Central Receiver Plants Research Articles

Techno-Economic Analysis of Central Receiver Plants According to the Optical Error of the Solar Field

Among the concentrated solar power technologies (CSP), the central receiver (CR) technology is the most promissing to achieve the lowest levelized cost of energy (LCOE) and the one expected to play one of the major roles in the energetic mix in the next years. For that purpose, succesful CR projects are needed, starting by the contruction and erection of a reliable heliostat field that fulfils its design specifications. In this work, the loss of energy production and the consequently rise of LCOE is investigated as function of the optical error of the heliostats. For that, a reference CR plant is defined in which the heliostat field layout and the receiver are optimized to collect the maximum annual energy. An aiming strategy is also implemented to obtain more realistic results. For instance, for a reasonable deviation of about 40-50% compared to the optical reference error, the annual collected energy can drop to a considerable 5%.

Numerical investigation to assess the techno-economic feasibility of solar central receiver system for off-grid power in Saint Martin's Island, Bangladesh

Bangladesh is a small country, located in south-east Asia having a fast-progressing economy and exemplary development in industry, architecture and engineering sectors. With such developments, demand of power is also on the rise exponentially. Although the generation capacity of the country has seen a major boost, lack of proper distribution, negligence towards renewable energy resources and dependance on perishable fossil fuels (natural gas, coal, mineral oil etc.) pose a major risk of a significant power crisis in future. The only tourist favorite island of the country, known as Saint Martin's Island lacks national grid connection and stable source of power to mitigate the inhabitants' electricity need. This study intends to analyze the technical and economic feasibility of solar powered central receiver system to provide steady and cheap means of power generation at the island in an environment friendly manner. A detailed and optimized model has been designed for simulating a 1 MW solar powered central receiver plant using SolarPILOT and System Advisor Model (SAM) software. Modelled power plant can generate 3304 MWh electricity yearly with a gross efficiency and capacity factor 12.29% and 41.9% respectively at 38.61 Cents/kWh levelized cost of electricity (LCOE) which is much cheaper than the current rate at Saint Martin's Island. The promising performance of the powerplant designed in this study would encourage future research and innovations in case of off-grid electricity generation employing solar thermal energy in Bangladesh to ensure sustainable development.

Dispatchable solar power using molten salt directly irradiated from above

Concentrating solar power (CSP) with thermal energy storage (TES) presents the major advantage over solar photovoltaics of dispatchability. High thermodynamic efficiencies achieved by collecting and storing heat at higher temperatures, and recent maturing of the technology, are making molten-salt central receiver plants the preferred option for CSP. To explore potential further improvements in CSP efficiency and cost the world’s first direct absorption molten salt volumetric receiver/storage system was built at pilot scale, commissioned and monitored. In this demonstration a 100 kWth beam-down tower directs solar radiation through a final concentrator into the open aperture of a 1.94 m high and 1.25 m internal diameter tank receiver situated near the ground. The receiver tank is filled with 3,800 kg of 60–40 wt% NaNO3-KNO3 and serves as a stratified or mixed single tank thermal store that can satisfy evening peak loads or provide baseload power through the night. Compared to the parasitic loads of a conventional tower-receiver plant, the energy needed for salt transport from receiver to TES and morning preheat is negligible for this new system. The hot-spot problem of tubular receivers is eliminated and. the combined receiver/storage tank reduces component costs. In-situ initial melting was accomplished using solar energy as the primary input. Thermal stratification was maintained by daily cycling of a divider plate and occasional mixing plate actions and hot spots were never observed during several months’ operation between 250 and 500 °C. Three cycles of complete salt freezing and in-situ on-sun re-melting were tested with no operational difficulty and no discernible damage.

A Discussion of Possible Approaches to the Integration of Thermochemical Storage Systems in Concentrating Solar Power Plants

One of the most interesting perspectives for the development of concentrated solar power (CSP) is the storage of solar energy on a seasonal basis, intending to exploit the summer solar radiation in excess and use it in the winter months, thus stabilizing the yearly production and increasing the capacity factor of the plant. By using materials subject to reversible chemical reactions, and thus storing the thermal energy in the form of chemical energy, thermochemical storage systems can potentially serve to this purpose. The present work focuses on the identification of possible integration solutions between CSP plants and thermochemical systems for long-term energy storage, particularly for high-temperature systems such as central receiver plants. The analysis is restricted to storage systems potentially compatible with temperatures ranging from 700 to 1000 °C and using gases as heat transfer fluids. On the basis of the solar plant specifications, suitable reactive systems are identified and the process interfaces for the integration of solar plant/storage system/power block are discussed. The main operating conditions of the storage unit are defined for each considered case through process simulation.

