Feed PV metadata into ML model

[JackKelly]

Remember that for the National Grid ESO use-case (and, in general, for the TSO use-case), we won't have PV metadata for the vast majority of the ~ 1 million PV systems in the UK!

How to deal with missing data? Could have two-stage model: First predict probability distribution of PV yield, independent of PV metadata. Then, if we have PV metadata, refine that probability distribution with a second ML model.

Or simple one-stage model where we somehow encode 'missing data'.