Joint project DynaSalt II

 

Motivation

The salt receiver technology, along with the open volumetric air receivers, belongs to the tower technologies known as the second generation, which have been under development since the early 1990s. Salt melts offer excellent heat transfer properties and moderate costs. Additionally, they have the advantage of being easily storable, enabling the separation of solar thermal energy generation and utilization.

Solar thermal power plants, especially solar receivers, always operate under transient conditions and, as a result, rarely reach a steady state. The position of the sun constantly changes, causing variations in the irradiation on the receiver surface. Moreover, clouds can lead to short-term fluctuations in local irradiation on the receiver. The main objective of a receiver control system is to maintain a consistent temperature of the hot salt despite these rapid and long-term fluctuations. Alongside maximizing production, the control system must implement changes gradually to ensure the longevity of the receiver and other components.

The challenge in receiver control lies in maintaining permissible boundary temperatures of the salt melt at the receiver outlet to ensure a continuous energy flow, while also avoiding exceeding the operational limits of the receiver itself. This situation becomes particularly critical during dynamic operation, where radiation power varies. Rapid increases in radiation power can easily surpass permissible temperature gradients, potentially causing damage or complete destruction of the receiver. An example of such an operational scenario is the passage of clouds. Currently, energy potentials during cloud passages are often underutilized due to precautionary measures that prematurely put the system in standby mode. The control system developed in this project aims to maximize this potential by allowing continuous operation during cloud passages.

 

Project Goals and Methods

This project aims to develop a model-based control system for the transient, single-phase operation of salt melt receivers and evaluate its effectiveness through simulations. The primary goal of this control system is to enhance the efficiency of salt melt receivers by minimizing shutdown times, subsequently reducing the overall cost of electricity generation.

To achieve this, an initial reduced model will be created, incorporating the relevant dynamics required for the control system. This model will also enable the estimation of unmeasurable states and disturbances, such as solar irradiation. In the subsequent step, nonlinear model predictive control methods will be employed to optimize the receiver outlet temperature while adhering to all operational limits.

 

Project partner	Associated partner
DLR - German Aerospace Center FH Aachen, SIJ - Solar-Institute Jülich LeiKon GmbH	General Electric (Switzerland) GmbH