Experimental study on the influence of input solar flux, air flow rate, and absorber parameters on honeycomb ceramic air receiver performance

Honeycomb ceramic absorbers are considered to be one of the most practical options for the air receiver of a solar central receiver plant. To explore the influence of the average input solar heat flux, air flow rate, and absorber geometric parameters on the honeycomb ceramic air receiver performance, six samples were tested under different conditions and the outlet air temperature, thermal efficiency, and anti-interference characteristics of the receivers were determined. The investigation showed that as the input solar flux or air flow rate increased, the change in the outlet air temperature and thermal efficiency had opposite trends. The sample with the shortest length, thinnest wall, and highest porosity had the best performance. Among the three absorber geometry parameters, the porosity was the dominant factor affecting the receiver outlet temperature and thermal efficiency.

Thermo-economic analysis of photovoltaic, central tower receiver and parabolic trough power plants for Herat city in Afghanistan

In Afghanistan, more than 60% of the population does not have access to a reliable source of electrical energy. A thermo-economic analysis is conducted to compare the performance of a Photovoltaic (PV), Central Tower Receiver (CTR) plant and a Parabolic Trough Collector (PTC) plant with and without storage for the city of Herat, in Afghanistan. The nominal capacity of both plants is 110 MWe. The PTC plant with energy storage has the highest efficiency of about 43% that is approximately 50% more than the PV plant, however, the PV plant has more uniform power production profile. The output power of PTC with energy storage is 25% more than output power of PTC without energy storage and output power of CTR plant is half of PTC plant with energy storage. The Levelized Cost of Electricity (LCOE) is 0.146 $/kWh for CTR plant, 0.063 $/kWh for PV plant, 0.1076 $/kWh for PTC plant with energy storage, 0.104 $/kWh for PTC plant without storage and 0.12 $/kWh for PTC plat without storage and without backup fossil fuel systems. Increase of incentive by 10% leads to decrease of LCOE by about 20% for PTC and 13% for PV and 12% for CTR power plants.

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.

Electric power regulation and modeling of a central tower receiver power plant based on artificial neural network technique

This paper addresses an intelligent control scheme using the artificial neural network (ANN) technique for modeling and simulating a central tower receiver (CTR) plant with thermal energy storage (TES). The multilayer perceptron neural network (MLPNN) was implemented with two input parameters, one output parameter, and one hidden layer. The inputs comprise the receiver inlet temperature and the receiver thermal power. The output includes the mass flow rate of heat transfer fluid. A total of 888 datasets and three types of training algorithms, Levenberg-Marquardt (LM), Quasi-Newton, and Scaled Conjugate Gradient, are applied for training the proposed MLPNN model. Among all the investigated learning algorithms, the adopted LM with 40 neurons in the first hidden layer displayed superior ability to efficiently estimate the required performance compared to other learning algorithms. Based on the statistical evaluations, the optimized LM delivered preferred values for the root mean square error (0.0037), the coefficient of variance (0.0011), and the coefficient of determination (0.9999) during the training process. Hence, the MLPNN with LM-40 is an effective technique to precisely control the mass flow rate and subsequently the receiver outlet temperature regardless of the variations in the direct solar radiation and receiver inlet temperature. Furthermore, the generation strategy was modified to regulate CTR/TES output through electricity generation according to the hot storage system conditions. The performance of the adopted CTR-ANN model is presented and compared with the System Advisor Model (SAM) results. The results demonstrate better compatibility between the adopted CTR-ANN model and SAM outputs. The simplicity and minimum required input data of our proposed model make it appropriate for evaluating the power system reliability by using the Monte Carlo method.

Comparative energy and exergy studies of combined CO<SUB align="right">2 Brayton-organic Rankine cycle integrated with solar tower plant

The present study investigates the performance of a combined power cycle used for solar tower (central receiver) plant. The combined cycle employs a supercritical carbon dioxide (S-CO2) Brayton cycle as a topping cycle cascaded by an organic Rankine cycle (ORC). In order to evaluate the system performance, a thermodynamic analysis is conducted through energy and exergy approaches for each subsystem and hence evaluation of its overall energy and exergy efficiencies. Furthermore, the energy and exergy efficiencies of the integrated system are parametrically studied under different operating conditions. The benefits of using CO2 as a working fluid in a Brayton cycle are elaborated in the context of high-temperature solar tower technologies. The opportunity of recovering the topping cycle low-grade heat is investigated, through the proposal of utilising an n-butane ORC as a bottoming cycle.

