# pvl_clearsky_haurwitz

Determine clear sky GHI from Haurwitz model

## Contents

- Syntax
- Description
- Inputs
- Outputs
- Example
- References
- See also

## Syntax

`[ClearSkyGHI]= pvl_clearsky_haurwitz(ApparentZenith)`

## Description

Implements the Haurwitz clear sky model for global horizontal irradiance (GHI) as presented in [1, 2]. A report on clear sky models found the Haurwitz model to have the best performance of models which require only zenith angle [3].

## Inputs

- `ApparentZenith` - The apparent (refraction corrected) sun zenith angle in degrees.

## Outputs

- `ClearSkyGHI` - the modeled global horizonal irradiance in W/m^2.

Initial implementation of this algorithm by Matthew Reno (Sandia and Georgia Tech).

## Example

    Location.latitude = 35.04;
    Location.longitude = -106.62;
    Location.altitude = 1619;
    % Create 1-min time series for Jan 1, 2012
    DN = datenum(2016, 4,1):1/(24*60):datenum(2016, 4, 1, 23, 59, 59);
    Time = pvl_maketimestruct(DN, -7);
    [SunAz, SunEl, ApparentSunEl, SolarTime]=pvl_ephemeris(Time, Location);
    ApparentZenith = 90-ApparentSunEl;
    ClearSkyGHI = pvl_clearsky_haurwitz(ApparentZenith);
    dHr = Time.hour+Time.minute./60+Time.second./3600; % Calculate decimal hours for plotting
    figure
    plot(dHr,ClearSkyGHI)
    title('Clear Sky Irradiance on June 1, 2012 in Albuquerque, NM','FontSize',14)
    xlabel('Hour of the Day (hr)')
    ylabel('GHI (W/m^2)')

## References

- [1] B. Haurwitz, "Insolation in Relation to Cloudiness and Cloud Density," Journal of Meteorology, vol. 2, pp. 154-166, 1945.

- [2] B. Haurwitz, "Insolation in Relation to Cloud Type," Journal of Meteorology, vol. 3, pp. 123-124, 1946.

- [3] M. Reno, C. Hansen, and J. Stein, "Global Horizontal Irradiance Clear Sky Models: Implementation and Analysis", Sandia National Laboratories, SAND2012-2389, 2012.

## See also

`pvl_maketimestruct` , `pvl_ephemeris` , `pvl_spa` , `pvl_makelocationstruct` , `pvl_clearsky_ineichen`

Copyright 2014 Sandia National Laboratories