Techno-economic assessment of a concentrating solar air heater and packed-bed thermal energy storage for medium-temperature industrial process heat

Among the solar thermal technologies, the Linear Fresnel collector can provide solar heat for industrial processes in the medium temperature range of 150–400 °C. Hot air is widely used as a process medium in several industrial processes, such as drying, curing, and cooking. Although steam, pressurized water, and thermal oil are widely used heat transfer fluids in the solar field, the use of air appears as an interesting alternative; it reduces installation costs as well as the risks associated with leakages, and it enables a direct coupling with the air-based thermal processes. This work proposes an innovative layout using Linear Fresnel collectors for direct solar air heating up to 350 °C in an open-to-atmosphere circuit, avoiding liquid heat transfer fluid in the solar field and heat exchangers. A packed-bed thermal energy storage using copper slags as the filler material is coupled with the concentrating solar air heater to increase the solar fraction to the medium- temperature industrial process. A comprehensive techno-economic analysis is carried out to assess the viability of the proposed concept, establishing the design methodology and operation strategy for improving economic performance. The solar system of 360 kW peak thermal power is integrated on an air-based industrial process having a natural gas burner as the conventional heat source, considering four different demand profiles. A methodology for optimizing the packed-bed size is implemented. A levelized heat cost between € 50 - 60 € / M W h is achieved by the combined system. Besides, the demand profiles 24/7 and 10/5 are found to have the highest potential to integrate the proposed system, enabling high solar fraction up to 0.6 with limited cost increase.