Conventional Parabolic Trough Research Articles

Performance Analysis of a Solar Cascaded Absorption Cooling System Using a Performance-Enhanced Parabolic Trough Collector

Abstract This article proposes an innovative approach to improve the performance of solar cooling systems by utilizing a cascaded absorption cooling (CAC) system. This article also examines the viability of coupling an NH3–H2O absorption system with an H2O–LiBr absorption system to simultaneously satisfy both a refrigeration load and an air-conditioning load. Results of this analysis shows that the CAC system uses 7.1% less thermal energy than the sum of the energies used by the ammonia absorption system and the LiBr absorption system if they were to operate separately to meet the same cooling load. In addition, the article investigates the impact of a performance-enhanced parabolic trough collector (PEPTC) on the thermal and exergetic efficiencies of the solar cooling system. By employing a PEPTC, the area required for the solar field in a given solar cooling system will be reduced by 14% compared to the area required by a conventional parabolic trough collector (PTC). Combining the CAC system with the PEPTC results in a 22% increase in the overall efficiency of a cooling plant compared to a conventional PTC coupled with an ammonia system and a LiBr system in the same plant. In summary, it is suggested that the simultaneous utilization of the proposed CAC system and the PEPTC can considerably improve the efficiency of solar cooling systems. Doing so will lead to sustainable cooling alternatives.

Carnot battery application in a parabolic trough concentrating solar power plant: System modelling, validation and analyses on the interplay between stored energies

A Carnot battery application in a conventional parabolic trough concentrating solar power (CSP) plant is examined. During solar thermal charge cycles, electric heaters import renewable energy (RE). This is stored as thermal energy in the plant’s storage system, thereby boosting solar thermal charge cycles. The plant discharges stored thermal energy to support baseload power generation and RE time-shifting. A computational model of the system is developed and validated as reasonably accurate. This is used to investigate potential interplays between stored solar thermal energy and imported RE within the Carnot battery. Results show that for certain storage capacities, solar multiples, heater capacities and heater set-point temperatures, imported RE is stored at the loss of solar thermal energy. Such configurations overcharge storage with imported RE, thereby curtailing solar thermal energy unnecessarily. This leads to operational trade-offs within the CSP Carnot battery, which are not thoroughly assessed in the literature. Via parametric analyses, the paper demonstrates the usefulness of the plant utilisation factor (UF, a less common CSP metric) in measuring the dynamics and magnitude of thermal energy storage (TES) overcharge. The paper develops fundamental insights from the aforementioned design variables, for practical applications in CSP Carnot battery designs that aim to mitigate solar thermal curtailment. Key findings show that: (1) “tipping points” of UF provide constraints on maximum heater capacity to avoid TES overcharge; (2) heater and TES capacities are negatively correlated at the onset of TES overcharge; (3) sufficiently small TES capacities can mitigate overcharge entirely; (4) TES overcharge is aggravated by higher heater set-point temperatures; (5) smaller sized parabolic trough solar fields reduce and delay solar thermal curtailment from heater integration.

Numerical simulation of solar parabolic trough collector with helical grooves using Cu nanoparticles

In this study the effects of modification with creation of grooves as well as the use of nanoparticles with the base fluid has been considered. The main objective during the investigation is to predict the effect of enhancement in thermal efficiency with variation in thermal as well as hydraulic performance of the system. The use of nanoparticles improves the thermal conductivity as well as the hydraulic performance of the PTCs. It is seen that at lower values of Pop (Pop less than 0.20); the difference between the thermal efficiency (η) of conventional parabolic trough collector (CPTC) and parabolic trough collector with internal circular cut helical grooves (HG) systems are about 11.31–13.11 % higher. While the η of HG with copper nanoparticles (HG + Cu) is the highest and lowest thermal performance index (TEI) with 60.4 % and 0.159 respectively among three PTCs. Therefore, the η can be increased either by enhancement in thermal performance or by hydraulic performance.

