Modeling and Performance Simulation of an Innovative Concept of Linear Fresnel Reflector based CSP System

Concentrating solar power technology is one of the most promising alternative energy technologies.In recent past,Linear Fresnel Reflector systems have received great attention and novel designs have been proposed keeping in view the objective to enhance its functionality and performance.For achieving the same objective,this study presents a novel concept where a conventional LFR is enclosed in a greenhouse called greenhouse-LFR.It was expected that such an enclosure can:(1)increase the incoming solar radiation,(2)further improve the overall efficiency due to simplified cleaning process and(3)reduce the capital cost for the construction of LFR support system.A complete thermal and optical analysis was presented for modeling and performance evaluation of the solar field of both conventional-LFR and novel greenhouse-LFR.Sets of non-linear equations for each system were solved using Newton-Raphson method.More detailed optical analysis was further performed for conventional-LFR considering the seasonal variations.The results concluded that the greenhouse-LFR is better than the conventional-LFR as it had higher efficiency and useful heat with lesser heat losses.For greenhouse-LFR,the maximum thermal efficiency was 73.2%whereas for conventional-LFR it was 37.2%.Also,there was an average increase of useful heat by 3 times in the month of February and 4.7 times in the month of September.SolTrace^(TM) analysis indicated significant spillage loss when a conventional-LFR was used without a secondary reflector or slight curvature of the mirrors.

Daily, monthly and annual thermal performance of a linear Fresnel reflector to drive an organic Rankine-cycle system

The organic Rankine cycle(ORC)coupled with a linear Fresnel reflector(LFR)utilizes a low-grade heat source.This article presents the study of a small-scale LFR-ORC power-generation plant under the climatic conditions of Almatret,Spain.The mathematical modelling is performed using thermodynamic equations and simulations are conducted to evaluate the optical performance of the LFR system and thermal performance of the ORC plant.Therminol-62 is used as a heat-transfer fluid(HTF)in the solar field,whereas NOVEC^(TM) 649 is used as the working fluid in the ORC power system.The LFR is integrated with a thermal-storage unit based on a two-tank system and stores the solar thermal energy via a heat exchanger.The thermal-energy output of the receiver tube of the LFR system is 108 kW and thermal losses are 7.872 kW during the peak time operation of a day at 1:00 p.m.The mechanical power output of the ORC turbine is 7.296 kW using the specific design conditions and the two-tank thermal-storage system adds 4 operation hours to the power plant after sunset.

Comprehensive Review of Line-Focus Concentrating Solar Thermal Technologies: Parabolic Trough Collector (PTC) vs Linear Fresnel Reflector (LFR)

In the present review,parabolic trough collector(PTC)and linear Fresnel reflector(LFR)are comprehensively and comparatively reviewed in terms of historical background,technological features,recent advancement,economic analysis and application areas.It is found that although PTC and LFR are both classified as mainstream line-focus concentrating solar thermal(CST)technologies,they are now standing at different stages of development and facing their individual opportunities and challenges.For PTC,the development is commercially mature with steady and reliable performance;therefore,extension of application is the main future demand.For LFR,the development is still in rapid progress to commercial maturity,yet indicating very promising potentials with high flexibility in novel designs and remarkable reduction in capital and operational costs.The question,which has to be answered in order to estimate the future perspectives of these two line-focus CST technologies,becomes which of these characteristics carries more weight or how to reach an optimal trade-off between them.

Influence of Dust Accumulation on the Solar Reflectivity of a Linear Fresnel Reflector

Solar reflecting and heat collecting systems are generally operated outdoors year-round,and the optical performance of the reflector is reduced by dust accumulation on the surface.In this study,the dust accumulation on a linear Fresnel reflector was investigated.The relative reflectivity of the mirror before and after dust accumulation and the physical and chemical characteristics of the dust were measured using an ultraviolet spectrophotometer,scanning electron microscope,and X-ray diffractometer.The results showed that the dust density on the mirror increased,and the relative reflectivity decreased with an increase in the dust accumulation time.During 48 days of dust accumulation,the average relative reflectivity decreased 9.4%for a 1 g/m^(2)increase in the dust density.Additionally,the dust density on the mirror increased while the relative reflectivity decreased with a decrease in the mirror tilt angle.The rate of decrease of the relative reflectivity was higher for the aluminum mirror than that of the silver mirror after dust accumulation.The main component of the dust particles in the test area was SiO_(2),and the particle size range of the dust was 0.9 um to 87µm.According to the physical and chemical properties of the dust and the shielding effect of the dust on the mirror,a model to predict the influence of natural dust accumulation on the relative reflectivity of the linear Fresnel reflector was proposed.The predicted results deviated about 1%from the test results.

