Bob101:
I have been working on a mobile project that needs to know the direction of true north.The project I am interested in is a vehicle mounted solar tracker that will be used in Europe and northern Africa to keep our leisure batteries topped up.
I don't understand why you're trying to deal with magnetic declination and so on. It seems that the objective is to predict the position of the sun so you can point a solar collector at it. To do that you need to know the lat/log, time and direction of North. But just how accurately do you need to know which way is North? Or put another way, just how directional is your solar collector? If it's a flat PV panel, it's not very directional at all. Surely, a GPS position and time fix plus a bog standard uncorrected magnetic compass is going to get you better accuracy than you need. If you don't think it is, then what sort of accuracy are you aiming for, and why?