Solar Thermal Concentrator Research Articles

Influence of partial solar energy storage and solar concentration ratio on the productivity of integrated solar still/humidification-dehumidification desalination systems

This paper presents the productivity and operational performance of a newly developed integrated solar still - two effects humidification-dehumidification desalination system (SS-HDH). The influence of partial solar thermal energy storage and solar Concentration Ratios (CR) on the transient performance and daily productivity is investigated. Other design, operation and environmental conditions include solar still basin water heights (h) and phase change materials (PCM) without and with Nano-particles are investigated. A transient comprehensive mathematical model is developed using mass and energy balance equations for the different system elements. The model results are validated with the available experimental and numerical data. Results of consecutive days indicated that the system daily production and basin water temperature increase in the second and third day due the stored energy in the system. Furthermore, increasing CR linearly raises the daily productivity and increases basin maximum water temperature (above the CaCO3 scale deposits defined limit of 70 °C) due to the added energy. However, increasing the basin water height, h, reduces the productivity and basin maximum water temperature. Without PCM, the results show that the maximum water production is 11.6 L/m2 per day at h = 0.2 m and CR = 2. This is considered the optimum parameters for high water production while avoiding scale formation on the solar still basin surface. Adding PCM without or with Nano-particles has a slight effect on both the daily production and the maximum basin water temperature. However, at CR = 2, and h = 0.1 m, the maximum productivity is about 11 L/m2 per day using Glaubers salt with 10% volume fraction of Cuo-Nano particles. Besides, the basin water temperature is below 70 °C to avoid a potential scale formation. The proposed SS-HDH suits more a small scale (of up to 100 L/day) house roof distillation unit for direct water need of a family.

ORC Based Solar Power Generator

Renewable energy technologies are clean sources of energy that have a much lower environmental impact and are non-depleting. This paper provides review of an Organic Rankine Cycle (ORC) based Thermal Power Generator that converts Solar Energy into Electricity for its use in a residential society. The solar thermal dish concentrator coupled with ORC is a developing technology that eliminates the traditional centralized power generation and distribution system and delivers electricity directly with the help of an ORC. The solar radiation is absorbed by the concentrator that heats the water which is then used in ORC to produce electricity. From the results that we obtained it was found out that the proposed system is currently somewhat economically unviable in India but it can be highly beneficial and cost effective in the near future if the key system components are designed and manufactured in India under the Government of India’s startup India initiative.

Solar-driven interfacial evaporation

As a ubiquitous solar-thermal energy conversion process, solar-driven evaporation has attracted tremendous research attention owing to its high conversion efficiency of solar energy and transformative industrial potential. In recent years, solar-driven interfacial evaporation by localization of solar-thermal energy conversion to the air/liquid interface has been proposed as a promising alternative to conventional bulk heating-based evaporation, potentially reducing thermal losses and improving energy conversion efficiency. In this Review, we discuss the development of the key components for achieving high-performance evaporation, including solar absorbers, evaporation structures, thermal insulators and thermal concentrators, and discuss how they improve the performance of the solar-driven interfacial evaporation system. We describe the possibilities for applying this efficient solar-driven interfacial evaporation process for energy conversion applications. The exciting opportunities and challenges in both fundamental research and practical implementation of the solar-driven interfacial evaporation process are also discussed. The thermal properties of solar energy can be exploited for many applications, including evaporation. Tao et al. review recent developments in the field of solar-driven interfacial evaporation, which have enabled higher-performance structures by localizing energy conversion to the air/liquid interface.

Fixed Nadir Focus Concentrated Solar Power Applying Reflective Array Tracking Method

The Sun is one of the most potential renewable energy develoPMent to be utilized, one of its utilization is for solar thermal concentrators, CSP (Concentrated Solar Power). In CSP energy conversion, the concentrator is as moving the object by tracking the sunlight to reach the focus point. This method need quite energy consumption, because the unit of the concentrators has considerable weight, and use large CSP, means the existence of the usage unit will appear to be wider and heavier. The addition of weight and width of the unit will increase the torque to drive the concentrator and hold the wind gusts. One method to reduce energy consumption is direct the sunlight by the reflective array to nadir through CSP with Reflective Fresnel Lens concentrator. The focus will be below the nadir direction, and the position of concentrator will be fixed position even the angle of the sun’s elevation changes from morning to afternoon. So, the energy concentrated maximally, because it has been protected from wind gusts. And then, the possibility of dAMage and changes in focus construction will not occur. The research study and simulation of the reflective array (mechanical method) will show the reflective angle movement. The distance between reflectors and their angle are controlled by mechatronics. From the simulation using fresnel 1m2, and efficiency of solar energy is 60.88%. In restriction, the intensity of sunlight at the tropical circles 1KW/peak, from 6 AM until 6 PM.

