Central Receiver Solar Power Plant Research Articles

Genetic algorithm optimization of heliostat field layout for the design of a central receiver solar thermal power plant

The heliostat field layout in a central receiver solar thermal power plant has significant optical losses that can ultimately affect the overall output power of the plant. In this paper, an optimized heliostat field layout based on annual efficiency and power of 50 MW for the local coordinates of Quetta, Pakistan, is proposed. The performance of two different heliostat field layouts such as radial staggered and Fermat's spiral distribution are evaluated and different design points in a year are considered for the analysis. The field layouts are then optimized using a rejection sampling based Genetic Algorithm (GA). It considers the output power and mean overall efficiency for vernal equinox, summer solstice, autumnal equinox, and winter solstice as objective functions. The GA optimizes the heliostat field parameters, namely, security distance (DS), tower height (TH), heliostat width to length ratio (WR), and the length of heliostats (LH). The study system was developed in MATLAB for validation. It was observed that for the radial staggered layout, the number of heliostats decreased by 364 and the efficiency was improved by 8.52 % using GA optimization relative to unoptimized results field layout. The annual efficiency for Fermat's spiral configuration was improved by 14.62 % and correspondingly, the number of heliostats decreased by 434.

Effect of Actual Recuperators’ Effectiveness on the Attainable Efficiency of Supercritical CO2 Brayton Cycles for Solar Thermal Power Plants

One of the most promising concentrated solar power technologies is the central receiver tower power station with heliostat field, which has attracted renewed research interest in the current decade. The introduction of the sCO2 recompression Brayton cycles in the near future installations instead of the Rankine cycle is very probable, due to the prospects of a significant efficiency improvement, process equipment size and capital cost reduction. In this study, energy and exergy analysis of a recompression Brayton cycle configuration for a central receiver power station are performed. Special emphasis is given to the computation of actual performance for the High-Temperature Recuperator and the Low-Temperature Recuperator. The results define realistic thermal and exergetic efficiency limits for the specific cycle configurations applied on a central receiver solar power plant with variable turbine entry temperature. Thermal efficiency, predicted with the improved accuracy of heat exchanger computations, does not exceed the 50% target. Overall, a realizable total power plant efficiency of 37% at 900 K turbine entry temperature is predicted, which is a significant improvement on the current state-of-the-art with steam Rankine cycles.

Atmospheric attenuation measurement system for commercial solar plants based on optical spectrum analysis

The measurement of the solar radiation attenuation is one of the main challenges in concentrating solar power technologies. This work presents a new strategy for this measurement, based on the analysis of the VIS and IR spectra, and its related system. The optical design of the system and its implementation in a central receiver solar power plant is described, and the experimental results are detailed. We present, to the best of our knowledge, the first measurements of the atmospheric attenuation spectrum in a solar power plant. This system provides direct measurements of real atmospheric attenuation values, which opens the way to analyze the impact of aerosols and meteorological conditions at surface level in this attenuation.

Performance Analysis and Optimization of Central Receiver Solar Thermal Power Plants for Utility Scale Power Generation

The paper puts forth the design, performance analysis, and optimization of a 100 MWe central receiver solar thermal power plant with thermal energy storage capability, which can be utilized effectively to meet the renewable energy targets of the Kingdom of Saudi Arabia (KSA). In this paper, three representative sites in KSA are selected for analysis as these sites experience an annual average direct normal irradiance (DNI) of more than 5.5 kWh/m2/day. The optimization approach presented in this work aims to arrive at the best possible design parameters that suit a particular location in accordance with its DNI profile. From the analysis, an annual energy of 559.61 GWh can be generated in Yanbu with eight hours of thermal energy storage, 18.19% plant efficiency, and a capacity factor of 61.1%. The central receiver plant in Abha would be able to offer an annual energy of 536.31 GWh with the highest plant efficiency of 18.97% and a capacity factor of 60.7%. The performance of the proposed design in the two locations of Yanbu and Abha fares better when compared to the operational plant data of central receiver plant in Crescent Dunes. Based on the findings, the proposed 100 MWe central receiver Solar thermal power plants can be effectively implemented in KSA to meet the energy demands of the region.

