// Compute apparent sunrise and sunset times on a tilted surface of any orientation
// Duffie and Beckman (1991) eqn 2.20.5e to 2.20.5i
public static void CalcApparentSunsetHourAngle
(double Lat // (i) latitude [radians]
, double Decl // (i) declination [radians]
, double Slope // (i) slope of receiving surface [radians]
, double Azimuth // (i) azimuth angle of receiving surface [radians]
, out double AppSunrise // (o) apparent sunrise hour angle [radians]
, out double AppSunset // (o) apparent sunset hour angle [radians]
, out double Sunset // (o) true sunset hour angle [radians]
)
{
// Declarations
double aux1, aux2, aux3, disc;
double cosInc, SunZenith, SunAzimuth;
double A, B, C;
// Calculate true sunset and parameters A, B and C
Sunset = Astro.GetSunsetHourAngle(Lat, Decl);
A = Math.Cos(Slope) + Math.Tan(Lat) * Math.Cos(Azimuth) * Math.Sin(Slope);
B = Math.Cos(Sunset) * Math.Cos(Slope) + Math.Tan(Decl) * Math.Sin(Slope) * Math.Cos(Azimuth);
C = Math.Sin(Slope) * Math.Sin(Azimuth) / Math.Cos(Lat);
// Pathological case: the sun does not rise
if (Sunset == 0)
{
AppSunrise = AppSunset = 0;
return;
}
// Normal case
aux1 = A * A + C * C;
disc = aux1 - B * B;
// Check discriminant. If it is positive or zero, the sun rises (tangentially)
// on the surface. In that case, calculate apparent sunrise and apparent
// sunset
if (disc >= 0)
{
aux2 = C * Math.Sqrt(disc) / aux1;
aux3 = A * B / aux1;
AppSunrise = Math.Min(Sunset, Math.Acos(aux3 + aux2));
AppSunset = Math.Min(Sunset, Math.Acos(aux3 - aux2));
if ((A > 0 && B > 0) || (A >= B))
{
AppSunrise = -AppSunrise;
}
else
{
AppSunset = -AppSunset;
}
}
// If discriminant is negative, the surface is either always or never
// illuminated during the day. To find which case applies, compute the
// cosine of the angle of incidence on the surface at noon. If it is less
// than zero, then the surface is always in the dark. If it is greater
// than zero, then the surface is always illuminated
else
{
Astro.CalcSunPositionHourAngle(Decl, 0, Lat, out SunZenith, out SunAzimuth);
cosInc = GetCosIncidenceAngle(SunZenith, SunAzimuth, Slope, Azimuth);
if (cosInc < 0)
{
AppSunrise = AppSunset = 0;
}
else
{
AppSunrise = -Sunset;
AppSunset = Sunset;
}
}
}
// Calculation for inverter output power, using efficiency curve
public void Calculate
(
int DayOfYear // Day of year (1-365)
, double Hour // Hour of day, in decimal format (11.75 = 11:45 a.m.)
)
{
double itsSLatR = Utilities.ConvertDtoR(itsSLat);
double itsSLongR = Utilities.ConvertDtoR(itsSLong);
double itsMLongR = Utilities.ConvertDtoR(itsMLong);
try
{
if (DayOfYear < 1 || DayOfYear > 365 || Hour < 0 || Hour > 24)
{
throw new CASSYSException("Sun.Calculate: Invalid time stamp for sun position calculation");
}
}
catch (CASSYSException cs)
{
ErrorLogger.Log(cs, ErrLevel.FATAL);
}
// Compute declination and normal extraterrestrial Irradiance if day has changed
// Compute Sunrise and Sunset hour angles
if (DayOfYear != itsCurrentDayOfYear)
{
itsCurrentDayOfYear = DayOfYear;
itsCurrentDecl = Astro.GetDeclination(itsCurrentDayOfYear);
itsCurrentNExtra = Astro.GetNormExtra(itsCurrentDayOfYear);
// Variables used to hold the apparent/true sunset and sunrise hour angles
double appSunRiseHA; // Hour angle for Sunrise [radians]
double appSunsetHA; // Hour angle for Sunset [radians]
double trueSunsetHA; // True Sunset Hour angle [radians]
// Invoking the Tilt method to get the values
Tilt.CalcApparentSunsetHourAngle(itsSLatR, itsCurrentDecl, itsSurfaceSlope, Azimuth, out appSunRiseHA, out appSunsetHA, out trueSunsetHA);
// Assigning to the output values
AppSunriseHour = Math.Abs(appSunRiseHA) * Util.HAtoR;
AppSunsetHour = Util.NoonHour + appSunsetHA * Util.HAtoR;
TrueSunSetHour = Util.NoonHour + trueSunsetHA * Util.HAtoR;
TrueSunRiseHour = TrueSunSetHour - Astro.GetDayLength(itsSLatR, itsCurrentDecl);
// If using local standard time then modify the sunrise and sunset to match the local time stamp.
if (itsLSTFlag)
{
TrueSunSetHour -= Astro.GetATmsST(DayOfYear, itsSLongR, itsMLongR) / 60; // Going from solar to local time
TrueSunRiseHour = TrueSunSetHour - Astro.GetDayLength(itsSLatR, itsCurrentDecl);
}
}
// Compute hour angle
double SolarTime = Hour;
if (itsLSTFlag)
{
SolarTime += Astro.GetATmsST(DayOfYear, itsSLongR, itsMLongR) / 60; // Going from local to solar time
}
double HourAngle = Astro.GetHourAngle(SolarTime);
// Compute azimuth and zenith angles
Astro.CalcSunPositionHourAngle(itsCurrentDecl, HourAngle, itsSLatR, out Zenith, out Azimuth);
// Compute normal extraterrestrial Irradiance
NExtra = itsCurrentNExtra;
// Compute air mass
AirMass = Astro.GetAirMass(Zenith);
}
