Towards cost reduction in concentrating solar power: innovative design for an efficient fresnel based solar field

Energía termosolar (de concentración) es uno de los nombres que hacen referencia en español al término inglés “concentrating solar power”. Se trata de una tecnología basada en la captura de la potencia térmica de la radiación solar, de forma que permita alcanzar temperaturas capaces de alimentar un ciclo termodinámico convencional (o avanzado); el futuro de esta tecnología depende principalmente de su capacidad para concentrar la radiación solar de manera eficiente y económica. La presente tesis está orientada hacia la resolución de ciertos problemas importantes relacionados con este objetivo. La mencionada necesidad de reducir costes en la concentración de radiación solar directa, asegurando el objetivo termodinámico de calentar un fluido hasta una determinada temperatura, es de vital importancia. Los colectores lineales Fresnel han sido identificados en la literatura científica como una tecnología con gran potencial para alcanzar esta reducción de costes. Dicha tecnología ha sido seleccionada por numerosas razones, entre las que destacan su gran libertad de diseño y su actual estado inmaduro. Con el objetivo de responder a este desafío se desarrollado un detallado estudio de las propiedades ópticas de los colectores lineales Fresnel, para lo cual se han utilizado métodos analíticos y numéricos de manera combinada. En primer lugar, se han usado unos modelos para la predicción de la localización y la irradiación normal directa del sol junto a unas relaciones analíticas desarrolladas para estudiar el efecto de múltiples variables de diseño en la energía incidente sobre los espejos. Del mismo modo, se han obtenido analíticamente los errores debidos al llamado “off-axis aberration”, a la apertura de los rayos reflejados en los espejos y a las sombras y bloqueos entre espejos. Esto ha permitido la comparación de diferentes formas de espejo –planos, circulares o parabólicos–, así como el diseño preliminar de la localización y anchura de los espejos y receptor sin necesidad de costosos métodos numéricos. En segundo lugar, se ha desarrollado un modelo de trazado de rayos de Monte Carlo con el objetivo de comprobar la validez del estudio analítico, pero sobre todo porque este no es preciso en el estudio de la reflexión en espejos. El código desarrollado está específicamente ideado para colectores lineales Fresnel, lo que ha permitido la reducción del tiempo de cálculo en varios órdenes de magnitud en comparación con un programa comercial más general. Esto justifica el desarrollo de un nuevo código en lugar de la compra de una licencia de otro programa. El modelo ha sido usado primeramente para comparar la intensidad de flujo térmico y rendimiento de colectores Fresnel, con y sin reflector secundario, con los colectores cilíndrico parabólicos. Finalmente, la conjunción de los resultados obtenidos en el estudio analítico con el programa numérico ha sido usada para optimizar el campo solar para diferentes orientaciones –Norte-Sur y Este-Oeste–, diferentes localizaciones –Almería y Aswan–, diferentes inclinaciones hacia el Trópico –desde 0 deg hasta 32 deg– y diferentes mínimos de intensidad del flujo en el centro del receptor –10 kW/m2 y 25 kW/m2–. La presente tesis ha conducido a importantes descubrimientos que deben ser considerados a la hora de diseñar un campo solar Fresnel. En primer lugar, los espejos utilizados no deben ser plano, sino cilíndricos o parabólicos, ya que los espejos curvos implican mayores concentraciones y rendimiento. Por otro lado, se ha llegado a la conclusión de que la orientación Este-Oeste es más propicia para localizaciones con altas latitudes, como Almería, mientras que en zonas más cercanas a los trópicos como Aswan los campos Norte-Sur conducen a mayores rendimientos. Es de destacar que la orientación Este-Oeste requiere aproximadamente la mitad de espejos que los campos Norte-Sur, puediendo estar inclinados hacia los Trópicos para mejorar el rendimiento, y que alcanzan parecidos valores de intensidad térmica en el receptor todos los días a mediodía. Sin embargo, los campos con orientación Norte-Sur permiten un flujo más constante a lo largo de un día. Por último, ha sido demostrado que el uso de diseños pre-optimizados analíticamente, con anchura de espejos y espaciado entre espejos variables a lo ancho del campo, pueden implicar aumentos de la energía generada por metro cuadrado de espejos de hasta el 6%. El rendimiento óptico anual de los colectores cilíndrico parabólicos es 23 % mayor que el rendimiento de los campos Fresnel en Almería, mientras que la diferencia es de solo 9 % en Aswan. Ello implica que, para alcanzar el mismo precio de electricidad que la tecnología de referencia, la reducción de costes de instalación por metro cuadrado de espejo debe estar entre el 10 % y el 25 %, y que los colectores lineales Fresnel tienen más posibilidades de ser desarrollados en zonas de bajas latitudes. Como consecuencia de los estudios desarrollados en esta tesis se ha patentado un sistema de almacenamiento que tiene en cuenta