Effect of various heat transport fluids on central receiver solar thermal power plant

Abstract Increasing the operating temperature of receiver and storage of thermal energy in plants increases the efficiency of power plant and also reduces the cost of power generation. The allowable peak incident flux on the receiver has limitations depending upon the type of heat transport fluid inside the receiver. Specific heat and density of fluid influences volume of fluid required for thermal energy storage in storage tank. Selection of heat transfer fluid used in receiver, storage tank thus plays important role in configuration and performance of power plant. Computer code is developed and simulation is done to study the influence of heat transfer fluids on receiver and storage tank.

Thermal losses in central receiver solar thermal power plant

Central receiver solar thermal power plant with high temperatures is innovative technology for sustaining ecological thermal power generation. The mathematical modeling and simulation of central receiver solar power plant with cavity receiver is done in this paper to predict the thermal power losses from cavity receiver. Results obtained are verified with evidence from solar experiments. A tool is developed with the help of Visual basic to use weather data for simulation. Hitec salt is used as heat transport fluid to obtain high temperatures upto 550°C and is used to produce steam which drives the turbine. Simulation of plant allows to study the performance of entire power plant prior to its actual construction and is done for 10 MWe central receiver solar power plant. The receivers efficiency in absorbing and transferring solar energy to the working fluid is critical in the central receiver concept since plant performance, capital cost and ultimately the cost of energy produced are significantly affected by the receiver’s efficiency. The thermal losses including loss due to convection and radiation losses are considered in the cavity receiver of power plant. Results are obtained for generation of power with change in hourly weather data of Jaipur. From hourly simulation, the thermal losses throughout the day, i.e. in the morning, afternoon and evening are determined for the day receiving the highest solar radiation. Monthly thermal losses and hence power generation under the climatic conditions of Jaipur can be predicted throughout the year.

Thermodynamic Analysis of the Combined CSP and Desalination in Algeria

The aim of this work is thermodynamic analysis of the combine of central receiver solar power plant and multi-effect desalination (MED). The performance of the solar plant and the desalination plant both working together is tested in the MOSTAGANEM area one of coastal sites in north Algeria. In the case studies, 50 MWe and 22568 m3/day have been considered as net electric power and fresh water production respectively. The radiometric and meteorological data in this work, arise directly from the software METEONORME 7.

Life cycle assessment of a future central receiver solar power plant and autonomous operated heliostat concepts

Abstract Up-scaling in power plant size and new innovative concepts in the solar field design are among the most promising ways to reduce the costs of future concentrated solar tower power plants. Besides the economic benefits, the knowledge about the ecological impacts of new concepts is of increased interest in view of the climate targets set. This paper aims to assess the ecological impacts of two autonomous operated heliostat concepts within a future solar tower power plant. Both concepts include a photovoltaic (PV) energy supply for the heliostats, combined with either an LiFPO4 or an LiNMC battery system. Both are compared with a conventional energy supply system. The analysis for comparing the different heliostat concepts is embedded in a life-cycle assessment (LCA) of a 440 MW solar tower plant with a 12,166 MWhth molten salt thermal storage. For the solar tower power plant and the autonomous operated heliostat concepts new LCA inventories were developed. The environmental impacts assessed include the Global Warming Potential (GWP), which is found between 15 and 105 gCO2eq/kWhel, for the entire solar plant depending on the share of fossil fuel co-firing. Indirect life cycle emissions excluding fossil fuel co-firing and thus associated with the life-cycle of the power plant components show, that the conventional solar field is the main contributor to GWP with 9.5 gCO2eq/kWhel. Results for both autonomous concepts demonstrate, that reductions in the impact on climate change are at about 10% compared to the solar field with conventional heliostats. Thus it is demonstrated, that heliostat concepts with an autonomous renewable energy supply lead to considerable reductions in life cycle emissions.

Improved performance of open volumetric receivers by employing an external air return system

In solar central receiver power plants open volumetric receivers using air as heat transfer fluid are an alternative to the currently predominant receiver types, namely salt and steam receivers. In order to improve their competitiveness, the receiver performance has to be improved. In the current study an external air return system has been integrated in the Solar Tower Julich and its influence on power plant performance has been investigated. With this system, the parasitic losses caused by the fans are reduced by up to 34%. The measured air return ratio is mostly unaffected, but the current data suggest, that the internal and external convective losses of the receiver are reduced when an external air return system is applied. A positive influence of the total mass flow on the air return ratio has been identified for the current data while other parameters like the return air temperature turned out to be less significant.

