Solar Thermal Electric Plants Research Articles

Modelling of Solar Thermal Electricity Plants in the POSYTYF Research Project for an Extensive Integration of Renewable Energy Sources

This article presents a simplified simulation model of a concentrated solar thermal power plant developed in the framework of the European research project POSYTYF (POwering SYstem flexibiliTY in the Future through RES). Increasing the share of Renewable Energy Sources (RES) in modern power grids is of critical importance for the transformation of the energy markets worldwide. However, the stability of the grid and the limited participation in ancillary services of RES limit their use, especially when high penetration is expected from them. A solution to overcome these issues is to increase the share of so-called dispatchable RES (hydropower, biomass, concentrating solar thermal power). The main objective of the POSYTYF project is to group several renewable and non-renewable energy sources into a Dynamic Virtual Power Plant (DVPP). The simplified simulation model of a parabolic-trough solar thermal power plant developed consists of sub-models for the solar field, thermal energy storage system and power block and it has been validated with real DNI profiles and production data of a commercial STE plant in Spain. The differences between the simulation and real data of daily net production for the days analysed are lower than 1%. Parts of this paper were published as journal article “Using time-windowed solar radiation profiles to assess the daily uncertainty of solar thermal electricity production forecasts”, Journal of Cleaner Production, Volume 379, Part 2, 2022. Mario Biencinto, Lourdes González, Loreto Valenzuela (https://doi.org/10.1016/j.jclepro.2022.134821).

Using time-windowed solar radiation profiles to assess the daily uncertainty of solar thermal electricity production forecasts

This work is aimed at analysing the impact of real-time weather forecasting on the simulation of solar thermal electricity plants. A novel method is presented that allows generating random solar radiation profiles to assess the uncertainty of forecasting solar thermal electricity production. Rather than a weather prediction model, this work proposes a fast and simple method for the generation of synthetic solar radiation data that focuses on the dynamics relevant for electricity production, not requiring long historical data series or meteorological details. Variable window lengths are used to reproduce the growing uncertainty of forecasts with longer time horizons. In addition, a simplified model of solar thermal power plant is described and implemented in MATLAB®. Both the solar profile generator and the plant model are used to simulate massive cases for four representative days with eight forecasting hours based on electricity markets. The results show uncertainty values for day-ahead predictions from 15% to 60% in cloudy days and from 2% to 40% in sunny days, with decreasing ranges for intra-day forecasts.

Atmospheric extinction of solar radiation measurement in solar thermal electric plants

espanolSe ha desarrollado un sistema optico de medida de la extincion atmosferica de la radiacion solar. El sistema utiliza aplicacion y procesamiento de imagenes opticas para obtener informacion cientifica de interes. El sistema contribuye a hacer mas eficiente la tecnologia solar de concentracion ayudando a combatir el cambio climatico. Las futuras plantas solares de torre seran de mayor potencia y mayores distancias heliostato-receptor central que las actuales, cobrando la extincion atmosferica de la radiacion solar gran importancia. Hasta ahora, la extincion se habia determinado con modelos parametricos poco realistas. Por ello, se ha desarrollado un procedimiento para medir extincion atmosferica basado en un sistema optico. Se realizaron simulaciones y calculos con codigos de transferencia radiativa para estimar los niveles de extincion esperados y basandose en estos niveles se desarrollo el sistema optico. El sistema consiste en dos camaras digitales identicas de alta resolucion enfocadas hacia una diana lambertiana, las cuales toman imagenes simultaneas. Las imagenes se convierten en matrices con valores numericos y tras una serie de complejas operaciones se obtiene la radiacion solar extinguida. La extincion diaria medida ha sido monitorizada por primera vez en el panel de control de la sala de operaciones de una planta de torre junto con el resto de variables meteorologicas de control para el funcionamiento diario de una planta. EnglishAn optical system has been developed to measure the atmospheric extinction of solar radiation. The system applies optical imaging and image processing to obtain scientific information of interest. The system contributes to making solar concentration technology more efficient, helping to combat climate change. Future solar tower plants will have higher power and greater heliostats-central receiver distances, making important the atmospheric extinction of solar radiation effect. Until now, the extinction had been determined with unrealistic parametric models. Therefore, a procedure for measuring extinction based on an optical system has been developed. Simulations and calculations with radiative transfer codes were carried out to estimate the extinction levels expected. Based on these levels, the optical measurement system was developed. The system consists of two identical high-resolution digital cameras foccused at a Lambertian target at different distances taking simultaneous images. These images are converted into matrices with numerical values and after a series of complex operations the extinguished solar radiation is obtained. The daily extinction measured has been monitored for the first time in the control panel of a tower plant operating room with the rest of the meteorological control variables for the daily operation.

