Concentrated Solar Power Tower Research Articles

Electricity generation costs of concentrated solar power technologies in China based on operational plants

Recent years witnessed a sharp increase of CSP (concentrated solar power) plants around the world. CSP is currently at its early stage in China, with several demonstration and utility-scale plants underway. China's rising electricity demand, the severe environmental pollution from coal-fired power plants, and favorable renewable energy policies are expected to result in a large-scale CSP deployment in the next years. Detailed CSP studies for China are however hardly available. To fill this knowledge gap, this study collects plant-specific data in a national CSP database in collaboration with local CSP experts. On this basis, this study analyzes and benchmarks the costs of parabolic trough CSP, tower CSP, and dish CSP technologies in China by applying an LCOE (levelized cost of electricity) model. The current LCOE for the different CSP plants falls in a range of 1.2–2.7 RMB/kWh (0.19–0.43 US$/kWh). Among the three CSP technology variants discussed, our sensitivity analysis indicates that the tower CSP variant might have the greatest potential in China. We expect a future cost reduction potential of more than 50% in 2020 and a high share of local content manufacturing for tower CSP.

Statistical Analysis and Verification of Performance for CSP Subsystems

Abstract The long term success of the concentrating solar power (CSP) industry depends on having accurate and reliable measurements and predictions of performance. Agreed-upon standards for performance characterization are still lacking. This contrasts with more mature technologies such as gas turbine combined cycle power plants, where performance and testing specifications are well established in spite of system complexities. Lack of standardization inevitably results in extra cost and risk to market participants and the spread of misinformation through hidden “apples-to-oranges” comparisons. To cite just one example, there are multiple distinct metrics for characterizing heliostat tracking accuracy, and the differences can easily go unnoticed. Here we propose rigorous and accurate statistical approaches to two key performance analysis problems for tower CSP. We highlight their advantages over previous approaches, and analyze detailed operational data. Further, we demonstrate why they are sufficiently straightforward and general enough for adoption as industry standards.

Robotized Inspection of Vertical Structures of a Solar Power Plant Using NDT Techniques

Concentrated solar power (CSP) plants are expansive facilities that require substantial inspection and maintenance. A fully automated inspection robot increases the efficiency of maintenance work, reduces operating and maintenance costs, and improves safety and work conditions for service technicians. This paper describes a climbing robot that is capable of performing inspection and maintenance on vertical surfaces of solar power plants, e.g., the tubes of the receiver in a central tower CSP plant. Specifically, the service robot’s climbing mechanism is explained and the results of the nondestructive inspection methods are reviewed. The robot moves on the panels of the receiver in the tower and aligns the sensors correctly for inspection. The vertical movement of the climbing kinematics is synchronized with the movement of the tower’s crane. Various devices that detect surface defects and thickness losses inside the tube were integrated into the robot. Since the tubes are exposed to very high radiation, they need to be inspected regularly.

Molten nitrate salts at 600 and 680 °C: Thermophysical property changes and corrosion of high-temperature nickel alloys

This paper examines the effects of long-term, high-temperature corrosion processes on materials used in concentrated solar power tower systems. More specifically, the heat transfer fluid and the containment metal are examined at operating temperatures of 600 and 680°C. A 60/40% NaNO3/KNO3 mixture of molten salt and nickel-based alloys HA230 and In625 were tested for up to 4000h at the given temperatures. HA230 and In625 alloys showed metal losses of 688 and 594μm/year, respectively, after 1000h at 680°C. The solar salt used in this study showed significant decreases (as much as 60°C) in melting point. Further experiments showed that the primary reason for the decrease in melting point is due to high nitrite concentrations in the molten salt. However, other thermophysical properties of aged solar salt appear to change little during high-temperature corrosion tests.

Optical Analysis and Thermal Modeling of a Window for a Small Particle Solar Receiver

Concentrated solar power (CSP) systems use heliostats to concentrate solar radiation in order to produce high temperature heat, which drives a turbine to generate electricity. A 5 MWth Small Particle Solar Receiver is being developed for power tower CSP plants based on volumetric absorption by a gas-particle suspension by the support from the U.S. Department of Energy under the SunShot Initiative. The radiation enters the pressurized receiver (0.5MPa) through a curved window, which must sustain the thermal loads from the concentrated solar flux and infrared reradiation from inside the receiver. The thermal load from the solar flux on the window is calculated by using the computer code MIRVAL from Sandia National Laboratory which uses the Monte Carlo Ray Trace (MCRT) method, along with two other codes developed by the authors. Thermal loading was calculated from energy absorbed at various points throughout the window from both the heliostat field and inside the receiver. Transmission and reflective losses were also calculated for different window materials in order to find out how much radiation will enter the receiver or will be lost. The three dimensional temperature distribution of the window is analyzed by an energy balance taking into account spectral volumetric absorption, spectral surface emission, conduction within the window, and convection from both surfaces. A maximum window temperature of 800°C must be enforced to prevent cracking and/or devitrification due to overheating. Several grades of quartz are considered for this study with detailed spectral calculations. For a chosen material, the window temperature was found to be held under 800°C. The results showed that most of the heat load on the window comes from the inside of receiver due to spectral variation.