la variación del flujo térmico en el receptor a lo largo del día, especialmente para campos con orientación Este-Oeste. Este invento permitiría el aprovechamiento de la energía incidente durante más parte del año, aumentando de manera apreciable los rendimientos óptico y térmico. Abstract Concentrating solar power is the common name of a technology based on capturing the thermal power of solar radiation, in a suitable way to reach temperatures able to activate a conventional (or advanced) thermodynamic cycle to generate electricity; this quest mainly depends on our ability to concentrate solar radiation in a cheap and efficient way. The present thesis is focused to highlight and help solving some of the important issues related to this problem. The need of reducing costs in concentrating the direct solar radiation, but without jeopardizing the thermodynamic objective of heating a fluid up to the required temperature, is of prime importance. Linear Fresnel collectors have been identified in the scientific literature as a technology with high potential to reach this cost reduction. This technology has been selected because of a number of reasons, particularly the degrees of freedom of this type of concentrating configuration and its current immature state. In order to respond to this challenge, a very detailed exercise has been carried out on the optical properties of linear Fresnel collectors. This has been done combining analytic and numerical methods. First, the effect of the design variables on the ratio of energy impinging onto the reflecting surface has been studied using analytically developed equations, together with models that predict the location and direct normal irradiance of the sun at any moment. Similarly, errors due to off-axis aberration, to the aperture of the reflected energy beam and to shading and blocking effects have been obtained analytically. This has allowed the comparison of different shapes of mirrors –flat, cylindrical or parabolic–, as well as a preliminary optimization of the location and width of mirrors and receiver with no need of time-consuming numerical models. Second, in order to prove the validity of the analytic results, but also due to the fact that the study of the reflection process is not precise enough when using analytic equations, a Monte Carlo Ray Trace model has been developed. The developed code is designed specifically for linear Fresnel collectors, which has reduced the computing time by several orders of magnitude compared to a wider commercial software. This justifies the development of the new code. The model has been first used to compare radiation flux intensities and efficiencies of linear Fresnel collectors, both multitube receiver and secondary reflector receiver technologies, with parabolic trough collectors. Finally, the results obtained in the analytic study together with the numeric model have used in order to optimize the solar field for different orientations –North-South and East-West–, different locations –Almería and Aswan–, different tilts of the field towards the Tropic –from 0 deg to 32 deg– and different flux intensity minimum requirements –10 kW/m2 and 25 kW/m2. This thesis work has led to several important findings that should be considered in the design of Fresnel solar fields. First, flat mirrors should not be used in any case, as cylindrical and parabolic mirrors lead to higher flux intensities and efficiencies. Second, it has been concluded that, in locations relatively far from the Tropics such as Almería, East-West embodiments are more efficient, while in Aswan North- South orientation leads to a higher annual efficiency. It must be noted that East-West oriented solar fields require approximately half the number of mirrors than NS oriented fields, can be tilted towards the Equator in order to increase the efficiency and attain similar values of flux intensity at the receiver every day at midday. On the other hand, in NS embodiments the flux intensity is more even during each single day. Finally, it has been proved that the use of analytic designs with variable shift between mirrors and variable width of mirrors across the field can lead to improvements in the electricity generated per reflecting surface square meter up to 6%. The annual optical efficiency of parabolic troughs has been found to be 23% higher than the efficiency of Fresnel fields in Almería, but it is only around 9% higher in Aswan. This implies that, in order to attain the same levelized cost of electricity than parabolic troughs, the required reduction of installation costs per mirror square meter is in the range of 10-25%. Also, it is concluded that linear Fresnel collectors are more suitable for low latitude areas. As a consequence of the studies carried out in this thesis, an innovative storage system has been patented. This system takes into account the variation of the flux intensity along the day, especially for East-West oriented solar fields. As a result, the invention would allow to exploit the impinging radiation along longer time every day, increasing appreciably the optical and thermal efficiencies.

