Accessing GHI and DNI solar irradiance data

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#1

Hello Ninjas,

A few users have contacted us about the raw solar irradiance data that sits behind the renewables.ninja models. At the moment, you can tick the ‘include raw data’ option to access the ‘direct’ and ‘diffuse’ components of irradiance. These are specific to the tilt and azimuth of the particular panel you are simulating, and so are difficult to compare with other studies.

Two measures that are widely used are the GHI (global horizontal irradiance) and DNI (direct normal irradiance). These are not yet available as a default option to select, but it is possible to extract these from renewables.ninja. Here is how:

  • DNI: if you select 2-axis tracking and raw data, the “direct” column will correspond to DNI.
  • GHI: if you set tilt angle to 0 (a horizontal panel) and select raw data, the sum of the “direct” and “indirect” columns will correspond to GHI.

Admittedly, this is not the most elegant way to access this data; but by using the API, it could be automated. We are looking to include this data automatically in a future release of the ninja - but no promises on the timescale just yet…

Kind regards,
Iain

#2

Hey!

•GHI: if you set tilt angle to 0 (a horizontal panel) and select raw data, the sum of the “direct” and “indirect” columns will correspond to GHI.

Just for a clarification, this would also require treating the direct radiation with (before adding it to diffuse component):
((60 * df[‘direct’] * np.cos(df_b[‘sun_zenith’])) / (np.cos(np.arccos(np.sin(df_b[‘sun_alt’])) * df_b[‘duration’]))

Right? I have few pages of proofs leading to this solution (mainly because I’m a bad mathematician, could have done it in one).

At least this allowed me to change the angle/azimuth freely for gsee-tool from just one downloaded dataset and still receive ±0,01% same values for direct and diffuse as files manually downloaded from ReNinja for any combination of angle/azimuth. Not having this meant that the direct component was off for other angles/azimuths, and thus the GHI was off.

-Valtteri