Solar Hot Water Panel Installation

Mine are in series.  Logistically, I don't know how you would do it in parallel unless the arrays were one over the other.  You'd have to do some creative plumbing.  And I see no advantage with evacuated tubes to do parallel.  With flat plate collectors, parallel probably makes sense because the water is actually flowing through the panel.  But with evac tubes, it only goes through the manifold.  Adding all of the additional copper would only make the system more expensive, increase the risk of fault, and reduce overall efficiency due to the extra pipe resistance and heat loss.  Upon further reflection, I would say that connecting evacuated tube collectors in series is the only way to go unless you have some special circumstances (I can't think of what they may be).