The effect of scour protections in offshore wind farms

The installation of offshore scour protection systems in offshore wind farms allows avoid the effect of scour phenomenon around these structures. Up to date, numerous research projects have been carried out to justify the necessity of the scour protection systems and also to optimize their design. Protection systems based on riprap is frequently used due to its low cost and easy availability compared to other solutions such as geotextile bags or prefabricated concrete blocks. The sizing of these structures can be performed according to a series of recommendations that can optimize the costs associated with them, but there have been only few studies with real data up to now which have allowed identify the need for such protections. This investigation aims to assess the functionality of the scour protections adopted through the available data about their characteristics and the scour depth developed around the foundations. In this sense, this paper presents the results of a study that analyzes the functionality of scour protections in different European offshore wind farms.

When defense backfires: Detrimental effect of a plant’s protective trichomes on an insect beneficial to the plant

The plant Mentzelia pumila (family Loasaceae) has leaves and stems densely covered with tiny hooked trichomes. The structures entrap and kill insects and therefore are most probably protective. But they are also maladaptive in that they incapacitate a coccinellid beetle (Hippodamia convergens) that preys upon an aphid enemy (Macrosiphum mentzeliae) of the plant. The adaptive benefit provided by the trichomes is evidently offset by a cost.

The effect of innovation on hotel market value

The purpose of this article is to analyze the effect of hotel innovations on firm value. Specifically, this study fills a research gap in the previous literature by examining this effect through market value and by distinguishing the potentially different impacts of distinct innovation types: product, process, organization and marketing. This research contributes to consolidating the empirical evidence of hotel innovation and performance by analyzing whether distinct types of innovation lead to different levels of results. The findings show that innovations are perceived to have a positive impact on the future sales of the company: in a four-day period (0,+3), there is an increase in stock exchange returns of 1.53%. In terms of innovation types, process and marketing innovations are found to have a higher positive effect on hotel market value than product and organization innovations; which is explained by potential cost differences among innovations.

The impact of the internet on the pricing strategies of the European low cost airlines

This study seeks to analyse the price determination of low cost airlines in Europe and the effect that Internet has on this strategy. The outcomes obtained reveal that both users and companies benefit from the use of ICTs in the purchase and sale of airline tickets: the Internet allows consumers to increase their bargaining power comparing different airlines and choosing the most competitive flight, while companies can easily check the behaviour of users to adapt their pricing strategies using internal information. More than 2500 flights of the largest European low cost airlines have been used to carry out the study. The study revealed that the most significant variables for understanding pricing strategies were the number of rivals, the behaviour of the demand and the associated costs. The results indicated that consumers should buy their tickets before 25 days prior to departure.

The effect of electricity tariffs over the operating costs of the Spanish wastewater treatments plants

Given the complex structure of electricity tariffs and their steady growth in Spanish, we've studied its effect over the operating costs of the wastewater treatment plants (WWTP), concluding that in the last three years the revisions of electricity rates have meant increases in electricity costs of 64.5% in the rate 3.1.A and 79.1% in the rate 6.1. This has caused the cost of electricity, which was the most important, has increased from a 44% of total operating costs in the year 2009, to more than a 56% in the year 2012.

Federal tax policy : its effect on health care costs, coverage and the uninsured /

"October 1992."

Cost-Effectiveness Analysis of Adaptive Monitoring Strategies for Depression Treatment

Thesis (Master's)--University of Washington, 2016-06

Moderating effect of allocentrism on the pay referent comparison-pay level satisfaction relationship

Pay referent comparisons (comparisons of one's salary to that of others) such as other-inside (salary of other people in the organisation), other-outside (the market rate), and cost-of- living, have been shown to influence pay level satisfaction. Bordia and Blau (1998) identified family as another referent that had a significant effect on pay level satisfaction in a sample of public and private sector employees in India. The finding was interpreted in view of the importance of family in collectivistic cultures. In the study reported here, the moderating influence of an individual differences variable, allocentrism-idiocentrism (the individual level conceptualisation of collectivism-individualism) on pay referent comparison-pay level satisfaction relationship was investigated. A sample of 146 employees from three public sector organisations in India participated in the study. In line with the predictions, results showed that after controlling for age, tenure, and pay level, pay referent comparisons explained more variance in pay level satisfaction for allocentrics than for idiocentrics. Family and pay level were stronger explanatory variables of pay level satisfaction for allocentrics and idiocentrics, respectively, while cost of living was a significant explanatory variable for both sub-groups.

