How to encode the map of installed PV capacity?

[JackKelly]

Detailed Description

Once we have the map of installed PV capacity in nowcasting_dataset (see issue openclimatefix/nowcasting_dataset#184), we need to figure out how best to encode this map.

Context

The map isn't a map of individual PV sites. Instead it's the PV capacity per LLSOA. Jamie says:

LSOAs vary in size. The biggest ones are in Scotland. The largest is ~1200 km2 !! The median size is 0.418 km2 though, so in general they're pretty small.

Possible Implementation

The simplest encoding is probably as a bitmap, at the same spatial resolution as the satellite imagery. Each row (pixel) of data would encode:

• the amount of installed PV
• An embedding of the LLSOA ID? (Maybe that's not required?)
• The geographical position
• The datetime encoding at t0? We can probably assume the installed PV capacity is static per ML example. So each example only needs a single map of installed PV capacity. But we probably do need to provide a datetime encoding, so the attention mechanism can see that the map is "close" to the other data modalities.