Analysis of a hybrid dry cooling system for solar thermal electricity plants in deserts

This work analyses a new concept of hybrid dry cooling system composed of a latent heat storage module and an air-cooled condenser intended for solar thermal electricity plants located in desert locations with low water availability. This hybrid system is expected not only to improve the power block efficiency but also to reduce parasitic consumptions of air-cooled condensers, taking advantage of the temperature oscillations in such locations. For evaluating those advantages, a simulation model of a solar thermal plant that includes either conventional dry or hybrid cooling system has been developed with TRNSYS, so that both approaches can be compared. The annual behaviour of the corresponding plants in terms of electricity production has been simulated for various desert locations, different cooling system configurations and two phase change materials (PCM) for the latent module: RT35HC and Paraffin C21, with melting temperatures of 35 °C and 40 °C, respectively. Also, suitable operation strategies have been evaluated in order to optimize the performance of the hybrid cooling concept. Simulation results show that an increase in net electricity from 0.3% to 0.6% for Paraffin C21 or from 0.1% to 0.5% for RT35HC could be obtained per year if a hybrid cooling system is used. The use of a PCM with higher melting points such as Paraffin C21 seems to provide better results in terms of net annual production, particularly in locations with high ambient temperatures at night (like Abu Dhabi or Aswan). Although issues like electricity prices, financial and equipment costs should also be considered, a preliminary economic analysis shows that the cost-to-latent heat ratio of the PCM should be below 4.5∙10-3€/kJ to enable the feasibility of the proposed concept.

Direct steam generation solar systems with screw expanders and parabolic trough collectors: Energetic assessment at part-load operating conditions

This paper explains a numerical optimization of a novel screw expander-based solar thermal electricity plant to evaluate the energetic benefits in specific case studies. In the proposed solar electricity generation system, which is based on the steam Rankine cycle, water is used as working fluid and storage, parabolic trough collectors as a thermal source and screw expander as power machine. Such solar system offers major advantages over conventional power plants adopting steam turbines: low operating pressures, good exploitation of low temperature heat sources, acceptable efficiency in energy conversion with steam-liquid mixtures and reduced size. Since screw expanders can operate at off-design working conditions in several situations when installed in direct steam generation solar plants, the chief purpose of the present study is to develop a thermodynamic model to analyse the energy performance of the planned solar power system when off-design operating conditions befall. To assess maximum efficiency of the whole power plant at part-load operating conditions, numerical optimization is then performed in a specific range of fluctuating evaporation temperatures under fixed condensation pressures.

Exergetic Analysis of a New Direct Steam Generation Solar Plant Using Screw Expanders

Screw expanders are volumetric machines particularly suitable in energy conversion with steam–liquid mixtures and for the exploitation of low temperature heat sources. This study explored the main criteria to evaluate the thermodynamic advantages and exergetic assessment of an innovative solar electricity generation system: Screw expanders are utilized as power machines and parabolic trough collectors as a thermal source. Such a direct steam generation solar system, which is based on the Rankine cycle, offers benefits in comparison with usual power plants with dynamic expanders: The best exploitation of low temperature heat sources, satisfactory thermal efficiency with steam–liquid mixtures, lower evaporation pressures, and reduced size. Under real working conditions, screw expanders can work at part-load operating conditions; thus, the chief purpose of the present paper was to analyze the exergetic advantages of the planned solar power system when solar radiation and off-design working conditions fluctuate. Initially, the polytropic expansion phase with a specific numerical model is described to evaluate the energy losses that affect the thermodynamic performance of screw expanders when installed in the planned renewable energy power plant. Subsequently, to explore the exergy harnessing in the exhausted steam at off-design working conditions and then to appraise the maximum exergetic efficiency of the proposed screw expander-based solar thermal electricity plant, numerical optimization was performed in a broad range of evaporation and condensation temperatures.

