On 2023-03-07 20:30, Shengteng Li via TRNSYS-users wrote:
The total solar radiation on a tilted surface should equal the sum of the beam radiation on the tilted surface, sky diffuse radiation on the tilted surface, and ground reflected radiation on the tilted surface, as shown in following:
I_balance=It_tot-( It_beam+I_d*f_sky+I_h*refl_gnd*f_gnd) I_balance should be zero. However, it is not zero and it varies with time. It is only zero when slope=0, i.e., a horizontal surface.
I believe that your mistake is that the equations you are using only work with an isotropic sky assumption (a parameter in the weather model). When I repeat your exercise in TRNSYS 18 with a 60-degree collector slope, and an isotropic sky assumption, the balance is almost perfectly zero for the entire year. When I change the assumption to a different radiation mode, the balance fails to hold. For further details I would encourage you to explore the references for the solar radiation processing used in the weather routines.
Jeff ---- Jeff Thornton President Thermal Energy System Specialists (TESS) 3 N. Pinckney Street - Suite 202 Madison WI 53703 (608) 274-2577 www.tess-inc.com