I am working with WRF v4.7.1 and examining the implementation of PV panels in phys/module_sf_bep_bem.F, specifically within the upward_rad() subroutine. I have a question regarding the calculation of gfl when PV panels are present on the roof.
In the current code, gfl is calculated as:
gfl=(1.-albr_u)*rs*(1-pv_frac_roof)+emr_u*rld*(1-pv_frac_roof)+pv_frac_roof*emr_u*sigma*tpvlev(id,iz)**4 &
-emr_u*sigma*(tr_av(id,iz)**4.)+(1-gr_frac_roof)*sfr(id,iz)+(sfrv(id,iz)+lfrv(id,iz))*gr_frac_roof+(1.-gr_frac_roof)*lfr(id,iz)
where emr_u is the emissivity of the roof.
However, I am wondering why the longwave emission term from the PV panels uses emr_u instead of the emissivity of the PV panels themselves. Would it not be more consistent to write:
gfl=(1.-albr_u)*rs*(1-pv_frac_roof)+emr_u*rld*(1-pv_frac_roof)+pv_frac_roof*em_pv*sigma*tpvlev(id,iz)**4 &
-emr_u*sigma*(tr_av(id,iz)**4.)+(1-gr_frac_roof)*sfr(id,iz)+(sfrv(id,iz)+lfrv(id,iz))*gr_frac_roof+(1.-gr_frac_roof)*lfr(id,iz)
where em_pv is the emissivity of the PV panels (e.g., 0.79)?
In the current code, gfl is calculated as:
gfl=(1.-albr_u)*rs*(1-pv_frac_roof)+emr_u*rld*(1-pv_frac_roof)+pv_frac_roof*emr_u*sigma*tpvlev(id,iz)**4 &
-emr_u*sigma*(tr_av(id,iz)**4.)+(1-gr_frac_roof)*sfr(id,iz)+(sfrv(id,iz)+lfrv(id,iz))*gr_frac_roof+(1.-gr_frac_roof)*lfr(id,iz)
where emr_u is the emissivity of the roof.
However, I am wondering why the longwave emission term from the PV panels uses emr_u instead of the emissivity of the PV panels themselves. Would it not be more consistent to write:
gfl=(1.-albr_u)*rs*(1-pv_frac_roof)+emr_u*rld*(1-pv_frac_roof)+pv_frac_roof*em_pv*sigma*tpvlev(id,iz)**4 &
-emr_u*sigma*(tr_av(id,iz)**4.)+(1-gr_frac_roof)*sfr(id,iz)+(sfrv(id,iz)+lfrv(id,iz))*gr_frac_roof+(1.-gr_frac_roof)*lfr(id,iz)
where em_pv is the emissivity of the PV panels (e.g., 0.79)?