Solar hot water system review
Its been 3 years since I installed my drain back system and am satisfied with its performance. I live in California and the system provides all the hot water we need from mid-February to early November if it gets 3 hours of sunlight per day. The electrical usage is about 400 watts per day to run the pumps and this represents about a 25X energy savings over using electric elements only.
Lessons learned and comments:
-First bump in the road was damage to the panels. When the boxes arrived, they looked to be in great shape but I didnt realize that the black scuff mark on the panel box was actually a major 3 dent into the back of one panel. Unfortunately, when you sigh off on the shipping invoice without noting damage, you are holding the bag. In all honesty, Alternative Energy Store people refused to help so I had to go through the Hot water system manufacturer and Fed Ex freight for help. 2 month later I got a 50% shipping refund from Fed Ex and took the panel apart myself to fix it. Tricky moving that 4x8 sheet of glass by hand but the repair was successful. Now I always uncrate and inspect all shipped items from freight companies before signing off and would strongly recommend this practice.
-I installed the drain back tank on top on the 80 gallon hot water heater as shown in the picture but would recommend installing the drain back tank to the side. The stand that comes with the drain back tank was very shaky and instead I built a heavy duty shelf above the 80 gallon tank for the drain back tank to sit on. Problem with this arrangement is the plumbing is very tight making access difficult. Also, you cant replace the anode rods of the 80 gallon hot water heater without completely disassembling the structure-a major undertaking.
-When I purchased the system 3 years ago it came with a small stainless steel Taco pump to circulate the water from the 80 gallon storage tank to the drain back tank. The larger steel Taco pump circulated water from the drainback tank to the panels and back. The reason that steel(a less costly component), and not stainless steel is used for this pump is that since this water loop is closed, the small amount of oxygen in the system should not cause the pump to rust. Despite using distilled water for this part of the system, I got black paste building up in the drain back tank site glass and the water flow meter such that you could not read them. I flushed the system with distilled water several times, ensured there were no leaks allowing additional oxygen to get in, cleaned the site glasses many times, and reviewed all fitting and components to rule out another source of the corrosion. Still, the black paste returned. I did replace the larger steel taco pump last year, at my expense, with a stainless pump and this solved the problem. I see that the systems now come with both pumps made of stainless steel so I suspect this was also problem for others.
-Ive calculated the energy saving several ways and have concluded that our water usage requires about 8000 to 10,000 watts per day to heat. The 2 pump drain back system uses on average 400 watts per day. Thus, you are producing 20-25x heat using this system. We turn the backup heat off from late march and dont turn it back on till late November.
-Side notes. The electrical usage was closer to 320 watts/day the first year but went up over time and has now leveled at 400 watts/day. Not sure if this is a function of our water usage or a degradation of the solar panels coating.
If you are considering installing the system yourself, I would strongly recommend the following book:
Solar Hot Water Systems: Lesson Learned 1977 to Today by Tom Lane
-Feel free to ask any questions or share any experience you may have had installing your own system_
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