AN ANALYSIS METHODOLOGY OF THE EFFECT OF USING DIFFERENT TRACKING TIME-STEPS ON THE NET ENERGY GAIN OF A CSP POWER PLANT

in central receiver solar power plant, heliostat tracking accuracy affects the optical efficiency and the amount of energy received at the target. In the present article, an integrated analysis of the effect of using different solar tracking time-steps on the energy consumption and gain of a central receiver system is developed. The drive system energy consumption is calculated by using a Solidworks model of the heliostat mechanical drive system. This Solidworks model is interfaced to a Labview model containing the model of the electrical drive and control systems. The solar energy collected at the receiver is calculated using Monte Carlo ray tracing software.

Innovative sensible heat transfer medium for a moving bed heat exchanger in solar central receiver power plants

Renewable energies are gaining importance due to the steadily increasing scarcity of fossil fuels, the ongoing climate change and last but not least the risks which accompany the use of nuclear power. In this growing market, solar thermal power plants offer a centralized, potentially load following electricity production. To serve this need, the integration of thermal energy storage systems is essential. The Moving Bed Heat Exchanger MBHX storage concept for CSP systems using sensible heat transfer medium aims at using a low cost solid storage media. This concept requires intermediate bulk cycles to transfer heat between the solar field and the storage material (the bulk). Heat Transfer Fluids (HTF) such as synthetic oils (mobiltherm 603) are typically used. In this work, granular materials such as sand and rocks are studied to present an additional HTF to represent an efficient and cost-effective alternative. Low cost solid particulates can store and transport heat at temperatures over 1000°C. For the purpose of heat recovery, a moving bed heat exchanger (MBHX) is applied and tested. In this study, the dense granular mass is gravity-driven through a heat exchanger. The performance of the MBHX with the utilization of Sand, Basalt, and a Mixture of Sand and Basalt as a granular material was experimentally investigated. It is found that the effectiveness of the MBHX using a mixture of 50% sand and 50% basalt improved by 30% compared to using sand alone.

Assessment of solar thermal tower technology under Algerian climate

Among all Concentrating Solar Power technologies available for power generation, the solar power tower, also known as central receiver system, is attracting a lot of interest day to day.In the present work, a thermal performance comparison of two mature central receiver solar thermal power plants namely the Rankine cycle with a tubular water/steam receiver and the Brayton cycle with volumetric air receiver is carried out. The investigation has been carried out under the Algerian climate whereby various regions have been selected to provide a comprehensive analysis. TRNSYS-STEC software package has been used for simulating the thermal performance.The results show that, though economically slightly not as competitive as the volumetric air receiver Brayton cycle technology, the water/steam receiver Rankine cycle technology is more suitable particularly under lower solar radiation intensity. The gas turbine requires higher operating temperatures which are usually difficult to reach throughout the year.

Optimization of a recompression supercritical carbon dioxide cycle for an innovative central receiver solar power plant

Peculiar thermodynamic properties of carbon dioxide (CO2) when it is held at or above its critical condition (stated as supercritical CO2 or sCO2) have attracted the attention of many researchers. Its excellent thermophysical properties at medium-to-moderate temperature range have made it to be considered as the alternative working fluid for next power plant generation. Among those applications, future nuclear reactors, solar concentrated thermal energy or waste energy recovery have been shown as the most promising ones. In this paper, a recompression sCO2 cycle for a solar central particles receiver application has been optimized, observing net cycle efficiency close to 50%. However, small changes on cycle parameters such as working temperatures, recuperators efficiencies or mass flow distribution between low and high temperature recuperators were found to drastically modify system overall efficiency. In order to mitigate these uncertainties, an optimization analysis based on recuperators effectiveness definition was performed observing that cycle efficiency could lie among 40%–50% for medium-to-moderate temperature range of the studied application (630 °C–680 °C). Due to the lack of maturity of current sCO2 technologies and no power production scale demonstrators, cycle boundary conditions based on the solar application and a detailed literature review were chosen.