Design and testing of concentrated photovoltaic arrays for retrofitting of solar thermal parabolic trough collectors

A new design and retrofit approach for a concentrated photovoltaic thermal (CPV-T) system based on a parabolic trough collector is presented. The design differs from previous hybrid architectures, employing a significantly simplified topology in order to reduce costs while keeping electrical efficiency high. To achieve this ambitious goal, the absorber tube of a conventional parabolic trough collector used in thermal systems is replaced by a newly developed hybrid absorber equipped with multi-junction solar cells. This offers the advantage that existing solar thermal parabolic trough facilities can be easily retrofitted, making the system scalable and cost-effective. A scaled prototype of the system was designed and tested in Graz, Austria. During on-sun tests an average electrical system efficiency of 26.8% with a simultaneous thermal efficiency of 48.8% was measured using a geometric concentration ratio of 150 (DNI based). This leads to an overall average system efficiency of 75.5%. Moreover, a solar cell peak efficiency of 30% was achieved, one of the highest measured solar-to-DC efficiencies for a parabolic trough-based solar collector. Special attention was paid to the temperature difference between the solar cells and the heat transfer fluid in order to ensure sufficient cooling of the cells and maximize thermal efficiency. The electrical, thermal and overall efficiencies at different heat transfer fluid temperatures were measured (17°C - 90°C) and their coefficients were derived. This work serves as an experimental proof-of-concept for the application of solar cells in parabolic trough collectors, thereby opening up new possibilities for cost reduction of CPV-T systems.

A novel parabolic trough receiver by inserting an inner tube with a wing-like fringe for solar cascade heat collection

In this work, a novel parabolic trough receiver (NPTR) with an inner tube and wing-like fringe was proposed to improve heat-collecting efficiency as well as provide different grades of thermal energy. Thermal oil and water, which flow respectively in absorber and the inner tube, are selected as high and low temperature heat transfer fluids. A three-dimensional computational fluid dynamics model was developed to investigate the performance of the NPTR. Effects of geometrical parameter and thermal conductivity of inner tube on the performance of NPTR were studied in details. Based on the results, the NPTR with β = 180° is recommended as the suggested design. Moreover, performance of the suggested design under different direct normal irradiances (300–1000 W/m2) and inlet temperature of oil (400–650 K) were evaluated. Compared to the conventional parabolic trough receiver, the heat loss of NPTR is effectively reduced by 33.1–50.1%, and the overall efficiency can be improved by 0.61%–7.67%. Moreover, the proportions of oil and water heat gains in the total input solar energy are ranged in −18.8–63.5% and 8.39–77.6%, and the temperature gains of oil and water are ranged in −1.4–19.5 K and 5.4–18.8 K, respectively.

Performance analysis of direct absorption-based parabolic trough solar collector using hybrid nanofluids

Addition of a small amount of nanoparticles to the working fluids of a parabolic trough collector does not only enhance the heat transfer properties and thermal conductivity of basefluid but also improves the thermal efficiency of the system. The current investigation presents a comparative analysis of experimental performance of a conventional parabolic trough collector and direct absorption parabolic trough collector for capturing solar thermal energy. Two separate nanomaterials, Al2O3 (with high scattering properties) and CuO (with high absorption properties), were selected for the preparation of the hybrid nanofluids. A customized experimental setup was developed to evaluate their photothermal performance. The nanofluid samples in the concentration range of 0.01–0.5 wt% were investigated under a natural solar flux. Thermal efficiency of conventional parabolic trough collector was increased by 31% using hybrid nanofluid as compared to basefluid. The thermal efficiency enhancement of direct absorption parabolic trough collector was observed as 19% higher than that of conventional parabolic trough collector due to higher heat transfer rate, solar trapping and volumetric absorption. These binary nanofluids can be potential working fluids in various applications based on solar thermal energy.

