Parabolic Trough Power Plants Research Articles

Numerical analysis on the thermal behavior of high temperature latent heat thermal energy storage system

High temperature latent heat thermal energy storage technology is a promising option for future cost reduction in parabolic trough or tower power plant. However, low thermal conductivity of phase-change material (PCM) is the major shortage of latent heat thermal energy storage. This paper proposed a new thermal energy storage system (TESS) that metal foam and fins were used to enhance the effective conductivity of PCM. Three-dimensional physical model was established for representative element extracted from TESS. Considering the natural convection in the liquid part of PCM, volume-averaged mass and momentum equations were employed with the Brinkman–Forchheimer extension to Darcy law to simulate the porous resistance. A local thermal equilibrium model was developed to obtain temperature field. The governing equations were solved with finite-volume approach and enthalpy method was employed to account for phase change. The model was firstly validated against low temperature experiments from the literature and then used to predict the charging and discharging behavior of the present TESS. The position of solid/liquid interface was explored and the effects of design parameters, including that of metal foam pore density and porosity, configuration of fin and Rayleigh number, on melting and solidifying rate and energy stored in each time step were revealed and discussed. The results indicate that metal foam and fins can effectively improve the heat transfer performance for thermal storage system and decrease charging and discharging time.

A Comparative Thermoeconomic Study of Hybrid Solar Gas-Turbine Power Plants

The construction of the first generation of commercial hybrid solar gas-turbine power plants will present the designer with a large number of choices. To assist decision making, a thermoeconomic study has been performed for three different power plant configurations, namely, simple- and combined-cycles along with a simple-cycle with the addition of thermal energy storage. Multi-objective optimization has been used to identify Pareto-optimal designs and highlight the trade-offs between minimizing investment costs and minimizing specific CO2 emissions. The solar hybrid combined-cycle power plant provides a 60% reduction in electricity cost compared to parabolic trough power plants at annual solar shares up to 20%. The storage integrated designs can achieve much higher solar shares and provide a 7–13% reduction in electricity costs at annual solar shares up to 90%. At the same time, the water consumption of the solar gas-turbine systems is significantly lower than conventional steam-cycle based solar power plants.

Parabolic trough concentrators for hot water generation: Comparison of the levelized cost of production

With the objective of demonstrating the technical and economic viabilities of a hybrid solar energy system applied to hot water generation, a simulation of a parabolic trough power plant with an auxiliary electrical heater system is presented. This article reports the procedure to obtain the characteristic equation of the useful heat value when N parabolic troughs are operated in series; the equation takes into account the heat loss through the pipes and the use of a heat exchanger. Additionally, this work reports a theoretical case study of a hybrid system that supplies hot water via solar energy and an auxiliary electrical system. The solar fraction and the global efficiency of the hybrid solar power plant are calculated. Using the results from the simulation, a cost analysis of the hybrid solar power plant was done where the levelized cost of thermal power generated is obtained; this in turn shows that the levelized cost of a conventional electrical heater system is one and a half times more than that of the hybrid system.

Investment Analysis of a New Solar Power Plant

The aim of this study is to propose a guideline for solar energy investment. Two solar energy investment methods are discussed for the investors: Photovoltaic (PV) Power Plants and Parabolic Trough Power Plants (PTPP). In this study, parabolic trough investment is discussed with Molten Salt technology which is one of the most advanced thermal energy storage systems. This technology is crucial for solar investment because it distinguishes these systems from other types of power plants by enabling electricity generation on cloudy days and/or during the night. Investment analysis of both plant types are completed with engineering and economic feasibility studies. This study focuses on solar energy potential of the city of Konya, Turkey and 10 MW installed capacity is applied for 25 years in both plant types as a case study. Comparison of obtained results is heavily based on net present value (NPV) approach. Empirical results demonstrate that the proposed methods are viable approaches for solar investment in Konya. On the other hand, it generates a guideline for investors in other countries by applying the solar insolation variables of the location to thermodynamic equations which are proposed in this article. However, the investment strategy varies depending on the solar potential and decision maker’s risk attitude.