Impact of cost uncertainties and solar data variations on the economics of central receiver solar power plants: An Australian case study

Central receiver solar power plants are becoming an increasingly important technology worldwide and appear to be well suited to areas with moderate to high solar availability in Australia. However, the lack of large commercial installations in Australia results in a heavy reliance on cost and performance data from international literature when assessing possible installations. High variability in costs was found and, in combination with solar variability, this leads to considerable uncertainty when estimating the cost of electricity for potential projects. A stochastic methodology is presented that allows for changes in size of the plant, storage capacity, site location, costs of different plant items, and performance variations over the plant's lifetime. The developed methodology is used to produce a distribution of LCOE estimates. Three Australian sites, namely Alice Springs, Kalgoorlie and Mildura, are used as examples to examine the impact of changes of multiple variables on LCOE estimates. Analysis of these case studies shows a limited influence of storage capacity on LCOE, but considerably higher dependence on plant size and site selection. This suggests that the methodology could be applied to select an optimum plant design to meet specific targets or to compare the benefits of prospective projects at different sites.

Development and Performance Assessment of a Moving Bed Heat Exchanger for Solar Central Receiver Power Plants

Abstract A concept for a moving bed heat exchanger (MBHX) for solar central receiver power plants with a particle-based storage is presented and substantiated with experimental results. The design of the tube bundle considers the rheological bulk properties and was supported by CFD simulations. The adapted MBHX and a conventional reference design were subject of a comparative performance assessment. Both the granular flow distribution as well as the thermal efficiency were examined for both designs. Due to the shorter contact time of the particles at the tube wall in the adapted tube bundle, the newly developed MBHX exhibits a better thermal performance with heat transfer coefficients up to 240 W/m2K for moderate superficial bulk velocities of 5 mm/s. Hence, this concept is considered a promising technology component option for future particle-based CSP plants.

Thermodynamic optimisation and analysis of four Kalina cycle layouts for high temperature applications

The Kalina cycle has seen increased interest in the last few years as an efficient alternative to the conventional steam Rankine cycle. However, the available literature gives little information on the algorithms to solve or optimise this inherently complex cycle. This paper presents a detailed approach to solve and optimise a Kalina cycle for high temperature (a turbine inlet temperature of 500 °C) and high pressure (over 100 bar) applications using a computationally efficient solution algorithm. A central receiver solar thermal power plant with direct steam generation was considered as a case study. Four different layouts for the Kalina cycle based on the number and/or placement of the recuperators in the cycle were optimised and compared based on performance parameters such as the cycle efficiency and the cooling water requirement. The cycles were modelled in steady state and optimised with the maximisation of the cycle efficiency as the objective function. It is observed that the different cycle layouts result in different regions for the optimal value of the turbine inlet ammonia mass fraction. Out of the four compared layouts, the most complex layout KC1234 gives the highest efficiency. The cooling water requirement is closely related to the cycle efficiency, i.e., the better the efficiency, the lower is the cooling water requirement.

Compensation of heliostat drift by seasonal sampling

Heliostat image drift is a common phenomenon in central receiver solar power plants. Several geometrical errors produce drift of the heliostat solar spot at receiver surface, increasing radiation spillage. A heuristic drift compensation method is proposed, based on a polynomial approximation to the drift trajectories. Results of the practical implementation of the proposed method for the control of 10 heliostats in a solar tower facility are presented. A substantial improvement of heliostat tracking is observed on the experimental tests. Because heliostat drift experimental monitoring is a time consuming task, a numerical analysis of the yearly behavior of the compensation method, based on simulations of heliostat drift, was carried out. In these simulations, the behavior of the daily RMS deviation of the concentrated solar spot centroid is evaluated for a whole year, as the polynomial correction is applied. The simulations serve also to test the effectiveness of the proposal polynomial method in a wider range of conditions. Thus, heliostats with a variety of primary error values are simulated. Random wind induced vibrations are introduced in the simulation to evaluate the effectiveness of the calibration method under noise conditions. It is found that a very effective calibration can be achieved with a few sampling events of the heliostat behavior during the year, taking only a few minutes. The RMS deviation can be reduced to values of the order of the wind induced noise level. The proposed polynomial compensation looks like a promising alternative to be implemented in heliostat fields.