Compact, semi-passive beam steering prism array for solar concentrators

In order to maximize solar energy utilization in a limited space (e.g., rooftops), solar collectors should track the sun. As an alternative to rotational tracking systems, this paper presents a compact, semi-passive beam steering prism array which has been designed, analyzed, and tested for solar applications. The proposed prism array enables a linear concentrator system to remain stationary so that it can integrate with a variety of different solar concentrators, and which should be particularly useful for systems which require a low profile (namely rooftop-mounted systems). A case study of this prism array working within a specific rooftop solar collector demonstrates that it can boost the average daily optical efficiency of the collector by 32.7% and expand its effective working time from 6h to 7.33h. Overall, the proposed design provides an alternative way to "follow" the sun for a wide range of solar thermal and photovoltaic concentrator systems.

Modeling and designing of the solar thermal parabolic trough concentrator and its environmental effects

Concentrating solar power (CSP) system is a favorable application because of its potential to constantly generate large‐scale electricity. Today, there are many CSP plants in the world. Therefore, the aim of this study is to analyze these systems in detail. To measure the efficiencies of these systems, a model is created and a microsystem is experimentally tested. As a result, the gas boiler modeled in this study generates a monthly amount of 3.222,317 kWh, and the collector generates a monthly amount of 1.709,8 kWh. In addition, we also analyzed the CO2 emission status, and CO2 emission reduction was calculated as 5.279,6 kg, demonstrating the environment‐friendly nature of the system. This study introduces a model of CSP plant prior installation. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 967–974, 2017

Design and indoor testing of a compact optical concentrator

We propose and analyze designs for stationary and compact optical concentrators. The designs are based on a catadioptric assembly with a linear focus line. They have a focal distance of around 10 to 15 cm with a concentration ratio (4.5 to 5.9 times). The concentrator employs an internal linear-tracking mechanism, making it suitable for rooftop solar applications. The optical performance of the collector has been simulated with ray tracing software (Zemax), and laser-based indoor experiments were carried out to validate this model. The results show that the system is capable of achieving an average optical efficiency of around 66% to 69% during the middle 6 (sunniest) h of the day. The design process and principles described in this work will help enable a new class of rooftop solar thermal concentrators.

Directly absorbing Therminol-Al2O3 nano heat transfer fluid for linear solar concentrating collectors

This paper reports experimentally measured thermal and optical properties of Al2O3-Therminol®55 nano heat transfer fluid (nHTF) in conjunction with a specially developed line focusing Fresnel lens based solar thermal concentrator. Solar collector tests were conducted under real life outdoor ambient and solar radiation conditions. A range of volumetric proportions of Al2O3 (0.025–0.3vol%) have been covered. Highest thermal conductivity and refractive index were measured for nHTF with 0.1vol% concentration of Al2O3 with higher concentrations (>0.1vol%) concluded to be unfit for their use in the solar collector applications due to likely agglomeration and sedimentation in the hours of low or nil sunshine when fluid is not circulating. Thermal conductivity enhanced by 11.7% for 0.1vol% Al2O3 concentration nHTF. A highest temperature of 132.8°C was delivered by the solar collector using 0.1% concentration Al2O3 nHTF at a flow rate of 0.5lps. This was 44.7°C higher than that achieved by pure Therminol®55 (88.1°C) even though the DNI during 0.1% nHTF test was considerably lower than that for the later. The solar concentrator thermal efficiency increased with the proportion of NPs attaining a maximum of 52.2% for 0.1vol% Al2O3 nHTF. Directly absorbing nHTFs along with the solar collector developed in this study are predicted to be strong candidate to replace conventional metallic tube receiver using concentrators due to advantages of size compaction and higher thermal conversion efficiency.