Assessment of a Solar Parabolic Trough Power Plant for Electricity Generation under Mediterranean and Arid Climate Conditions in Algeria

In Algeria, the climate is transitional between maritime in the north and semi-arid to arid in the middle and the south. The Sahara which represents more than 80% of the total area of Algeria is characterized by the high level of solar energy potential. In the other hand, concentrating solar thermal technologies represent 70% of the total power to be installed in the framework of the national plan of renewable energy and energy efficiency which consists of installing up 22000 MW of power generating capacity from renewable sources between 2011 and 2030 to achieve. The most important part of this plan is dedicated to the parabolic trough technology. In this purpose, this article presents an assessment of a plant of 100 MW for electricity generation based on parabolic trough technology. This plant will be located in four typical sites of Algerian climate conditions (Tamanrasset, Bechar, Ghardia and Alger). The NREL's SAM software (system Advisor Model) is used to evaluate the plant's energetic and economic performances such as monthly energy production, annual energy output and Levelized cost of energy (LCOE).

Feasibility Study of Parabolic Trough Solar Power Plant under Algerian Climate

Because of clean renewable electric power technologies is the human's future, a great number of parabolic trough power plants with different configurations are being considered for deployment in different locations in our world. It is necessary to study the operating performance of the concentrator solar power plant located in typical sites of Algeria, in this work for reference of the feasibility study of this technology in Algeria, it is essential that the plant designs will be optimized for each specific location. This paper is divided in three big sections; the first one is the implantation of parabolic trough solar power plants in different Algerian locations to see if this installation gives us usable electricity. The second section is to determine the best combination of available solar technological components (collectors, receivers, heat transfer fluids) and finally to make an economic study and gives a solution to minimize the levelized cost of electricity. The results shows that Algeria is one of the best world locations to produce usable electricity from solar thermal energy also the results could be useful to make decisions to realize such projects

Solar collector field design and viability analysis of stand-alone parabolic trough power plants for Indian conditions

The parabolic trough collector is one of the most proven and commercial concentrating solar power (CSP) technologies. The implementation of parabolic trough in large scale power plants is an effective solar energy option in an arid and semi-arid region. In this article, analysis of solar parabolic trough collector field for power generation is carried out using different working fluids like oil and water. The analysis of collector field for power generation is carried out based on the various geometric parameters (rim angle, collector aperture); collector configurations (spacing distance, shading distance, land area) and solar radiation. The land area required for different plant operating hours and insolation conditions are analyzed. The optimum configuration of the collector field is found as 6m aperture, rim angle (Ψrim)=65° with spacing distance between the collector rows equivalent to shading distance after 2h of sunrise at δ=0° and plant operates between 1h after sunrise and before sunset. Techno-economic feasibility analysis of solar trough power plant is carried out for 58 locations in India. The annual power generation capacities of solar trough power plant are estimated for various locations such as eastern (14), western (18), northern (15) and southern (11) regions of India. The levelised costs of electricity generation of stand-alone solar parabolic trough power plant are estimated with oil and water as working fluids and it is found that Rs. 11.00 (¢ 24) and Rs. 11.84 (¢ 26) for oil and DSG respectively for Jodhpur.

Mechanical and thermal properties of cement composite graphite for solar thermal storage materials

The comprehensive survey on an attractive thermal storage material consisted of aluminate cement and graphite is obtained in this paper. The effect of different water/cement (w/c) ratio and graphite content on compressive strength and thermal properties including thermal conductivity, volume heat capacity and thermal expansion coefficient of hardened aluminate cement pastes were investigated to pursue the optimum material design for solar parabolic trough power plant. It is observed that thermal conductivity and volume heat capacity were improved with the decrease of w/c and the increase of graphite content. The results show that w/c is a key factor affecting thermal properties of pastes and graphite even has some influence on the hydration process. After heat treatment at 350°C for 6h, compressive strength and thermal properties descended in a certain extent. XRD and FTIR were used to characterize the evolution of hydration products together. Furthermore, the properties obtained from the paper will lay the foundation for thermal storage materials of solar thermal power plants in the future.

