Parabolic Trough Solar Thermal Plant Research Articles

Harnessing solar power in industry: Heuristic optimisation design and transient thermal modelling of parabolic trough solar collector networks

This study presents the development of a transient model for designing and optimising parabolic trough solar thermal plants for industrial processes. The model is validated against published experimental data and other models from the literature. A heuristic optimization methodology based on Particle Swarm Optimization (PSO) to maximise the Present Value of the Life Cycle Energy Savings (PVLCES) is employed. This methodology is applied to three case studies. The results highlight the versatility of PTC (parabolic trough collector) technology in handling a wide range of temperatures. Additionally, the study reveals the optimal PTC aperture width dimensions that maximise the capture of solar thermal energy while increasing the solar fraction. Specifically: For low-temperature processes, the optimum aperture width is 5.0 m; in medium-temperature processes, the optimum aperture width increases to 5.5 m; for high-temperature applications, the optimal value is 5.8 m. Finally, the optimised networks achieve the following heat load-to-area ratios: Low-temperature applications: 0.57 kW/m²; medium-temperature applications: 0.58 kW/m²; high-temperature applications: 0.6 kW/m².

Design considerations for the dimensioning of parabolic trough solar thermal plants

Solar heaters of the parabolic trough type, PTC, are a proved technology that has a wide diversity of industrial applications. The prediction of the thermal conditions in these devices plays a fundamental role in the development and design of thermal plants capable of meeting the heat load requirements. To this end highly complex thermal models have been derived which are difficult to solve and implement. This work puts forward a PTC transient thermal model which was validated using experimental data and compared against other theoretical models existing in the open literature. Along with this model, a novel sequential solution procedure is proposed with which a better follow up of variable outputs is obtained. A parametric analysis was carried out of for the main design variables using the Present Value of the Life Cycle Energy Savings (PVLCES) and Total Integrated Heat (TIH) using daily typical data in the winter and summer seasons for the city of Guanajuato. Due to its transient nature, the model can be implemented in research where optimisation tools are required such as Deep Learning, Machine Learning and Control, which are basic in the dimensioning of thermal solar plants.

Hierarchical set-point optimization and feedforward strategy for collector defocusing of a solar plant

One of the main control objectives in parabolic trough solar thermal plants is to maintain the outlet temperature around an operating point. For this, a synthetic oil flow is used as the main control variable. However, another crucial system of the plant is the defocusing safety system of the collectors to prevent the oil temperature from exceeding an upper limit to prevent its degradation. This will occur, in general, when the oil flow reaches the maximum possible and is not able to regulate anymore the temperature. This mechanism is generally applied based on heuristic rules and partial or total defocus, which leads to a large number of actuator actions and temperature oscillations. In commercial plants, this defocus mechanism is applied firstly to the last collector, and as necessary, other collectors are defocused. In addition, it must be taken into account that loops’ parameters will be, in general, different.In this work, a FeedForward-based strategy is proposed to control the outlet temperature of collectors 1, 2 and 3 of a solar plant using the defocus angle as the manipulated variable. It is also proposed to dynamically obtain the set-point temperatures for the first 3 collectors through an optimization based on the concentrated parameter model. The results of the simulations are presented in different situations where the good performance of the strategy is observed. It is shown how the dynamic modification of the set-points can avoid possible energy losses on occasions where a fixed set-point of temperature is not the optimal option.

Comparative technical and economic study of Hybrid Solar-Geothermal Power Plant in Ethiopia

This paper presents a techno-economic assessment of a hybrid solar-geothermal power plant that is modelled taking into account the available geothermal and solar energy resources at the Tendaho-1 (Dubti) geothermal field in Ethiopia. The hybrid power plant combines a single-flash geothermal power plant with a parabolic trough solar thermal plant to increase the energy level of geothermal steam. The geothermal fluid from one of the production wells at the geothermal site and the direct normal solar irradiance prevailing in the area offer the primary sources of energy used in the modelling. A thermodynamic analysis based on the principles of mass and energy conservation and a figure of merit analysis that allows evaluating the energy and economic performance of the hybrid power plant were performed. The technical and economic efficiency assessment was performed by comparing the performances of the hybrid power plant with a power system consisting of stand-alone geothermal and solar power plants. Results of the techno-economic assessment showed that for the same amount of energy inputs, depending on the available thermal energy storage capacity, a hybrid power plant generates up to 10.4% more electricity than a power system of two stand-alone power plants while generating a higher net present value at a lower cost of generation. In addition, the hybrid power plants with and without thermal storage system exhibit an economic figure of merit values of 2.62 and 3.42, i.e. the cost of solar resource per kWh of electricity in the hybrid energy system is reduced by 70.5% and 61.5%, respectively.

