Slag as Thermal Energy Storage system feedstock for Concentrated Solar Power applications.

RESLAG project aims to remove the constrains that current storage technologies for Concentrated Solar Power application have. Two different Thermal Energy Storage concepts will be validated to define new storage systems based in new materials and fluids that will facilitate the integration of the renewable energies in the electric grid.

Pilot a: Thermal Energy Storage system using air as heat transfer fluid (HTF) (led by DLR)

Slag from steel industry as an inventory material for thermal energy storage (TES) of CSP tower plants offers cost reduction potential, due to its classification as waste.

For a successful market introduction of this technology, efficient and up-scalable solutions for the TES are a prerequisite. Investigations to clarify open questions concerning the implementation in large installations in combination with slag-pebbles as inventory are needed. The European project REslag is dedicated to this.


Development activities:

  • Conception of TES design
  • Thermal analysis of the TES
  • Pilot scale tests of a set-up of slag pebbles and various insulation options
  • Simulation of flow distribution using different distributors

Thermo-mechanical calculations of the container wall and the slag pebbles

The concept demonstrator pilot is based on an existing test bed for high-temperature storage at DLR Germany, HOTREG:

Pilot b: Thermal Energy Storage system using molten salt as heat transfer fluid (HTF) (led by ENEA)

The key point of this technology is the replacement of the molten salt for low-cost steel slag, obtaining more cost-effective and efficient systems.

This pilot will consist in developing a storage tank system operating in the typical molten salt temperature range (approx. 300-560 ºC), in which molten salt is partially replaced by steel slag as energy storage material.


Pilot b conceptual scheme which use molten salt as HTF.

This pilot will be carried out in the Concentrated Solar Power plant of ENEA Casaccia research Centre (Italy).