Concentrated solar thermal power generation is becoming a very attractive renewable energy production system among all the different renewable options, as it has have a better potential for dispatchability. This dispatchability is inevitably linked with an efficient and cost-effective thermal storage system. Thus, of all components, thermal storage is a key one. However, it is also one of the less developed. Only a few plants in the world have tested high temperature thermal energy storage systems. In this paper, the different storage concepts are reviewed and classified. All materials considered in literature or plants are listed. And finally, modellization of such systems is reviewed.

State of the art on high temperature thermal energy storage for power generation. Part 1—Concepts, materials and modellization

Metasurfaces: From microwaves to visible

Thermal energy storage technologies and systems for concentrating solar power plants

The development of energy saving technologies is very actual issue of present day. One of perspective directions in developing these technologies is the thermal energy storage in various industry branches. The review considers the modern state of art in investigations and developments of high-temperature phase change materials perspective for storage thermal and a solar energy in the range of temperatures from 120 to 1000 °C. The considerable quantity of mixes and compositions on the basis of fluorides, chlorides, hydroxides, nitrates, carbonates, vanadates, molybdates and other salts, and also metal alloys is given. Thermophysical properties of potential heat storage salt compositions and metal alloys are presented. Compatibility of heat storage materials (HSM) and constructional materials have found its reflection in the present work. Data on long-term characteristics of some HSMs in the course of repeated cycles of fusion and solidification are analyzed. Article considers also other problems which should be solved for creation of commercial high-temperature heat storage devices with use of phase change materials.

High-temperature phase change materials for thermal energy storage

Recent developments in phase change materials for energy storage applications: A review

Thermal energy storage for direct steam generation

Material aspects of Solar Salt for sensible heat storage

This paper is focussed on thermal storage technologies using phase change materials (PCMs) in the temperature range of 120-300 °C for solar thermal power generation and high temperature process heat. As state-of-the-art reference system a steam accumulator is described, which typically has a volume-specific thermal energy density of 20-30 kWh/m³. Regarding efficiency, a fundamental demand on thermal storage is the minimization of temperature differences between working fluid and storage medium. This requires isothermal storage systems for processes using water/steam. An obvious solution is, therefore, the application of PCMs.
The selection of the PCMs depends strongly on the operation conditions of the respective application. At present, the main emphasis is directed to alkali metal nitrates and nitrites and their mixtures. For example, the eutectic mixture of the binary system KNO3-NaNO3 has been identified as an excellent system to be used for processes using saturated steam at around 25 bar. At around 5 bar the ternary system KNO3-NaNO2-NaNO3, commonly used as heat transfer fluid, can also be used as a PCM. To overcome the low thermal conductivity of the salt systems, approaches of increased surfaces area and increased thermal conductivity using expanded graphite (EG) have been investigated. Using EG/PCM-composites the effective thermal conductivity can be increased from below 0.5 W/(mK) to 3-20 W/(mK).
Three design concepts have been developed. In the macro-encapsulated design, the PCM is enclosed in metal tubes, giving a short distance for heat transfer and increasing the heat transfer area. In the second design, the heat exchanger tubes are embedded in EG/PCM-composite storage material. The third design option uses graphite foils arranged perpendicularly onto the heat exchanger tubes and a suitable salt system filled in between. The upgrade of existing steam accumulators using these PCM concepts is also proposed.

Latent heat storage above 120°C for applications in the industrial process heat sector and solar power generation

Thermophotovoltaics is the science and technology associated with the direct generation of electricity from high temperature heat Potential applications include combined heat and power, portable and auxiliary power, radioisotope space power, industrial waste heat recovery and concentrated solar power This book aims at serving as an introduction to the underlying theory, overview of present day components and system arrangements, and update of the latest developments in the field The emphasis is placed on the understanding of the critical aspects of efficient thermophotovoltaic system design The aim is to assist researchers in the field

Thermophotovoltaics: Basic Principles and Critical Aspects of System Design

Solid sensible heat storage is an attractive option for high-temperature storage applications regarding investment and maintenance costs. Using concrete as solid storage material is most suitable, as it is easy to handle, the major aggregates are available all over the world, and there are no environmentally critical components. Long-term stability of concrete has been proven in oven experiments and through strength measurements up to 500 °C. Material parameters and storage performance have been validated in a 20-m3 test module with more than 23 months of operation between 200 °C and 400 °C and more than 370 thermal cycles. For an up-scaled concrete storage design with 1100-MWh capacity in a modular setup for a 50 MWel parabolic trough power plant of the ANDASOL-type, about 50 000 m3 of concrete is required and the investment costs are approximately 38 million euro. The simulation of the annual electricity generation of a 50 MWel parabolic trough power plant with a 1100-MWh concrete storage illustrates that such plants can operate in southern Europe delivering about 3500 full load hours annually; about 30% of this electricity would be generated by the storage system. This number will increase further, when improved operation strategies are applied. Approaches for further cost reduction using heat transfer structures with high thermal conductivity inside the concrete are analyzed, leading to a 60% reduction in the number of heat exchanger pipes required. For implementation of the structures, the storage is build up of precast concrete blocks.

Thomas Bauer

Papers

Thermal energy storage for direct steam generation

Material aspects of Solar Salt for sensible heat storage

Latent heat storage above 120°C for applications in the industrial process heat sector and solar power generation

Thermophotovoltaics: Basic Principles and Critical Aspects of System Design

High-Temperature Solid-Media Thermal Energy Storage for Solar Thermal Power Plants