Potential Map for the Installation of Concentrated Solar Power in Northeast of Brazil Using Analytic Hierarchy Process (AHP)

Brazil has a predominantly renewable energy matrix, with large participation of water resource in domestic supply of energy. Data from 2019 National Energy Balance show that renewable sources (water, biomass, wind and solar photovoltaic) together represented 83% of domestic electric supply in 2018, where the remaining percentage (16.7%) represented non-renewable sources. The generation of electricity through thermal solar technology was not representative. However, it is known that Brazil presents high potential for the installation of solar thermal plants, especially in the Northeastern Region, where direct normal solar irradiation values are high. It is observed that the (high) costs of the projects associated to the absence of a specific incentive program make Concentrating Solar Power (CSP) plants installation more and more time consuming. As a way to contribute to the insertion of solar thermal energy in Brazil, this article presents a methodology for the location of parabolic trough solar thermal plants of 80 MW for the State of Bahia, located in the Northeastern Region of Brazil. Such methodology was based on the application the Analytic Hierarchy Process (AHP) method and the Geoprocessing Technologies to define potentially available sites for the implementation of the projects. For the analysis, parameters related to energy production in the solar power plant, electric, roadways and water infrastructure of the plant were taken into account, as well as the occupation, slopes and land use. Considering the analyses performed, it was confirmed that Bahia disposes of many sites with great generation potential, especially in the western region of the State (at Barreiras), where favorable conditions were found for the development of the technology. Localities situated in other region of the State were also confirmed as suitable, however with less site availability for the insertion of plants. Methodology validations were also carried out and indicated that the model reached the proposed objective, faithfully representing the real-world simplifications that were made.

Performance optimisation of parabolic trough solar thermal power plants – a case study in Bangladesh

ABSTRACTIn this paper, parabolic trough solar thermal plants are proposed. Two key parameters, solar multiple (SM) and full load hours of thermal energy storage (TES), are optimised by maximising the annual energy and minimising the levelized cost of electricity (LCOE). This work presents a comparative study, based on the 4E (energy–exergy–environment–economic) analysis, of the optimised plant with a reference plant. The performance evaluation of the optimised plant is carried out in eight different locations of Bangladesh. The result obtained shows that the salt plant has the best performance compared to that of the thermal oil plant. The salt plant requires a lower LCOE of 9.86 ¢/kWh. It also possesses a maximum capacity factor of 39.5% and generates the highest annual energy of 171.1 GWh. From the feasibility study, Cox’s Bazar is found as the best location of eight different regions of Bangladesh.

Automatic generation control of a solar thermal and dish‐stirling solar thermal system integrated multi‐area system incorporating accurate HVDC link model using crow search algorithm optimised FOPI Minus FODF controller

This article demonstrates the automatic generation control of a multi-area system incorporating various sources. Area-1 and area-2 consist of thermal and parabolic trough solar thermal plant (PTSTP) of fixed and random solar insolation, respectively, and area-3 comprises of thermal and realistic dish-stirling solar thermal system units. A maiden effort has been made to use a fractional order (FO) proportional-integral minus FO derivative with filter coefficient (FOPI-FODF) controller as a secondary controller. The controller gains are optimised using a novel algorithm called crow search algorithm. Comparisons of system dynamic response with and without renewable energy sources for FOPI-FODF, and for some commonly used integer order and FO controller's reveals the better performance of FOPI-FODF controller. A study comparing both fixed and random solar insolation in PTSTP of different areas have been tested. An accurate high-voltage direct current (AHVDC) line model is designed using inertia emulation strategy and is placed instead of AC tie line, and with parallel AC tie lines resulting in better system dynamic performances than AC tie line alone. The selection of the optimum location of AHVDC line in parallel AC tie line exposes the AHVDC line connected with the area where the system is disturbed.

Design of a 25 MWe Solar Thermal Power Plant in Iran with Using Parabolic Trough Collectors and a Two-Tank Molten Salt Storage System

Nowadays, parabolic trough solar thermal plants are prevalent around the world. In different areas concerning the amount of solar radiation, their standard size is approximately between 20 and 100 MWe. Certainly, the right size of the solar field is the first selection with regard to nominal electrical power. A vast area will be economically unreasonable whereas a small area will mainly cause the power plant to operate at the part-load condition. This paper presents an economic modeling of a solar parabolic trough plant, operating at 25 MWe in Yazd, Iran. The varying types of collector dimensions have been investigated; then, by selecting autumnal equinox (22 September) at 12:00 PM as the design point, thermal performance of the solar power plant has been featured annually, in all conditions. The total operating time of the power plant is about 1726 hours (1248 hours in full-load condition). In the end, the effect of thermal storage tanks has been analyzed to save extra solar heat and use it at nights in hot months. By implementing a storage system, the total operating time will be increased to 3169 hours (2785 in full-load condition). Moreover, 7974 GJ useful thermal energy can be obtained from the solar field and storage system.

