OK, he’s not exactly a retired rocket scientist; he’s a retired airplane product development engineer – but Gary Reysa has built his own homemade very simple-tech solar hotwater system that is the functional and thermal equivalent of commercial systems costing 6 or 7 times as much!
This simple design has survived Montana winters with temperatures down to minus 30F with not even a hint of a problem, while providing an unusually high solar fraction of 94% (75% is typical of commercial solar hot water systems.)
Same Principal as Commercial Solar Hot Water
Incoming cold water from the street passes through the large pipe coil immersed in the storage tank and is heated by the hot storage tank water before it gets to your existing hot water tank – which provides backup heating when needed.
The system uses a unique heat exchanger consisting of a large pipe coil that is immersed in the heat storage tank. The pipe coil preheats water headed for your conventional hot water heater. There is enough hot water stored right in the immersed pipe coil to support a 15 minute shower — after the hot water in the pipe coil is exhausted, the pipe coil acts as a conventional heat exchanger, picking up heat from the heat storage tank.
Extra Collector Space
It uses a larger collector and storage area than commercial systems use. This should improve winter performance and result in a higher year round solar fraction. Since you are building the collector and tank, the added materials cost and effort to oversize these elements is minimal. The tank provides more storage capacity than usual for more cloudy day reserve and more thermal inertia.
Set at a Steep Tilt
The collectors are at this steep angle to improve winter performance, and reduce summer overheating. (Sometimes commercial solar thermal systems are set on rooftops at whatever angle the roof has. This is not good as it typically means that they get far too much summer sun (risking stagnation shutdowns) and too little low-sky winter sun)
Sturdy Off-the-Shelf Construction
Aside from the need to replace an off the shelf controller, it has required no maintenance. The heat storage is just a large tank lined with pond liner. The controller that turns the pump on when the collector is hotter than the storage tank water is an off the shelf item.
And if; like the retired rocket scientist – you have some wide open spaces on hand, you could even build your own giant solar hotwater shed like his. This hotwater tank container is entirely devoted to making the homestead toasty: