Background

Solar thermal power plants on a large scale can continuously generate power by means of thermal heat storages. They are therefore potentially applicable for baseload power supply. Typical sizes are about 50 MW (e.g. the plant Andasol 3 in Spain). From Smaller thermal storages the heat is more quickly lost and therefore the installation is not profitable or not baseload applicable. Since the availability of efficient small decentralized implementations for all energy resources and technologies is desirable, alternative heat storages are needed. The chemical storage of heat can be such an alternative. As a concept it is known for many years but it is quite far from a broad technical implementation in the energy system.

Goal

With this project chemical storages were investigated, which could be coupled efficiently instead of thermal storages with small solar plants (some kW up to few MW). Novelties were especially the use of micro-structured components for the reaction "Methylcyclohexane <=> Toluene + 3H₂" and of nano-structured materials for storing the hydrogen.

In the scope of the sub-project a research accompanying system analytical study of sustainability aspects was carried out. Goal of this study was to optimise the SolChem concept and to identify the position of the concept in comparison to other technologies, e.g. electrolytic generation of hydrogen from solar power and direct re-generation of power in turbines or fuel cells in the absence of sunlight. The focus was on environmental aspects. Based on the results application fields, in which the SolChem concept can contribute to a sustainable energy system, shall be identified.

Results

The work was done over the total project duration. The applied methods largely were material flow and life cycle based (e.g. environmental Life Cycle Assessment - LCA). The system analysis was divided into five work packages.

1. Basic system and method related definitions
2. Data generation
3. Modelling
4. Operational simulation under a variety of boundary conditions
5. LCA calculation and weak point analyses

An essential feature was the strong co-operation with the project partners. Modelling and data generation were done in agreement and with support of the technical partners; core processes were described largely by data from the project. Afterwards, the operation of the system has been designed and simulated on the basis of real irradiation data at various European locations. Special attention was paid to the different demands on the storage system as a result of short- and of long-term electricity demand fluctuations (day/night and summer/winter, resp.). Critical process parameter for short-term fluctuations is, for example, duration of response; for long-term fluctuations storage density and shelf life are important.

In early stages of technology development well-grounded statements of LCAs are difficult to achieve. Initial results show that the usable time of the catalysts in the reactors have great influence on the results of the LCA. Furthermore contribution of construction of the plant is very influential in relation to the operation. Consequently, the service life of the entire system is of great relevance.