Hybridizing PV, sand storage, solar thermal energy for steam generation – pv magazine International
A Finnish-Swedish consortium has designed a hybrid system that uses photovoltaics and solar thermal energy separately to provide steam to industrial facilities. The PV unit is coupled to a sand-based thermal storage system and reportedly contributes to lower the levelized cost of energy of the entire system.
A Swedish-Finnish team of researchers has designed an energy system for steam generation in the food & beverage industry that utilizes solar thermal energy and photovoltaics linked to sand-based heat storage.
The proposed system combines a solar thermal plant based on parabolic trough collectors (PTCs) connected to water storage and a photovoltaic facility coupled to a sand-based high-temperature heat storage system. The two facilities are planned to provide heat separately to the same industrial facility, with the PV unit being used when the solar thermal plant is unable to meet the heating demand.
The scientists explained that the operation of the solar thermal plant should always be prioritized as it generates steam at the most economical heating cost. Furthermore, they said the system should also rely on a third backup heating system, like a typical commercial boiler, which should only be used when both solar installations are insufficient to meet the heating demand.
The group modeled the hybrid system with TRNSYS software, which is used to simulate the behavior of transient renewable systems. It then used Python software to simulate the interaction of the solar collector and the load.
Four different scenarios were investigated: a reference case where heat is provided exclusively by the conventional boiler; a system configuration based on the boiler and the solar thermal plant coupled to water storage; a hybrid system using the boiler and the PV plant linked to sand storage; and a system using both solar technologies connected to their respective storage systems.
The researchers assumed the system and the industrial building to be located in Sevilla, southern Spain.
Through their techno-economic analysis, they found the fourth system configuration using both solar technologies provides the lowest levelized cost of heat (LCOH) of €83.5 ($93.9)/MWh. The highest LCOH was offered by the system based on the conventional boiler alone at €100/MWh, while the system based on PV steam generation without solar thermal energy achieved an LCOH of €90/MWh. The system based on solar thermal energy without PV reached an LCOH of €84/MWh.
“In a combined system, the PTC and PV systems complement each other to achieve better economic and land area performance, while also achieving a very high combined solar fraction,” the scientists said, adding that this hybrid system provides the best area savings of approximately 20,000 m2. They also emphasized that the solar thermal unit is able to meet 30% of the industrial facility’s heating demand, with the PV unit and the boiler covering 60% and 10%, respectively.
They introduced the system in the study “Techno-economic assessment of a novel hybrid system of solar thermal and photovoltaic driven sand storage for sustainable industrial steam production,” published in Energy Conversion and Management. The research team comprises scientists from the Dalarna University in Sweden, Finnish sand storage system provider Polar Night Energy Oy, and Sweden-based solar thermal specialist Absolicon Solar Collectors AB.
Polar Night Energy developed a sand storage system that pv magazine reported about in July 2022. The system is embedded in a high steel container and is able to store electricity in the form of heat for several months at temperatures ranging between 500 C and 600 C. The system uses common dry sand without any special treatment as the storage medium and works with pipes containing air. When this air is heated up, it is pumped through the pipes and reaches the sand, which is in turn heated up to up to 600 C.
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