Year-round performance assessment of a solar parabolic trough collector under climatic condition of Bhiwani, India: A case study
Introduction
In the current scenario, the demand for energy is increasing and conventional energy sources are depleting continuously at an alarming pace. Therefore, the scarcity of conventional resources of energy in near future has necessitated the search for some sustainable, competent and green-energy alternatives. Here comes the importance of renewable energy sources, which can play a crucial task in tackling the rising demand of energy. Nowadays, the energy coming from the Sun appears highly encouraging renewable power sources as far as availability, security, purity and surrounding facets are concern. The availability of the solar energy on the earth’s surface is around 5000 times of the world’s current power requirement [1]. It has found applications in various educational and industrial thermal systems such as for water or air heating, production of steam, drying, water distillation, space cooling and heating, hydrogen production, cooking, electricity production, heat generation for engineering process, integrated power plants, refrigeration and air conditioning [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14].
Concentrated solar power (CSP) plants are the most capable alternatives for power production having concentrating types of solar collectors. SPTC is a well established and experienced technology used in industry for solar exploiting. These are extensively used in a wide range of household and urbanized applications such as hot water production, formation of steam and heat production for manufacturing processes [15], [16]. Most of the installed SPTC works at temperatures <400 °C having synthetic oil as working medium [17].
The chronological improvement of CSP technologies to produce uncontaminated electrical energy is effectively analyzed [18] and highlighted 73.58% contribution of PTC technology in the overall producing capacity of CSP plants globally. A number of reviews related to CSP technology and PTC [1], [19], [20] enlighten their utilities in different areas.
A significant amount of literature [21], [22], [23], [24], [25], [26], [27], [28], [29] has been devoted toward development of different energy models to predict the thermal, optical and combined thermo-optical performance of the PTC.
Edenburn [21] calculated the performance of a PTC analytically by estimating the heat transfer considering both vacuum and gap filled with air. The obtained results showed well justification with experimental data of Sandia National Laboratory collector test facility. The energy losses by conduction and convection in annular solar receivers are studied and reported a considerable amount of heat losses due to conduction at Ra < 1000 and both conduction and convection heat losses at Ra > 1000 in the annular space [22]. A simplified method for estimating long duration performance of concentrating and non-concentrating solar collectors is described and concluded that yet for small temperature applications, concentrating collector can perform better than the flat plate collector [23]. A 2-D modeling for the SPTC has been carried out by isolating the receiver into constant temperature longitudinal segments and considering the insolation fluctuation on the boundary with energy equilibriums employed at various system nodules [24].
Guven and Bannerot has proposed an expression for estimating the intercept factor [25] and also carried out optical analysis of parabolic trough collector considering the influence of optical errors (random and non-random) associated with solar trough collectors [26].
Marif et al. [27] developed 1-D numerical model for estimating the thermo-optical behavior of a PTC using implicit finite difference scheme and energy equilibrium methodology in the climactic situations of Algerian Sahara. It was reported that one axis East–West and Horizontal East–West tracking modes were most suitable during the entire year. In addition, the thermal efficiency measurement remains about 69.73–72.24% which increases by 2% with lower water temperature and decreases with high synthetic oil temperature. Further, Mokheimer et al. [28] proposed a simulation code employing engineering equation solver (EES) to predict the thermo-optical performance of PTC considering different weather data in Dhahran and also carried out the cost analysis of solar field. The study reported that optical efficiency was found in the range of 61–73.5% and the ratio of PTC’s cost to area of solar field reduced considerably with enlargement in the size of solar field. The authors recommended 60 hectare or larger solar field size. Yilmaz and Soylemez [29] carried out a mathematical modeling of PTC using EES to assess the performance characteristics with various working conditions. The study revealed that collector efficiency has been highly affected by optical losses as compared to thermal losses and increase in wind speed for air-filled absorber tube relative to vacuum and not much influenced by type of working fluid used. Annulus with vacuum has been an excellent option for improvement of performance of collector due to reduced heat loss.
Forristall [30] presented both 1-D and 2-D models of heat transfer for PTC based on EES and showed that 2-D model grants superior accuracy than 1-D model for the long absorbers (>100 m). Additionally, the influence of various collector parameters on the collector efficiency is also analyzed.
