Show NMAE on plot

[peterdudfield]

Detailed Description

Following on from #142 , would be good to show a normalised MAE too.

Context

• useful to see metrics in % too

Possible Implementation

1. Show MAE / capacity of the site
2. Show MAE / mean(generation)

[peterdudfield]

You have to get the site capacity from the site object - you have to use this function to get the site info - https://github.com/openclimatefix/pv-site-datamodel/blob/main/pvsite_datamodel/read/site.py#L14

[peterdudfield]

I think 2. has been done.

Do you think you can also add in 1.
MAE / site capacity. This is a useful reference, as the ML metrics are made using this

[peterdudfield]

To get site capacity might have to use https://github.com/openclimatefix/pv-site-datamodel/blob/main/pvsite_datamodel/read/site.py#L14 this function to get the site object. You can the get the capacity from this site object