Probabilistic modeling of a parabolic trough collector power plant – An uncertainty and sensitivity analysis

In this work, an uncertainty and sensitivity analysis for the annual performance of a parabolic trough collector plant based on a probabilistic modeling approach of the solar-to-thermal energy conversion process has been accomplished. Realistic probability functions have been assigned to the most relevant solar field performance parameters. The Latin Hypercube sampling method has been used to create equal probable parameter combinations. The so obtained sample matrix has been used to run multiple annual electricity yield simulations in SimulCET, a validated parabolic trough collector plant simulation software, developed by the National Renewable Energy Center (CENER) in Spain García-Barberena et al., 2012. This procedure has led to a representative distribution for the annual plant performance, given the uncertainty in the input data. For this study the parabolic trough power plant model has been run in solar driven operation mode, without the use of thermal storage or fossil fuel back up. While being aware of the great influence of the solar irradiation on the power plant performance, only one single reference meteorological year has been used as solar input data. This has been done in order to emphasize the influence of technical design- as well as solar field maintenance parameters, factors that can be controlled or affected by mankind. In order to assess and rank the impact of each varied model parameter a multiple linear regression has been performed. The standardized regression coefficients, the Pearson correlation coefficients as well as the coefficient of multiple determination R2 are discussed. Varied parameters are the collector mirror reflectance, the collector mirror cleanliness factor, the collector glass tube transmittance, the collector receiver tube absorptance, and the collector receiver tube heat loss characteristic. Based on existing and published bibliography, a set of parameter distributions and ranges have been chosen for this work and the simulation results show that the cleanliness factor has the strongest influence on the model output. The cleanliness is followed (in this sequence) by the mirror reflectance, the glass tube transmittance, the receiver tube absorptance and, finally, by the receiver tube heat loss characteristic.

Techno-economic analysis of combined concentrating solar power and desalination plant configurations in Israel and Jordan

Combined concentrating solar power (CSP) and desalination plants represent a realistic future option for the production of electricity and fresh water for countries of the world’s sunbelt. In this paper, parabolic trough power plants for electricity production have been analysed in combination with multi-effect distillation (MED) and ultrafiltration/reverse osmosis (RO) desalination plants for two sites in Israel (Ashdod) and Jordan (Aqaba). Both RO and MED desalination plants were designed for a fresh water production capacity of 24,000 m3/d. The power block of the CSP plant was selected to meet the steam consumption of the MED plant at the design point, which led to a gross electrical power generation capacity of the power block of 42 MWel. Due to the low availability and generally high cost of coastal land, the CSP + RO plant consists of two separate units. It was assumed that the CSP plant is located at an inland location where there is land available. The RO plant is located at the sea, while the MED plant is located at the CSP site. The pumping of the seawater and the water transmission system add about 0.2 $/m3 to the levelized water costs of the CSP + MED plant compared with a plant located at the sea. Three different sizes of high temperature heat storages (0 h, 6 h and 12 h of additional full load operation of the steam turbine) were applied to find the most economic setup. At current prices for heat storage units, systems with huge heat storage capacities become economic only at high feed-in tariffs for electricity and thus high revenues. The price of the electricity generated by the CSP plant was varied to show the influence of the feed-in tariff on the water generating costs. The levelized costs of water (LCOW) strongly depend on the electricity price. Water costs in Ashdod are higher than those in Aqaba due to the lower solar irradiance. For Aqaba, LCOW of about 1 $/m3 can be realized if a feed-in tariff of about 0.24 $/kWh for electricity from renewable energy sources is established.