Using the effect size to model change in preference values from descriptive health status

Objectives: This pilot study describes a modelling approach to translate group-level changes in health status into changes in preference values, by using the effect size (ES) to summarize group-level improvement. Methods: ESs are the standardized mean difference between treatment groups in standard deviation (SD) units. Vignettes depicting varying severity in SD decrements on the SF-12 mental health summary scale, with corresponding symptom severity profiles, were valued by a convenience sample of general practitioners (n = 42) using the rating scale (RS) and time trade-off methods. Translation factors between ES differences and change in preference value were developed for five mental disorders, such that ES from published meta-analyses could be transformed into predicted changes in preference values. Results: An ES difference in health status was associated with an average 0.171-0.204 difference in preference value using the RS, and 0.104-0.158 using the time trade off. Conclusions: This observed relationship may be particular to the specific versions of the measures employed in the present study. With further development using different raters and preference measures, this approach may expand the evidence base available for modelling preference change for economic analyses from existing data.

Effect of water depth and water velocity upon the surfacing frequency of the bimodally respiring freshwater turtle, Rheodytes leukops

This study examines the effect of increasing water depth and water velocity upon the surfacing behaviour of the bimodally respiring turtle, Rheodytes leukops. Surfacing frequency was recorded for R. leukops at varying water depths (50, 100, 150 cm) and water velocities (5, 15, 30 cm s(-1)) during independent trials to provide an indirect cost-benefit analysis of aquatic versus pulmonary respiration. With increasing water velocity, R. leukops decreased its surfacing frequency twentyfold, thus suggesting a heightened reliance upon aquatic gas exchange. An elevated reliance upon aquatic respiration, which presumably translates into a decreased air-breathing frequency, may be metabolically more efficient for R. leukops compared to the expenditure (i.e. time and energy) associated with air-breathing within fast-flowing riffle zones. Additionally, R. leukops at higher water velocities preferentially selected low-velocity microhabitats, presumably to avoid the metabolic expenditure associated with high water flow. Alternatively, increasing water depth had no effect upon the surfacing frequency of R. leukops, suggesting little to no change in the respiratory partitioning of the species across treatment settings. Routinely long dives (>90 min) recorded for R. leukops indicate a high reliance upon aquatic O-2 uptake regardless of water depth. Moreover, metabolic and temporal costs attributed to pulmonary gas exchange within a pool-like environment were likely minimal for R. leukops, irrespective of water depth.

The effect of motor control exercise versus placebo in patients with chronic low back pain

Background: While one in ten Australians suffer from chronic low back pain this condition remains extremely difficult to treat. Many contemporary treatments are of unknown value. One potentially useful therapy is the use of motor control exercise. This therapy has a biologically plausible effect, is readily available in primary care and it is of modest cost. However, to date, the efficacy of motor control exercise has not been established. Methods: This paper describes the protocol for a clinical trial comparing the effects of motor control exercise versus placebo in the treatment of chronic non-specific low back pain. One hundred and fifty-four participants will be randomly allocated to receive an 8-week program of motor control exercise or placebo (detuned short wave and detuned ultrasound). Measures of outcomes will be obtained at follow-up appointments at 2, 6 and 12 months after randomisation. The primary outcomes are: pain, global perceived effect and patient-generated measure of disability at 2 months and recurrence at 12 months. Discussion: This trial will be the first placebo-controlled trial of motor control exercise. The results will inform best practice for treating chronic low back pain and prevent its occurrence.

