@danks, on the other hand ... if you've got time on your hands now is a great time to invest in training
I'm going on a course next week that I had booked for November last year (if we can remember what happened then) in fact over the next three months I've got 6 training courses booked not just for me also for my guys that way we are fully geared up in all aspects of renewables and the Green Deal, - I make sure that we have 'redundancy' in all areas of knowledge so we are not just realiant on one particular expert.
Yes it's going to cost money and time, however it was all part of our five year plan that we put together two years ago, it's just that the training got put back becasue of the silly season, the money is the same, the time is slightly cheaper this year.
Looking at it long term renewables are here to stay.
So in answer to the OP's question having had experience of employess doing both, I would recommend the C&G 2399, however don't do just solar PV - add in other renewables as well - Heat pumps are coming to the fore add in Solar Thermal as well.