Thermal energy storage technologies and systems for concentrating solar power plants

Solar energy can be used to evaporate water and generate steam, however this usually requires expensive optical concentrators. Ni et al. demonstrate a low-cost solar receiver based on thermal concentration that generates steam at 100 ∘C without the need for optical concentration.

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Steam generation under one sun enabled by a floating structure with thermal concentration

Power generation systems are attracting a lot of interest from researchers and companies. Storage is becoming a component with high importance to ensure system reliability and economic profitability. A few experiences of storage components have taken place until the moment in solar power plants, most of them as research initiatives. In this paper, real experiences with active storage systems and passive storage systems are compiled, giving detailed information of advantages and disadvantages of each one. Also, a summary of different technologies and materials used in solar power plants with thermal storage systems existing in the world is presented.

State of the art on high-temperature thermal energy storage for power generation. Part 2—Case studies

A concentrating solar power (CSP) system converts sunlight into a heat source which can be used to drive a conventional power plant. Thermal energy storage (TES) improves the dispatchability of a CSP plant. Heat can be stored in either sensible, latent or thermochemical storage. Commercial deployment of CSP systems have been achieved in recent years with the two-tank sensible storage system using molten salt as the storage medium. Considerable research effort has been conducted to improve the efficiency of the CSP system and make the cost of electricity comparable to that of the conventional fossil-fuel power plant. This paper provides a comprehensive summary of CSP plants both in operation and under construction. It covers the available technologies for the receiver, thermal storage, power block and heat transfer fluid. This paper also reviews developments in high temperature TES over the past decade with a focus on sensible and latent heat storage. High temperature corrosion and economic aspects of these systems are also discussed.

Review on concentrating solar power plants and new developments in high temperature thermal energy storage technologies

This paper reviews central receiver designs for concentrating solar power applications with high-temperature power cycles Desired features include low-cost and durable materials that can withstand high concentration ratios (~1000 suns), heat-transfer fluids that can withstand temperatures >650 °C, high solar absorptance, and low radiative and convective heat losses leading to a thermal efficiency >90% Different receiver designs are categorized and evaluated in this paper: (1) gas receivers, (2) liquid receivers, and (3) solid particle receivers For each design, the following information is provided: general principle and review of previous modeling and testing activities, expected outlet temperature and thermal efficiency, benefits, perceived challenges, and research needs Emerging receiver designs that can enable higher thermal-to-electric efficiencies (50% or higher) using advanced power cycles such as supercritical CO 2 closed-loop Brayton cycles include direct heating of CO 2 in tubular receiver designs (external or cavity) that can withstand high internal fluid pressures (~20 MPa) and temperatures (~700 °C) Indirect heating of other fluids and materials that can be stored at high temperatures such as advanced molten salts, liquid metals, or solid particles are also being pursued, but challenges include stability, heat loss, and the need for high-temperature heat exchangers

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Review of High-Temperature Central Receiver Designs for Concentrating Solar Power

Solar Two was a collaborative, cost-shared project between 11 U. S. industry and utility partners and the U. S. Department of Energy to validate molten-salt power tower technology. The Solar Two plant, located east of Barstow, CA, comprised 1926 heliostats, a receiver, a thermal storage system, a steam generation system, and steam-turbine power block. Molten nitrate salt was used as the heat transfer fluid and storage media. The steam generator powered a 10-MWe (megawatt electric), conventional Rankine cycle turbine. Solar Two operated from June 1996 to April 1999. The major objective of the test and evaluation phase of the project was to validate the technical characteristics of a molten salt power tower. This report describes the significant results from the test and evaluation activities, the operating experience of each major system, and overall plant performance. Tests were conducted to measure the power output (MW) of the each major system, the efficiencies of the heliostat, receiver, thermal storage, and electric power generation systems and the daily energy collected, daily thermal-to-electric conversion, and daily parasitic energy consumption. Also included are detailed test and evaluation reports.

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Final Test and Evaluation Results from the Solar Two Project

Concentrating solar power (CSP) technologies continue to mature and are being deployed worldwide. Power towers will likely play an essential role in the future development of CSP due to their potential to provide dispatchable solar electricity at a low cost. This Power Tower Technology Roadmap has been developed by the U.S. Department of Energy (DOE) to describe the current technology, the improvement opportunities that exist for the technology, and the specific activities needed to reach the DOE programmatic target of providing competitively-priced electricity in the intermediate and baseload power markets by 2020. As a first step in developing this roadmap, a Power Tower Roadmap Workshop that included the tower industry, national laboratories, and DOE was held in March 2010. A number of technology improvement opportunities (TIOs) were identified at this workshop and separated into four categories associated with power tower subsystems: solar collector field, solar receiver, thermal energy storage, and power block/balance of plant. In this roadmap, the TIOs associated with power tower technologies are identified along with their respective impacts on the cost of delivered electricity. In addition, development timelines and estimated budgets to achieve cost reduction goals are presented. The roadmap does not present a single path formore » achieving these goals, but rather provides a process for evaluating a set of options from which DOE and industry can select to accelerate power tower R&D, cost reductions, and commercial deployment.« less

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Power Tower Technology Roadmap and Cost Reduction Plan

Power towers are capable of producing solar-generated electricity and hydrogen on a large scale. Heliostats are the most important cost element of a solar power tower plant. Since they constitute {approx} 50% of the capital cost of the plant it is important to reduce heliostat cost as much as possible to improve the economic performance of power towers. In this study we evaluate current heliostat technology and estimate a price of $$126/m{sup 2} given year-2006 materials and labor costs for a deployment of {approx}600 MW of power towers per year. This 2006 price yields electricity at $$0.067/kWh and hydrogen at $3.20/kg. We propose research and development that should ultimately lead to a price as low as $$90/m{sup 2}, which equates to $$0.056/kWh and $2.75/kg H{sup 2}. Approximately 30 heliostat and manufacturing experts from the United States, Europe, and Australia contributed to the content of this report during two separate workshops conducted at the National Solar Thermal Test Facility.

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Heliostat Cost Reduction Study

A prototype direct absorption central receiver, called the solid particle receiver (SPR), was built and evaluated on-sun at power levels up to 2.5 MW th at Sandia National Laboratories in Albuquerque, NM. The SPR consists of a 6 m tall cavity through which spherical sintered bauxite particles are dropped and directly heated with concentrated solar energy. In principle, the particles can be efficiently heated to a temperature in excess of 900°C, well beyond the stability limit of existing nitrate salt formulations. The heated particles may then be stored in a way analogous to nitrate salt systems, enabling a dispatchable thermal input to power or fuel production cycles. The focus of this current effort was to provide an experimental basis for the validation of computational models that have been created to support improved designs and further development of the solid particle receiver. In this paper we present information on the design and construction of the solid particle receiver and discuss the development of a computational fluid dynamics model of the prototype. We also present experimental data and model comparisons for on-sun testing of the receiver over a range of input power levels from 1.58―2.51 MW th . Model validation is performed using a number of metrics including particle velocity, exit temperature, and receiver efficiency. In most cases, the difference between the model predictions and data is less than 10%.

Gregory J. Kolb

Papers

Final Test and Evaluation Results from the Solar Two Project

Power Tower Technology Roadmap and Cost Reduction Plan

Heliostat Cost Reduction Study

Development and Evaluation of a Prototype Solid Particle Receiver: On-Sun Testing and Model Validation

Economic evaluation of solar-only and hybrid power towers using molten-salt technology