I built a solar hot tub using the information I gathered from www.builditsolar.com. The water solar collector is pretty much the way Gary (the other Gary) built his with copper pipe, aluminum heat exchanger and Plexiglas patio cover material. There are cheaper ways to build them now, but that was what was popular at the time.I like the cpvc version that doesn’t need solder. The storage tank is like Gary’s, but it had to live outside so I built it with house siding and a real roof that hinges at the back to give access to the tank. It works great most of the year. I bought the hot tub from a neighbor for almost nothing and pulled it apart removing the 220 volt pump replacing it with 1/2″ pex tubing that is attached to a 150′ coil of 1″ pex in the “dog house” sitting next to it. While I had the walls off I packed in as much fiberglass insulation as I could fit between the tub and the new walls. The dog house holds 200 gallons of water. A 12 volt computer cooling pump is operated by a 12 volt controller to circulate the water through the hot tub as needed.
The large collector on the roof is 6′ x12′. The smaller collectors are electric solar collectors that I soldered together while I was recovering from my last disk rupture (L4-5). Four months and one epidural later I was able to assemble the system. The electric panels charge two 6 volt Costco golf cart batteries ran in series which run the two water pumps (one to the collectors when the sun shines and one from the dog house to the modified hot tub. The entire system is off the grid and free except for whatever maintenance that may come up in the future. The system keeps 400 gallons of water at the correct temperature without outside power. The building that holds up my collectors is my recording studio. It is 8′ wide and 12′ long and is trailer-able to move to my next home if needed. It too can be completely off the grid.
The last photo shows the disorganized brains of the project. The disconnect on the upper left switches off power to the system from the two batteries. The two controllers to the right keep track of the temp in the collectors, storage tank and the hot tub and turn things on and off as needed. The two small 12 volt water pumps in the bottom left corner pump the water from the tank to the collectors as needed. The pump from the storage tank to the hot tub is mounted under the hot tub. It is also a 12 volt pump. but smaller that the others since it is a closed system and does not have to pump water up 13 feet like the others.