Thermal energy storage (TES) with phase change materials (PCM) in solar power plants (CSP). Concept and plant performance

Concentrated solar power (CSP) is today recognized as a unique renewable energy for electricity generation due to its capability to provide dispatchable electricity incorporating thermal energy storage (TES). Molten salts TES is the most widespread technology in commercial CSP but the industry is looking for cheaper and more efficient TES systems and phase change materials (PCM) have been highlighted as potential low cost and high energy TES systems. This paper presents a completely new concept of PCM energy storage systems to be used in solar thermal electricity plants with its technical assessment. A cascade type PCM storage system is evaluated, using four buckets with the PCM organized based on melting temperature and the latent energy of the materials. Daily, monthly, and annual transient simulations of the plant performance are carried out. The main conclusion is the similarity between this new concept and the commercial two-tank indirect molten salt system. The cumulative power production over the year is similar and the net production of both systems is well matched.

Thermal and hydraulic evaluation of a linear Fresnel solar collector loop operated with molten salt and liquid metal

In this paper, results of a thermal-hydraulic analysis of a linear Fresnel solar collector loop using molten salt or liquid metals as heat transfer fluid are presented. The purpose of this study is to compare the benefits and challenges of using liquid metals (e.g. sodium) or molten salts (e.g. solar salt) as heat transfer fluid into line focusing Solar Thermal Electric plants. Similar studies have been conducted for point focussing Solar Thermal Electric plants but line focussing plants have not been thoroughly investigated yet. After reviewing and comparing the main thermo-physical properties of sodium and solar salt, results from thermal-hydraulic simulations, using the best-estimate system code TRACE from the US Nuclear Regulatory Commission, are presented for various plant operation scenarios. The results show that sodium offers several advantages over solar salt when used as heat transfer fluid, among which: wider operation temperature range, faster start-up procedures, quicker response of the control system and ultimately potentially higher energy yield, mostly thanks to its hundredfold higher thermal conductivity. These benefits may result in increased interest into this technological concept and might lead to further developments of Solar Thermal Electric plant design with reduced levelised cost of electricity generation.

Atmospheric extinction levels of solar radiation at Plataforma Solar de Almería. Application to solar thermal electric plants

To integrate Solar Thermal Electric (STE) Plants energy production into the electric power supply system of a country, it's necessary to solve some uncertainties about availability of solar resource. One of these is the accurate knowledge of solar radiation reaching solar receiver. Solar radiation is attenuated by aerosols and molecules present in the Atmosphere. Estimation of this phenomenon is complicated due to environmental factors on which it depends. Currently there are some methodologies in literature to estimate it (parametric models, simulations tools, radiative transfer codes (RTC) or visibility instrumentation). A new approach to estimate the extinction in STE Plants has been elaborated. Developed model uses atmospheric realistic conditions present in a real location. With this purpose, a Typical Aerosols Year (TAY) has been elaborated using NREL Methodology for Typical Meteorological Years. TAY has been created processing aerosol data provided by an AERONET station located at PSA. Using TAY has been obtained the typical spectral transmittances levels at PSA, with RTC. Attenuation model results from transmittances levels, has been used to acquire production and economic losses due to extinction in a simulated STE Commercial Plant at PSA. Results have been compared with others in the literature for the same emplacement.