Evaluation of the efficiency of dual compound parabolic and involute concentrator

A two-stage line axis solar thermal concentrator consisting of a compound parabolic and an involute reflector was designed, and its thermal and optical performance was compared with that of a dual concentrator. The configuration of the reflectors with tubular absorber yields the highest possible concentration and uniform temperature distribution on the absorber. To reduce the heat loss from the absorber, the concentrator was covered with evacuated glass tube. The dual concentrator increases ray acceptance, which is defined as the ratio of the reflector aperture area to the glass cover diameter; hence, the concentrator can utilize incident solar radiation more effectively with only a slight increase of 28% in the glass cover circumference. This suggests the use of dual concentrators in multiple concentrator units owing to their lower component cost. The performance was evaluated by using a ray-tracing model for two-dimensional (2D) geometry. The average optical efficiency of dual and single concentrators was 57% and 37%, respectively. The thermal efficiency of the dual concentrator was 21% higher than that of single one at the absorber temperature of 373K for the gray surface absorber. On the other hand, the selective surface absorber significantly increased the performance, suggesting that the concentrator can be used in high-temperature applications such as steam generation. Annual and seasonal performances were analyzed as well. Assuming infinite length of the line-axis concentrator's absorber pipe allows ignoring the end effects; thus, a 2D approach was adopted. As a result, the dual concentrator showed better performance for all seasons; however, the solar utilization time of both concentrator types became shorter during the winter and summer solstices because of the weak insolation resulting from the orientation of the concentrators. Therefore, a slight seasonal adjustment or a modification of the geometry is required for longer utilization.

Optimized solar thermal concentrator system based on free-form trough reflector

A solar thermal concentrator system is proposed comprising a free-form-trough (FFT) reflector and a cylindrical heat-pipe receiver. The profile of the reflector is designed using a free-form surface creation (FFSC) method such that each incident ray is directed to a certain user-specified point on the heat-pipe surface. The light ray paths within the concentrator system are analyzed using a skew-ray tracing approach. A method is then proposed for optimizing the geometry of the concentrator system in such a way as to achieve a uniform irradiance distribution on the heat-pipe surface. The validity of the proposed optimization approach is demonstrated by means of ZEMAX/SolidWorks-Flow simulations. The results show that the proposed FFT concentrator yields a significant improvement in both the irradiance uniformity and the heating efficiency compared to conventional cylindrical-trough and parabolic-trough concentrators.

Pilot demonstration of concentrated solar-powered desalination of subsurface agricultural drainage water and other brackish groundwater sources

The energy–water nexus is addressed with the experimental demonstration of a solar-powered desalination process system. This system was designed for high-recovery treatment of subsurface agricultural drainage water as a reuse strategy as well as other brackish groundwater sources. These water sources may exhibit wide fluctuations in salinity and makeup and pose a high risk for operational troubles due to high scaling potential. A first-of-its-kind open-cycle vapor-absorption heat pump is coupled with a multiple-effect distillation train and a large parabolic trough solar thermal concentrator. Without the heat pump, the distillation operation showed a minimum thermal energy consumption of 261.87kWhth/m3. With the heat pump, the thermal energy consumption was reduced by more than 49% to 133.2kWhth/m3. This reduction in thermal energy requirement directly translates into a 49% reduction in solar array area required to power a process with the same freshwater production rate as a system without an integrated heat pump. An optimized design was modeled and the thermal energy performance of a commercial system is projected at 34.9kWhth/m3 using a 10-effect MED operating at 85% recovery.

Optical modeling of a solar dish thermal concentrator based on square flat facets

Solar energy may be practically utilized directly through transformation into heat, electrical or chemical energy. We present a procedure to design a square facet concentrator for laboratory-scale research on medium-temperature thermal processes. The efficient conversion of solar radiation into heat at these temperature levels requires the use of concentrating solar collectors. Large concentrating dishes generally have a reflecting surface made up of a number of individual mirror panels (facets). Optical ray tracing is used to generate a system performance model. A square facet parabolic solar concentrator with realistic specularly surface and facet positioning accuracy will deliver up to 13.604 kW of radiative power over a 250 mm radius disk (receiver diameter) located in the focal plane on the focal length of 1500mmwith average concentrating ratio exceeding 1200. The Monte Carlo ray tracing method is used for analysis of the optical performance of the concentrator and to identify the set of geometric concentrator parameters that allow for flux characteristics suitable for medium and high-temperature applications.

