how to calculate heat loss coefficients in LFR systems ?

Dear Rahmi,

The polynomial heat loss equations in SAM's linear Fresnel model calculate thermal loss from the receivers as a function of the difference between the heat transfer fluid (steam) temperature and ambient dry-bulb temperature. The equation coefficients represent the heat loss characteristics of a particular receiver design. SAM's default values are for the Novatec Solar Boiler.

For an example of how coefficients for these equations can be derived, you can refer to the results from Sandia National Laboratories' tests of the SEGS LS-2 solar collector in Kolb et al (1994) ( PDF 5 MB ).

Best regards,
Paul.