Integrating desalination with concentrating solar thermal power: A Namibian case study

This paper reports on a feasibility study into the integration of a multi-effect distillation plant with a central receiver plant to generate electricity for the Namibian grid, and fresh water for the community and mining operations at Arandis. Arandis receives on average 2528 kWh/m2/year of solar irradiation, is only 48 km from the coast and 580 m above sea level, making it attractive for a cogeneration plant. Desalination is energy intensive, but the required energy is freely available from the waste heat rejected at the condenser of a Rankine cycle. In this study, high level thermodynamic models of a multi-effect distillation and central receiver plant were developed to better understand the economics of such a cogeneration plant. Results indicate that a 100 MWe central receiver plant combined with a multi-effect distillation plant, is capable of servicing the current water demand in the region. Despite the high capital costs of central receiver plant, as well as pumping seawater inland, the plant is economically viable within the proposed tariff structure for renewable energy in Namibia, and existing water tariffs. Profit parity between a cogeneration plant and a stand-alone, dry-cooled central receiver plant is reached for top brine temperatures above 65 °C. Under these conditions, water sales would subsidize electricity production. However, it is not price competitive with a grid-powered reverse osmosis plant on the coast. The most significant barriers in making cogeneration plant competitive against more conventional desalination methods such as reverse osmosis are the high capital cost of the cogeneration plant, and pumping seawater inland.

Assessing the performance of hybrid CSP + PV plants in northern Chile

Electricity systems in Chile are characterized by a variable hourly demand in the central grid and an almost constant demand in the northern grid, which require different operation strategies for solar power plants depending on their location. Hybridizing a CSP plant with a PV system can increase the overall plant capacity factor by allowing thermal energy to be stored while the PV plant is in production and thus help to achieve a fully dispatchable solar electricity production system. A power generation and economic analysis of two hybrid CSP+PV plant models were developed considering a range of plant capacities based on parabolic trough or central receiver plants, combined with a PV system. Environmental conditions were considered for a site in the Atacama Desert, which is a hotspot of solar energy development in the country and shares the solar radiation characteristics of northern Chile. The study conducts a parametric analysis and optimization of the storage and power block sizes for the CSP plants in terms of the levelized cost of energy (LCOE), when the nominal capacity of the PV plant is varied. The annual production of the plants is calculated using the Transient System Simulation program (TRNSYS), which uses a new component library developed for that purpose. From the results of the simulations, the high potential for hybrid CSP+PV plants in the Atacama Desert is clear, because the high levels of irradiation available in northern Chile provide a competitive electricity cost, allowing investors to access PPA contracts at competitive prices and achieving competitive costs with respect to other energy sources.

Impact of HRSG characteristics on open volumetric receiver CSP plant performance

The use of near-ambient pressure air as the heat transfer fluid in central receiver concentrating solar power (CSP) plants operating the water/steam cycle presents a number of potential benefits that have attracted research attention to the concept. In such plants, an open volumetric solar receiver (OVR) is used to heat air entrained from the atmosphere and a heat recovery steam generators (HSRG) is employed to transfer heat from the air to the water/steam cycle. An aspect of this technology that has not been previously addressed in the literature is the impact that the selection of HRSG configuration and operating parameters has on overall plant performance, and in particular, which HRSG characteristics allow for the best utilisation of solar energy. The results presented in this paper address these questions by evaluating the impact of HRSG operating characteristics on the performance of a 100MWe OVR central receiver plant. Investigations are carried out on the basis of coupled OVR/HRSG/water/steam cycle models implemented and solved in the EES© programming environment. Single and multi-pressure HRSG arrangements with and without reheating are examined. In specific terms, sensitivities to the variation of receiver outlet temperature, air return strategy, air return ratio, HRSG pinch-point temperature difference, deaerator outlet temperature and duct velocity are evaluated and discussed.

