Numerical modeling and performance assessment of elongated compound parabolic concentrator based LCPVT system
In this work, a non-imaging low concentrating 2.5X Compound Parabolic Concentrator (CPC) truncated to 1.7X has been explored. CPCs inherently form non-uniform distribution of flux on the PVT module which has been mitigated by the integration of optimized homogenizer referred to as Elongated CPC (ECPC). The study involves detailed optical, thermal, and electrical modeling of the ECPC based Low Concentrating Photovoltaic Thermal (LCPVT) system. Optical simulations provide insight into the flux distribution on the PVT panel surface, which is further coupled with a thermal and electrical model for precise prediction of the performance of the system. These models are validated experimentally with a 315 Wp solar panel integrated with ECPC based LCPVT system. Performance evaluation of the system has shown peak thermal efficiency of ∼40% at ΔT of 16 °C, peak electrical efficiency of 12%, and an overall peak exergy efficiency of 15% at 38 Liters per hour (LPH) flow rate. A comparison of outlet water temperature results obtained from the numerical model and experiments has shown an excellent match with a relative error of 4%. Results also show that the increase in mass flow rate from 22 LPH to 38 LPH improves the electrical efficiency by 3% however a drop in ΔT of 2–3 °C is observed.
Design and analysis of dense array CPV receiver for square parabolic dish system with CPC array as secondary concentrator
In this paper, a two-stage square parabolic concentrating photovoltaic (CPV) receiver dish with an overall geometric concentration ratio of 500 suns is designed to provide a uniform intensity distribution on high-efficiency triple-junction solar CPV cell module. The system comprises of a square parabolic dish with an aperture area of 9 m2 as a primary concentrator and an array of the compound parabolic concentrator integrated optical homogenizer of 0.27 × 0.27 m2 as a secondary concentrator in tandem with the dish. The CPV module consists of an array of 12 × 12 triple junction CPV cells with each cell connected in parallel or series combination and integrated CPC homogenizer dedicated to each cell. The homogenizer length is selected based on the peak to average ratio of concentrated flux with the aim to maximize the optical and electrical performance of the CPV system. Monte Carlo ray-tracing model is used to predict the flux distribution. The predicted solar flux distribution on individual CPV cells are used as input to determine the electrical performances of the CPV module with three different cell interconnections. For optimized homogenizer length of 0.005 m and receiver height of 3.7 m, the maximum optical and CPV module efficiencies are obtained as 68.30% and 32.03% respectively. A year-round electrical power output of developed CPV system is 2.19 MWh which is up to 33.54% higher as compared to conventional CPV system. The proposed novel geometric design could accommodate the bypass diode for each cell, effectively reducing the current mismatch effects.
Inverse heat transfer technique for estimation of focal flux distribution for a concentrating photovoltaic (CPV) square solar parabola dish collector
For a CPV system, prediction of focal flux distribution at the receiver area will give insight to more effective, energy efficient designs and to estimate power output. An experimental method for in-situ prediction of heat flux distribution profile using inverse heat transfer technique on a flat plate receiver for a CPV square parabolic dish is presented. An IR camera is used to measure the temperature of the concentrated receiver surface. The receiver domain is discretised into several heat flux elements and heat flux values for each grid is then estimated using the measured infrared (IR) pixel temperature and ordinary least square. A 3-D steady state heat conduction equation with convection and radiation heat loss boundary is regarded as the forward problem. The simulated temperatures generated from the solution of forward problem using the predicted heat flux distribution and measured temperature distribution are in close agreement. For validation purpose, the concentrated heat flux is also measured using Gardon and Schmidt-Boelter heat flux sensor. The peak predicted focal heat flux on the receiver is found to be 37.41 kW/m2 whereas the heat flux value measured by the flux sensor is 39.15 kW/m2 within the deviation of 4.4%.
Thermal modeling, characterization, and enviro-economic investigations on inclined felt sheet solar distiller for seawater desalination
Sustainable desalination can be achieved by adopting renewable energy-based low-cost and low-impact desalting techniques. In this investigation, capability of inclined felt sheet solar distiller in desalting seawater is assessed by evaluating its performance, distillate water quality, economics, and environmental impacts. The distiller with 1.18-m2 aperture area produced around 4.60 L/day of distillate for a cumulative incident solar radiation intensity of about 20.52 MJ/m2 day. Its pollutant removal efficiency is very much superior to other available solar stills reported in literatures. Thermal model developed for estimating distiller’s performance is able to predict its productivity with reasonable accuracy (only 8.0% deviation from experimental values) and was used for estimating distiller’s performance in various seashore locations in India with varying clear days (191 to 246). Yearly mean distillate production and thermal and exergy efficiencies of the proposed distiller range between 3.60 to 4.50 L/day, 36.45 to 42.39%, and 2.85 to 3.65%, respectively, in east seashore locations of India. Moreover, 18.46 tons of CO2, 132.72 kg of SO2, and 54.20 kg of NO emission can be mitigated by adopting the distiller for potable water production. Distillate production cost of inclined felt sheet solar distiller is in the range of 1.15 to 2.29 INR/L and highly depends on the interest rate at which the distiller is financed. Generation of reasonable quantity of high-quality potable water at low cost with huge environmental benefits makes proposed inclined felt sheet solar distiller a suitable option for quenching thirst in coastal and remote locations.