Mechatronic Platform with 12m2 Solar Thermal Concentrator for Rural Power Generation in Africa

Electrical power generation through Stirling type engines make use of concentrated solar radiation as the source of high- temperature heat. From a sustainable electrical power generation point of view, most rural African villages experience good concentrations of solar radiation, but rolling out reliable CSP solutions for tapping into this resource at rural African sites poses some system design challenges. This paper proposes a design for a 12m2 parabolic dish frame which includes novel modifications over to the latest lightweight solar concentrators and aims to simplify assembly and installation of the solar concentrator platform at remote rural sites with unskilled support. The paper details the mechanical and mechatronic design challenges, solutions and selected results achieved in the quest to develop a stand-alone electrical power supply system for off- grid rural communities, research which ultimately aims to produce a locally manufactured knock-down do-it-yourself CSP power generation kit, suitable for distribution throughout Africa.

Description and characterization of an adjustable flux solar simulator for solar thermal, thermochemical and photovoltaic applications

A high flux solar simulator for indoor performance assessment of systems in solar thermal, thermochemical and high concentration photovoltaic research offers repeatability under controlled climate conditions. This paper presents a new high flux solar simulator where a 7kW xenon short arc lamp coupled with a truncated ellipsoid reflector is used as the light source. The flux mapping method is used to evaluate performance of this high flux solar simulator on the basis of flux distribution, temporal instability, spatial non-uniformity, peak flux, conversion efficiency and power intercepted on a circular target placed at the focal plane. The input current of the simulator is adjusted in the range of 113–153A to quantify the maximum and minimum peak flux output per power settings of the solar simulator, which yield different flux distribution at different power level. A theoretical comparative analysis of manufacturer’s sensor scaling factor of the circular foil heat flux gage with literature is performed and an optimum scaling factor of 491.46kWm−2/mV is selected to relate measured incident flux with CCD (charge-coupled device) camera’s greyscale value of acquired image. It was observed that at an input current of 153A, the simulator delivers a peak flux of 3583kWm−2, temporal instability of radiative output less than 3%, and cumulative beam power of 1.642kW at a circular target radius of 110mm placed at the focal plane. A conversion efficiency at 153A and 110mm radius was determined to be 47%. For a photovoltaic cell size of 1.5mm radius, the solar simulator provides an average incident flux in the range of 1200–3000 suns with class ‘A’ temporal instability and class ‘B’ spatial non-uniformity. The simulator is capable of adjusting peak flux in the range of 2074–3583kWm−2 and can produce a theoretical black body stagnation temperature of 1857K.

Medium temperature concentrators for solar thermal applications

Medium temperature solar thermal applications have received remarkable interest in the recent years in both residential and industrial sectors. Solar concentrating systems can serve properly such applications with a temperature range of 80–250°C, taking advantage of their sun light focusing characteristic and high thermal and optical performance. Improvements and developments in the field of medium temperature solar thermal concentrators over the last 6 years are reviewed and analyzed in this article. Different types of solar thermal concentrators are examined, and a critical comparison among different concentrators is carried out based on the performance and the applicability. The most successful solar thermal applications are also presented along with the recent developments in sun-tracking technologies. It has been shown that the choice and design of the optimal concentrating system is largely dependent on the specific characteristics and nature of each application.

Optimized variable-focus-parabolic-trough reflector for solar thermal concentrator system

A solar thermal concentrator system is proposed comprising a cylindrical heat-pipe receiver and a variable-focus-parabolic-trough (VFPT) reflector in which the focal length varies as a function of the vertical displacement of the incidence point relative to the horizontal centerline of the receiver. The light ray paths within the concentrator system are analyzed using a skew-ray tracing approach. A method is then proposed for optimizing the geometry of the concentrator system in such a way as to optimize the uniformity of the irradiance distribution on the heat-pipe surface. The validity of the proposed optimization method is demonstrated by means of ZEMAX/SolidWorks-Flow simulations. It is shown that the optimized VFPT concentrator yields a significant improvement in both the irradiance uniformity and the heating efficiency compared to conventional cylindrical-trough and parabolic-trough concentrators.