Hydrogen permeation model of parabolic trough receiver tube

Hydrogen gas formed by the thermal decomposition of organic heat transfer fluids can permeate through parabolic trough receiver tubes into the vacuum annulus, leading to significant heat losses in the receiver which reduces the parabolic trough power plant efficiency. This problem is quite important as these systems are being developed to drive down the cost of electricity. Thus, hydrogen permeation in parabolic trough power plants must be understood to develop strategies to reduce or prevent hydrogen gas accumulation in the receiver annulus. Hydrogen permeation model for parabolic trough receivers was developed based on measurements of hydrogen permeability of solar-selective coatings. The model was then used to study the effects of the hydrogen generation rate, the hydrogen pressure in the receiver tubes and the hydrogen barrier coating on the hydrogen permeation into the annulus. The hydrogen generation rate plays a significant role in the hydrogen permeation process, with the hydrogen pressure, permeability and adsorb area all related to balancing the hydrogen permeation rate with the hydrogen generation rate.

High-Temperature Solid-Media Thermal Energy Storage for Solar Thermal Power Plants

Solid sensible heat storage is an attractive option for high-temperature storage applications regarding investment and maintenance costs. Using concrete as solid storage material is most suitable, as it is easy to handle, the major aggregates are available all over the world, and there are no environmentally critical components. Long-term stability of concrete has been proven in oven experiments and through strength measurements up to 500 °C. Material parameters and storage performance have been validated in a 20-m3 test module with more than 23 months of operation between 200 °C and 400 °C and more than 370 thermal cycles. For an up-scaled concrete storage design with 1100-MWh capacity in a modular setup for a 50 MWel parabolic trough power plant of the ANDASOL-type, about 50 000 m3 of concrete is required and the investment costs are approximately 38 million euro. The simulation of the annual electricity generation of a 50 MWel parabolic trough power plant with a 1100-MWh concrete storage illustrates that such plants can operate in southern Europe delivering about 3500 full load hours annually; about 30% of this electricity would be generated by the storage system. This number will increase further, when improved operation strategies are applied. Approaches for further cost reduction using heat transfer structures with high thermal conductivity inside the concrete are analyzed, leading to a 60% reduction in the number of heat exchanger pipes required. For implementation of the structures, the storage is build up of precast concrete blocks.

Modeling and Simulation of a Parabolic Trough Power Plant

AbstractIn Portugal, the increase in the production of electricity based on renewable energy sources has been achieved based mainly on hydro and wind resources. The sun has been underexploited so far. The Portuguese territory presents high levels of solar radiation, and thus it is urged to find solutions that take advantage of this widely recognized fact. In this context, it is important to come forward with concentrated solar power systems as an option. The most mature of these technologies is the parabolic trough. The purpose of this paper is to report the outcomes of a study concerning a parabolic trough power plant, with thermal storage. This paper aims to present a model of a parabolic trough power plant, including the associated thermal storage system, to validate it against results reported in the literature and to build up a simulator enabling the assessment of the performance of the plant for several locations in the Portuguese territory. Based on the obtained results, some conclusions regarding the behavior of the system are drawn.

Technical and Economical Performance of Parabolic Trough Collector Power Plant under Algerian Climate

Parabolic trough solar technology has been proven at nine commercial Solar Electric Generating System (SEGS) power plants that are operating in the California Mojave desert. Simulation using different models when planning this kind of projects and choose the best site for this technology minimizes the risks of these projects. For this purpose, a detailed performance model of the 30 MW SEGS VI parabolic trough power plant was created in the TRNSYS simulation environment using the Solar Thermal Electric Component model library. Both solar and power cycle performance were modeled, but natural gas-fired hybrid operation was not. Good agreement between model predictions and plant measurements was found, with errors usually less than 10%. Also, an economical study has been established to determine the best site, based on the cost of electricity generation. The result shows that Bechar's site is the best site for this technology because of its lowest levelzed electricity cost and its high irradiance level. While the model could be improved, it demonstrates the capability to perform detailed analysis for this technology.

