What type of Solar is this on a house?

[SunForTheSunGod]

https://www.zillow.com/homedetails/4614-Hamlet-Place-Madison-WI-53714/55414456_zpid/?utm_campaign=androidappmessage&utm_medium=referral&utm_source=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.