I did some analysis on this recently with a load of simulations. If you ignore the sunlight bouncing back from the surface (and I suspect this might still be th

I did some analysis on this recently with a load of simulations. If you ignore the sunlight bouncing back from the surface (and I suspect this might still be the case if you don't ignore it), then the best orientation that maximises winter generation is to have the panels pointing towards the equator and tilted to directly face the Sun at its lowest point at noon in winter. Pointing them lower down (like vertically) reduces the generation. If you're reasonably far from the equator then this is still fairly close to vertical, probably good enough for snow to slide off them. If you're close to the equator, then vertical North-South panels will generate very little indeed.