Design of CSP plants with optimally operated thermal storage

Concentrated solar power plants are increasingly considered worldwide, in order to meet the demand for renewable power generation. A distinctive feature of these plants is the possibility of integrating thermal energy storage such that full-load operation can be sustained for several hours in the absence of solar radiation. A number of design software tools are available for sizing the plant and evaluating the return on investment. These usually assume a short-sighted strategy for storage management. This work presents a new methodology aimed at assessing the potential of optimal control techniques when applied to the operation of energy storage systems in general. The design method is applied to a test case, a state-of-the-art central receiver plant with direct storage, using molten salts as working fluid, and operating in a context of variable electricity prices. The system modeling and optimization problems are formulated and implemented using modern high-level modeling languages, demonstrating the potential of the approach. The different operating strategies are compared based on a detailed financial analysis. A wide system design space is explored, and the results presented for all the foreseeable combinations of solar field size and storage system capacity, considering two plant locations, i.e., Daggett (US-CA) and Almeria (ES). Potential gains up to 10% in terms of yearly revenue are estimated, in case improved control strategies are adopted. These figures translate into increases of more than 30% of the investment profitability by considering over-life financial figures. It is further shown how, in case of state-of-the-art systems, it is always profitable to adopt optimal control to the end of increasing electricity production. However, the potential of these techniques is discussed also under the point of view of investment cost reduction, since the same yearly revenue can be harvested with smaller energy storage, if optimally operated. This aspect, unveiled here for the first time, might become significant if technologies with different cost structure are of interest, i.e., in case the storage cost constitutes a comparatively large part of the total investment. The novel method is thus an additional decision tool allowing to treat the storage operation strategy as a new relevant variable for the design of next generation energy systems.

Thermal Analysis of a Multi Effect Distillation Plant Powered by a Solar Tower Plant

Abstract Decreasing water resources and steadily rising water demand drive research towards new approaches for safe and reliable water supply for the municipal, agricultural and industrial sectors. One solution for fresh water provision is sea water desalination using solar thermal energy. This paper describes the coupling of a Multi Effect Distillation (MED) plant with a Clausius-Rankine cycle powered by a solar central receiver system. A steady state model of an MED plant is developed and a correlation for the Gained Output Ratio (GOR) as function of heating steam temperature, specific seawater massflow and specific heat transfer surface of the desalination plant is deduced. This correlation is integrated into a model of a central receiver plant, comprising the heliostat field, a molten salt receiver system, two-tank storage and the steam cycle. A showcase simulation for the location Al-Kosseir, Egypt is performed to show the trade-off between electricity and water production for a cogeneration situation.

The Variable Geometry Central Receiver System Concept. First Results and Comparison with Conventional Central Receiver Systems

In line with the global trend for improving efficiency of existing solar power plants, the CTAER has developed and built a variable geometry central receiver facility, in which the solar field rotates around the tower axis following the sun's position during the day. The goal of this new approach is to increase the optical efficiency of the field by significantly reducing the angle of incidence of the Sun on the heliostats. This paper presents the advantages of this new variable geometry design and describes the main features of the experimental facility based on this approach as built by CTAER in Almeria. It also compares a conventional solar central receiver plant (i.e., with stationary heliostats and receiver) and an equivalent variable geometry power plant. For this study we employed published data from a real solar central receiver plant with known production (Abengoa's PS10). The results of the study show an increase in annual energy collection and distribution by the variable geometry plant, leading to a potential reduction in the number of heliostats required compared to a conventional central receiver plant for the same annual energy collection.

Model based Open-loop Correction of Heliostat Tracking Errors

The heliostat field is by far the most expensive part of a typical Central Receiver (CR) plant. To achieve high conversion efficiencies, heliostats with very high tracking accuracy are needed, but errors are introduced due to manufacturing-, installation- and alignment tolerances as well control system granularity. Mechanical error profiles are unique for every heliostat and cause tracking errors that vary over the course of days and seasons and therefore cannot be corrected by once-off angle offset corrections. Developments in microcontroller technology drives decentralization of CR control systems. Powerful open-loop error correction algorithms can run on low cost heliostat local controllers, enabling high tracking accuracy from lower cost heliostats with reduced tolerances.A prototype array of 18 heliostats, each 1 ft2 in size, was constructed to validate the field control system functionality and final tracking accuracy. Tests were conducted at SU's solar laboratory with an 18m tower and heliostat slant ranges of around 40 m. Prototype experiments indicate a daily open-loop RMS normal vector tracking error below 1 mrad. Strong correlation exists between successive days’ residual error curves, indicating that further model refinements may be possible, including frequency spectrum analysis (using FFT) to identify and correct for mechanism-specific periodic drivetrain errors.

