Vaisala has been providing satellite derived solar radiation data to our global customers for many years. During that period of time different datasets and techniques have become available for estimating clear sky irradiance, cloudiness and aerosols. Our five versions each use slightly different combinations of these algorithms. While V2.1 is the newest and generally has the best global validation statistics (but not always), we still offer all five of the versions that we have created over the years to our customers for a few very important reasons:

For the prospecting use case: Our customers have identified the bias in a particular version of our data and want the data to be consistent.

For operational projects: Our customers have built a business process (e.g. performance reconciliation or settlement) around a particular version of our data and want to be able to get consistent data for the lifetime of the project.

No one single model can be made uniformly “best” everywhere without running into the danger of over-fitting to the ground based observations. At Vaisala we believe in always telling you what, if any, site specific corrections were done to the regional satellite data. For all five current versions, NO site specific adjustments were done. See FAQ “The datasets give different answers which one is right”.