[TRNSYS-users] Total solar radiation, beam, diffuse, ground reflected solar radiation are not balanced

[thornton at tess-inc.com]

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