# In terms of the conventional construction components currently

The thermal performance is a factor determined under a heat balance evolving convection, conduction and radiation. Under the steady-state conditions, the useful heat delivered by a Solar Thermal Collector (STC) is equal to the ANA 12 absorbed by the heat transfer fluid minus the direct or indirect heat losses from the surface to the surroundings, therefore the equation for the thermal efficiency can be written asequation(6)ηth=QUGTAC=Fατα−FRULTi−TαGTwhere Ac is the aperture area of collector; FR is the heat removal factor due to the fact that the fluid entering the collector is heated in the direction of the flow, which is effected by the STC characteristics, fluid type, and fluid flow rate through the collector; QU is the useful solar energy; GT is the total (direct plus diffuse) solar energy incident on the collector aperture (W/m2); UL is the overall heat loss coefficient respectively; Ti is the temperature of the fluid entering collector (°C) and Ta is the ambient temperature (°C).