Evaluation of the potential of central receiver solar power plants: Configuration, optimization and trends

This paper presents a parametric analysis for a medium to large size (290–500MWth receiver thermal power) central receiver plant considering the present market trends. The analysis is divided in 4 steps:•Size and location analysis: for a medium to large size central receiver power plant, three turbine power and three different locations that are involved in the development of power tower plants, have been analyzed to assess the impact over the design characteristics of the solar field and receiver sub-systems and over the levelized electricity cost.•Technology analysis: as commercial power tower plants in operation today are mainly using steam and molten nitrate salts, the present analysis compares the two main technologies, without thermal energy storage to evaluate both under similar design conditions.•Storage analysis: thermal energy storage increases the value of electricity produced and the plant capacity factor for both technologies (steam and molten nitrate salts). For this reason, the analysis shows for each optimized solar field and receiver thermal power, the optimum combination of turbine power and thermal energy storage that minimizes the levelized electricity cost, for both technologies.•Component’s cost analysis: market trends are focused on the specific cost reduction by means of larger plant size and through an improved economy of scale. As a result, and based on baseline cost parameters widely accepted in solar industry, an analysis over the specific costs of major components on the electricity cost has been carried out, to lead where the research and development efforts should be made.

Transient molten salt two-tank thermal storage modeling for CSP performance simulations

Solar thermal power plants are a promising way of providing renewable electricity. Unlike other renewable energy technologies, solar thermal power plants have the ability to store thermal energy, which decouples the electric power generation from hours of available solar irradiation. Today, the only applied commercial thermal storage system is a two-tank sensible heat thermal storage based on molten salts. This work focuses on the transient heat loss modeling of such molten salt thermal energy storage tanks. More precisely, this paper proposes a degree of physical modeling which describes the governing heat transfer mechanisms sufficiently accurate, obtaining a suitable tool for concentrating solar power (CSP) performance simulations, applicable for parabolic trough collector, as well as for central receiver plants. A fully transient storage tank model has been developed and simulated over 3 sets of 6 reference days, providing typical weather conditions of a solar thermal power plant location as model input. The model has been successfully compared to heat loss data that was observed at real application molten salt storage tanks. Several modeling assumptions, used heat transfer correlations and simplifications are outlined. Modelica has been used as modeling language.

Jülich Solar Power Tower—Experimental Evaluation of the Storage Subsystem and Performance Calculation

Storage technology based on solid media heated in direct contact—so-called regenerators—is well suited to promote the market introduction of solar central receiver plants with air receivers. However, starting from existing technologies, several design issues need to be addressed. A test campaign was performed at the Solar Power Tower Jülich, an experimental central receiver plant, to experimentally verify the functionality and to quantify the performance of the plant’s storage subsystem. To this end, a gas burner used during commissioning of the plant, was reactivated and used to run a series of operation sequences. Computer simulations have been set up and applied to retrace the storage behavior to confirm the validity of the underlying models and to gain further insight into the relevant phenomena. The test results confirm the full functionality of the storage subsystem, the ability to perform cycling at high discharge heat rates and relatively low heat losses, supporting the view that the technology represents a promising basis for up-scaled implementations. Measurement data and simulation results are in good agreement, confirming the maturity of existing design tools.

A novel power block for CSP systems

Concentrating Solar Thermal Power (CSP) and in particular parabolic trough, is a proven large-scale solar power technology. However, CSP cost is not yet competitive with conventional alternatives unless subsidized. Current CSP plants typically include a condensing steam cycle power block which was preferably designed for a continuous operation and higher operating conditions and therefore, limits the overall plant cost effectiveness and deployment. The drawbacks of this power block are as follows: (i) no power generation during low insolation periods (ii) expensive, large condenser (typically water cooled) due to the poor extracted steam properties (high specific volume, sub-atmospheric pressure) and (iii) high installation and operation costs. In the current study, a different power block scheme is proposed to eliminate these obstacles. This power block includes a top Rankine cycle with a back pressure steam turbine and a bottoming Kalina cycle comprising another back pressure turbine and using ammonia–water mixture as a working fluid. The bottoming (moderate temperature) cycle allows power production during low insolation periods. Because of the superior ammonia–water vapor properties, the condensing system requirements are much less demanding and the operation costs are lowered. Accordingly, air cooled condensers can be used with lower economical penalty. Another advantage is that back pressure steam turbines have a less complex design than condensing steam turbines which make their costs lower. All of these improvements could make the combined cycle unit more cost effective. This unit can be applicable in both parabolic trough and central receiver (solar tower) plants. The potential advantage of the new power block is illustrated by a detailed techno-economical analysis of two 50 MW parabolic trough power plants, comparing between the standard and the novel power block. The results indicate that the proposed plant suggests a 4–11% electricity cost saving.