I installed my solar hot water system about six years ago. It’s a good system. I have two 4’x8’ AE-32 flat-plate collectors (manufactured by Alternate Energy Technologies), a Superstor Ultra stainless-steel tank (at 80 gallons, it’s a little small, but it’s what I could afford), and an El Sid DC pump from Ivan Labs. Since I installed the equipment myself, it cost significantly less than a professionally installed system.
This year I had my first maintenance issue with my solar thermal system. In March, the snow covering my solar collectors finally began to melt. Unfortunately, the solar collectors were bare of snow for several sunny days, while the small PV modules that provide power for the PV-direct pump were still snow-covered. Since the sun was shining on the solar thermal collectors but the pump wasn’t circulating the glycol solution, the fluid overheated. A significant amount of fluid was released through the system’s pressure/temperature relief valve before I realized what was going on.
The solution was fairly simple, but it was a pain. I bought a couple of gallons of glycol. I drained the old fluid from the system, and introduced a new antifreeze solution into the system, the same way I did when I commissioned the system a few years ago. The whole process took a few hours.
In the future, I’ll need to move the PV modules that are wired to the DC pump to a different location, so the snow will melt from the modules at about the same time that the snow melts from the collectors. That work will also take me a few more hours.
If I had had to hire a solar thermal contractor to perform this maintenance work, the work would have cost hundreds of dollars, eating into any energy savings that the solar hot water system provides.
My brother’s story
My brother Peter and his wife Elana own a single-family house in Roslindale, Massachusetts. When they bought the house in 1994, it came with a two-collector solar hot water system. The real-estate agent told them that the solar equipment was relatively new. On sunny days, Peter noticed that the pipes that circulated fluid from the collectors to the heat exchanger were hot. The system appeared to be working well.
I called Peter up recently and asked him to tell me about his solar hot water system’s maintenance history. “About six years ago, the tank started leaking,” he told me. “I made a few calls, and found a solar contractor who was willing to work on the system. He said it would cost $1,300 to install a new tank. That was a lot of money, and we weren’t sure whether it made sense to repair the system. But we’re worried about global warming, and we thought we should do our part. So we installed the new tank.”
A few weeks ago, however, the system developed a new problem. “I noticed that the glycol solution was leaking from the expansion tank onto the concrete floor,” Peter told me. “It looks like the expansion tank is shot. I called the same guy who replaced the storage tank, but I couldn’t reach him. It turns out that he’s not in business anymore. It’s really hard to find someone to maintain or fix these systems. I called a few solar contractors, but most of them said, ‘We only repair systems that we installed. We didn’t install your system, so it’s your problem.’ I kept calling around. Two contractors said that they would come give an estimate, but after a month of waiting, only one of them actually showed up. He said that it will cost $900 to replace the expansion tank and the glycol solution.”
Solar thermal systems have a long payback period
In the past, I’ve written a few articles noting that solar thermal equipment has a very long payback period. The average American family spends $267 per year for fuel to heat domestic hot water. Even if a solar thermal system saves 60% of your hot-water energy bill — an optimistic assumption — the equipment will only save the average family $160 per year. If the system costs $6,000 to install — many systems cost more — it will have a simply payback period of 38 years. A few years ago, a study by Stephen Winter Associates calculated that payback periods for two studied solar thermal systems ranged from 58 to 76 years.
These calculations don’t include maintenance costs. If my brother decides to bite the bullet and pay for a new expansion tank, the bill for his two maintenance problems will total $2,200 — eating up at least 14 years of energy savings.
Solar thermal systems are more finicky than PV systems
I wrote an article on solar hot water system maintenance costs for the November 2004 issue of Energy Design Update. I wrote, “There is a dearth of data on the costs of maintaining solar equipment. ‘I don’t have any good data on solar thermal system maintenance costs,’ said Jim Huggins, the solar thermal program director at the Florida Solar Energy Center (FSEC). ‘People have struggled with this for a long time, and most of the information we have is pretty anecdotal.’ …
“According to most installers, solar hot water systems require more maintenance than PV systems. ‘The solar thermal stuff is much more finicky, more difficult to troubleshoot and repair, than the solar electric equipment,’ says Richard Gottleib, the owner Sunnyside Solar in Guilford, Vermont. ‘Wiring doesn’t go bad. PV modules very rarely go bad. Inverters — well, they occasionally go bad, but the failure rate on the inverters is probably less than a half percent.’ …
“Danny Parker, a senior researcher at FSEC, said, ‘For a solar hot water system, the going assumption has been to budget 2% of the installed cost per year for maintenance.’ …
“ ‘I urge all of my clients to sign up for a maintenance contract,’ says Mike Tierney, president and co-owner of Aspen Solar Systems in Aspen, Colorado. ‘For a system with up to 100 square feet of collector area, I recommend a visit every two years. Once you get over 100 square feet of collectors, the system should be visited every year. During a visit, which costs about $200 to $300, I go through an 18-step inspection of the most important mechanical and electrical components.’ Doug Wells [a sales manager at Solar Works in Montpelier, Vermont] gives similar advice. ‘We recommend to our customers that they have us come out and do regular maintenance every couple of years, which would cost a few hundred dollars per visit,’ says Wells. ‘Unfortunately, they usually wait until something extreme happens before calling us, and then it ends up costing more.’ ”
To fix or not to fix?
My brother hasn’t decided yet what to do about the leaky expansion tank. For the time being, he has shut a few valves to disable the solar thermal system.
“I’m not sure whether it’s worth it to put another $900 into the system,” Peter told me. “It feels like it’s too soon to have another expensive problem with the system. I have a lot of construction skills, but I can’t fix this system, even though I am relatively savvy. And it’s not easy to find someone who knows how to fix this equipment. I’m frustrated with the whole thing, and I don’t know what to do at this point.”
Martin Holladay’s previous blog: “A Green Building Conference in Montreal.”