A Finnish-Swedish consortium has designed a hybrid system that uses solar electricity and solar thermal energy separately to produce steam for industrial plants. The photovoltaic unit is connected to a sand-based thermal storage system and is said to lower the flat energy costs of the entire system.
The proposed system combines a solar thermal plant based on parabolic trough collectors (PTCs) connected to water storage and a photovoltaic plant connected to a sand-based high-temperature thermal storage system. These two plants are planned to produce heat separately for the same industrial plant, and the solar power unit is used when the solar thermal plant cannot meet the heat demand.
The researchers explained that the operation of a solar thermal plant should always be prioritized because it produces steam with the cheapest heating costs. In addition, they said, the system should also rely on a third back-up heating system, such as a typical commercial boiler, which should only be used when both solar systems are insufficient to meet the heating demand.
The team modeled the hybrid system using TRNSYS software, which is used to simulate the behavior of transient renewable systems. It then used Python software to simulate the interaction between the solar collector and the load.
Four different scenarios were studied: a reference case where heat is produced exclusively by a traditional boiler; a system configuration based on a boiler and a solar thermal plant combined with water storage; a hybrid system using a boiler and solar power plant combined with sand storage; and a system that uses both solar technologies combined with corresponding storage systems.
Investigators hypothesized that the system and industrial building were located in Seville, southern Spain.
Based on their techno-economic analysis, they found that the fourth system configuration using both solar technologies offers the lowest levelized cost of heat (LCOH) of €83.5 ($93.9)/MWh. The highest LCOH was offered by a system based on a traditional boiler alone at a price of €100/MWh, while a system based on solar energy steam production without solar thermal energy reached an LCOH of €90/MWh. A system based on solar thermal energy without solar electricity reached an LCOH of €84/MWh.
“In the combined system, the PTC and PV systems complement each other to achieve better economic and land area performance while achieving a very high combined solar share,” the researchers said, adding that this hybrid system offers the best area savings of approx. 20,000 m2. They also emphasized that a solar thermal unit can satisfy 30 percent of an industrial plant’s heating needs, while a solar energy unit covers 60 percent and a boiler 10 percent.
They presented the system in a study “Technical-Economic Assessment of a New Hybrid System for Solar Thermal and Solar Powered Sand Storage for Sustainable Industrial Steam Production,” published Energy conversion and management. The research team includes researchers from Taalainmaa University in Sweden, Finnish sand storage system supplier Polar Night Energy Oy and Swedish solar thermal expert Absolicon Solar Collectors AB.
Polar Night Energy developed a sand storage system that pv magazine was reported in July 2022. The system is embedded in a tall steel tank and is able to store electricity in the form of heat for several months at temperatures of 500-600 C. The system uses ordinary dry sand without special treatment. storage medium and works with tubes containing air. Once this air is heated, it is pumped through pipes and reaches the sand, which in turn is heated to 600C.