Solar Hot Water Panel Installation

Hi Tony,
The lower over all temperature that you work in the more efficient the system will be. You will have less heat loss and the higher the temperature the panels run at, the less efficient they are. Also you may run into problems with super heating your exchange media on good collection days. I would parallel your panels. Best of luck!
Regards,
Dennis

I would agree with Dennis M. and Thomas A. but would also argue the point that, its not right for someone to suggest what you could or couldn't do with your Trendsetters based on information from just a quickly typed letter in a public forum. That would be like describing the world to someone else while looking through a straw. Forgive me for bring so critical Tony R.

So much depends on the specific applications as well as site specifics.

Obviously, two in series, could very well produce hotter mean temperatures on certain winter days and most assuredly produce too hot of mean temperature on certain summer days. (a matter of perspective) But! If there is a use for those hotter mean temperatures during the summer such as a pool, or steam sauna then its not really wasted. Even if these do not exist, there are ways to shade the collector during summer months. It could be plumbed with bypass making it either or. Where your panels will be mounted, may or may not be ideal. Specifics.

"Iron rusts from disuse, stagnant water loses its purity and in cold weather becomes frozen; even so does inaction sap the vigors of the mind."
Leonardo Da Vinci

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).