Design and optimisation of linear Fresnel power plants based on the direct molten salt concept

Abstract Thermal energy storage (TES) is an exclusive feature of solar thermal electric (STE) plants, allowing for solar energy to be efficiently stored and dispatched to the grid at a chosen point in time, thus providing an enhanced operation flexibility while potentially reducing the levelised cost of electricity generation (LCoE). The direct molten salt (DMS) concept, where a liquid nitrate/nitrite salt mixture is used both as heat transfer fluid in the solar field and as sensible heat storage medium in the TES represents currently the most promising technological option, in terms of LCoE optimisation and technology maturity, for STE plant with thermal energy storage. Here, different DMS plant configurations based on the linear Fresnel solar collector technology are investigated targeting to define optimal designs with regards to the LCoE. For this purpose, a simulation tool has been developed capable of describing the dynamic plant behaviour by means of best estimate methods to determine the annual yield and operational availability of linear focusing DMS STE plant, together with estimating the investment and annual operation costs of such plants. Simulations results from this tool have been validated against a well established thermo-hydraulic simulation tool (TRACE). The study concentrated on the following aspects: 1. Identification of optimal operational parameters of a STE plant with TES coupled to a power cycle 2. Economical evaluation of the chosen plant concepts and definition of optimal plant configurations 3. Investigation of LCoE reduction perspectives by means of higher operation temperatures These analyses exhibit for the given plant setup an optimum choosing a sub-critical reheat power cycle at 540 °C/165 bar and the so-called “Hitec” molten salt mixture as heat transfer fluid (HTF). However supercritical power cycles in a DMS STE plants are not considered and may bring further LCoE reductions. Additionally, in terms of LCoE, the study reveals an optimal plant capacity in the range of 100 MW el to 150 MW el . Finally, the study shows that a further increase in the temperature of both power cycle and solar field beyond the previously named optimal values leads to increased LCoE.

An analytical optimization of thermal energy storage for electricity cost reduction in solar thermal electric plants

Solar Thermal Electric (STE) plants can integrate Thermal Energy Storage (TES) in order to generate electricity when the energy source (Sun radiation) has vanished. TES technology has become a very important asset for this type of renewable energy source, but it has induced a rise in electricity cost in many cases. One of the reasons is the need of larger solar fields as the TES capacity increases because the solar field has to provide thermal power both to generate electricity and to charge the storage. The economic effects of improving the plant performance seem to have some internal complexities that must be investigated covering the internal relations among the main parts of a STE plant: the solar field, the power block and the energy storage. This paper presents an analytical study of these relations aimed at deriving a better understanding of the cost/performance behavior of STE plants. As the power block is a mature and commercial technology with well-established efficiencies and specific costs (in $/W, for instance), it has been taken as the reference element in modelling the plant. The other parts of the plant, i.e., the solar field and the energy storage, have been characterized in cost and energy management by a set of high-level parameters. Of course, a coarse definition cannot give very accurate results for a specific design, but it can be the guideline for the selection and sizing of a plant. It is worth noting that each type of solar thermal power plant has a different parametric scenario, corresponding to its essential design window. In this paper, comparisons among plants with different parametric scenarios are restricted to one-axis concentration solar fields, where the coarse model is easily characterized. The results show that the optimum plant configuration, in terms of TES capacity and solar field size, depends on the solar field and TES costs relative to power block cost. Moreover, it is shown that some parametric scenarios always lead to an increase in the cost of electricity when the energy storage capacity is enlarged. On the contrary, parametric scenarios associated to cheaper solar fields yield a much better economic result when TES is embodied in the plant. Additionally, TES efficiency is also identified as a parameter with high impact in the performance of the whole system. This result seems obvious, but the model gives numerical values that can help to optimize the selection process in a project. For instance, it is assessed that the lower the TES efficiency, the greater the relevance of reducing solar field costs is in order to obtain low electricity generation costs. As a general conclusion, the model points out that Fresnel-type solar fields are much better suited than parabolic trough collectors for integrating thermal energy storage. This implies that Fresnel plants present a higher potential to cover the peaks of electricity demand, which results into bigger profits.

