Souliotis et al. [31] compared three Integrated Collector Storage Solar Water Heaters (ICSSWH) with a Flat Plate Thermosiphonic Unit (FPTU). ICSSWH used in this experimental investigation were like those of Fig. 4e and f, with an acceptance angle of 90° (ICS2) and 60° (ICS3) respectively. They were mounted in horizontal position. The results of the investigation showed that ICSSWH behavior is comparable to that of FPTU before sunset. However, in the nighttime heat losses of ICSSWH were higher than FPTU. Anothercomparison is made between ICSAwith single glazing and ICSB with double-glazing. In the range of the mean storage water temperature/irradiance, between 0.01 and 0.06 K/Wm2, the mean daily efficiency of the ICSA (between 0.42 and 0.59) is higher than that of the ICSB (between 0.40 and 0.53). Over this range the main daily efficiency of the ICSB (between 0 and 0.46) is higher than that of the ICSB (between 0.34 and 0.42).
Table 4 shows a comparison among thermal efficiencies of thermal solar collectors with innovative geometries. Focusing only on the efficiency, the best performances have been reached by the works of Youcefi et al. [19] and Ozgen et al. [24], but this parameter is not the only one to take into account when evaluating an innovative geometry, even if it is one of the most important. The overall construction effort, LCA, environmental impact etc. are important parameters as well. Under those points of view, the analyzed papers do not give an exhaustive analysis, leaving to possible future works the opportunity to determine this.
4. Integrated solar thermal collectors
This paragraph is dedicated to integrated flat solar thermal collectors, whose characteristics allow accomplishing the strict regulations in terms of environmental impact and landscape constraints. An important advantage of this typology of solar
collectors is related to the aesthetics. Hazami et al. [32] analyzed the performance of a solar storage collector containing: