What type of Solar is this on a house?

[SunForTheSunGod]

https://www.zillow.com/homedetails/4...ource=txtshare

I'm hoping someone can help me identify the type of solar installed in the house that's pictured in the zillow link above. I'm a total neophyte to the solar game, but I was psyched to find some older looking panels on a house I might be interested in.

The previous owners don't know the install date or the brand/model of the panels. The house was built in 1975. The solar is used to help with the heating, and is operated by a single toggle switch. The previous owners didn't turn the gas heat on until the temperature dropped below 38 degrees, otherwise the solar took care of the heating.

A few questions:
1. What is this type of system called?
2. How many panels is it comprised of? Is each section an individual panel, or are there probably larger panels underneath?
3. What would be a best guess for an installation year?
4. Is this style still produced? What might be options for upgrading this current system?

Thanks in advance for any insights or advice!

[organic farmer]

I do not see any solar panels in the photos.

What you describe is a Solar-Thermal system.

[sdold]

I don't see any solar panels (electric or water-heating) either, but I'd buy that place just for that basement!

[J.P.M.]

Best guess answers to your questions:
1.) Looks something like a "Trombe wall".
2.) Most likely, but no guarantees: no panels as such. Maybe some type of hybrid system. See Google or other sources of info under "Trombe Wall". Or, if you're local to Madison, contact the Solar Radiation lab and U. of W. They probably forgot more about Trombe Wall theory than anyplace on this earth. The person that did or does own the home might even be found there - see my rant below.
3.) S.W.A.G: ~~1975- 1990 ?
4.) Such systems are (or probably were) mostly one of a kind and site built.

Since there's nothing that looks like solar equipment that's visible on any roof surface, and there's a portion of the south wall of the dwelling that looks like it's dark and covered with some sort of glazing, I'd guess that wall feature is the solar heating device referred to by the real estate slug's description.
In any case, unless that house is super insulated (it ain't) or the inhabitants walk around the house in parkas, I don't believe it'll handle all the heating load below ~ 40 F. Been there. Done that.
If it's a "Trombe Wall", (after its most vocal and well known proponent, a French person by the name of Felix Trombe. For info, Google is your friend), or a similar hybrid type system without any integral heat storage, it's a type of solar heating system that simply uses dark surfaces behind the glazing with or without thermal mass, and in either case, transfers heat to the interior of the dwelling either by natural or forced convection. If it's a true Trombe wall, the thermal storage helps control the thermal swings (think of a 6"- 12 " thick concrete wall painted flat black with spaces for air circulation front and back, to and from the heated space). If no thermal storage, the system will be a bit less expensive to build but will tend to overheat, produce larger temperature swings and tend to cook the dwelling interior.
My guesses, and maybe this is a bit off the wall, but stick with me here:
1.) Madison WI right? Propinquity may have a role to play in this mystery.
2.) Unravelling the mystery a bit, the University of Wisconsin at Madison is (or has been) the home of one of the best, largest and probably the most widely known centers of solar energy academic research in the world.
3.) If that's some sort of Trombe wall or other similar device without thermal mass on the home that's for sale, I wouldn't be surprised if it was once owned by someone who was or is associated with the U of W Solar Radiation lab and was installed as sort of a labor of love or preference.
FWIW, The U. of W. campus is relatively close by. Also, the trees look sort of young and were probably not causing any shading when the system may have been installed.
4.) More FWIW, such systems work best when installed in new construction when they can be incorporated as part of the building design. This looks like sort of a bolt on affair which while possible, is not the most practical design from a thermal, economic or, as may seem obvious, esthetic standpoint. That last point is what makes me want to think that the system was put in for an owner who was a solar proponent and who was primarily an academician and not real well versed in the practical aspects of solar energy applications. Think of noise and air duct leakage for forced convection systems, and poor thermal performance and poor temperature distribution for natural convection systems for starters.
My experience with the U of W Solar Radiation lab folks left me with the impression the folks there were better at solving differential equations and writing papers than engineering, designing and building practical alternate energy systems that were fit for purpose.

[J.P.M.]

I don't see any solar panels (electric or water-heating) either, but I'd buy that place just for that basement!

Ever been in a basement in the upper Midwest or the Northeast in the winter?
Besides, basements fill up with stuff worse and sooner than any garage of a home without a basement and all of it will take on a lovely smell of basement stank in short order. In addition, all the accumulated stuff will need to go down and up a set of stairs for at least one round trip.
Basements in cold climates are all mostly damp and will probably need a dehumidifier about 6-8 months of the year, or they'll quickly come to smell like a wet Airedale year-round.