Concentrated Solar Power system with Thermal Energy Storage
STEM® - Solar Thermo-Electric Magaldi

CSP (Concentrated Solar Power) technology with TES (Thermal Energy Storage) is able to provide an ‘energy trifecta’ by delivering on-demand thermal energy, steam and electric power, even in absence of sun (e.g. on cloudy days or several hours after sunset).
Known as STEM®, Magaldi developed an innovative modular CSP technology with thermal energy storage revolutionizing the solar power sector in the 1-20 MWe range, by using recyclable and eco-friendly materials. It is able to dispatch high temperature fluid, which can be used directly for industrial purposes or for the production of electricity.

A STEM® module is made of:

• Heliostats field;
• Secondary reflector;
• Receiver and storage module.

Solar radiation is captured by heliostats and concentrated on a secondary reflector, which focuses it directly into a central ground-based receiver containing a fluidized storage bed of silica sand and then heated by the concentrated sunlight. The receiver contains a heat exchanger within the fluidized sand bed operating in the range of 650-750°C. Fine particle sized fluidized sand guarantees high heat capacity and thermal diffusivity, thus improving solar-to-electric efficiency.

STEM® technology is characterized by:

• High storage capacity. Thanks to the heat stored in the sand, STEM® is able to ensure the steam generation even on cloudy days or several hours after sunset;
• High temperature steam generation. The fluidized sand bed into the receiver operates at temperatures in the range of 650-750 °C. Storing heat at high temperatures in a relatively inexpensive medium (sand) improves solar-to-electric efficiency and significantly reduces thermal energy storage costs with the additional advantage of no need of particles conveyance, since the receiver, storage and heat exchanger are all integrated into one ground-based device;
• Modularity. STEM® allows to combine a variable number of solar generation units to enhance power generation and storage capacity. Thanks to the modularity feature, any additional module can be installed to increase the production at any later stage to meet potential higher energy demand. Moreover, it helps to meet requirements of distributed energy projects, by installing generation plants in the vicinity of end users, saving the costs of long distance grid;
• High dependability. STEM® modularity enables an increased reliability in power generation since, even when a module is under maintainance, the other modules guarantee the plant operation;
• Long working life-time. STEM® components have a long service life. This allows to benefit for decades from fundamental services of STEM®, hence to consider it as an infrastructure available for the medium/high DNI. Once CAPEX is paid, the cost of energy generation only depends on OPEX.
• Hybridization. STEM® technology is highly suitable for hybridization with both renewable and fossil fuel energy sources, thus providing more flexible and continuous operation, day and night, year-round. In particular, STEM® can be coupled with a PV plant, able to power STEM® auxiliary components during the daytime;
• Dual functionality/cogeneration. STEM® allows both producing electricity and high-quality steam, thus making it ideal for power or industrial processes applications (e.g. water desalination or distillation for agricultural, chemical and mineral processing industries);
• Environmental friendliness. STEM® is a renewable energy technology made of eco-friendly and recyclable materials.
• Solid particles technology. STEM® uses solid particles heated by concentrated sunlight, thus eliminating the risks associated with the use of diathermic oils or molten salts and the related operational and disposal costs.

STEM® technology is geared towards covering the energy needs of small industrial and residential areas with high insolation, not connected to the power grid. Energy generation is, in fact, closely related to the direct solar radiation (DNI or Direct Normal Irradiance), which is higher in the Countries belonging to the so called ‘Sun-belt area’.
STEM® is also a safe, clean alternative to Diesel engines in high DNI remote areas where fuels and energy supply is complicated. It also perfectly suits communities seeking to reduce dependence on power generated by imported oils/fossil fuels and decrease vulnerability to price and supply fluctuations. It is also the clean alternative to batteries, which are very polluting and containing hazardous waste and toxic contents, while STEM® is producing energy in a completely green mode.
Moreover, STEM® high quality thermal energy is the convenient solution to purify polluted water of rivers, lakes and groundwater and contributes to increase availability of drinking and irrigation water by sea water desalination, supporting agricultural projects helping arid territories becoming green.
The availability of power and fresh water at low cost is the fundamental determinant of the social and economic development of many tropical and subtropical areas of the world.