Solar Hot Water Retrofit

When our house was built in 1988, a solar hot water system was installed. Although providing hot water reliably throughout the seven years we have lived here, the twenty year old system was needing some attention.

Leaking solar hot water storage tank In particular, the solar storage tank had started to leak, and standing water under one’s house is never really desirable.

Since the California Center for Sustainable Energy (CCSE) was offering workshops on how to take advantage of the California Solar Initiative, a program put in place to provide over $2.1 billion in solar incentives, that seemed like a good place to start. The one evening workshop provided some good information on the different types of solar hot water systems, as well as a list of qualified contractors. The best news was that retrofitting an existing system would qualify for the incentive rebate, in theory at least.

After calling a few contractors on the list, we settled on Son Energy to do the work. However, we learned that the type of system installed in our house, an open loop system, would not qualify for the rebate due to CCSE regulations. Based on our location, we would have to install a closed loop system to qualify — at substantially more cost than retrofitting our existing system, even after the rebate. So going for the rebate would actually cost us more money and not allow us to leverage our existing solar hot water system that has been working just fine for twenty years. Draw your own conclusions about government programs.

To be fair, I understand — to a point. A closed loop system is recommended in our area because the outside temperature occasionally drops low enough to freeze water. Our system, an open loop system, works like this:

  1. Cold water enters solar storage tank
  2. A pump exchanges cold water in the storage tank with hot water in the solar collectors heated by the sun
  3. On a sunny day, the water in the storage tank remains hot, being constantly circulated to the solar collectors on the roof
  4. Heated water in the storage tank is fed into the conventional hot water heater
  5. The conventional hot water heater kicks in only when water in solar storage tank is not already hot enough (at night or on cloudy days)
  6. Water from the tap is drawn from the conventional hot water heater, which doesn’t work very hard (if it has to work at all) since it is fed water that is already hot

Since we live east of San Diego where the weather is usually sunny (when the sun is not blocked by smoke), the conventional hot water heater is not called upon to perform heating duties all that often. The only drawback is that water sitting in the collectors might freeze if the temperature drops far enough, causing cracks and leaks in the collectors.

In a closed loop system, a glycol based anti-freeze solution circulates between a heat exchanger type of storage tank and the collectors on the roof, and house water is heated in the exchanger by the hot glycol from the collectors. Water is never exposed to the collectors on the roof, so less risk of freezing issues.

With our open loop system I might have to bypass the solar collectors during the coldest nights of the year, opening a relief valve on the collectors when the temperature is expected to reach freezing. Otherwise the collectors would probably crack and leak. I can live with that.

New solar hot water system Okay, so forget the rebate. We replaced our solar storage tank, replaced our conventional propane hot water heater, and refurbished our solar collectors. Well, the good folks at Son Energy did all the plumbing work, while I worked on figuring out how to get a 28 inch diameter solar storage tank through at 23 inch door (see photos).

While it would have been nice to receive some kind of rebate for improving/upgrading our existing solar system, it still feels good to know we are using the sun to power our hot showers. Using solar energy to heat our water will pay for the improvements easily over time (6-7 years based on the estimated cost of yearly operation sticker on the conventional water heater).

I have to believe others in our situation would skip the improvements without a rebate. Most solar hot water systems installed in our area in the 80s and 90s were open loop systems. I personally know of a couple households that simply removed their open loop systems when they needed maintenance work. I’m sure if a rebate were available to offset the cost of repairs they would still have solar hot water. Even after the rebate, a new system is still quite expensive. Not leveraging existing (aging) closed loop systems installed in our area seems to go against the intent of the California Solar Initiative.

Anyway, we are very happy with the installation and the new equipment:

I was tempted to go with the impressively efficient Vertex water heater by A. O. Smith, having seen good things about it, but the extra cost is not justified given we use the sun to heat our water most of the time, not gas.

Check out more photos of the retrofit if you like.

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