A survey of solar concrete shell collectors for parabolic troughs

Concrete shell collectors offer an alternative to conventional parabolic trough collectors. The principle design concept is derived from existing barrel rooves that effectively bridge large spans in halls or buildings with minimum material usage. The concrete troughs merge the bearing structure and mirroring surface to just one shell of a few centimeters. They are made of high-strength concrete and track the sun via pure axial rotation or lateral movements that avoid any lifting works. In the present contribution, basic constraints in materials, geometry, and static calculation are derived and converted into a framework of possible designs. This contribution thereby presents a survey of concepts that range from small-scale prototypes to full-scale realizations of 140 m2 apertures and large-aperture concepts with a 10 m width. Design concepts with bearing and drive systems as well as optimization-based form findings are introduced to elaborate shells of minimum weight with solid sections, stiffeners, and hollow cores.

An efficient solar-aided waste heat recovery system based on steam ejector and WTA pre-drying in solar/lignite hybrid power plants

An efficient solar-aided waste heat recovery system based on steam ejector and WTA pre-drying was proposed. In the proposed system, solar energy collected by parabolic trough collector is used to generate a little high-grade steam, inducing steam waste heat in steam ejector and producing large amount of medium-grade drying steam. By absorbing waste heat in steam ejector and integrating with coal pre-drying, the solar energy could be considered amplified in the steam ejector and converted into the dried coal’s heating value. The results reveal that, for a typical 1000 MW lignite-fired power plant, 46.6 MWth of steam waste heat could be recovered efficiently by collecting 21.6 MWth of solar energy. The proposed system could produce 36.2 MWe of additional power with 1.62% of thermal efficiency increase. The cost of solar generated electricity of the proposed system is 0.028 USD/kWh, which is significantly lower than that of the conventional parabolic trough concentrating solar plants and solar-aided power generation system. The off-design performance reveals that the proposed system could solve the fluctuation of solar energy by dried coal storage.

Heat recovery of nano-fluid based concentrating Photovoltaic Thermal (CPV/T) Collector with Organic Rankine Cycle

This study proposed a novel configuration of solar concentrating receivers that utilize Nano-fluids for spectral splitting and coupled with Organic Rankine Cycle (ORC) for heat recovery. 1-D modelling of a conventional Parabolic Trough Collector was performed for validation and results were in the range of ±5% of experimental data. Model was further advanced for 1-D thermal modelling of Concentrating Photovoltaic Thermal (CPV/T) and Nano-fluid Filter based CPV/T (NFCPV/T) Collectors that were coupled with ORC. Highly efficient triple-junction InGaP/InGaAs/Ge was selected as PV cells for concentrating solar system while R1233zd was chosen as working fluid for ORC. Optical modelling of water/Ag solution as Nano-fluid was integrated with overall system and performance results of CPV/T and NFCPV/T combined with ORC were compared. Comparative study of electrical (ηelectrical), thermal (ηthermal) and overall (ηoverall) efficiencies demonstrated that NFCPV/T outperformed CPV/T especially at concentration ratios greater than 7 with values of 1.8%, 3.3% and 5.1% respectively. Parametric study of input variables were conducted to identify those inputs that have most considerable influence on key outputs. DIRECT optimization of system performance (ηsystem) demonstrated that NFCPV/T coupled with ORC has markedly higher ηsystem of about 2.71% compared to CPV/T. These results highlight effectiveness of proposed NFCPV/T configuration.

Enhancement of solar energy collection with magnetic nanofluids

Nowadays, energy crisis has caused widespread concerns about sustainable energy. Solar energy, as sustainable, renewable energy, has attracted many attentions. Compared to other solar energy utilizations, solar collectors are more efficient and commercial devices to collect solar energy. In our present study, well-dispersed magnetic nanofluids (MNFs) are reported that they exhibit excellent optical thermal conversion performance under the suitable magnetic intensity and direction. In this work, the colloidal stability of MNFs was improved by controlling pH within neutral value. One kind of surface modifications, oleic acid, was carried out to enhance the interaction between particles and surfactants. The hydrodynamic diameter was found to be very close to the real size of particle. Meanwhile, a highly efficient solar collection system was built based on controlling the optical thermal performance of MNFs by magnetic fields. The experimental results showed that the thermal efficiency of solar collectors increased with MNFs. The thermal efficiency of MNFs is much higher than base liquid with the concentration of only 0.05 vol.%. Moreover, in the presence of the external magnetic field, the solar collector efficiency increases to the maximum, 25% higher than the conventional parabolic trough and 12% higher than the selective surface absorber. The study indicates that MNFs, even of low-content, have good absorption of solar radiation, and can improve the outlet temperatures and system efficiencies. All these studies show the potential of MNFs in solar thermal conversion applications.

