Yeah, better than none at all I suppose. I'm just inland of you, so the months you need the panels to be most efficient is like mid-Nov. to mid-Mar. Non-optimal placement, especially with respect to direction will give you some extension to your season, but not as much as possible. I'd go with the shed roof location. If they don't make enough heat for you, they can always be relocated. In summer you probably don't need them.

I still say that the side facing the pool on that detached garage would be the bomb. You would have to add pipe to and from in addition to what you have to add anyway. 250' sound longer than what the aerial view shows. I'm thinking 60 feet from the pump to the closest corner of the garage? That's 120 more. Then, I'm not there and pictures can be deceiving. Busting up concrete is no fun either. Any way to bore under it?