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.

LFR发电系统中直流辅助电源的设计与实现

针对线性菲涅尔式太阳能热发电系统中对直流电源的需求,设计了一款基于UC2842的多路输出直流辅助电源.该电源输入为交流220×(1±0.10)V,直流输出分别为24 V、15 V、5 V,整个电路包括整流电路、功率变换电路、输出整流电路和控制电路等部分,并使用Saber软件对所设计的电源进行仿真验证.仿真结果表明,该直流辅助电源三路输出直流电压稳定,能够满足实际需求,可以为线性菲涅尔太阳能热发电系统的单片机、辐照度测试仪、隔离驱动电路、控制器等小功率器件提供可靠的直流工作电压.

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.

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.

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.

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.

线性菲涅耳聚光系统无遮挡镜场布置的矢量分析法

利用矢量分析,得到线性菲涅耳反射装置任一镜元的入射角、反射矢量、跟踪倾角计算公式。通过坐标变换,得到适合于阴影与遮挡计算的坐标系并计算出障碍镜元在被遮挡镜元所在平面上的阴影坐标,通过对阴影坐标的分析,给出镜元之间无阴影与遮挡的最小间距并经实验验证,分析了具体算例情况下的镜元间距。

菲涅耳太阳能聚光系统跟踪倾角的矢量算法

提出了线性菲涅耳反射装置中太阳跟踪倾角的计算方法。该聚光装置中每一个反射镜面(简称镜元)需实时跟踪太阳,使太阳入射光反射至固定位置的线性吸热器上。但是,从目前的太阳位置算法中得到的太阳高度角、方位角并不能直接用来控制跟踪,必须进行复杂计算,得到每一镜元相应的跟踪倾角,然后控制电机使其旋转至相应位置。通过将太阳矢量适当分解,简化计算得到适合于菲涅耳太阳能聚光装置反射定位的旋转倾角并经实验验证。

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。

线性菲涅耳聚光镜场辐射量计算方法

在聚光太阳能热利用设计时,有必要计算聚光装置倾斜镜面或孔径表面的太阳直接辐射。线性菲涅耳聚光反射装置是对连续抛物面聚光镜的一种离散化近似,该聚光装置中每一行反射镜面(简称镜元)均实时跟踪太阳,故每一镜元的太阳光入射角、跟踪倾角均时刻变化,这便使系统太阳辐射计算变得相对复杂。首先利用矢量分析,得到线性菲涅耳反射装置任一镜元的入射角计算公式,然后计算整个镜场的实时辐射通量,最后得到整个镜场在有效工作期间内的累积辐射量。通过对反射光在吸热器平面的偏移分析,得到线性菲涅耳聚光反射镜场的最佳塔高计算方法。

线性菲涅耳太阳能聚光镜场遮挡性能分析

首先利用矢量分析,得到线性菲涅耳反射装置任一矩形镜元的入射角、反射矢量、跟踪倾角计算公式。然后通过坐标变换以及射线追踪法,得到被遮挡镜元所在平面上的阴影与遮挡分布,通过统计分析,给出线性菲涅耳镜场的阴影与遮挡效率。最后通过分析线性塔高、镜元间距、镜元宽度对LFR镜场阴影与遮挡效率的影响,给出线性菲涅耳聚光镜场的阴影与遮挡效率计算模型。

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。

线性菲涅耳不同镜场光学性能比较

首先通过矢量分析,得到线性菲涅耳(LFR)东西场镜场中任意矩形镜元的入射角、反射矢量、跟踪倾角计算公式,然后利用南北场的相关公式,对这两种不同的LFR镜场分布的末端损失、大气衰减、余弦系数等光学效率进行分析比较,针对不同应用,找出合理的镜场分布方式,为LFR系统的大规模应用提供重要的参考与指导。

线性菲涅尔一次镜场光学效率分析

对线性菲涅尔太阳能集热一次镜场的光学效率进行了数值计算。用最大采光半角θ、反射镜列数n和镜场填充率μ来描述镜场,计算一次镜场光学效率随光线入射角γ的变化趋势。该算法的计算结果与Trace Pro及Sol Trace的计算结果一致。分析表明：线性菲涅尔一次镜场的光学效率受相邻反射镜列间的遮挡和阴影影响,加大光线入射角,镜场效率明显下降;在无阴影和无遮挡的情况下,随着入射角γ的增加,与光线垂直入射相比,镜场效率按cosγ/2倍率下降。通过计算得到光线垂直入射时,镜场不发生遮挡的临界镜场填充率及其对应的光学效率。研究结果显示：减小最大采光半角能显著增加镜场光学效率;当最大采光半角为45~60°、在正午前后6~8 h,不发生阴影和遮挡的临界镜场填充率一般低于75%;与抛物线槽式聚光器相比,设计良好的线性菲涅尔一次镜场反射镜的阴影和遮挡,使正午前后6~8 h的平均光学效率下降5.0%~8.3%。

