ORC-PLUS – Investigation of Operating Strategies for Demand-responsive Electricity Generation by Solar-thermal Power Plants in the Low Power Range

When assessing the operation of solar-thermal power plants, not only the yearly yield is of decisive importance, but also the time, at which the power plant output is available. Operating strategies decide, what fraction of the solar thermal power is stored in the storage unit and what fraction is converted in the power plant. During the »ORC-PLUS« project, different operating approaches are compared based on a dynamic system simulation. The strategy with the objective of covering the load peak in the evening at location Morocco is of interest.

An existing linear Fresnel power plant with ORC process with a rated output of 1 MW_el is extended with a novel one-tank storage system and the solar field is expanded for the »ORC-PLUS« research project. The one-tank storage system is a directly integrated stratified tank. Using the overall storage capacity, the power plant unit can be operated for four hours at rated output. The plant operation must be adjusted to integrate the storage system.

One of the investigated operating strategies focuses on covering the load peak between 6 pm and 10 pm at the Morocco location. In this period, the electricity price for industrial customers is significantly above the daily average. For this reason, power generation is particularly attractive in this period. This demand cannot be covered using solar power plants without the use of storage technologies. On days with low irradiation, storage charging is prioritized over direct electricity production in the power plant unit, which supports the evening electricity production. Based on a weather forecast the decision is taken, whether a prioritization is necessary. On days with high irradiation, the excess energy of the solar field is usually sufficient to fully charge the storage system until the evening. This results in an optimum use of solar irradiation. The same plant without storage system would never produce electricity during the typical evening peak hours. Including storage and using the developed strategy electricity can be produced during 87 % of the evening peak time.