A model for improved solar irradiation measurement at low flux

Accurate measurement of solar radiation heat flux is important in characterizing the performance of CSP plants. Thermopile type Heat Flux Sensors (HFSs) are usually used for this purpose. These sensors are typically reasonably accurate at high heat fluxes. However measurement accuracy drops significantly as the measured radiation is below 1 kW/m2, this often leads to underestimation of the actual flux. At the Masdar Institute Beam Down Solar Thermal Concentrator (BDSTC), measurement of fluxes ranging from 0 kW/m2 to more than 100 kW/m2 is required. To improve the accuracy of the sensors in the lower range around 1 kW/m2, we have performed a test under ambient (not-concentrated) sunlight. Such low irradiation levels are experienced in characterizing the concentration quality of individual heliostats. It was found during the test that the measurement at this low range is significantly affected by ambient conditions and transients in the HFS cooling water temperature. A Root Mean Square Error (RMSE) of more than 100 W/m2 was observed even though we kept the transients in water temperature to a minimum. Hence we devised a model to account for this measurement error at this flux range. Using the proposed model decreased the RMSE to less than 10 W/m2. The application of the model on existing heat flux measurement installations is facilitated by the fact that it only employs easily measurable variables. This model was checked by using a test data set and the results were in good agreement with the training data set.

A new type of solar concentrator employing a cone-cylinder combination

Most conventional solar thermal radiation concentrators have some sort of symmetry which allows them to concentrate solar thermal energy for their operation. We report a new system that utilises the symmetry of a cone and a cylinder combination to simulate the concentration of solar radiation on a ring containing a fluid (water). A halogen lamp is used as the source of radiation to simulate solar radiation in this work. The temperature of the water in the ring with the concentrator is found to rise to a steady state of 55.4°C after the ring is exposed to radiation for a period of 1,200 sec while water in the ring without the concentrator exposed to the same radiation attains a steady state temperature of 33.2°C for the same exposure time of 1,200 sec.

Generation of operational maps of global solar irradiation on horizontal plan and of direct normal irradiation from Meteosat imagery by using SOLARMET

The physical model SOLARMET, elaborated in ENEA (Italian National Agency for New Technologies, Energy and Environment), provides hourly average global solar irradiance on a horizontal surface (GHi) and hourly average direct normal solar irradiance (DNi) for Italy based on primary satellite images in the visible band. In the present study, the hourly estimates of surface radiation generated by SOLARMET have been summed up to produce monthly average daily irradiation maps. Hourly and monthly maps were done for the years 1996 and 2002. The parameters of this model were obtained by comparing the Meteosat satellite data with ground data gathered in 2002. Differences, relative to 1996, between SOLARMET estimates and observations obtained over two radiation networks of Italian ground sites are presented: the Meteorological Service of the Italian Air Force and National Agro-Meteorological Network; In total 51 ground stations. The comparison between SOLARMET and the previous Italian method carried out in ENEA shows an improvement due to SOLARMET. Such comparison between the values derived using SOLARMET and previous ENEA methodologies and with data from ground-based stations was possible only for monthly averages of daily global radiation due to an almost total lack of direct radiation ground data in Italy. The operational monthly solar radiation maps, showing solar energy potentials, permit the selection of construction sites to solar energy project developers. In Italy, these data are necessary for installing solar thermal concentration power plants in support of the R&S program recently funded to demonstrate the possibility of these technologies.

A method for evaluating and selecting renewable and non-renewable energy technologies

This paper offers a simple method of evaluating the existing renewable and non-renewable energy technologies. The evaluation method is based on the weights given to the importance of six selection criteria: the economic viability; the conversion efficiency; the present level of the technological development; the environmental impacts; the after-production clean-up cost; the renewability and abundance of the source. This paper also outlines the main shortcomings of the energy technologies, based on which they are rated. These ratings together with the weights assigned to the selection criteria produce normalised scores for each technology which are then used for comparison. The existing energy technologies are evaluated from five different points of view, in which the importance of (the weights given to) the economic viability and the environmental impacts of the technologies are varied. The results show that in a society that assigns the highest importance to the economics of the energy production technologies, the non-renewable sources are the most attractive, but become less desirable, when the environmental impacts of the technologies are given any weight. In particular, even with a moderate weight (of two out of a maximum weight of four) given to the environmental impacts, the renewable technologies, especially solar thermal concentrator has become the technology of choice.