As shown in the figure, around 80% of the solar gains are used for hot water pre-heating, while 20% of the solar gains are used for feed water pre-heating for the steam boiler.
The collector utilization ratio (u_coll) ranges from 7% in winter to 38% in summer. The system utilization ratio (u_sys) varies between 5% and 36% respectively.
The annual specific useful collector yield measured in 2014 reaches 419 kWh/m²a, the specific heating energy transferred to the feed water per-heating of the steam boiler (HXf) amounts to 63.3 kWh/m²a and the specific heating energy transferred to the water heating circuit (HXh) reaches 326 kWh/m²a.
The system integration losses (storage, HX and tubing) of 30 kWh/m²a, correspond to 7% of the transferred useful collector heat.