A little more info on my solar water collector:
Because of my more temperate climate where the winter temperatures seldom drops below 20F at night for any length of time and usually above 35 during the day I chose to build a "drain back" system for my domestic hot water (DHW) the future one for floor heating will be a glycol antifreeze system.
For my testing I bought a submersible pond pump with a 5 gpm flow rate with a 12 foot head, experimenting over time I throttled the pump down to about 1 gpm for the best results. Less may have been better yet but had a hard time keeping a constant rate that low with my simple homemade dump relief valve.
A drain back system self regulates the water temperature using a differential controller, one temp probe is in the storage tank and another at the collectors top inside discharge pipe. If the tanks drops below 110F and the collector is above 110F then the pump starts and harvests all the heat, once the heat is gone or the tank is above set-point then the pump stops and all the water in the lines drain back into the tank so it won't freeze in the collector. That is over simplified but the general concept.
The stagnation temperature of a collector can reach 250F when no water is flowing, in March mine went to 150F in 10 minutes with no water.
As said before I already bought some Wirsbo joist traks made of fairly thick aluminum so as not to need the aluminum flashing smashing system. 1/2" copper pipe snaps in snugly and will only use silicon grease for a fill as no gluing would be needed. I did not use selective coatings as flat black BBQ paint worked good enough for me, the 2 sun-tuff poly panels also worked good at $40 for both sheets needed for a 4'x8' collector are very light and indestructible to ice-hail and other weather (within reason).
I have not cost out the new system yet but will be more then my original one at $200 and would probably put it around $300 but also much easier to build, more efficient, and most likely needing fewer panels too. Copper has gone up since I built mine but would guess around $100 for all pipe and fittings, the plates another $100, the sun-tuff $50, and misc another $50. This is just for the collector and no ancillary pumps and controllers.
I have taken down and stored all my solar heat and voltaic systems to finish the house to get ready for sale, going off on a tangent and playing with these neat contraptions have set me back a full year on my cabin, had I stayed on task I would already be living in the new place (are you reading this Jax?). Building a solar electric panel, solar water heater, solar oven, solar space heater, chest freezer to refrigerator modification, instant ice maker, rocket stove, and now completely side tracked with pressure canning all set me back considerable money and not working since 2007 wasn't a smart thing to do.
What a great job. The before and after pics are fabulous!! 
