We recently replace a solar hot water storage tank on a job I worked on in 1984.  The system has been working well needing only a tempering valve and solar sensor replacement.  The rest of the system is in great shape.

The original tank was made by AO Smith.  It was 120 gallons glass lined steel tank and came with a 10 gallon reservoir tank that sat on top of the storage tank.  This 28 year old tank is the oldest I’ve seen as most tanks only last 15 to 20 years before needing replacing.  Not bad for a tank that came with a 7 year warranty.  These tanks have wrap around system side heat exchangers attached to their lower half.  This separated the potable water in the tank from the non-potable solar loop.  The solar tank was set up as a pre-heat to the primary electric water heater tank.

What’s really cool about solar drainback design is its simplicity.   First, all piping between the panels and the reservoir most slope downhill and they only have one or two moving parts, the solar pump(s).   When heat is available the solar pump turns on and pushes water up through the collectors carrying solar energy back through the exchanger transferring the heat into the storage tank.  When no heat is available the pump is off.  If the pump shuts off, gravity takes over and the water running through the panels and piping just stops and drains back into the reservoir.  This design means that drainback systems have the least maintenance and the absorbers in the collector will last three times longer than any other system.

Drainback system typically uses a small 7 to 10 gallon reservoir tank.  Reservoir tanks are available with or without a heat exchanger, as are solar storage tanks.  Testing dating back to the 1980’s has found that heat exchanger design and location are the most limiting factor in system performance.  Many of the systems available today are only 60% to 70% efficient, and will only collect up to 70% of the available solar energy hitting the panels.

Over the years Sunworks has used many different tanks for both new systems and when replacing old solar storage tanks, trying to find the best solution, and we did.  We now use a new design and tank utilizing a load side heat exchanger.  The new tank is unpressurized with the heat exchanger located inside near the top.  The new tank services as both solar storage tank and drainback reservoir making it an all-in-one.

Water inside the new tank is the same that runs through the solar collectors for maximum solar gain making the system much more efficient.  It is never emptied or refilled.  When hot water is needed in the home it first runs through the load side heat exchanger before entering the primary tank.

The new tank should last 30 to 40 years and if needed the heat exchanger is replaceable.  The all-in-one design saves space, maintenance, uses less plumbing and works for both new and old systems.  We love it!

Check out our design and call Sunworks to see if solar hot water heating will work in your home.