An Experimental Investigation on the Effect of Ferrofluids on the Efficiency of Novel Parabolic Trough Solar Collector Under Laminar Flow Conditions

ABSTRACTThe paper is related to the use of magnetic nanofluids (ferrofluids) in a direct absorption solar parabolic trough collector, which enhances thermal efficiency compared to conventional solar collectors. By applying the right magnetic intensity and magnetic field direction, the thermal conductivity of the fluid increased higher than typical nanofluids. Moreover, the ferrofluids exhibit excellent optical properties. The external magnetic source is installed to alter the thermo-physical properties of the fluid, and the absorber tube does not have selective surface allowing ferrofluids to absorb the incoming solar irradiance directly. In this paper, an experimental investigation of the performance of small scale direct absorption solar collector using ferrofluids as an absorber was conducted. Nanoparticle concentrations of 0.05 vol% at the operational temperatures between 19°C and 40°C were used in the current study. The results show that using ferrofluids as a heat transfer fluid increases the efficiency of solar collectors. In the presence of the external magnetic field, the solar collector efficiency increases to the maximum, 25% higher than the conventional parabolic trough. At higher temperatures, the ferrofluids show much better efficiency than conventional heat transfer fluid. The study indicated that nanofluids, even of low-content, have good absorption of solar radiation, and can improve the outlet temperatures and system efficiencies. The study shows the potential of using ferrofluids in the direct absorption solar collector.

Numerical investigation and experimental validation of the impacts of an inner radiation shield on parabolic trough solar receivers

Conventional parabolic trough solar receivers are widely used to harvest heat energy at temperatures ranging from 400 °C to 550 °C. However, high temperatures cause excessive heat loss in solar receivers. Two types of novel solar receivers with an inner metal radiation shield (RS), one with solar selective absorbing coating on the outer surface and one without, were proposed and constructed to improve the thermal performance of solar receivers. Experiments were conducted in an enthalpy difference lab, and mathematical models with spectral radiant distributions were established to predict the thermal performance of the solar receivers. A comparison between the simulated and experimental results showed satisfactory consistencies. Predictions were obtained using the models with the root mean square deviation of less than 6%. The novel solar receiver without solar selective absorbing coating on the outer surface of the RS showed superior performance at absorber temperatures exceeding 550 °C. At the absorber temperature of 600 °C, the percentage of heat loss reduction of the receiver with solar selective absorbing coating and of that without reached 23.4% and 24.2%, respectively.

Deformation and optics based structural design and cost optimization of cylindrical reflector system

It is a stated goal of renewable energy research to make solar power reach price parity with power from fossil fuel based power plants. Solar-thermal plants are capital intensive and do not benefit strongly from economies of scale. Hence, reducing unit costs is the most effective path to an economically attractive technology. Conventional parabolic trough systems have numerous limitations not least of which are the expensive mirror and support requirements required to maintain high precision in the optics. Further, the flexible hosing necessary to enable a moving receiver leads to excessively high pressure drops and pumping costs. While linear Fresnel systems address much of these shortcomings, they require accurate field alignment of a large number of independent reflecting elements leading to complex maintenance issues. Here we propose a relatively simple design with a small number of reflecting elements with a stationary receiver which is facile to fabricate, transport and install while also be far most cost effective. We also present a structural cost optimization together with optical ray tracer analysis using in-house ray tracer code. The concept has been validated with experiments. The proposed optimum design can be considered as a step toward achieving the economically attractive line concentrator technology.