Review and validation of Solar Thermal Electricity potential methodologies

With the strong dependence of national economies on energy, interest in solar energy potential assessments is increasing in countries with high solar radiation levels. This article reviews four methodologies proposed in the literature by four different organizations (IDAE, Greenpeace, NREL, and DLR) and proposes a new one (LRS) for assessing the potential of Solar Thermal Electricity (STE) generation in a given country. Derived from these five methodologies, nine cases are studied (IDAE, GP2, NREL1, NREL3, DLR2, DLR2′, LRS1, LRS2, and LRS3). In this study, we followed a two-step STE potential assessment procedure. In the first step, suitable areas for locating STE plants in the country are identified. In the second step, STE plants are assumed to be built and operated in the suitable areas selected in the first step, and the annual electricity generated by these hypothetical plants is estimated.To compare the assessed methodologies, all cases have been applied to the same test country: Spain. Because a relatively large number of commercial STE plants are in operation in Spain, the location of these commercial plants was used to define a simple but effective validation test. A validation process is proposed for the IN-OUT decision based on the buffers containing each existing STE plant. Inside each buffer, a mix of suitable and unsuitable pixels is often included. Thus, the process starts with the decision whether a plant could be considered “IN” the suitable area or not. After the evaluation of the percentage of pixels considered as suitable inside the buffer, and comparing with only the power block pixel location, the second option was selected since it provides good results and simplifies any further treatment. The validation process also considers a minimum of near 90% of the STE plants “IN” suitable areas in order to consider a specific case valid. This means that if a case leaves out more than 10% of the real STE plants, it was considered far from reality and rejected. Cases IDAE, NREL3, DLR2, and the new LRS3 have been validated using the described validation procedure and the last three have very close results with similar levels; this is an important outcome that aims to compare potential assessments performed in different countries by different institutions.

Calcium aluminate based cement for concrete to be used as thermal energy storage in solar thermal electricity plants

A concept for thermal energy storage (TES) in concrete as solid media for sensible heat storage is proposed to improve the cost and efficiency of solar thermal electricity (STE) plants. Mortar and concrete mixes were designed with calcium alumina cement (CAC) blended with blast furnace slag (BFS), using aggregates of different sources and size for stability performance after long term at high temperature. Seventy-five thermal cycles of 24h length, within the temperature range 290°C to 550°C, have been used to simulate the expected operating conditions of TES. The dehydration processes at microstructural level have been evaluated and correlated with mechanical properties. Dehydration processes and consecutive heat/cool cycles induce changes in concrete at micro- and macro-level. The stabilization of damage with the charge/discharge heat cycles for thermal fatigue depends significantly on the aggregate type used. CAC is a suitable binder to use in thermal energy storage systems able to maintain its properties under repetitive heat cycles.

Highly reflective polymeric substrates functionalized utilizing atomic layer deposition

Reflective surfaces are one of the key elements of solar plants to concentrate energy in the receivers of solar thermal electricity plants. Polymeric substrates are being considered as an alternative to the widely used glass mirrors due to their intrinsic and processing advantages, but optimizing both the reflectance and the physical stability of polymeric mirrors still poses technological difficulties. In this work, polymeric surfaces have been functionalized with ceramic thin-films by atomic layer deposition. The characterization and optimization of the parameters involved in the process resulted in surfaces with a reflection index of 97%, turning polymers into a real alternative to glass substrates. The solution we present here can be easily applied in further technological areas where seemingly incompatible combinations of polymeric substrates and ceramic coatings occur.