Annual performance improvement for solar steam turbines through the use of temperature-maintaining modifications

Steam turbines in solar thermal power plants experience a much greater number of starts than those operating in base-load plants. By maintaining higher internal temperature during idle periods, faster start-up times can be achieved, increasing the flexibility of the plant as well as increasing net electrical production. Prior work by the authors identified a number of methods for achieving this, with strong increases in daily production predicted; only two specific start-up cases were studied however. In order to obtain a more representative evaluation of the performance increase that can be achieved through increased dispatchability of the turbine, the annual improvement needs to be studied. Building on the existing results, a dynamic system model of a parabolic trough power plant has been established and used to determine the distribution of different cool-down times experienced throughout the year, with a view to evaluating the potential annual production increase. A modification of the start-up curves allows an increase in annual electrical production between 6.4% and 2.4% depending upon the operating mode (free operation versus day-time operation). Through application of a combination of heat blankets and an increase in gland steam temperature, further annual production increases between 2.2% and 3.1% are predicted.

Comparative system analysis of direct steam generation and synthetic oil parabolic trough power plants with integrated thermal storage

Abstract Parabolic trough power plants are currently the most commercially applied systems for CSP power generation. To improve their cost-effectiveness, one focus of industry and research is the development of processes with other heat transfer fluids than the currently used synthetic oil. One option is the utilization of water/steam in the solar field, the so-called direct steam generation (DSG). Several previous studies promoted the economic potential of DSG technology ( Eck et al., 2008b , Price et al., 2002 , Zarza, 2002 ). Analyses’ results showed that live steam parameters of up to 500 °C and 120 bars are most promising and could lead to a reduction of the levelized electricity cost (LEC) of about 11% ( Feldhoff et al., 2010 ). However, all of these studies only considered plants without thermal energy storage (TES). Therefore, a system analysis including integrated TES was performed by Flagsol GmbH and DLR together with Solar Millennium AG, Schott CSP GmbH and Senior Berghofer GmbH, all Germany. Two types of plants are analyzed and compared in detail: a power plant with synthetic oil and a DSG power plant. The design of the synthetic oil plant is very similar to the Spanish Andasol plants ( Solar Millennium, 2009 ) and includes a molten salt two-tank storage system. The DSG plant has main steam parameters of 500 °C and 112 bars and uses phase change material (PCM) for the latent and molten salt for the sensible part of the TES system. To enable comparability, both plants share the same gross electric turbine capacity of 100 MWel, the same TES capacity of 9 h of full load equivalent and the same solar multiple of the collector field of about two. This paper describes and compares both plants’ design, performance and investment. Based on these results, the LEC are calculated and the DSG plant’s potential is evaluated. One key finding is that with currently proposed DSG storage costs, the LEC of a DSG plant could be higher than those of a synthetic oil plant. When considering a plant without TES on the other hand, the DSG system could reduce the LEC. This underlines the large influence of TES and the still needed effort in the development of a commercial storage system for DSG.

Analysis of the influence of operational strategies in plant performance using SimulCET, simulation software for parabolic trough power plants

Abstract This paper analyzes the influence of operational strategies on the performance of parabolic trough (PT) solar power plants with the aid of SimulCET a computer program for the simulation of the energy behavior of PT plants developed by the National Renewable Energy Centre of Spain (CENER). SimulCET uses state of the art techniques to simulate solar energy absorption and others energy conversion processes that take place in a PT plant. The simulation of these energy conversion processes is based on both empirical and physically derived expressions and produces highly accurate electricity generation estimates. The holistic approach adopted in SimulCET to carry out the analysis of PT solar power plants makes this program a very effective tool in optimizing the operation of such plants. Furthermore, SimulCET’s capabilities for simulating the operation of gas boilers make it possible to compare different operational strategies scenarios, and enable the testing of new hybrid plants concepts. To assess the validity of the results generated by SimulCET, these results were compared with current experimental data. The comparison showed good agreement among daily averaged estimates and the corresponding measured energy values. The comparison of SimulCET daily estimations against twelve reference days of measured data showed a mean deviation of −3.14% in terms of daily total gross electricity production. This paper focuses on the simulation and analysis of different PT plant operational strategies to explore the consequences and side effects of the way the fossil fuel is used, which have been seldom analyzed up to now, although they may significantly affect the long term performance of the plant. Four different operational strategies were compared. In all of them, the yearly amount of gas used was the maximum allowed for a solar PT power plant to be considered eligible to receive the benefits of the Spanish feed-in tariff legislation. Differences in gross electric energy output larger than 10% and differences in yearly gas consumption of up to 15% were obtained during the simulation of the PT power plant running for a year under each one of the four operational strategies considered. The results of these simulations make clear the need for further techno-economic optimization of the operational strategies defined, since revenues, costs and other operational factors depend not only on the amount of gas used, but also on when this gas is burned.