Renewable hydrogen production by solar-powered methanol reforming

The present study demonstrates the possibility of generating hydrogen by methanol steam reforming at temperatures of 235–260 °C inside a non-concentrating solar collector, ideally for stationary fuel cell systems. In contrast to the current state-of-the-art, the solar collector provides all heat required for heating and evaporation of the reactants, endothermic reaction, and compensation of heat losses, without any external heat supply (such as from combustion of fuel or electric heating) and without the need for concentration of sunlight (as in conventional parabolic trough systems). Without the need for solar concentration, the system is simpler and more compact than conventional systems, and it can utilize all direct and indirect incident sunlight. The solar collector-reactor achieves hydrogen generation up to 6.62 LSTP min−1 per m2 collector area (equivalent to 1088 W m−2 LHV) under 1 sun, with solar-to-hydrogen efficiencies up to 78% and total energetic efficiencies (considering solar and fuel input) up to 43%.

A novel Compound Elliptical-type Concentrator for parabolic primaries with tubular receiver

The Parabolic Trough (PT) is the most used concentrator in CSP (Concentrated Solar Power). However, this concentrator technology is facing a significant challenge to increase its overall efficiency and cost-effectiveness. Meanwhile, other low-cost solutions such as Fresnel concentrators are also being perceived as potentially attractive. In order to achieve the lower cost goal, new optical solutions can be considered, in parallel with improvements coming, for instance, through the use of new materials or manufacturing solutions. But conventional PTs can still be improved to yield, for instance, higher concentration values, a possible starting point for higher conversion efficiency. These new solutions, in turn, can also be useful for other technologies and applications (Fresnel Concentrators, Central Tower Receivers, etc.). However it is easier to develop and test these solutions in conjunction with parabolic primaries (continuum primary). And that is the topic of this paper: to present a new Compound Elliptical-type Concentrator for a parabolic primary with a tubular receiver. A comparison is made between this new concentrator and two other concentrators (a conventional PT concentrator and a XX SMS (Simultaneous Multiple Surface) concentrator), as well as a calculation of the total amount of collected energy (kWh) for a particular location, Faro (Portugal). The paper ends with a discussion of the results obtained, their impact and possible applications in the future.

Experimental Study on Thermal Efficiency of Parabolic Trough Collector (PTC) Using Al<sub>2</sub>O<sub>3</sub>/H<sub>2</sub>O Nanofluid

Dispersing small amounts of solid nano particles into base-fluid has a significant impact on the thermo-physical properties of the base-fluid. These properties are utilized for effective capture and transportation of solar energy. This paper attempts key idea for harvesting solar energy by using alumina nanofluid in concentrating parabolic trough collectors. An experimental study is carried out to investigate the performance of a parabolic trough collector using Al2O3-H2O based nanofluid. Results clearly indicate that at same ambient, inlet temperatures, flow rate, concentration ratio etc. hike in thermal efficiency is around 5-10 % compared to the conventional Parabolic Trough Collector (PTC). Further, the effect of various parameters such as concentration ratio, receiver length, fluid velocity, volume fraction of nano particles has been studied. The different flow rates employed in the experiment are 2 ml/s, 4 ml/s and 6 ml/s. Volumetric concentration of 0.02%, 0.04% and 0.06% has been studied in the experiment. Surfactants are not introduced to avoid bubble formation. Tracking mode of parabolic trough collector is manual. Results also reveal that Al2O3-H2O based nanofluid has higher efficiency at higher flow rates.

