Build a class that inherits from RawGSPDataSource which overrides the method which chooses locations. Go through each GSP in order.
Tell the model class whether it should be computing national PV. If so, in the end_of_batch_validation method, keep a dataframe which accumulates the total PV generation (actual and predicted) for each timestep. Be careful of batches which include the last few GSPs, and the next one. Remember to multiply by GSP capacity!
RawGSPDataSource
which overrides the method which chooses locations. Go through each GSP in order.