Qu et al. [31] developed 1-D model at steady-state for the receiver tube to enhance the overall performance of the system. Notably, around 55% of thermal efficiency is achieved with an aperture area of 13.8 m2 and solar insolation of 900 W/m2. Padilla et al. [32] also carried out a 1-D investigation for optimization of the PTC and identified its performance using various working conditions. Results showed better comparison with experimental results as compared to other studies.
An experimental study has been performed to compute the thermal efficiency and heat losses of the parabolic trough collector at Sandia National Laboratories (SNL) used in LS-2 Solar Thermal Electric Generation Systems (SEGS) [33] and also proposed 1-D model of heat transfer at steady-state considering the thermal resistance network.
Moreover, many studies have been accomplished in order to assess the effects of various parameters on the performance of parabolic trough collector. The performance analysis of PTC using water and synthetic oil as working fluid was accomplished by Odeh et al. [34]. The authors presented the equations of thermal efficiency and a heat losses model of PTC based on receiver surface temperature, with different heat carrier fluid and for various sizes of receiver. The effects of various parameters such as emittance of receiver, wind speed, receiver surface temperature and solar insolation magnitude on heat losses have also been described. Additionally, a 2-D modeling was carried out by Tao and He [35] for coupled fluid flow and heat transfer process in PTC tube. Fluid flow and heat transfer performance was analyzed considering the impacts of diametric ratio of absorber tube, Ra and thermal conductivity of tube wall. It was observed that when Ra > 105, the effects of natural convection on heat transfer must be considered in annulus gap and inside the tube. As the tube diameter ratio increases, the heat transfer in internal tube increases and decreases in annulus gap. Accordingly, due to increase of thermal conductivity of tube wall, the heat transfer increases in annulus space and decreases in internal tube. If the thermal conductivity exceeds from 200 (W/m K), the heat transfer is less influenced by it. The performance of the vacuum shell was studied by Daniel et al. [36]. The authors reported improved performance corresponding to the vacuum shell configuration than the non-evacuated tube with and without selective coatings.
A number of investigations have been reported to estimate the behavior of solar trough using different working fluids. A heat transfer model was proposed by Ouagued et al. [37] for estimating the behavior of a tracking parabolic trough collector using different heat transfer fluids named Syltherm 800, Therminol D12, Syltherm XLT, Santotherm 59, Santotherm LT, Marlotherm X and Marlotherm SH under Algerian climactic conditions. This study reported that Syltherm 800 can attain a temperature in the range of 700–800 K, while temperature of other working fluids varies between 600 K and 750 K. Finally, it was concluded that Syltherm 800 had the best heat capacity as compared to other working fluids during the whole year. Jradi and Riffat [38] developed both optical and thermal model to predict the long term performance of PTC under climactic conditions of Beirut. The peak thermal efficiency of 72%, highest heat energy generation per day of 22.267 kW h and maximum water exit temperature of 387 K in July have been achieved by using mass flow rate of water 0.010 kg/s and aperture area approximately 6 m2. Kasaeian et al. [39] calculated the thermal performance of PTC for various absorbers with nano-fluids as heat carrier fluid and reported enhanced thermal potential with nano-fluids. When 0.2% and 0.3% MCNT/mineral oil nano-fluid has been employed as a substitute of pure oil, the total collector efficiency is improved about 4–5% and 5–7% respectively.
The above literature survey indicates that a limited amount of studies have been carried out on performance evaluation of PTC under the actual meteorological and environmental conditions. There is no detailed study available on the year-round performance using PTC under the Indian weather conditions where the plentiful solar energy is available. In addition to that very few investigations considered both optical and thermal modeling of PTC with horizontal and inclined plane of the collectors. In a step further, the current research work focuses on developing the detailed thermo-optical model in order to compute the behavior of a particular PTC having a non-evacuated receiver tube with black paint coating and also verifies the position of collector (horizontal and inclined). Further, the developed model is applied to the specific SPTC system to predict its performance characteristics during the year under the climatic states of Bhiwani as a case study.
