Deviations between satellite and ground measurement irradiance data

[Vinh Thinh]

Dear all,

 

I am reaching out whoever can help me with this topic. For several projects for which I am assessing the meteo data, there has been a potential misalignment between the on-site plane of array irradiation data registered by sensors (such as pyranometers or solarimeters) and Solargis satellite data. For this reason, I am questioning whether such occurrence has ever been encountered by someone else and if so, what has been the take-away. I am open to discussion on this topic.

Thank you and best regards,

Vinh

 

[Auriane Canesse]

Getting high quality irradiance measurements in the field can be difficult and the two main sources of errors we see from our users are:

1. Shaded sensors, especially for trackers. This can be identified by comparing your data to clearsky expectation on good weather day, and looking for unexpected decreases. The pattern should repeat from one day to the next.
2. Sensor misalignments, either in azimuth or tilt (or both). Even small discrepancies have an impact. If you can easily download POA irradiance from solargis, chose a clear day and download data for several azimuth and tilt values around your expected geometry. Then check if one of the alternative geometries fits your measured data better.

If your sensor is misaligned, you can still use the data in PVsyst as we first decompose POA irradiance into GHI and DHI. You just have to use the real tilt and azimut when importing data.