentrated photovoltaic (CPV). It is discussed in beam down optical system, NIS presents advantages to eliminate dark image, to reduce the solar disc effect, to improve the uniformity of the illumination, etc. comparing to the imaging secondary. The authors have emphasized that the geometrical shape of optical components in non-imaging optics can generally be high order surfaces not restricted to the quadratic surface in imaging optics and mostly “CPC” in early developed non-imaging optics. This paper has discussed the general criteria and two practical approaches for designing NIS. We listed some of the examples in this paper to form NIS by rotating a segment of linear or quadratic or cubic curve around the central axis of primary reflector. The method to calculate the parameters of such segment is described. Although in present discussion, we are referring the usage in PV concentrator, the method is generally applied in other optical fields.     

Design and construction of non-imaging planar concentrator for concentrator photovoltaic system

A novel configuration of solar concentrator, which is the non-imaging planar concentrator, capable of producing much more uniform sunlight and reasonably high concentration ratio, is designed and constructed. This design is envisioned to be incorporated in concentrator photovoltaic (CPV) systems. The work presented here reports on the design, optical alignment and application of the prototype, which is installed at Universiti Tunku Abdul Rahman (UTAR), Malaysia. In the architecture of the prototype, 360 flat mirrors, each with a dimension of 4.0 cm × 4.0 cm, are arranged into 24 rows and 15 columns with a total reflection area of about 5760 cm². In addition to that, illumination distribution for the prototype is simulated and its results are then compared with the experiment result.     

Performance of a concentrated photovoltaic energy system with static linear Fresnel lenses

A new type of greenhouse with linear Fresnel lenses in the cover performing as a concentrated photovoltaic (CPV) system is presented. The CPV system retains all direct solar radiation, while diffuse solar radiation passes through and enters into the greenhouse cultivation system. The removal of all direct radiation will block up to 77% of the solar energy from entering the greenhouse in summer, reducing the required cooling capacity by about a factor 4. This drastically reduce the need for cooling in the summer and reduce the use of screens or lime coating to reflect or block radiation.All of the direct radiation is concentrated by a factor of 25 on a photovoltaic/thermal (PV/T) module and converted to electrical and thermal (hot water) energy. The PV/T module is kept in position by a tracking system based on two electric motors and steel cables. The energy consumption of the tracking system, ca. 0.51 W m⁻², is less than 2% of the generated electric power yield. A peak power of 38 W m⁻² electrical output was measured at 792 W m⁻² incoming radiation and a peak power of 170 W m⁻² thermal output was measured at 630 W m⁻² incoming radiation of. Incoming direct radiation resulted in a thermal yield of 56% and an electric yield of 11%: a combined efficiency of 67%. The annual electrical energy production of the prototype system is estimated to be 29 kW h m⁻² and the thermal yield at 518 MJ m⁻². The collected thermal energy can be stored and used for winter heating. The generated electrical energy can be supplied to the grid, extra cooling with a pad and fan system and/or a desalination system. The obtained results show a promising system for the lighting and temperature control of a greenhouse system and building roofs, providing simultaneous electricity and heat. It is shown that the energy contribution is sufficient for the heating demand of well-isolated greenhouses located in north European countries.     

Sandblasting durability of acrylic and glass Fresnel lenses for concentrator photovoltaic modules

The impact of sandblasting on Fresnel lenses for concentrator photovoltaic (CPV) modules must be carefully considered when CPV systems are installed in desert areas. In this study, the transmittance after sandblasting of acrylic polymethylmethacrylate (PMMA) and glass substrates was evaluated, and their durability was assessed. The transmittance decreased as the momentum of the blown sand increased. The conversion efficiency of the CPV modules was estimated using equivalent circuit calculations, and the influence of sandblasting on the output of the CPV modules was quantitatively predicted. The coefficients of degradation for the PMMA and glass CPV modules were 0.17 and 0.08 points per unit of momentum, respectively. The durability of the CPV module with the glass Fresnel lens is approximately twice that with the PMMA lens.     

Concept and design of modular Fresnel lenses for concentration solar PV system

In this paper, we propose a new configuration of solar concentration optics utilizing modularly faceted Fresnel lenses to achieve a uniform intensity on the absorber plane with a moderate concentration ratio. The uniform illumination is obtained by the superposition of flux distributions resulted from modularly faceted Fresnel lenses. Based on the concept of modularly faceted Fresnel lenses, the cost effective 3-D concentration solar PV system is designed for future applications. Mathematical treatments for deriving the flux distribution and the concentration efficiency at the absorber plane are introduced. As an example, the distribution of the solar flux, at the cell position, is simulated using ray-trace technique for 9, 25, 49, 81, and 121 suns concentration systems. The irradiance distributions at the cell plane are estimated to be uniform within 20%, with a transmission efficiency larger than 70% for low and medium concentration ratios (less than 50 suns).     

Relationship of parallel model and series model for permanent magnet synchronous motors taking iron loss into account

This paper investigates the relationship of parallel model and series model for permanent magnet synchronous motor taking iron loss into account. The expressions of flux linkage, terminal voltage, and electromagnetic torque are compared. It follows from the investigation that the parallel and series models are mathematically the same. In addition, the properties of the models are exhibited. The parallel model is superior in understanding the physical meaning to the series model. The series model is superior in low order of the state variables to the parallel model.     

Multi-farm economic analysis of perennial energy crops in Central Greece, taking into account the CAP reform

This study analyses farm level economic impacts of biomass production from perennial crops including Arundo donax L. (arundo), Miscanthus x giganteus (miscanthus), Panicum virgatum L. (switchgrass) and Cynara cardunculus L. (cardoon). Regional biomass supply curves are estimated with a dynamic, multi-farm, mathematical programming model. Micro-economic data for the model are generated from farm surveys covering 52 farms containing a total of 400 parcels, in Central Greece. The study also examines the potential effects of the Common Agricultural Policy reform in 2003 on regional biomass supply. Simulations show that the policy reform toward decoupled subsidies lowers the cost of biomass between 15 and 25 euro per tonne. Switchgrass appears to be the most attractive option, followed by cardoon and miscanthus. Due to high specific machinery cost, arundo is never preferred. Relative to the agricultural policy setting of Agenda 2000, the biomass potential increases more for farms of small economic size and farms with a higher share of cotton.     

Combined nongray radiative and conductive heat transfer in multiple glazing taking into account specular reflection and absorption

The problem of combined nongray radiative and conductive heat transfer in multiple glazing subjected to solar irradiation is analyzed. A spectral solar model proposed by Bird and Riordan is used to calculate direct and diffuse solar irradiance. The radiation element method by ray emission model, REM², is used to analyze the spectral dependence of radiative heat transfer. Specular reflection at boundary surfaces is taken into account. The spectral dependence of radiation properties of glass such as specular reflectivity, refraction angle, and absorption coefficient is taken into account. The steady‐state temperature and heat flux distributions in the glass layer are obtained and the insulating efficiency of multiple glazing is examined. The overall heat transfer coefficients predicted by the present method are compared with those based on the JIS method. The values obtained by the present method are slightly lower than those obtained by the JIS method. To investigate the spectral variation of radiative heat flux attenuated in the glass layer, the spectral heat flux at the room‐side surface and incident radiation are compared. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 712–726, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10125