Performance analysis of a Kalina cycle for a central receiver solar thermal power plant with direct steam generation

Solar thermal power plants have attracted increasing interest in the past few years – with respect to both the design of the various plant components, and extending the operation hours by employing different types of storage systems. One approach to improve the overall plant efficiency is to use direct steam generation with water/steam as both the heat transfer fluid in the solar receivers and the cycle working fluid. This enables operating the plant with higher turbine inlet temperatures. Available literature suggests that it is feasible to use ammonia-water mixtures at high temperatures without corroding the equipment by using suitable additives with the mixture. The purpose of the study reported here was to investigate if there is any benefit of using a Kalina cycle for a direct steam generation, central receiver solar thermal power plant with high live steam temperature (450 °C) and pressure (over 100 bar). Thermodynamic performance of the Kalina cycle in terms of the plant exergy efficiency was evaluated and compared with a simple Rankine cycle. The rates of exergy destruction for the different components in the two cycles were also calculated and compared. The results suggest that the simple Rankine cycle exhibits better performance than the Kalina cycle when the heat input is only from the solar receiver. However, when using a two-tank molten-salt storage system as the primary source of heat input, the Kalina cycle showed an advantage over the simple Rankine cycle because of about 33 % reduction in the storage requirement. The solar receiver showed the highest rate of exergy destruction for both the cycles. The rates of exergy destruction in other components of the cycles were found to be highly dependent on the amount of recuperation, and the ammonia mass fraction and pressure at the turbine inlet.

Comparative System Performance Analysis of Direct Steam Generation Central Receiver Solar Thermal Power Plants in Megawatt Range

This work proposes and analyses several integration schemes specially conceived for direct steam generation (DSG) in megawatt (MW) range central receiver solar thermal power plants. It is focused on the optical performance related to the heliostat field and the arrangement of receiver absorbers, and the management of steam within a Rankine cycle in the range between 40–160 bar and 400–550 °C at design point. The solar receiver is composed of one single element for saturated steam systems or two vertically aligned separated units, which correspond to the boiler and the superheater (dual-receiver concept), for superheated steam solar thermal power plants. From a fixed heliostat field obtained after layout optimization for the saturated steam solar plant the heliostat field is divided in two concentric circular trapezoids where each of them independently supplies the solar energy required by the boiler and the superheater for the different steam conditions. It has been observed that the arrangement locating the boiler above the superheater provides a slightly higher optical efficiency of the collector system, formed by the solar field and the receiver, compared with the reverse option with superheater above boiler. Besides, two-zone solar fields provide lower performances than the entire heliostat layout aiming at one absorber (saturation systems). Optical efficiency of two-zone solar fields decreases almost linearly with the increment of superheater heat demand. Concerning the whole solar collector, heliostat field plus receiver, the performance decreases with temperature and almost linearly with the steam pressure. For the intervals of steam pressure and temperature under analysis, solar collector of saturated steam plant achieves an optical efficiency 3.2% points higher than the superheated steam system at 40 bar and 400 °C, and the difference increases up to 9.3% points when compared with superheated system at 160 bar and 550 °C. On the other hand, superheated steam systems at 550 °C and pressure between 60 and 80 bar provide the highest overall efficiency, and it is 2.3% points higher than performance of a saturated steam solar plant at 69 bar. However, if saturated steam cycle integrates an intermediate reheat process, both would provide similar performances. Finally, it has been observed that central receiver systems (CRS) producing saturated steam and superheated steam at 500 °C operating at 40 bar provide similar performances.

Dynamic Drift Compensation for Heliostats

In central receiver solar power plants the accuracy of heliostat aiming affects directly the plant efficiency. This accuracy depends on multiple factors, some of which are alignment and operation parameters like: canting, pedestal leveling, elevation and zenith orientations, structural deformation, and clock-date timer accuracy to calculate solar position. All of those factors produce drift of the heliostat concentrated radiation spot. The error parameters differ from heliostat to heliostat in a field, and affect each one in a different manner, depending on their location in the field. Trying to compensate by software for every single error parameter, and for each heliostat is a hard, time consuming, and impractical task. Instead of that, a dynamic drift compensator may be used to fix the problem. This corrector works well for certain period of time, requiring a recalibration whenever the heliostat image shifts beyond the tolerance region. This method requires less effort, resulting in a practical solution to drift correction. This work reports on the implementation of a dynamic drift compensator based on a static third order polynomial function, at the Heliostat Test Field in Hermosillo, Sonora, Mexico. The results are compared to theoretical predictions based on error parameters for one heliostat.