Performance improvement of a desiccant based cooling system by mitigation of non-uniform illumination on the coupled low concentrating photovoltaic thermal units
A Low Concentrating Photovoltaic Thermal system typically employs compound parabolic concentrator to focus sunlight and enhance the quality of both thermal and electrical energy extracted. One of the major issues during this process is the introduction of non-uniform illumination on the photovoltaic panels which can cause hot-spots and significantly reduce both the reliability and the electrical output from this system. This non-uniform illumination can be mitigated by integrating homogenizers which are typically linear extensions to the compound parabolic concentrators profile also referred to as elongated compound parabolic concentrators. In this work, the performance of a 2.5× Elongated Compound Parabolic Concentrator truncated to 1.7× and connected to a desiccant based cooling system has been explored. For a detailed analysis of the system, a coupled 3-D optical, electrical, thermal and process efficiency model has been developed. A full-scale prototype of the modelled system is also fabricated using a 380-Watt peak photovoltaic panel. Experiments conducted on the developed system showed a peak outlet water temperature of 56 °C at a mass flowrate of 24 L per hour. Comparative studies between compound parabolic concentrators and elongated compound parabolic concentrators based low concentrating photovoltaic thermal system is also presented to showcase the overall improvement in the process efficiency due to the mitigation of non-uniformity. Using a 400 mm length of the homogenizer the spatial non-uniformity factor was found to drop from 0.5 to 0.29 under normal incidence angle and results in a rise of 12% in the electrical output when compared to a compound parabolic concentrators-based system. The coefficient of performance of the desiccant-based air-cooling system is found to increase by 50% when coupled with two series-connected elongated compound parabolic concentrators based low concentrating photovoltaic thermal system. The improvement in coefficient of performance is mainly because of thermal and electrical energy savings from the developed system amounting to 352 kWhe/year and 665 kWhth/year, respectively. Further, the mitigation of non-uniform illumination showed a performance improvement of 5% in the coefficient of performance of the air-cooling system compared to a compound parabolic concentrators-based system.
Stability analysis of the thermocline thermal energy storage system during high flow rates for solar process heating applications
The thermal energy storage system is a pivotal system for solar thermal plants for improving reliability. The stability in the thermocline is more significant to clarify and improve the performance of thermal energy storage tank which legitimately shows the quality of the thermocline. In this stability analysis investigation, the modern engineering energy storage material concrete was used as a filler material for high-temperature thermal energy storage applications as a result of the intrinsic properties. A comprehensive laminar and k-ε turbulent flow energy transport model accounts for the heat transfer fluid and filler material with adiabatic and non-adiabatic conditions using LTNE (Local Thermal Non-Equilibrium model). The axial, radial, and diagonal temperature differences were identified which was used to calculate the stability of the thermocline. A thermal energy storage tank size of 1 m height and 0.250 m diameter with a 0.030 m size of filler material packed with an average porosity of 0.3 for the storage capacity of 150 kWh/m3 is used for solar process heating applications considered for the present study. The thermocline stabilities are performed with Reynolds numbers, Re varied from 1 to 3000. It is found that the Re = 1 provides better stability in the axial and radial direction as well as diagonal than other Reynolds number. It is observed that Re = 1 provides superior discharging efficiency for nearly 5.84 hrs which is highly suitable for solar process heating applications and the discharging efficiency consistently drops, when Re increases from 1 to 3000. The wall condition of the tank and velocity of the heat transfer fluid is highly disturbing the thermocline in the radial direction and it creates a ‘spike’ profile in the axial direction. Based on the newly introduced stability scale, the effective length of packing and timing to achieve stability is identified for H/D = 4. From that result, the top and bottom layer of the thermocline tank porosity is also found which is used to decide the porosity of the packed bed distributors. The identified porosity for the top and bottom distributors in the ɛ = 0.3 thermal energy storage tank is less than 0.3 is more suitable for provide the uniform flow in the tank.
