Right now we have 3, 4'x12' hydronic collectors and 2, 4'x8' air heating collectors. The air heaters were free and the water heaters were $250 for the 3.
There have been more, but i have turned other people on to them.
We once pulled a 4'x20' foot pool heating collector from the side of the road on trash day. It was a heater for an outdoor
shower from april to october and had several inncarnations. We circulated it with pv and an rv diaphram pump, but they will thermosyphon. It would bring 48 gallons to 150°f., by noon-thirty or so depending on conditions. They have no cover.
Dont believe the tripe about 'yeah but if there is ever anything but 70 degree weather, they are useless and you must use evacuated tubes'
I dont know how many systems will never be installed because of that misunderstanding. Evacuated tubes have plenty of performance edge, but in my case below zero degree weather is no bar to operation and simply does not invalidate their usefulness and value.
We have watched 150 degree fluid temps circulate during strings overcast days, in february at 20 deg., though with evacuated tubes. Flat plates can still hit 250-300 degrees, stagnating and just under that for low efficiency, high temp operation, just not at extreme delta-T., ambient versus collector temp.
Even during poor production, flat plates can pre-heat incoming water to a much better temp than ground temp in winter. This 'useless production adds up to way less fuel usage or way more utility than to not have it in place and usually a well designed system will provide 50-75 percent or more reduction in fuel use. The fueled heater is backup for solar shortfalls, not the other way around.
Many households will only require a single collector to attain this offset.
The guy i worked for when i was younger, had a salvage
yard of all kinds of collectors and absorbers, stacks of them organized by type and maker.
These things produce 10's of millions of btu per year and are precious.
Borosilicate or water white, iron free, pyrex, it goes by all kinds of names, but if you want a family heirloom, look for glass covers, aluminum frames, stainless screws, selective surface coatings (metals not paints), copper absorbers, unions, and a metal backing sheet for survivability and support of the insulation back sheet. If it does not have all these feaatures, it is not a show stopper! The details are just the mark of a high performanc collector. Specs and name plates may be faded or otherwise missing, so researching what you have can be hard unless it has a nicely embossed metal tag riveted on, another good sign.
This is one of my favorite things ever! They are hand made at Maine by a guy named...Guy Marsden
http://arttecsolar.com/
It is a differential thermostat that will accept pv direct or battery power, is built solid, servicable and inexpensive. Does not have a touch screen with an ip address, but thats the point.
We built all kinds of systems with no controller at all. The pv panel is sized to operate at 80% or better scavenging efficiency if done right. Performance is improved with automated temperature based control.
On pv direct with the art tec, your circulator can still modulate a little but it is not precise. Good enough it starts and stops at appropriate conditions.
Love to share these and hear what people are doing.