STE Plants: Beyond Dispatchability Firmness of Supply and Integration with VRE

Abstract The Solar Thermal Electricity (STE) community is certainly concerned about the difference in the deployment trend when compared with Variable Renewable Energies (VRE). The installed capacities in wind and PV have reached 350 GW and 160 GW respectively while STE plants have only achieved 4 GW. The explanation is easy: the current generation costs of wind and PV plants are lower than those of STE plants and a large majority of installations were sited in industrialised countries – where no additional backup was required. Large shares of VRE bring significant reductions on the operation time of flexible conventional plants and even lead to curtailments on renewable energy sources as well. In developing countries, the situation is quite different. These must not only increase, but mainly multiply their installed capacity in the next years for meeting the demand needs at all times. Therefore, this increase of installed capacity power cannot be exclusively based, e.g. in PV and/or wind plants, as the evening peak has to be covered every day. Such investments in VRE must then be backed up by new combined cycles. This also why STE could already be selected as the best choice in several Sun Belt countries. However, the main challenge for STE plants is not only to offer some flexible dispatch features, but also to be able to respond to the requested dispatch profile under any circumstances. Achieving this goal with huge solar plans and storage systems will be certainly not cost competitive in the short term. Therefore, “smart” combinations between storage and hybridisation solutions will need to be developed. In this paper, different conceptual alternatives for firm supply features of STE plants are analysed and the advantages of high-performance hybrid solutions combined with storage capabilities are featured. Nevertheless, a fruitful coexistence and the reaping of synergies with VRE at large regional and seasonal scales are also addressed. Although there is still a large potential for further VRE plants deployment, policy makers everywhere will realise sooner rather than later, that the true market value of firm supply as delivered by the last generation of STE plants –besides their substantial positive macroeconomic impacts in the countries’ economy. And so will hybrid STE plants with storage be the prevailing concept in the future.

Assessment of Different PCM Storage Configurations in a 50 MWel CSP Plant with Screw Heat Exchangers in a Combined Sensible and Latent Storage – Simulation Results

Abstract Effective and economic storage solutions have an important role to enable Solar Thermal Electricity plants (STE) to generate dispatchable power. A thermal storage can increase the value of STE by providing firm electricity in times of peak load or ancillary services. Latent storages are suited optimally for direct steam generating STE systems: due to the isothermal behavior of the phase change materials (PCM) during melting /crystallization, exergy losses during storage charging/discharging are minimized. Up to now latent heat storages are, due to technical and economic issues, not used commercially in STE systems. The PCM have a very low heat conductivity – therefore a sophisticated heat exchanger design is needed to build such storages with sufficient charging/discharging power. An innovative storage concept, uses a screw heat exchanger to transport the PCM from a cold to a hot tank or vice versa during phase change. This concept separates heat exchange and storage tanks.Existing concepts do not have this ability. In annual yield calculations the use of this heat exchanger as part of a thermal storage in a 50 MW el direct steam generating solar thermal power plant has been assessed. After setting up of a cost structure, the respective levelised cost of electricity (LCOE) have been used as comparison criterion for two storage systems with different designs. It can be shown, that a storage system with three storage tanks yields lower LCOE than one with two storage tanks. There is further potential for cost reductions, such as the optimization of the heat exchanger area and the temperature difference between the heat transfer fluid and the PCM.

Development of W–SiO2 and Nb–TiO2 solar absorber coatings for combined heat and power systems at intermediate operation temperatures

Two new absorber coatings for mid-temperature operation (300–350°C) in collectors for solar thermal electricity plants are presented in this study. The absorbers consist of two cermet layers of either W–SiO2 or Nb–TiO2, deposited on a molybdenum infrared reflector and coated with an antireflection layer of silicon oxide. The optimization of the optical performance was made in two steps. First, the layer structure was optimized in model calculations. The optical constants used in this modelling were derived directly from sputtered films of the cermet constituents using reflectance and transmittance measurements. The absorber coatings were then sputter-deposited using parameters from the modelling. The results show good agreement between modelled and sputtered optical performance evaluated as solar absorptance and thermal emittance at 350°C. The optimal values reached for W–SiO2 was 0.91 in combination with 0.08 and 0.93 in combination with 0.09 for Nb–TiO2. The materials characterization from XRD, AES and TEM shows that the composite coatings contain nano-metal inclusions, meaning that they are cermet coatings. Scratch tests show that the coatings adhere well to the substrate of stainless steel. Temperature testing at 350°C in vacuum for up to 1500h shows that both coatings are stable under such conditions. Only a slight change occurs during the first 72h that decreases the emittance but does not change the solar absorptance. ERDA confirms that there is no detectable level of ion migration between layers, only a small decrease in hydrogen content was observed, which indicates outgassing.

