CSP – Concentrating Solar Power
STEM® - Solar Thermo-Electric Magaldi

STEM® is based on modular units for power production and thermal energy storage. Several modules can be combined together to produce the superheated steam flow rate (at around 500°C), to be used to generate electricity or heat.
Solar radiation captured by heliostats field is concentrated on a secondary reflector (beam down) and subsequently focused into a receiver, positioned at ground level.
The receiver is based on a fluidized bed technology: 270 tons of fluidized sand, at an operating temperature of 550-650°C, are used to effectively transfer and store the solar thermal energy. Up to 8.2 MWh thermal energy can be stored per module, thus allowing the release of the required energy at night, or in absence of sun radiation (e.g. 2 MWh for 4 hours, 1.3 MWh for 6 hours, or 0.8 MWh for 10 hours).
Different configurations of STEM® can be applied, according to the Customer need.

STEM® as solar accumulator integrated to a PV plant
STEM® is an ideal component to be combined with existing or dedicated PV plants to grant continuity of green power production during night time.
During day, electric power is directly produced from sunlight with the PV plant, which also feeds the STEM® auxiliaries, allowing solar energy to be effectively stored in the fluidized bed receiver.
The fluidized bed receiver, in this way, works as a TES of solar power, that can be used during night for steam or power generation.
In a typical arrangement, each STEM® module is equipped with 390 heliostats (surface 7 m2 each), rated at an input solar power of 1.05 thermal MW, used for Thermal Energy Storage. Land occupation of one module is approx. 12000 m2. Different values of input solar power can be obtained by different sizes of the heliostats field.
As an example, considering a STEM® system composed of 10 modules, each integrated to a 500 kW PV plant, the expected generation of net energy per year can be calculated as follows (assuming a 28% Power Block efficiency):
DNI=1920 kWh/m2/year – South Italy 4550 MWhe during night from STEM
DNI=2700 kWh/m2/year – Australia 6500 MWhe during night from STEM
DNI=3200 kWh/m2/year – Chile 7700 MWhe during night from STEM

STEM® technology is particularly suitable to cover the energy needs in remote sites without grid connection.
The great availability of the heat storage and the flexibility of production makes it possible to cover energy needs such as desalination of water, air conditioning and production of industrial steam, thus sustaining the economic and social growth of isolated areas.
Compared to existing CSP technologies, STEM® introduces two main innovative elements. First of all, the modularity (it’s to say the combination of a variable number of solar generation units) allows to realize generation systems of different configuration, power and capability. Additional modules can be installed at a later stage, shall the power demand increase. But the main innovation is its ability to store the solar energy and deliver it when needed, even at night or in cloudy periods.
Moreover, the absolute lack of poisonous emissions into the environment (both in case of normal operation or failures) as well as the non-use of cooling water and any chemicals, makes STEM® technology the best way to produce green energy in remote zones.
Even from the standpoint of the landscape, STEM® system confirms its commitment towards the environment. In fact, compared to traditional Power Tower systems, STEM® does not have a huge visual impact since its highest structure does not exceed the height of 22 m meanwhile other CSP tower systems reach over 100 m.

STEM® key strengths:
• Dependability: The simple operational process and the modular configuration give STEM® a competitive advantage over other CSP technologies. Even if one module is under maintenance, the other modules guarantee continuity to the production of steam.
• Flexibility: Fluidized bed technology using sand as storage medium and the possibility to connect the modules in parallel or in series enable the system to generate electricity according to the demand load.
• Modularity: The base modules can be combined together to meet the required power demand. It is possible to add modules at a later stage, in case demand increases.
• Hybridization: STEM® technology can be integrated with both renewable and fossil fuel plants, to guarantee a continuous operation, day and night, year-round. The receiver is designed to also allow the combustion of low heating value fuels, such as biogas.
• Cogeneration: High temperature steam generated can be used for district heating and cooling, water desalinization, greenhouses.
• Environmental friendliness: STEM® technology only uses absolute eco-friendly materials: glass for heliostats, steel for structures and sand for thermal storage, so that, even in case of decommissioning or at the end of its working life, all materials are completely recyclable.
• Long service life: STEM® system is almost static and it is designed to be operational for decades. Batteries, on the other hand, need to be substituted after a certain number of cycles.
• Ideal solution for remote areas: STEM® operates locally on demand without the need to build large power plants and expensive distribution grids.