Page 282 - ISES SWC50

This device is completely passive, which means that is does not need pumps, active components and power supply
for operation; it simply uses the solar energy to purify water. In addition, this process is efficiently operated by
a thermal power density of less than 1 kW m (non-concentrated solar power) and at a maximum temperature
-2
of 65°C. However, future developments may involve the use of concentrated solar power (e.g. by means of the
two-axis solar concentrator installed at internal lab, which could be beneficial for improving the performance and
industrial scalability of this passive desalination device.

The engineering complexity and geographical requirements of desalination techniques make their deployment
difficult in certain regions of the world, such as desert climates, countries with no direct access to brackish or
seawater. The atmosphere contains around 13,000 km of freshwater, which is an order of magnitude higher
3
than rivers (primary fresh water source) and this water is also a widely accessible resource in all regions around
the world. Prof.s G. Fracastoro and M. Simonetti, with their group, are studying solar-driven atmospheric water
harvesting systems based on adsorption techniques, introducing an innovative iso-thermal process (patented) and
a new hygroscopic bio-compatible material (patent pending). The activity is carried on in partnership with Princeton
University (NJ, US) both on the research and technology transfer grounds, through the spin-off company Aquaseek.
They used sorption technologies also to study open-loop solar cooling systems. The NAC-wall, one-of-a-kind
machine, demonstrated a desiccant-evaporative cooling cycle, based on the use of SAPO-34 zeolite, regenerated
by solar thermal energy, activated by full buoyancy-driven ventilation. It can perform also in hybrid ventilation mode,
achieving an electrical COP of 26, and a thermal COP of 0.75.

Tubular receivers in central tower systems suffer the high mechanical stresses caused by the temperature gradient
typically established along the tube and across its circumference due to the one-side heating. Prof. L. Savoldi and
her group design, test and analyze new solutions for the removal of high heat fluxes from absorber tubes, moving in
the two parallel directions of enhancing the heat transfer by tailored turbulence promoters and metal porous media/
foams.

The specific focus of the tests, typically performed at the Plataforma Solar de Almeria within the EU SFERA
projects using pressurized air as a Heat Transfer Fluid (HTF), is the assessment of the role of turbulence promoters/
porous media in reducing the peak wall temperature when a strong one-side heating is present, contributing to the
reduction of the thermal gradients between the irradiated and the non-irradiated (back) side of the receiver. Suitable
Computational Fluid Dynamic (CFD) 3D models are developed and validated against experimental data, and further
used to perform the enhancement of the heat transfer to the HTF.

Internal view of PV systems The oldest PV plant with
@13P (about 30-kw) ratedpower of 1.5 kW

Lab scale prototype of destination Two-axis solar concentrator

264 | ISES SWC50 - The Century of Solar-Stories and Visions