Wind load and structural analysis for standalone solar parabolic trough collector
Solar energy is one of the emerging technologies and the use of concentrating power technology is increasing in solar power plants. Parabolic trough collector is a concentrating solar power technology that is situated in the open terrain and subjected to wind loads. The structural stability of these devices under such loads determines the ability to accurately concentrate the rays at the absorber tube, which affects the overall optical and thermal efficiencies. A detailed numerical analysis is carried out at different wind loads and design conditions. It is observed that for a change in velocity from 5 m/s to 25 m/s, slope deviations increase from 1.21 mrad to 3.11 mrad at the surface of the reflector exceeding the shape quality of the mirror panels. Higher yaw angles and pitch angles of 60° and 120° are observed to be decisive in the design of collectors. Roof-mounted collectors experience a 40% higher drag force than ground-mounted collectors at a 0° pitch angle. For the Aluminium trough, the slope deviation at the surface of the reflector is higher by 4.62% than glass. The study will be helpful for engineers and scientists in the design of the parabolic trough collectors.
4-E (Energy-Exergy-Environment-Economic) analyses of integrated solar powered jaggery production plant with different pan configurations
Conventional jaggery making process utilizes the bagasse for boiling of sugar cane juice which releases pollutants into the atmosphere and high particulate matter from these emissions causes air pollution. In this article, solar powered jaggery industry with freeze pre-concentration is proposed with conventional and modified heating pans. The system performance, environmental impacts and economic feasibility were assessed by carrying out 4E (Energy-Exergy-Environment-Economic) analyses using the developed mathematical model. These systems were designed to produce 300 kg of jaggery per day when operated for 7.5 h in 3 batches with average solar direct normal irradation of 662 W/m2 and 343 °C. These systems are integrated with auxiliary heating for uninterrupted production in the absence of sunlight. These systems can mitigate nearly 2015.95 to 3062.15 tons of CO2 emission during its 25 years of lifespan under 300 clear days of operation each year. Jaggery produced by this technique is rich in its colour and completely safe for human consumption as no artificial clarificants are used. Amount invested in these systems can be recovered in a span of 12.03 to 13.45 years for jaggery selling price of USD.0.514/kg or INR.36/kg.
Optical modeling of corrugation cavity receiver for large-aperture solar parabolic dish collector
This article presents an optical investigation of a corrugation cavity receiver for a 100 m2 parabolic dish collector (PDC). The performance of PDC depends on the selection of the receiver and its mounting distance from the collector base (H) to receive a high amount of reflected radiation. This work performs optical modeling for PDC with a designed corrugation cavity receiver using commercial software, ASAP® 2013. The motivation for this study is derived from the fact that the entrapped internal reflection within the receiver optimizes the system’s optical efficiency. The receiver geometry is such that it attributes to increasing internal reflection and average heat flux intensification. The present optical model is validated with the available literature. The influential geometrical and optical parameters of the receiver have been optimized by simulation by varying the aperture diameter (da,r) from 0.504 to 0.604 m, surface absorptivity (α) from 75 to 95%, receiver coil’s outer and inner pitch (Po and Pi) from 0.00667 to 0.00909 m, and angle of taper (θi) from 50° to 56° for H = 5.35–5.65 m. The performance of the optimized receiver is compared with the conical cavity receiver and is found to be excellent among all values of H. This optical modeling can be expected to be helpful for engineers and researchers in designing the optimized optical receiver for solar parabolic dish collector systems.
Optical and electrical performance investigation of truncated 3X non-imaging low concentrating photovoltaic-thermal systems
Compound Parabolic Concentrators (CPC) have non-uniform distribution of flux when integrated to a Photovoltaic-Thermal (PVT) module. The non-uniform distribution of flux deteriorates the electrical and thermal performance of the solar panel. To reduce this effect, optimized homogenizers are integrated to CPC of concentration ratio 3X truncated to 2.5X and 2X. The study aims to demonstrate the effect of integration of homogenizer on the electrical performance of the system. Optical simulations carried out for full scale model (1 m × 2 m solar PVT panel area) with homogenizers, referred as Elongated Compound Parabolic Concentrators (ECPC), showed a reduction in the peak local concentration of 55% and 66% for the 2.5X and 2X cases at normal angle of incidence. Optically coupled electrical simulations are carried out, which are further validated using a scaled down prototype tested under solar simulator. The experimental results show peak electrical efficiency of 13.9% (2X) and 13.6% (2.5X) for CPC and 14.1% (2X) and 13.9% (2.5X) for ECPC. Further, benefits of homogenizer are evident near half acceptance angle, when improvement in electrical efficiency by ~23 ± 2% and ~37 ± 2% is observed for ECPC of concentration ratio 2X and 2.5X in comparison to CPCs of similar configuration. In addition, the effect of temperature on electrical performance has also been studied by conducting experiments for actively cooled and uncooled condition. A reduction in 10% electrical efficiency is reported for uncooled condition compared to actively cooled condition.