Energy storage layouts for concentrated solar plants - A comparison of process control

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.