The recently developed concept of nearly Zero-Energy Building
(nZEB) introduced by the recast directive on the Energy Performance
of Buildings (EPBD) [1] combined with the 20–20–20 target
objective [2] are considered important challenges linked to energy
consumption reduction, particularly with regard to the construction
sector that accounts for nearly 40% of total energy use. The
potential of improving energy efficiency in this sector is high in
view of the old uninsulated buildings and plants.
The major problem with exploiting renewable energy sources
and waste energy is the difficulty in conserving heat for long peri-
ods of time. In the past, attention has been focused on improving
the single components used to exploit renewable energy or waste
heat. Improving storage efficiency over long time periods, especially
when renewable energy sources need to be preserved, is currently
considered a major challenge. In this respect, the most
widespread small- to large-scale renewable technologies concern
solar energy. Some examples of these technologies are solar thermal
plants that produce heat to provide warmth for buildings or
domestic hot water, as well as hybrid desiccant cooling systems
and solar-driven absorption plants. The most widespread solar collectors
are the flat-plate and evacuated tube type; the latter are
used to reach high temperatures or to reduce the area of the solar
field. While other kinds of collectors can be found on the market,
their use is limited to special applications. The unglazed type, for
example, is used to heat swimming pools; the concentric tube collectors,
parabolic trough solar collectors, and solar parabolic dish
collectors are all used for power plant systems.