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Thermal Storage
Latent heat storage based on salt 18.7.2016

Direct steam generating powerplant PE1: the demonstrator will be built here
© Novatec Solar

„SALSA“ makes steam and waste heat useable

The Fraunhofer Institute for Solar Energy Systems ISE, Novatec Solar and

Köllemann are developed a salt-based latent heat storage called SALSA.

This is to used for waste heat recovery in industrial processes. In the

end of 2016, the storage was integrated and tested in the southern

Spanish power plant PE1.

Project status Project completed
Type of storage Latent heat storage: Salt
Research objective Components for charching and discharching; auxiliary equipment
Temperature type high temperature
Storage/Charging indirect
Storage capacity short (hours to days)
Number of cycles One per day
Charging temperature 200-300 °C
Discharge temperature 280-180 °C
Storage capacity 3 MWh
Energy storage density 200 MJ/m³
Project duration December 2012 until November 2016

The actual status in the field of latent heat storages for high temperature is sparse. No such commercial systems are available for solarthermal power plants. However, this type of storage is very efficient if it is used in combination with (solar) steam applications. Therefore, this development is very signifcant. The aim is a functional storage for direct steam generating power plants or for the use of waste heat in the industry.

  • Simplified schematic of a direct steam generating system for electricity and heat extraction with fresnel collector and storage © Fraunhofer ISE
  • Direct steam generating powerplant PE1: the demonstrator will be built here © Novatec Solar
  • Two-shafted screw heat exchanger with open trough and hollow screw shaft, screw flights and double lined casing © Köllemann
  • Laboratory for testing of the innovative storage prototype: screw heat exchanger with two transport screws and a storage tank © Fraunhofer ISE
  • Inlet of the molten phase change material (sodium nitrate/potassium nitrate) in the screw heat exchanger with instant crystallization on the screw flights © Fraunhofer ISE
  • Phase change material in granular state. The bulk density was increased by improving the operational conditions © Fraunhofer ISE
  • Schematic view of the charging of the storage in a power plant. © Fraunhofer ISE
  • Schematic view of the discharging of the storage in a power plant. © Fraunhofer ISE

The goal of the project is the development of a efficient latent heat storage to store heat from steam processes. It has the follwing innovative features: the heat transfer area and the capacity of the storage are not coupled due to the use of a screw heat exchanger (SHE), evaporation/condensation in a SHE and pressure resitance up to 100 bar. Two storage prototypes will be tested in small scale in the lab. Thereafter, a prototype in large scale will be planned, built, commissioned and tested in the solarthermal power plant PE1, owned by the project partner, Nocatec Solar GmbH. The results will serve as basis for an optimization of the storage concept. In parallel, the storage system will be modelled in a simulation environment.With annual yield calculations, the operation strategy and the cost effectiveness will be assessed. In 2016 a demonstrator storage will be built, integrated and tested in the solarthermal power plant PE1 in Calasparra, Spain by the partners Novatec Solar GmbH, Köllemann GmbH and Fraunhofer ISE.

Simulations to demonstrate cost-effectiveness

At the momenent the researchers plans the economic feasibility of the innovative storage concept with experimental evaluation and annual year calculations. In the follow-up project phase, the storage will be built, tested and assessed in large scale as a demonstrator storage in a solarthermal power plant. This project aim is to technically implement an innovative latent heat storage. In other consepts for latent high temperature storages, that have already been examinated, the heat transfer area is always coupled directly to the storage capacity. If the capacity is increased, the heat transfer area has to be increased in the same proportion to achieve the same charging/discharging power, because the heat exchanger is fixed in the storage tank. With the new concept developped in this project, these two factors could be decoupled and so the cost effectiveness for high capacities can be reduced.

Pressure resistance is to be tripled

Experimental investigation of two laboratory prototypes to optimize screw heat exchangers for a use in a latent heat storage. Goal of these experiments is to demonstrate a pressure resistance up to 100 bar (up to now, only 30 bar are possible), the simplification of the production process and the reduction of the overall storage system. Thereafter, a scale-up of the storage will be built as demonstrator storage to optimize the operational strategies and control of the system in a solarthermal power plant. For that reason, a mobile data acquisition system will be developped and used.

The SHE will be modelled and combined with modells for a solarthermal power plant to have a system modell. In annual yield calculations, operational strategies will be assessed with parameter variations and with the results, a cost estimation will be obtained for the innovative storage.

At the moment, the economic viability is assessed. It is expected, that both the material cost and the production cost can be reduced by a detailed analysis of the optimization potential of the SHE. The assumption of an increase of the production capacity in the case of large storage projects leads to further cost reductions. More detailed data about the economic viability will be available in project month 18.


Köllemann GmbH is a specialist for screw heat exchangers (SHE) and will therefore have the lead in the optimisation of a SHE and of the transport screws needed for the storage systems. At the site of Köllemann GmbH, a test center will be built in order to assess the transport charactersitics of salt in a scale-up of the prototype. When a concept for high pressure resistance is designed, Köllemann GmbH will construct and built it. Köllemann GmbH is responsible for the commissioning and the optimization of the demonstrator storage in Spain.

Novatec Solar GmbH as a specialist for Fresnel collectors and solarthermal power plants gives the specification fot the system simulation of a 50 MW power plant for the cost assessment. It supports the conduction of the simulation study with experiences from the operation of their direct steam generating solarthermal power plants. Novatec Solar GmbH builts the infrastructure for the construction of the demonstrator storage in their plant PE1. Then, the demonstrator with 3 MW and 3MWh storage capacity is built there, together with the necessary measurement and control equipment. During the commissioning phase and during the monitoring phase, Novatec assesses the control strategie during the operation of the comlete system.

Fraunhofer ISE, as a research institute, conducts a simulation study of the storage system. The SHE is modelled, a system modell for a direct steam generating power plant is built and in annual yield calculations, the influence of different parameters is assessed. A cost structure will be prepared, and with the results of the annual yield calculation, the cost viability of the storage system will be evaluated. The minimal cost per kWh will be an important index. A concept for high pressure resistance will be developped and assessed with an FEM software. This concept will be experimentally investigated in the lab. Fraunhofer ISE also decides the concept for the measurement and control systems of the demonstrator in PE1and improves this concept during the comissioning and monitoring phase.

Supported by: The Federal Government on the basis of a decision by the German Bundestag


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Research funding

The information system EnArgus provides information on research funding, including on this project (German only).