Assessment of a Global-to-Direct Empirical Model for the Long-term Characterization of Direct Normal Insolation

The statistical characterization of the solar resource (direct normal solar radiation) is a key point in the initial phases of a solar thermal electricity (STE) plant project. Ideally, this characterization should be based on long time series (at least 8 years) of on-site measured data of Direct Normal Insolation (DNI) and other meteorological parameters. Unfortunately, there are very few places around the world where such time series are available, so alternative methods have to be used. Most of them rely on the application of global-to-direct conversion models to long time series of Global Horizontal Insolation (GHI), measured or derived from satellite images, to estimate the long-term resource. Usually, a meteorological station including sensors for the measurement of DNI is installed at the selected project site at the beginning of the project. The data collected during the measurement campaign, which normally extends between a few months and 2 years, are used to adjust the conversion models and to correct the estimates. In this paper, a simple empirical model that relates monthly clearness index and monthly direct normal fraction is used to estimate monthly and annual long-term DNI from statistically representative monthly values of GHI. This model is adjusted with GHI and DNI data collected during measurement campaigns of different durations. We show that the accuracy of the proposed model is under ±5% and that this accuracy improves sharply with the duration of the test campaign. For this purpose, we have used 13 years of high quality DNI and GHI data from the radiometric station of the Group of Thermodynamics and Renewable Energies (GTER) of the University of Seville, Spain. The results suggest that, this simple empirical model is a good alternative to the present methodologies when short DNI measurement campaign but long-term GHI values are available.

Analysis of the Distribution of Measured and Synthetic DNI Databases and its Effect on the Expected Production of a Parabolic Trough Plant

The generation of a Typical Meteorological Year (TMY) is a common practice in solar energy projects. Therefore it is desirable that the TMY provides not only a good estimate of the solar resource in the long term, but also an adequate input for the estimation of the performance of the project during its lifetime. The main goal of this work is to analyze and compare the effect of using synthetic and measured time series on the statistical relationships between the annual Direct Normal Insolation (DNI) values and the corresponding electricity generation of a Solar Thermal Electricity (STE) plant. For this purpose we have used two DNI databases: (a) terrestrial database with thirteen years (2000 to 2012) of 5-second measurements for the location of Seville, Spain, and (b) synthetic database generated with the Meteonorm® V 6.1.0.23 software, by applying GHI-DNI conversion models to the measured monthly values of GHI for the same location. We have used the EOS code to estimate the electricity generation of a 50 MW parabolic trough plant with 8 equivalent hours of thermal energy storage (TES) capacity. The results show that the use of synthetic series introduces an additional uncertainty that has to be analyzed for each project, being in this study the differences between the measured and synthetic data around a 2-3% for the annual values and for the main statistical parameters.

On the sizing of a solar thermal electricity plant for multiple objectives using evolutionary optimization

Design, implementation and operation of solar thermal electricity plants are no more an academic task, rather they have become a necessity. In this paper, we work with power industries to formulate a multi-objective optimization model and attempt to solve the resulting problem using classical as well as evolutionary optimization techniques. On a set of four objectives having complex trade-offs, our proposed procedure first finds a set of trade-off solutions showing the entire range of optimal solutions. Thereafter, the evolutionary optimization procedure is combined with a multiple criterion decision making (MCDM) approach to focus on preferred regions of the trade-off frontier. Obtained solutions are compared with a classical generating method. Eventually, a decision-maker is involved in the process and a single preferred solution is obtained in a systematic manner. Starting with generating a wide spectrum of trade-off solutions to have a global understanding of feasible solutions, then concentrating on specific preferred regions for having a more detailed understanding of preferred solutions, and then zeroing on a single preferred solution with the help of a decision-maker demonstrates the use of multi-objective optimization and decision making methodologies in practice. As a by-product, useful properties among decision variables that are common to the obtained solutions are gathered as vital knowledge for the problem. The procedures used in this paper are ready to be used to other similar real-world problem solving tasks.