The History

Solar Hot Water systems are not some new piece of technology.  They have been around since at least the 1970s and many were installed during the oil crisis at that time.  Unfortunately, the price of oil went down and we all forgot about solar hot water.  The solar hot water companies went out of business and when people needed service on their panels, they could not get service.  But they could call their normal oil heat guy, and he said, take those stupid things down.

   People did, or worse yet, left the panels there, in disuse, and the technology naturally developed a reputation of "not working."  But actually, the panels did work, and do work. However, they are not maintenance-free like solar PV (electric) panels.  So an industry is needed for solar hot water.  That industry includes manufacturers, installers, and service personal.  Unfortunately, at this time, all three of those are in short supply.

  The best resource for the subject is "Solar Water Heating" by Bob Ramlow and Benjamin Nusz 2010.  They walk you through the history, economics, and the technology.

   Flat plate solar collectors with propylene glycol (antifreeze) are recommended by Ramlow and others for use in most of the USA.  There are other types of solar hot water collectors, but the advice was nearly universal in my literature study that flat plate collectors are the best choice for my application.  If there was ever any doubt in my mind, it was erased by the fact that all newly installed panels in my area of Massachusetts are flat plate type, and all the remaining old ones from the 1970s are also the flat plate type.