反射式线性菲涅尔集热器性能的实验研究与模拟分析

采用热网络法建立菲涅尔集热系统CPC腔式接收器的数值传热模型,搭建集热器系统,实验研究集热器效率、CPC腔的集热性能。利用数值传热模型分析太阳辐照度、镜场宽度、工质入口温度和质量流量的变化对系统出口温度和效率的影响,以期为菲涅尔集热器出口参数的控制提供依据。实验数据验证了模型的有效性,模拟结果显示,质量流量对工质出口参数影响最大;镜场宽度和辐照度对集热效率的影响最为显著;菲涅尔集热器的热效率可达68%。

严寒地区小型线性菲涅尔聚光集热器末端损失与补偿

针对严寒地区线性菲涅尔聚光集热器末端损失严重的问题,该文以呼和浩特地区小型线性菲涅尔聚光集热系统为研究对象,根据不同季节太阳位置的变化,理论分析并计算了沿水平南北轴放置的线性菲涅尔集热器自东向西跟踪过程的末端损失,得到其变化规律及补偿方法,并进行了试验验证。结果表明,一天中末端损失随时间的变化趋势与太阳高度角的变化趋势相同,与太阳方位角变化趋势相反,正午时刻末端损失最大,早晨和傍晚时刻末端损失最小;不同季节相同时间段内的末端损失,冬季最大,夏季最小,春季和秋季几乎相等;镜场调节试验结果表明,增大反射镜北端与水平面的夹角可以补偿末端损失,在夏至前后正午,当镜场北端抬高20°时,末端损失减少至集热器长度的1/10左右,瞬时集热效率达到65.9%,与反射镜调节前相比,正午瞬时集热效率提高54.5%,下午时间段内瞬时集热效率提高20%左右。研究结果可为减小严寒地区小型线性菲涅尔聚光集热器末端损失提供理论参考。

三运动复合线性菲涅耳反射式太阳聚光系统的性能研究

为改善线性菲涅耳反射式聚光系统的余弦损失对系统聚光效率的影响,提出了一种运动式线性菲涅耳反射聚光系统,该聚光系统依靠镜场与太阳保持反向运动来减小余弦损失.通过在广西柳州(北纬24°03')搭建的实验台架对系统的可行性和效率增加进行了验证.实验结果表明该新型系统对太阳光的聚光效率比固定式菲涅耳系统提高9%左右,与理论计算值相当.文中亦利用光学仿真分析对系统布置的优化进行了探讨.分析结果表明在现有系统参数的基础上,适当降低接收器高度可进一步减小余弦损失;在二次聚光器接收允许的范围内适当增大镜元间距还可减小镜场遮挡损失,继续提高系统聚光集热效率.

用于线性菲涅尔式聚光系统的复合抛物面聚光器

为了分析复合抛物面聚光器(Compound Parabolic Collector,CPC)的几何光学效率及影响因素,为线性菲涅尔式聚光系统的优化设计和实际应用提供理论依据。根据用于线性菲涅尔式聚光系统的CPC特点,在Matlab软件中建立模型并进行光线跟踪计算其几何光学效率。利用TracePro软件对几何光学效率模型进行验证。最后,采用该模型分析吸热管外径公差、吸热管位置偏移和线型误差对CPC几何光学效率的影响。结果表明间隙为32.5 mm、接收半角为55°、截取比为0.3的CPC配合外径为70 mm的吸热管,当吸热管外径公差小于-0.4 mm、水平方向存在偏移、垂直方向存在正偏移或线型轮廓增大等因素时,其平均几何光学效率迅速减小。实际应用中应尽可能避免以上因素,或者设计时减小CPC入射角的范围,从而降低对CPC平均几何光学效率的影响。

菲涅耳太阳能聚光系统几何矢量分析

提出了线性菲涅耳聚光反射装置中入射角、反射位置、跟踪倾角的矢量计算方法。该聚光装置中每个反射镜面(简称镜元)需实时跟踪太阳,将太阳入射光反射至固定位置的线性吸热器上,每一镜元的入射角、反射位置、跟踪倾角均时刻变化,系统设计时的计算非常复杂。利用目前太阳位置算法中得到的太阳高度角、方位角,通过矢量法,简化计算过程,推导出线性菲涅耳反射装置任一镜元的入射角、反射位置、跟踪倾角公式,便于菲涅耳太阳能聚光装置的分析应用,计算了2009年各月平均日的各量在具体算例情况下的变化。

基于射线追踪法的线性菲涅尔聚光镜场阴影与遮挡分析

线性菲涅尔式聚光镜场的阴影与遮挡直接影响着系统光学效率,对其进行分析计算至关重要.根据线性菲涅尔式聚光镜场反射镜单轴跟踪的特点,建立平面直角坐标系,推导出任意时刻每列反射镜的坐标方程,利用射线追踪法追踪任意时刻入射至每列反射镜边缘及经边缘反射至接收器的太阳光线,得到阴影与遮挡的长度,根据几何光学推导了由太阳方位角导致的阴影与遮挡未形成区域面积的计算公式,进而得出阴影与遮挡效率.该方法计算量小、执行效率高,可以准确计算线性菲涅尔聚光镜场的阴影与遮挡效率.