A design method and numerical study for a new type parabolic trough solar collector with uniform solar flux distribution

The non-uniform concentrated solar flux distribution on the outer surface of the absorber tube can lead to large circumferential temperature difference and high local temperature of the absorber tube wall, which is one of the primary causes of parabolic trough solar receiver (PTR) failures. In this paper, a secondary reflector used as a homogenizing reflector (HR) in a conventional parabolic trough solar collector (PTSC) was recommended to homogenize the solar flux distribution and thus increase the reliability of the PTR. The design method of this new type PTSC with a HR was also proposed. Meanwhile, the concentrated solar flux distribution was calculated by adopting the Monte Carlo ray-trace (MCRT) method. Then, the coupled heat transfer process within the PTR was simulated by treating the solar flux calculated by the MCRT method as the heat flux boundary condition for the finite volume method model. The solar flux distribution on the outer surface of the absorber tube, the temperature field of the absorber tube wall, and the collector efficiency were analyzed in detail. It was revealed that the absorber tube could almost be heated uniformly in the PTSC with a HR. As a result, the circumferential temperature difference and the maximum temperature could be reduced significantly, while the efficiency tended to decrease slightly due to the inevitably increased optical loss. Under the conditions studied in this paper, although the collector efficiency decreased by about 4%, the circumferential temperature difference was reduced from about 25 to 3 K and the maximum temperature was reduced from 667 to 661 K.

Progress on Integrated Compound Concentrator Design

Nonimaging optics has been playing an important role in both tracking and non-tracking devices used for solar applications. We will report on our progress on implementing the integrated design within a glass vacuum tube for a non-tracking solar thermal collector. Such a design allows a thermodynamically efficient concentrator to be used for any convex shaped absorber. The acceptance angle of the design is also optimized for the seasonal change of sun. To minimize the material cost of our design, the reflector is integrated with the shape of the evacuated tube. Compared to from the conventional parabolic trough receiver which utilizes bellows and double end seals, our design uses a single end metal glass seal and allows the other end to freely expand. A 0.7 meter prototype is constructed as a prototype. The optical efficiency and incident angular modifier are simulated using a ray tracing program to show that within the designed acceptance angle, the collector performs at around 78% optical efficiency.

Life-cycle assessment for BRRIMS solar power

This paper presents a life-cycle analysis for a new concept in solar thermal power generation. BRRIMS denotes Brayton-cycle, re-heated, recuperated, integrated, modular and storage-equipped. This concept envisages collection temperatures of around 250 °C, thermal storage in pebble beds, thermal-electric conversion in a piston–cylinder engine and air as the heat transfer fluid and working gas of the engine. The analysis applies to the manufacturing phase of the overall power plant and separately to the pebble bed thermal storage component. Three sustainability metrics are included – life-cycle greenhouse gas emissions, cumulative energy demand and energy payback time. On these metrics, the BRRIMS concept has broadly similar results to a conventional parabolic trough plant with molten salt thermal storage.

Increasing the efficiency of parabolic trough plants using thermal oil through external superheating with biomass

It is well understood that the cost of concentrating solar power (CSP) will need to decrease quickly to ensure competitiveness with photovoltaic (PV) systems and other forms of power generation. Research and development on CSP plant components is crucial in order to reduce costs but is typically time consuming. New CSP plant concepts combining proven technologies with CSP represent another option that can be implemented quickly.This paper investigates the use of several biomass materials to externally superheat steam in conventional parabolic trough plants. Currently, parabolic trough plants are easiest to finance and external steam superheating can overcome the lower efficiencies compared to other CSP technologies. Seven scenarios, each air and water cooled, with steam parameters ranging from 380°C at 100bar to 540°C at 130bar have been modeled, and the results presented here are based on a 50MWe plant with 7.5h molten salt thermal storage.Our results show that the peak solar to electricity net efficiency increases up to 10.5% while the specific investment can decrease immediately from AU$8.2m/MWe to AU$6.3m/MWe, a 23.5% reduction. That is significant considering the expected 17–40% CSP cost reduction targets by the end of this decade. The modeling shows that even major fuel and water price changes are significantly less relevant than small changes in the agreed electricity purchase price.The technical, economic and environmental analysis reveals that external superheating with biomass can provide significant benefits, is able to use a variety of fuels and despite a limited global market, could immediately enable the implementation of several hundred MWe of CSP capacity at lower cost.