Concentrating solar power (CSP) power cycle improvements through application of advanced materials

Abstract

Abstract. Concentrating solar power (CSP) systems with thermal energy storage (TES) capability offer unique advantages to other renewable energy technologies in that solar radiation can be captured and stored for utilization when the sun is not shining. This makes the technology attractive as a dispatchable resource, and as such the Electric Power Research Institute (EPRI) has been engaged in research and development activities to understand and track the technology, identify key technical challenges, and enable improvements to meet future cost and performance targets to enable greater adoption of this carbon-free energy resource. EPRI is also involved with technically leading a consortium of manufacturers, government labs, and research organizations to enable the next generation of fossil fired power plants with advanced ultrasupercritical (A-USC) steam temperatures up to 760°C (1400°F). Materials are a key enabling technology for both of these seemingly opposed systems. This paper discusses how major strides in structural materials for A-USC fossil fired power plants may be translated into improved CSP systems which meet target requirements. REVIEW OF STATE-OF-THE-ART CSP SYSTEMSIn 2014, EPRI completed a comprehensive review of molten salt as a heat transfer fluid and TES media for CSP applications [1]. Molten salt is used as a thermal energy storage media in over 25 parabolic trough plants, which use synthetic oil as the heat transfer fluid. The temperature of the salt is roughly 370°C (700°F), limited by the oil maximum operating temperature. In central receiver plants molten salt may be used in a direct configuration as both a heat transfer fluid and a storage fluid (Fig. 1). The molten salt is heated to 565°C (1050°F) in the receiver and then flows through a heat exchanger to produce steam for a conventional Rankine steam cycle. Two large-scale direct molten salt central receiver plants are currently in operation. Molten salt must always be maintained above its freeze temperature of 238°C (460°F) to avoid solidification in piping and other components. Both parabolic trough and central receiver CSP technologies typically employ a binary molten salt mixture (60 wt.% NaNO 3 and 40 wt.% KNO 3 ) because it offers an optimal balance of performance and cost relative to other salt compositions. Novel molten salt formulations, high temperature receivers using fluids such as supercritical CO 2 , solid particles and air, as well as advanced storage system designs are being explored in ongoing research by EPRI and others. Heat transfer fluids and storage media with wider temperature ranges than binary molten salt could make the value proposition for CSP with TES even stronger. For molten salt systems, materials of construction that can withstand corrosion above 600°C (1110°F) are a barrier to achieving higher thermodynamic cycle efficiencies. Today, traditional 300 series stainless steels are the workhorse of commercial CSP plants due to their superior corrosion behavior over traditional chromium molybdenum (CrMo) ste...

Influence of the oxidation on the optical properties of Mo-Si-Ti, Ta-Mo-Cr-Al and Ta-Mo-Cr-Ti-Al alloys

“…One of the major engineering barriers in the development of this category of these solar energy conversion systems is the maximum temperature at the receiver when directly exposed to air. The maximum operating temperature of the polycrystalline nickel-based alloys currently used in the design of industrial solar receivers is approximately 800 °C when 100,000 hours of use are considered [3]. In fact, previous investigations have revealed that Inconel 625 cannot withstand more than 36 h of exposure to air at 900 °C before oxide scale spallation occurs [4].…”

A New Approach to Low-Cost, Solar Salt-Resistant Structural Materials for Concentrating Solar Power (CSP) and Thermal Energy Storage (TES)

“…A disadvantage of using molten nitrates in thermal energy storage devices is their high corrosiveness towards metal piping and container walls [11,12]. Salt corrosion issues in long-term operation of about 30 years [12] currently necessitate the application of comparatively expensive Ni-base super alloys or austenitic stainless-steel grades [13]. For this reason, investment, and maintenance costs, involved in the usage of these high-price structural materials, are a major price driver and one of the main reasons for lacking competitiveness of CSP technology [14].…”

High temperature properties of AlN coatings deposited by chemical vapor deposition for solar central receivers

“…In power tower concentrating solar power systems (CSP), a large number of sun-tracking mirrors, known as heliostats, focus sunlight onto a receiver at the top of a tall tower. A heat-transfer fluid heated in the receiver is used to heat a working fluid, which, in turn, is used in a conventional turbine generator to produce electricity [1]. The challenge for a solar tower technology is related to ensuring the longevity of the receiver and demonstrating that the receiver material can handle high temperature fluxes across the 25-year lifespan of a plant.…”

“…Receivers working with air as the heat transfer fluid (HTF) can simplify the technology but the challenges, like absorber durability, receiver efficiency still remains to be solved. It can generally be said that for temperatures below 1073 K, nickel-based alloys with high chromium content are the most suitable for volumetric receivers due to their capacity to form oxides, which are black and highly absorbant [1]. The state-ofthe-art for solar absorbing materials used in solar towers, with air as HTF, is based on a commercially available black paint called Pyromark 2500s [3].…”