The main disadvantage of the ICS systems is the high thermal losses from
the storage tank to the surroundings, since most of the surface area of the storage tank cannot be thermally insulated, because it is intentionally exposed to be
able to absorb solar radiation. In particular, the thermal losses are greatest during the night and overcast days with low ambient temperatures. Due to these
losses, the water temperature drops substantially during nighttime, especially
during the winter. Various techniques have been used to keep this from happening. Tripanagnostopoulos et al. (2002) present a number of experimental
units in which a reduction in thermal losses was achieved by considering single
and double cylindrical horizontal tanks properly placed in truncated symmetric
and asymmetric CPC reflector troughs. Alternatively, if a 24h hot water supply
is required, these systems can be used only for preheating and, in such a case,
must be connected in series with a conventional water heater.