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Global and Diffuse Horizontal Solar Radiation

Clima displays hourly Global and Diffuse Horizontal Solar Radiationarrow-up-right values for a typical day for each month.

Example: Solar radiation graphs on typical monthly days for San Francisco, USA

Typical daily graphs showing the amount of energy gained from the sun have many uses, such as:

  • design the building with a passive approach, to control solar gains and reduce energy consumption (allow solar gain during months of heating demand and block them during periods of cooling demand, see for reference the degree days);

  • manage the direct solar gain through the glass, to evaluate solar shading devices (most useful in locations with high temperatures and a strong direct component);

  • manage the indirect solar gain transfer into the building with a time shift, exploiting the thermal mass, heating thick walls or concrete floors, or designing special rooms adjacent to the main spaces that rely on convection to transfer the heat, such as sunroom or ;

  • evaluating sustainable renewable energy solutions such as solar thermal or photovoltaic panels.

The integral of the curves in the graphs is the total energy (in Wh/m²), supplied by the sun. Be careful in considering the

Trombe wallarrow-up-right
different types of solar radiation.

Global, Diffuse and Normal solar radiation explained

Example of meterelogical station able to measure Global Horizontal, Diffuse Horizontal, and Direct Normal Solar Radiation. Source: CSIRO
  • Global Horizontal Irradiance (GHI) is the total irradiance from the sun on a horizontal surface. It is the sum of the Diffuse Horizontal Irradiance and the Direct Normal Irradiance, projected onto the horizontal plane using the solar zenith anglearrow-up-right (z).

GHI=DHI+DNI∗cos(z)GHI = DHI + DNI * cos(z)GHI=DHI+DNI∗cos(z)
  • Diffuse Horizontal Irradiance (DHI) is the radiation that arrives from the entirety of the sky dome, except the solar disc. Is the radiation that has been scattered by molecules and particles in the atmosphere. It is measured on a horizontal surface

  • Direct Normal Irradiance (DNI) is the measurement of the intensity of sunlight on a surface perpendicular (normal) to the sun, as such, in very clear sky conditions and low solar altitudes, the Direct Normal Irradiance can be higher than the Global Horizontal Irradiance.

Conceptual representation of Global Horizontal, Diffuse Horizontal and Direct Normal Solar Radiation
Measurement of Direct Irradiation on a horizontal and a normal plane