Section snippets
System description
SPTC primarily comprises of a parabolic reflector, absorbing receiver tube and supporting structure as shown in Fig. 1. Fig. 2 shows cross sectional view of the SPTC, which significantly demonstrates the placement of heat collection element (HCE) and also the shape of PTC. The absorber tube (HCE) is coated with black paint so that maximum amount of heat extracted from incoming solar insolation is absorbed and subsequently transferred to the working fluid. The description of each component is
Thermo-optical performance models
The modeling approach for PTC is based on energy equilibrium around the heat receiving element of collector. It comprises of the direct normal insolation, optical losses from reflector as well as from energy receiving element, heat losses from the receiver tube, and the gains in the heat transfer fluid (HTF). The energy balance in the absorbing surface of linear tubular receiver of PTC can be expressed as [41],where , and is the useful heat/energy gained by
Analytical simulation
The Simulink hourly insolation model in addition to performance model based on analytical expressions and the related parameters have been developed using Matlab R2012a and applied to the specific PTC system. Initially, an analytical model has been prepared for finding direct normal beam hourly insolation on inclined and horizontal planes. The data related to the parameters such as location longitude and latitude, monthly average hourly global and diffuse solar insolation and day of the year
Validation of the developed model
The obtained results from the proposed model for thermo-optical performance analysis of SPTC is justified by comparing against the experimental results available at Sandia National Laboratories (SNL) for a SPTC (LS-2 PTC) with working fluid as Syltherm 800 oil and water having single-phase using various operating conditions [33], [50]. The detailed specifications of the SPTC are highlighted in Table 1 and the same are used for validation. In the present modeling, authors used temperature of sky
A case study
The seasons in India can be broadly grouped into four classes: winter period (December to February), hot weather period (March to May), summer monsoon period (June to September) and post monsoon period (October to November) [52]. Large part of the country receives an average about 7000 MJ/m2 of global solar radiant exposure per year. Bhiwani is situated at 28°78′ latitude North and 76°13′ longitude East and New Delhi is positioned with 28°29′ latitude North and 77°08′ longitude East [49]. As the
Results and discussion
The simulations have been carried out using an hourly base by means of proposed model to evaluate the solar insolation and finally, the thermo-optical performance of SPTC for the particular day of every month throughout the year on horizontal and inclined plane. For obtaining the maximum solar energy incident on an inclined plane of SPTC all through the year, the 28°29′ tilt angle of solar collector is assumed which is equivalent to latitude angle of New Delhi. Further, it is considered that
Conclusions
A comprehensive thermo-analytical modeling of a mini-level SPTC has been proposed to simulate its physical behavior under climactic conditions of Bhiwani. The broad investigation on long-term basis was performed in terms of thermal and optical performance of a SPTC having a non-evacuated receiver tube coated with a black paint and covered with glass envelope. Additionally, the hourly direct normal beam radiations reaching on horizontal and an inclined plane of solar parabolic collector have
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2020, Renewable EnergyCitation Excerpt :The maximum heat energy of the system is found to be 2.38 kWh/day in the month of April and 2.46 kWh/day in the month of May for both horizontal and inclined levels respectively. Similarly, the maximum temperature rise of the HTF is 11.1 ̊ C and 12.2 ̊ C in the month of April in both horizontal and inclined planes for the mass flow rate of 0.01 kg/s [22]. The PTC receiver with cermet and black chrome coatings has been analyzed numerically and validated with SANDIA LS-2 experiment results [23].
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2019, Renewable and Sustainable Energy ReviewsCitation Excerpt :Transient flow models are proposed to study the effect of unsteady parameters for both single-phase and two-phase flow. Numerous studies proposed are based on lumped capacitance models mainly one dimensional [149–151] and few multidimensional models [152]. Other scholars [153,154] presented transient models to simulate the complex transient behavior of DSG in PTC and predict the thermal instabilities in DSG loops.
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2018, Thermal Science and Engineering ProgressCitation Excerpt :They proved that the location and the climate are determinant parameters on the thermal performance of the solar collector. Another study on thermal and optical performance of a solar PTC during a year under climatic conditions of India have presented by Kumar et al. [6]. A one dimensional steady state heat transfer model is developed and validated through a comparison with the experimental results of Sandia National Laboratories (SNL) [7].