General Thoughts on Solar Water Heating

Had a recent conversation with a co-worker that reawakened some feelings I have harbored about the use (and very often, misuse) of solar collectors for water heating. We spoke about the thermal system installed at her home, which was designed to offer supplemental heat for a radiant floor loop. This in-floor heating system is primarily operated with a gas boiler, which has been working overtime-her monthly propane bill in the winter is $500+. This wouldn't seem so shocking under normal circumstances. This is Colorado. The house is in a deep and sheltered valley, at high altitude. It's damn cold.

Here's the problem: the house was constructed of strawbales, and it's a one bedroom. So you've got a seriously well insulated structure, that's really small. This place should, on paper, stay fairly warm on it's own. The amount of energy required to heat it should be minimal. Did I mention she has had to run the domestic water a bit to flush the glycol (anti-freeze) out of the pipes before she takes a shower? Obviously there are big problems with this system, apart from the fact that it's not doing what it was originally designed to do.

This brings me to my point. After all of the experimentation that has occurred in this arena starting, lets say, in the early seventies, you'd think that we'd have dialed this technology in to the Nth degree by now. I asked if she knew when the building was constructed. Apparently, it's only a few years old. This startlingly bad system was recently commissioned. I think the truth is, we have dialed this stuff in pretty well. So what's the issue?

A little about my experience in this field. I had the pleasure (or horror!) of installing domestic solar hot water systems for four years or so. I also did a few tie-ins to radiant floor systems as well. This by no means makes me an expert, but I feel like I have had enough of an opportunity to see what works well, what the trouble spots are, and how the technology can be put to good use. The majority of the systems I worked on were more or less packaged deals, sort of "standardized" to work for the most homes. However, the company I worked for previously would entertain almost any customer and their wild fantasies as to what could be done with the power of the sun. This being said, I did see some systems, that probably would have made more heat if they'd been set on fire, and should have been.

My opinion on why there are so many failed or failing thermal systems is based on several factors:

1. We ask too much of the equipment. There are practical limits to the amount of heat that can be produced by a single flat-plate solar collector, not to mention harvested by the system. You may be able to provide enough heat for hot water in your house, but it is highly doubtful that you will heat your entire home with only one panel. I understand. These collectors cost thousands of dollars, and if four would do the trick nicely, why not get two and be happy with half of the bill taken care of by mother nature, right? Wrong.
2. There are all kinds of vagaries that affect the way these systems perform. Flow, pressure, thermosiphoning, etc. Most of us do not possess the skills to determine exactly what area of collector square footage will be required for a given goal, versus storage tank size, factoring in pump size and energy consumption... You'd need a team of NASA scientists to know exactly every detail that could have an effect on ultimate production. The best we can hope for in most cases is to under-produce (supplement) rather than over-produce (spend too much money and potentially create to much heat; read: steam, system failure).
3. Human beings. We make mistakes. Thermal systems offer amazing potential to make more of them. In my short (thank God) career of putting these things in, I cannot tell you how often my soldered joints failed. It seems like that's just the way plumbing goes sometimes. Bad fittings, valves, pin-hole leaks, all happen with regularity, and sometimes it's just installer error. Aside from what we can do wrong in the building process, there's our seemingly insatiable lust for bigger and more complicated systems of all types. This must have something to do with the need for a feeling of more power and control in our lives. The fact that you could potentially outsmart nature with a strong dose of electronics and engineering. I dunno. I know that I have witnessed systems grow with the logic of, "well if this works, wouldn't this work if we installed another valve here, and another pump here to do this?"

To be fair, solar thermal is much more reliable than it has ever been, and there are fewer troubled systems out there. I would like to think that this is the result of the "throttling back" of the industry, and the common realization that simpler is truly better when it comes to design. As for our plagued system here in Colorado, I suspect that it may have been installed by someone that was new to solar. My co-worker mentioned that she had heard that the glycol in the solar system was to be separated from the potable water supply by pressure alone. She also said that when it came out of the faucet, it was black, a sure sign that it had been burned by overheating at some point. That just ain't right. There are a lot of new faces entering this business everyday, some clearly with dubious technical know-how.

I am psyched that my first solar gig allowed me to see both the functional and the non-functioning, the useful and the useless in solar hot water. Though I appreciate the technology and desire my own system, I am now equally psyched not to be installing solar thermal at all.

Thanks for reading.