Assessing cost-effectiveness of drug interventions for schizophrenia

Objective: To assess from a health sector perspective the incremental cost-effectiveness of eight drug treatment scenarios for established schizophrenia. Method: Using a standardized methodology, costs and outcomes are modelled over the lifetime of prevalent cases of schizophrenia in Australia in 2000. A two-stage approach to assessment of health benefit is used. The first stage involves a quantitative analysis based on disability-adjusted life years (DALYs) averted, using best available evidence. The robustness of results is tested using probabilistic uncertainty analysis. The second stage involves application of 'second filter' criteria (equity, strength of evidence, feasibility and acceptability) to allow broader concepts of benefit to be considered. Results: Replacing oral typicals with risperidone or olanzapine has an incremental cost-effectiveness ratio (ICER) of A$48 000 and A$92 000/DALY respectively. Switching from low-dose typicals to risperidone has an ICER of A$80 000. Giving risperidone to people experiencing side-effects on typicals is more cost-effective at A$20 000. Giving clozapine to people taking typicals, with the worst course of the disorder and either little or clear deterioration, is cost-effective at A$42 000 or A$23 000/DALY respectively. The least cost-effective intervention is to replace risperidone with olanzapine at A$160 000/DALY. Conclusions: Based on an A$50 000/DALY threshold, low-dose typical neuroleptics are indicated as the treatment of choice for established schizophrenia, with risperidone being reserved for those experiencing moderate to severe side-effects on typicals. The more expensive olanzapine should only be prescribed when risperidone is not clinically indicated. The high cost of risperidone and olanzapine relative to modest health gains underlie this conclusion. Earlier introduction of clozapine however, would be cost-effective. This work is limited by weaknesses in trials (lack of long-term efficacy data, quality of life and consumer satisfaction evidence) and the translation of effect size into a DALY change. Some stakeholders, including SANE Australia, argue the modest health gains reported in the literature do not adequately reflect perceptions by patients, clinicians and carers, of improved quality of life with these atypicals.

Cost-effectiveness of cholesterol-lowering therapy with pravastatin in patients with previous acute coronary syndromes aged 65 to 74 years compared with younger patients: Results from the LIPID study

Background We compared cost-effectiveness of pravastatin in a placebo-controlled trial in 5500 younger (31-64 years) and 3514 older patients (65-74 years) with previous acute coronary syndromes. Methods Hospitalizations and long-term medication within the 6 years of the trial were estimated in all patients. Drug dosage, nursing home, and ambulatory care costs were estimated from substudies. Incremental costs per life saved of pravastatin relative to placebo were estimated from treatment effects and resource use. Results Over 6 years, pravastatin reduced all-cause mortality by 4.3% in the older patients and by 2.3% in the younger patients. Older patients assigned pravastatin had marginally lower cost of pravastatin and other medication over 6 years (A$4442 vs A$4637), but greater cost offsets (A$2061 vs. A$897) from lower rates of hospitalizations. The incremental cost per life saved with pravastatin was A$55500 in the old and A$167200 in the young. Assuming no treatment effect beyond the study period, the life expectancy to age 82 years of additional survivors was 9.1 years in the older and. 17.3 years in the younger. Estimated additional life-years saved from pravastatin therapy were 0.39 years for older and 0.40 years for younger patients. Incremental costs per life-year saved were A$7581 in the older and A$1.4944 in the younger, if discounted at 5% per annum. Conclusions Pravastatin therapy was more cost-effective among older than younger patients, because of their higher baseline risk and greater cost offsets, despite their shorter life expectancy.

The effect of non-standard employment on work-family balance

Across the last four decades, the structure of the Australian labour market has changed profoundly as non-standard forms of employment have become more prevalent. According to many researchers, the growth of non-standard work has been driven by employee preferences, particularly among married women, for greater flexibility to balance paid work with domestic responsibilities and other non-work related pursuits. In contrast, other researchers argue that the increasing prevalence of non-standard employment reflects employer demands for greater staffing flexibility. From this perspective, non-standard forms of employment are considered to have a negative effect on work-family balance. This paper explores whether non-standard employment is associated with improved or poorer work-to-family conflict and tests whether experiences vary by gender. It concentrates on three common forms of non-standard employment: part-time employment, casual and fixed-term work contracts and flexible scheduling practices (such as evening work, weekend work and irregular rostering). Analysis is based on 2299 employed parents from the first wave of the Household, Income and Labour Dynamics on Australia (HILDA) project. Results show that few scheduling measures are significant determinants of work-family balance. However, part-time employment is associated with reduced work-to-family strain for both men and women, even after controlling for various other employment and household related characteristics. Casual employment, in contrast, incurs the cost of poorer work-family balance for men. Surprisingly, HILDA data show that overall men experience greater work-to-family strain than women.