Thermal energy storage for direct steam generation

Parabolic trough power plants with direct steam generation are a promising option for future cost reduction in comparison to the SEGS type technology. These new solar thermal power plants require innovative storage concepts, where the two-phase heat transfer fluid poses a major challenge. A three-part storage system is proposed where a phase change material (PCM) storage will be deployed for the two-phase evaporation, while concrete storage will be used for storing sensible heat, i.e. for preheating of water and superheating of steam. A storage system with a total storage capacity of approx. 1 MW h is described, combining a PCM module and a concrete module. The storage modules have been constructed for testing in a DSG-test facility specially erected at a conventional power plant of Endesa in Carboneras (Spain). Commissioning of the storage system started in May 2010; testing under real steam conditions around 100 bar will begin in August 2010.

Economic Analysis and Life Cycle Assessment of Concrete Thermal Energy Storage for Parabolic Trough Power Plants

For parabolic trough power plants using synthetic oil as the heat transfer medium, the application of solid media sensible heat storage is an attractive option in terms of investment and maintenance costs. One important aspect in storage development is the storage integration into the power plant. A modular operation concept for thermal storage systems was previously suggested by DLR, showing an increase in storage capacity of more than 100%. However, in these investigations, the additional costs needed to implement this storage concept into the power plant, such as for extra piping, valves, pumps, and control, had not been considered. These aspects are discussed in this paper, showing a decrease in levelized energy costs with a modular storage integration of 2–3%. In a life cycle assessment a comparison of an AndaSol-I type solar thermal power plant with the original two-tank molten salt storage and with a “hypothetical” concrete storage shows an advantage of the concrete storage technology concerning environmental impacts. The environmental impacts of the hypothetical concrete based AndaSol-I decreased by 7%, considering 1 kW h of solar electricity delivered to the grid. Regarding only the production of the power plant, the emissions decreased by 9.5%.

Conceptual Design of a 2× Trough for Use Within Salt and Oil-Based Parabolic Trough Power Plants

Recent studies in the United States suggest that parabolic trough levelized energy costs (LECs) can be reduced 10–15% through integration of a large salt energy storage system coupled with the direct heating of molten salt in the solar field. While noteworthy, this relatively small predicted improvement may not justify the increased technical risks. Examples of potential issues include increased design complexity, higher maintenance costs, and salt freezing in the solar field. To make a compelling argument for development of this new system, we believe that additional technical advances beyond that previously reported will be required to achieve significant LEC reduction, greater than 25%. The new technical advances described include the development of a high-concentration trough that has double aperture and optical concentration of current technology. This trough is predicted to be more cost-effective than current technology because its cost ($/m2) and thermal losses (W/m2) are significantly lower. Recent trough optical performance improvements, such as more accurate facets and better alignment techniques, suggest a 2× trough is possible. Combining this new trough with a new low-melting point salt now under development suggests that a LEC cost reduction of ∼25% is possible for a 50 MW, 2× salt plant relative to a conventional (1×) 50 MW oil plant. However, the 2× trough will also benefit plants that use synthetic oil in the field. A LEC comparison of 2× plants at sizes ≥200 MW shows only a 6% advantage of salt over oil.