The electrical efficiency from the tests of standard PV modules and also the electrical and thermal efficiencies of all PV/T models were used to calculate the monthly energy output and from them the annual values for the weather conditions of Patras. In the calculations we considered PV and PV/T system slope equal to the latitude of Patras for both horizontal and tilted building roof installation. The complete systems include the necessary additional components (Balance Of System, BOS, for the electricity and the BOS for the heated air circulation) and therefore the final energy output is reduced due to the electrical and thermal losses from these systems. Estimating a minimum energy reduction of about 15% for the PV electrical energy that is converted in electricity (inverter), we take a value for BOS equal to 85% to calculate the final electrical energy output of the PV and PV/T systems. Regarding system thermal part, we consider also efficiency 85% for the final heat output (tubes, fan, etc) and we take these new values as the final use energies. The annual energy output per m2 of the considered PV modules and of the PV/T systems are
included in Table 2. The calculated values for PV and PV/T systems with BOS of 85% for both electrical and thermal system parts are calculated considering the annual solar input (1644.72 kWhm"2yr"1) on the plane of the PV module for Patras. The main scenarios for the practical use of the heated air are the following:

1. The heated air is used for twelve months. This consideration is for reference purposes and corresponds to application of annual needs in heated air, as for example in some industries.

2. The heated air is used for six months (November to April), while the rest six months (May to October) the heated air is ejected to the ambient, cooling the PV modules only. This consideration corresponds to typical PVT/AIR applications, as the space heating of buildings.

3. The heated air is used twelve months, six months (November to April) for the effective use of air (e. g. for space heating of buildings) and six months (May to October) for water preheating through heat exchanger. The thermal output in water preheating is lower than that of the air heating only, as there are additional thermal losses in the air — water heat exchanger.

From the given results we observe that the total energy output (electrical plus thermal) of PVT/AIR systems is higher than that of the standard PV modules, while regarding only the electrical output, it is higher only of PVT/UNGL-TILT and PVT/TFMS-TILT systems. The suggested TFMS modification in the air channel results to higher total energy output compared to the PVT/UNGL type systems and to higher electrical output compared to PVT/GL type systems. The practical use of the heated air only for six months is not efficient enough (almost 40% of that from the reference mode of the 12 months). In the case of water preheating for the rest six months, the total thermal energy output can be considered satisfactory (about 75% to that of the reference mode of the 12 months).