Solar Thermo Electric Magaldi (STEM®)
A patented small-scale CSP/CST system with thermal energy storage (TES)
To stay competitive with PV, Concentrated Solar Power (CSP)/Concentrated Solar Thermal (CST) technology includes a thermal storage system to dispatch energy on demand.
The use of TES in CSP/CST plants enables the production of electricity and thermal energy well after the sun has gone down, putting the technology in a position to hold a greater percentage of the energy mix.
Nearly all new CSP/CST plants operating or under construction are equipped with a TES system.
Magaldi developed and patented the STEM® technology to produce both electrical and thermal energy from solar radiation. This system, whose expected useful life is 30+ years, has all credentials to play a crucial role in the global decarbonization process.
The STEM®-CSP/CST system integrates a solid particle TES system to generate energy even on cloudy days and in the hours after sunset or before sunrise.
Solar radiation is captured through a heliostat solar field, concentrated on a secondary reflector (beam down), and focused on the fluidized bed receiver. The latter consists of insulated tanks that contain silica sand, fluidized and heated to temperatures above 600 °C. The fluidized bed receiver works as a TES system and effectively stores the solar thermal energy which can be extracted when needed for steam or power generation.
Silica sand vs. molten salts
Generally, the medium of choice in CSP/CST plants with TES is molten salts that, however, have some hard limits.
Magaldi based its system on a different material. The use of a cost-effective and locally available storage material like silica sand is a key factor for the STEM®-CSP/CST system.
The sand allows overcoming limitations faced with molten salts, thanks to:
- Capacity to reach higher temperatures: the melting temperature of silica sand is approx. 1500°C and, up to this point, it maintains its thermo-physical characteristics without a limited number of cycles.
- Compact design: the solar receiver, heat exchanger, and thermal energy storage are all integrated into one device. This results in a small-scale system with a reduced footprint, ideal for industrial complexes.
STEM®-CSP/CST can be mainly used for generating:
- Electric energy. The produced steam is used to drive a steam turbine, or, thanks to the extremely high temperatures reached by the sand bed, it is possible to use a supercritical CO2 Brayton cycle instead of the classic steam cycle;
- Thermal energy. The heat collected from solar radiation is used to generate steam or hot air for direct use in industrial thermal processes.
Electric and thermal energy generation can be carried out simultaneously.
STEM®-CSP/CST uses and applications may be many and different, making it an ideal solution for tomorrow’s distributed energy needs, being able to provide the user with thermal energy and steam when needed, for civil (energy, heat generation, and storage), agricultural (steam, clean water through desalinization) and industrial uses.
It can, therefore, represent a quick solution to foster local development in fringe and off-the-grid communities, without depending on costly and large distribution lines and networks.