Up to this point, only room heating demand has been considered without taking into consideration the domestic hot water demand. The DHW demand is constant during the whole year, and in this case two persons would need 106 kWh/month that means 1273 kWh/year, almost half value of the room heating needed.

If this thermal energy load is added to the previous total heating demand, and is covered by the pellets/wood boiler, 147 kg of pellets is needed to cover the 100% demand, (27 Euro for the whole season), a small quantity compared to the Italian energy demand standards. This solution has two advantages: the usable solar energy is greater (since will be less solar energy wasted) and the pellets/wood boiler will be used for a longer time, decreasing the pay back time of the heating system.

4.5 The electricity demand

A grid connected photovoltaic system of 2,1 kWp provides the whole electricity demand (Figure 12).

21 PV panels of 100 Wp each organised in three strings are positioned in the upper surface on the south solar wall.