Long-distance flux mapping using low-cost collimated pyranometers

Concentrating solar thermal power tower plants with capacities of 100MWe or greater require large heliostat fields with heliostats over 1500m (nearly a mile) away from the tower. The accuracy and performance of these heliostats must be evaluated and understood as new heliostat designs emerge to reduce costs. Conventional beam characterization systems that use photographs of the reflected beam on a tower-mounted target are typically not large enough to capture the beam at long distances, and the magnitude of the irradiance for long-distance heliostats is quite low (only a fraction of a sun), which can make the beam image difficult to discern from the ambient lighting on the target. The Long-Range Heliostat Target (LRHT) implements a technique for mapping low density flux images from heliostats and reflectors at slant ranges up to approximately 1700m.The LRHT is a vertical array of collimated pyranometers deployed to a test site via flat-bed trailer and quickly erected on an aluminum truss tower. Once the sensors have been aimed at the heliostat, the heliostat beam is swept azimuthally across the array whereupon the data is stitched into a flux map indicating horizontal and vertical beam dimensions and flux intensities. The LRHT was used to evaluate and compare beam shape, peak flux, and total power of heliostats and single facet reflectors at distances from 300 to 1700m. Results were compared to theoretically rendered flux maps created by computational ray tracing algorithms, and to photographs taken on the beam characterization system (BCS) at the National Solar Thermal Test Facility at Sandia National Laboratories.

Cost and performance analysis of concentrating solar power systems with integrated latent thermal energy storage

Integrating TES (thermal energy storage) in a CSP (concentrating solar power) plant allows for continuous operation even during times when solar irradiation is not available, thus providing a reliable output to the grid. In the present study, the cost and performance models of an EPCM-TES (encapsulated phase change material thermal energy storage) system and HP-TES (latent thermal storage system with embedded heat pipes) are integrated with a CSP power tower system model utilizing Rankine and s-CO2 (supercritical carbon-dioxide) power conversion cycles, to investigate the dynamic TES-integrated plant performance. The influence of design parameters of the storage system on the performance of a 200 MWe capacity power tower CSP plant is studied to establish design envelopes that satisfy the U.S. Department of Energy SunShot Initiative requirements, which include a round-trip annualized exergetic efficiency greater than 95%, storage cost less than $15/kWht and LCE (levelized cost of electricity) less than 6 ¢/kWh. From the design windows, optimum designs of the storage system based on minimum LCE, maximum exergetic efficiency, and maximum capacity factor are reported and compared with the results of two-tank molten salt storage system. Overall, the study presents the first effort to construct and analyze LTES (latent thermal energy storage) integrated CSP plant performance that can help assess the impact, cost and performance of LTES systems on power generation from molten salt power tower CSP plant.

Comparative Assessment of an Innovative Dry-Cooled CSP System

A comparative optimization assessment is carried out in order to identify the competitiveness of an innovative modular air-cooled condenser (MACC) system in relation to conventional water- or air-cooled condensers. Specifically, the technoeconomic performance of the combined cycle gas turbine (CCGT) technology, the parabolic trough concentrated solar power (CSP) technology, and the solar tower CSP technology are compared when all are integrated (a) with a MACC condenser of an optimum tube geometry and size, (b) with a conventional water-cooled condenser, and (c) with a conventional dry-cooled condenser. The comparison is performed across three different solar potential levels. The simulations are carried out using an optimization model based on the IPP v2.1 algorithm for the calculation of the electricity unit cost and other financial indicators of each technology under investigation. The results demonstrate that, under certain parameters, the investigated MACC condenser system can become a cost-competitive alternative to water- or dry-cooled condensers in various solar potential environments.

A Novel Multifunctional Energy System for CO2 Removal by Solar Reforming of Natural Gas

In this paper, a novel multifunctional energy system (MES) fueled by natural gas and solar radiation is proposed. In this MES, hydrogen and electricity are cogenerated and approximately 92% of CO2 derived from natural gas is removed. The solar concentrated process provides high-temperature thermal energy to the methane/steam reforming reaction. The resulting syngas enters a pressure swing adsorption unit to separate approximately 80% of hydrogen. This process significantly increases the concentration of carbon dioxide in syngas from nearly 19% to 49%, which decreases energy consumption in CO2 removal. As a result, the overall power efficiency of the new system becomes about 39.2%. Compared to a conventional natural gas-based hydrogen plant with CO2 removal and a concentrated solar power tower plant, the overall power efficiency of the new system is increased by 7.9 percentage points. Based on the graphical exergy analysis, the integration of synthetic utilization of natural gas and solar radiation, combination of the hydrogen production plant and power plant, and integration of the energy utilization processes and CO2 separation were found to play significant roles to improve thermodynamic performance. The result obtained here provides a new approach for highly efficient use of solar radiation by hybrid natural gas.