Energy Storage Layouts for Concentrated Solar Plants – A Comparison of Process Control

Energy Storage Layouts for Concentrated Solar Plants ? A comparison of Process Control

Flavio Manenti^1,*, Zohreh Ravaghi-Ardebili¹, Giovanni Manenti²

¹Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica ?Giulio Natta?, Piazza Leonardo da Vinci 32, 20133 Milano

²FBM Hudson Italiana SpA, R&D Dept., Via Valtrighe 5, 24030 Terno d'Isola (BG), Italy

Energy storage is a major process design and control issue in concentrated solar plants. The intrinsic discontinuous nature of solar energy forces to install units able to store energy under favourable conditions, then to release energy during night or unfavourable conditions. Accordingly, smoothed operations and continuous energy production can be guaranteed. Several technologies are today available for storage; tanks of molten salts, steam accumulators, high thermal capacity solids are among the most important.

Regardless the technology adopted for storage, the plant layout plays a key role in the process performance and control philosophy. Control of storage unit and steam generation station under steep load changes, as during sunrise and clouds passage, depends appreciably on layout. Storage devices can be installed either on the main process stream or be part of a secondary circuit linked to the main one; devices can be arranged either in series or in parallel and, again, devices of different type can be grouped. Fig. 1 shows different layouts for the specific case of molten salts.

This work deals with the comparison of process control for different storage layouts based on molten salts.  Results coming from process simulations of unsteady loads are reported and a general discussion on operability and controllability is done. For this purpose, the different layouts have been modelled by means of a commercial process simulator (Fig. 2), where specific fluid properties and units have been implemented. Same investigating approach can be adopted for storage systems based on different technologies.