thesky_daylight Module Reference

Daylight procedures. More...

Functions/Subroutines
real(double) function	extinction_sun_airmass (airmass)
	Compute an approximation for the bolometric atmospheric extinction factor for the Sun with a given air mass.
real(double) function	extinction_sun (alt)
	Compute an approximation for the bolometric atmospheric extinction factor for the Sun with a given altitude.
subroutine	solar_radiation (alt, beam_norm, beam_horiz)
	Compute the normal and horizontal beam (direct) solar radiation for a given altitude of the Sun, assuming a cloudless sky (and sea level)
subroutine	clearsky_bird (alt, io, rsun, press, uo, uw, ta5, ta3, ba, k1, rg, itot, idir, idif, igr)
	A simplified clear-sky model for direct and diffuse insolation on horizontal surfaces (a.k.a. as the Bird model)
subroutine	diffuse_radiation_perez87 (doy, alt, surfincl, theta, gbeam_n, gdif_hor, gdif_inc, gdif_inc_is, gdif_inc_cs, gdif_inc_hz)
	Compute diffuse radiation on an inclined surface using the older (1987) Perez model.
real(double) function	project_sunlight_on_surface (beta, gamma, sunaz, sunalt)
	Compute the projection factor of direct solar radiation (DNI) on a (sloped) surface.

Detailed Description

Daylight procedures.

Function/Subroutine Documentation

clearsky_bird()

subroutine thesky_daylight::clearsky_bird	(	real(double), intent(in)	alt,
		real(double), intent(in), optional	io,
		real(double), intent(in), optional	rsun,
		real(double), intent(in), optional	press,
		real(double), intent(in), optional	uo,
		real(double), intent(in), optional	uw,
		real(double), intent(in), optional	ta5,
		real(double), intent(in), optional	ta3,
		real(double), intent(in), optional	ba,
		real(double), intent(in), optional	k1,
		real(double), intent(in), optional	rg,
		real(double), intent(out), optional	itot,
		real(double), intent(out), optional	idir,
		real(double), intent(out), optional	idif,
		real(double), intent(out), optional	igr )

A simplified clear-sky model for direct and diffuse insolation on horizontal surfaces (a.k.a. as the Bird model)

Parameters

alt	Sun altitude above the horizon (rad)
Io	Solar 'constant' (W/m^2 - optional, default: 1361.5)
Rsun	Sun distance (AU - optional, default: 1)
Press	Air pressure at the observer's site, corrected for altitude (hPa - optional, default: 1013)
Uo	Ozone abundance in a vertical column (cm - optional, default: 0.34)
Uw	Percipitable water-vapor abundance in a vertical column (cm - optional, default: 1.42)
Ta5	Aerosol optical depth from surface in vertical path at 500 nm (optional, default: 0.2661)
Ta3	Aerosol optical depth from surface in vertical path at 380 nm (optional, default: 0.3538)
Ba	Aerosol forward-scattering ratio (optional, 0.82-0.86, default: 0.84)
K1	Aerosol-absorptance constant (optional, rural: 0.0933, urban: 0.385, default: 0.1)
Rg	Ground albedo (optional, fraction - default: 0.2)
Itot	Total insolation on a horizontal surface (W/m^2 - optional) (output)
Idir	Direct (beam) insolation on a horizontal surface (W/m^2 - optional) (output)
Idif	Diffuse insolation on a horizontal surface (W/m^2 - optional) (output)
Igr	Ground-reflection insolation from a horizontal surface (W/m^2 - optional) (output)

See also

Bird & Hulstrom, A simplified clear-sky model for direct and diffuse insolation on horizontal surfaces, SERI/TR-642-761 (1981)

Note

The value of Taa does not agree with tabulated values from the paper, and hence neither do dependent values (except for AM~1). When I substitute their values for Taa, everything matches perfectly. Error in their formula, or (hopefully!) in their table?

Definition at line 165 of file daylight.f90.

diffuse_radiation_perez87()

subroutine thesky_daylight::diffuse_radiation_perez87	(	integer, intent(in)	doy,
		real(double), intent(in)	alt,
		real(double), intent(in)	surfincl,
		real(double), intent(in)	theta,
		real(double), intent(in)	gbeam_n,
		real(double), intent(in)	gdif_hor,
		real(double), intent(out)	gdif_inc,
		real(double), intent(out), optional	gdif_inc_is,
		real(double), intent(out), optional	gdif_inc_cs,
		real(double), intent(out), optional	gdif_inc_hz )

Compute diffuse radiation on an inclined surface using the older (1987) Perez model.