Dynamic optimization of a hybrid solar thermal and fossil fuel system

This work illustrates the synergy that exists between solar thermal and fossil fuel energy systems. By adding degrees of freedom and optimizing the system, more solar energy can be harvested by operating in a “hybrid” mode, where a portion of the demand is met by solar energy, with the remainder provided by a supplemental fuel, such as natural gas. This requires allowing temperatures in the solar field and storage tanks to vary, permitting the system to meet the demand by a combination of solar and fossil energy, rather than one or the other, and by allowing the heat transfer fluid to bypass storage. The addition of thermal energy storage provides the opportunity for dynamic optimization, where the degrees of freedom can be exploited over the entire time horizon to yield optimal results: maximizing the total amount of solar energy harvested. The problem is solved using a simultaneous solution method that concurrently minimizes the objective function and solves the system’s constraints. This methodology is demonstrated on a parabolic trough solar thermal plant with a two-tank-direct thermal energy storage system. Results show that 9% more solar energy can be harvested on a sunny day by using this methodology. On a day with intermittent sunlight, 49% more solar energy can be harvested with the same system. Dynamic optimization enables more cost effective solar integration in areas with lower or intermittent sources of solar incidence.

Performance Analysis of a Rankine Cycle Integrated With the Goswami Combined Power and Cooling Cycle

Improving the efficiency of thermodynamic cycles plays a fundamental role in reducing the cost of solar power plants. These plants work normally with Rankine cycles which present some disadvantages due to the thermodynamic behavior of steam at low pressures. These disadvantages can be reduced by introducing alternatives such as combined cycles which combine the best features of each cycle. In this paper, a combined Rankine–Goswami cycle (RGC) is proposed and a thermodynamic analysis is conducted. The Goswami cycle, used as a bottoming cycle, uses ammonia–water mixture as the working fluid and produces power and refrigeration while power is the primary goal. This bottoming cycle, reduces the energy losses in the traditional condenser and eliminates the high specific volume and poor vapor quality presented in the last stages of the lower pressure turbine in the Rankine cycle. In addition, the use of absorption condensation in the Goswami cycle, for regeneration of the strong solution, allows operating the low pressure side of the cycle above atmospheric pressure which eliminates the need for maintaining a vacuum pressure in the condenser. The performance of the proposed combined Rankine–Goswami cycle, under full load, was investigated for applications in parabolic trough solar thermal plants for a range from 40 to 50 MW sizes. A sensitivity analysis to study the effect of the ammonia concentration, condenser pressure, and rectifier concentration on the cycle efficiency, network, and cooling was performed. The results indicate that the proposed RGC provide a difference in net power output between 15.7% and 42.3% for condenser pressures between 1 and 9 bars. The maximum effective first law and exergy efficiencies for an ammonia mass fraction of 0.5 are calculated as 36.7% and 24.7%, respectively, for the base case (no superheater or rectifier process).

Exergy analysis of an integrated solar combined cycle system

Exergetic analysis has become an integral part of thermodynamic assessment of any power generation system. Energy and exergy studies for power plants optimum design and for combined chemical industries received much attention recently. An Integrated Solar Combined Cycle System (ISCCS) is proposed as a means of integrating a parabolic trough solar thermal plant with modern combined cycle power plants. In this study attempt will be made to analyze the Integrated Solar Combined Cycle in Yazd, Iran using design plant data. Energy and exergy analysis for the solar field and combined cycle is carried out to assess the plant performance and pinpoint sites of primary exergy destruction. Exergy destruction throughout the plant is quantified and illustrated using an exergy flow diagram, and compared to the energy flow diagram. The causes of exergy destruction in the plant include: losses in combustor, collector, heat exchangers, and pump & turbines which accounts for 29.62, 8.69, 9.11 and 8% of the total exergy input to the plant, respectively. Exergetic efficiencies of the major plant components are determined in an attempt to assess their individual performances.

Solar multiple optimization for a solar-only thermal power plant, using oil as heat transfer fluid in the parabolic trough collectors

Usual size of parabolic trough solar thermal plants being built at present is approximately 50 MW e. Most of these plants do not have a thermal storage system for maintaining the power block performance at nominal conditions during long non-insolation periods. Because of that, a proper solar field size, with respect to the electric nominal power, is a fundamental choice. A too large field will be partially useless under high solar irradiance values whereas a small field will mainly make the power block to work at part-load conditions. This paper presents an economic optimization of the solar multiple for a solar-only parabolic trough plant, using neither hybridization nor thermal storage. Five parabolic trough plants have been considered, with the same parameters in the power block but different solar field sizes. Thermal performance for each solar power plant has been featured, both at nominal and part-load conditions. This characterization has been applied to perform a simulation in order to calculate the annual electricity produced by each of these plants. Once annual electric energy generation is known, levelized cost of energy (LCOE) for each plant is calculated, yielding a minimum LCOE value for a certain solar multiple value within the range considered.