There is a fascinating post on Building for Change about research at MIT into designing three-dimensional PV 'towers'. The idea is that, with cells aligned in a variety of ways, they will provide a steadier output than at present, being effective for more of the day and coping better with cloudy conditions.
They will be more expensive than current on-building installations since not all of the cells will be working all of the time, but this will be less of an issue as prices fall. By providing a more even output, they will interface better with the grid and individual users will need to 'top up' less. These are still early days, but it would be interesting to compare these with 'conventional' PV coupled with a storage system.
The towers could have a great future though. There is even talk of mobile towers used for recharging cars in a car park. Should we expect a lot of stand-alone totem poles in the future? They would work best out of the shadow of the building. But local authorities would have to resist the temptation to drape them with signs and banners.