Parameters

DoY	Day of year (Nday)
alt	Altitude of the Sun (radians)
surfIncl	Surface inclination wrt horizontal (radians) - 0 = horizontal, pi/2 = vertical
theta	Angle between surface normal vector and Sun position vector (radians)
Gbeam_n	Beam (direct) normal radiation (W/m2; in the direction of the Sun)
Gdif_hor	Diffuse radiation on a horizontal surface (W/m2)
Gdif_inc	Diffuse irradiation on the inclined surface (W/m2) (output)
Gdif_inc_is	Diffuse irradiation on the inclined surface - isotropic part (optional; W/m2) (output)
Gdif_inc_cs	Diffuse irradiation on the inclined surface - circumsolar part (optional; W/m2) (output)
Gdif_inc_hz	Diffuse irradiation on the inclined surface - horizon-band part (optional; W/m2) (output)

See also

Perez et al. Solar Energy Vol. 39, Nr. 3, p. 221 (1987) - references to equations and tables are to this paper. Most equations can be found in the Nomenclature section at the end of the paper (p.230). I use a and c here, not b and d.

Todo

Implement Perez et al. Solar Energy Vol. 44, Nr. 5, p. 271 (1990)

Definition at line 284 of file daylight.f90.

extinction_sun()

real(double) function thesky_daylight::extinction_sun

(

real(double), intent(in)

alt

)

Compute an approximation for the bolometric atmospheric extinction factor for the Sun with a given altitude.

Parameters

alt	TRUE altitude of the Sun (radians)

Return values

extinction_sun

The approximated bolometric atmospheric extinction factor for the Sun

Note

- extinction_fac = 1: no extinction, extinction_fac > 1 extinction.

• Hence, the flux, corrected for extinction, should be f' = f / extinction_fac(alt,ele)

Definition at line 91 of file daylight.f90.

References thesky_visibility::airmass(), extinction_sun(), and extinction_sun_airmass().

Referenced by extinction_sun(), and solar_radiation().

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extinction_sun_airmass()

real(double) function thesky_daylight::extinction_sun_airmass

(

real(double), intent(in)

airmass

)

Compute an approximation for the bolometric atmospheric extinction factor for the Sun with a given air mass.

Parameters

airmass

Airmass for the position of the Sun

Return values

extinction_sun_airmass

The approximated bolometric atmospheric extinction factor for the Sun

Note

- extinction_fac = 1: no extinction, extinction_fac > 1 extinction.

• Hence, the flux, corrected for extinction, should be f' = f / extinction_fac(alt,ele)
• Fit of the power extinction computed by the NREL SMARTS code (valid for airmass <= 38.2):
  • Gueymard, C, Professional Paper FSEC-PF-270-95, 1995
  • Gueymard, C, Solar Energy, Vol. 71, No. 5, pp. 325-346, 2001

Definition at line 48 of file daylight.f90.

References extinction_sun_airmass().

Referenced by extinction_sun(), and extinction_sun_airmass().

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project_sunlight_on_surface()

real(double) function thesky_daylight::project_sunlight_on_surface	(	real(double), intent(in)	beta,
		real(double), intent(in)	gamma,
		real(double), intent(in)	sunaz,
		real(double), intent(in)	sunalt )

Compute the projection factor of direct solar radiation (DNI) on a (sloped) surface.

This function returns the projection factor of direct sunlight on a surface with given orientation, useful for e.g. insolation on solar panels, solar collectors or windows. The projection factor equals the cosine of the angle between the normal vector of the surface and the position vector of the Sun.

Parameters

beta	Inclination angle of the surface (w.r.t. the horizontal) (radians)
gamma	Azimuth angle of the surface (0=south, pi/2=west, ±pi=north, -pi/2=east) (radians)
sunAz	Azimuth of the Sun (0=south, pi/2=west, ±pi=north, -pi/2=east) (radians)
sunAlt	Apparent altitude of the Sun (radians)

Return values

project_sunlight_on_surface

The projection factor for direct solar radiation (DNI) on a (sloped) surface (0-1).

Note

Note that different definitions for gamma and sunAz are possible, as long as they correspond.

See also

Celestial mechanics in a nutshell, Sect. 4.3: Insolation on an inclined surface (https://CMiaNS.sf.net).

Definition at line 433 of file daylight.f90.

References project_sunlight_on_surface().

Referenced by project_sunlight_on_surface().

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solar_radiation()

subroutine thesky_daylight::solar_radiation	(	real(double), intent(in)	alt,
		real(double), intent(out)	beam_norm,
		real(double), intent(out), optional	beam_horiz )

Compute the normal and horizontal beam (direct) solar radiation for a given altitude of the Sun, assuming a cloudless sky (and sea level)

Parameters

alt	TRUE altitude of the Sun (radians)
beam_norm	Normal beam radiation, perpendicular to the position vector of the Sun (W/m2) (output)
beam_horiz	Beam radiation on a horizontal surface (W/m2) (output)

See also

function extinction_sun()

Definition at line 117 of file daylight.f90.

References extinction_sun().

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