Solar Flux Measuring and Optical Efficiency Forecasting of the Linear Fresnel Reflector Concentrator after Dust Accumulation

The linear Fresnel reflector concentrator(LFRC)is widely used in the field of solar energy utilization due to its simple structure,low cost,and excellent wind resistance.Nevertheless,the LFRC operates outdoors all year round,and the dust accumulation on the mirror will reduce the optical efficiency of the system,so it needs to be perfected and improved.In this paper,a focal plane energy flux experimental device was designed to test the energy flux of the system under different dust accumulation times.The results indicate that,the dust density on the mirror increased and the energy flux on the focal plane decreased with increase of dust accumulation time.After undergoing dust accumulation for 35 days,the dust density on the mirror reached 4.33 g/m^(2)and the average energy flux on the focal plane decreased to 1.78 kW/m^(2).Additionally,the variation of reflectivity caused by dust accumulation on mirror was taken as the quantitative index,and a prediction model for the impact of dust on the optical efficiency of the system was proposed.The results will provide guidance for improving the optical efficiency of the LFRC.

线性菲涅尔式聚光系统的镜场布置与优化

单根真空集热管和复合抛物面聚光器(CPC)组成的接收器(单管接收器)对线性菲涅尔式聚光系统的镜场布置有特殊要求。本文根据单管接收器的特点,提出了利用CPC最大接受半角控制镜场高宽比实现镜场无阴影布置的方法。利用几何关系推导了镜场无阴影布置的数学表达式,并给出了数值计算方法。通过算例,将一次反射镜和镜场中心的距离与镜场地面覆盖率相结合对镜场布置进行了优化。研究结果表明:对于CPC最大接受半角为45°、反射镜宽度为380mm、而反射镜列数为21的镜场,当系统无阴影工作时间确定为6h时,相邻一次反射镜间距最大为537mm较为合理,而此时地面覆盖率为73.28%。该方法对于单管接收器线性菲涅尔聚光镜场的布置具有普适性,对线性菲涅尔式聚光系统的设计具有较好的指导意义。

用于线性菲涅尔式聚光系统的CPC仿真研究

以用于线性菲涅尔式聚光系统的CPC为研究对象,在Matlab环境下建立了数学模型。利用光线跟踪法对不同间隙、不同最大接受半角和不同截取比的CPC汇聚率进行仿真研究,结果表明用于线性菲涅尔式聚光系统的CPC对不同入射角光线具有特定的汇聚率,随着入射角的变化会出现极小值,极小值所对应的入射角仅与CPC最大接收半角相关,与截取比和间隙无关。仿真计算了间隙为50 mm、最大接受半角为45°、截取比为0.75的CPC汇聚率为80.15%。最后通过实验验证了仿真方法的有效性。

Design and optimization of CSP power plants for Pakistan:a comparative study

Despite having very high solar irradiance,Pakistan still does not have any installed concentrated solar power(CSP)plant.Several studies have shown that multiple locations within the country are suitable for CSP plants,but there is limited availability of comprehensive comparative studies.Therefore,this article presents a comparative analysis of different CSP technologies in Pakistan,focusing on their potential to address the country’s energy crisis.The study evaluates the pros and cons of different CSP technologies at various locations through site assessment,modelling,optimization and economic analysis using the System Advisor Model.Quetta and Nawabshah were selected as the locations for modelling multiple scenarios of 100-MW plants,using central receiver systems,parabolic trough collectors and linear Fresnel reflectors.The plants were integrated with thermal energy storage and the storage capacity was optimized using parametric analysis.The results showed that a central receiver system for the location of Quetta was the most favourable option,with an annual energy yield of 622 GWh at 7.44 cents/kWh,followed by a central receiver system for Nawabshah(608 GWh,9.03 cents/kWh).This study is the first to show that switching between line-concentrated and point-concentrated CSP technologies can open new opportunities for sites in Pakistan with relatively high solar resources,resulting in a 21.3%reduction in the levelized cost.

线性菲涅尔式聚光系统单管接收器的设计与优化

接收器是决定线性菲涅尔式聚光集热系统光学效率的关键部件之一.设计了一种适用于高温介质(>500°C)的线性菲涅尔式聚光系统的接收器,由单根真空集热管和CPC组成,并重点研究了CPC最大接受半角和截取比选择对其性能的影响.研究结果表明:CPC汇聚率随最大接受半角的增大而缓慢增大;若截取比小于0.65,则CPC汇聚率急剧下降;最大接受半角为45°、截取比为0.75的CPC开口宽度为475.49 mm,汇聚率为80.15%;基于该CPC的系统光热效率为58.06%,由此得出CPC实际汇聚率高于78.42%.

线性菲涅尔反射式太阳能热发电系统非均匀能流分布特征及优化

在线性菲涅尔反射式太阳能热发电系统的聚光集热系统中,其吸热管周向会形成不均匀的能流分布,导致吸热管局部温度过高,对系统的安全高效运行带来不利影响。提出一种基于遗传算法的优化方法,以复合抛物面聚光器(CPC)开口平面为瞄准线,改变单个一次反射镜的瞄准点,实现接收器表面能流分布标准偏差的最小化。通过算法优化,实现了79.53%的光学效率,且使吸热管上半部分能流分布达到40%,为光学效率和能流均匀性带来了有益的优化效果。