To determine the system operation with and without weather forecast and to compare our results with field information we use two parameters: annual solar cover coefficient т and annual coefficient of performance COP. The last one is classically computed for heat pumps and refrigeration machines, and we consider that it can be very useful for solar systems too. The two efficiency coefficients are define as follows:

т = — ^ 100 (13)

Ethw + Qloss

Where Qloss stands for the annual energy lost by the tank.

4.1 Comparison between cities

The performances of the above-described HWSH are computed in three different locations, having different solar radiation intensity: Paris (3.3 kWh/m2.day average value), Grenoble

(4.3 kWh/m2.day) and Nice (4.9 kWh/m2.day).