Operational Planning of Solar Plants with Parabolic Trough Collectors

The price of electrical energy is needed to determine the best operating modes and hourly electrical production. This changes with demand. Prediction models for elec­trical demand are useful for decision making and for the design of hierarchical con­trol schemes capable of optimizing electrical production, being necessary to model all plant subsystems; that is, the solar collector field, the thermal storage system and the power conversion system (PCS). Electrical demand may change substantially depending on the date and environmental conditions.

Since optimal scheduling of solar power plants depends greatly on predictions about solar radiation and other weather conditions, optimal scheduling windows for this type of plant are limited by the realistic predicting windows of weather con­ditions. There are three well differentiated levels: weekly planning, daily planning and tracking [144].

• Weekly planning. The planned production for the week is made at this stage. The weekly plan is made taking into account the weather forecast for the following seven days, the predicted network loads and prices, as well as the scheduled main­tenance operations.

• Daily planning. The objective of this stage is to determine the planned plant pro­duction schedule for the day. The decision mechanism has to take into account

E. F. Camacho et al., Control of Solar Energy Systems, Advances in Industrial Control, 369

DOI 10.1007/978-0-85729-916-1_8, © Springer-Verlag London Limited 2012

the state of the storage system, the weather prediction for the day as well as the price of electricity for the day.

• Tracking. The objective at this level is to control the planned production by gen­erating the appropriate set points to the different subsystems. At a lower level, different controllers such as those described in Chaps. 4 and 5 control the fun­damental process variables such as the outlet HTF temperature of the solar field subsystem. In this case, the mission of the set point optimizer is to determine the optimal outlet oil temperature for the given solar radiation level, inlet oil tem­perature and ambient temperature which optimizes the energy collected and mini­mizes ancillary energy consumption. The outlet HTF temperature set point is sent to the lower level controller, which regulates the HTF temperature as indicated in Chaps. 4 and 5.