Home & Garden Columns

About the House: The Benefits of Solar Water Heating

By Matt Cantor
Friday December 22, 2006

The practice of home inspection is tied, to a surprising degree, to a study of history. Some of that history is ancient and broad and some of it is as diaphanous as the study of the last five presidencies. 

When I first started inspecting houses in the late 1980s, one of the things I frequently saw was the tired and, more often, dead vestige of a solar heating system. Not the kind of systems that you’re seeing so many of today which generate electricity but systems that heat water. 

Jimmy Carter remains one of my favorite U.S. presidents and I’m glad I was here to see him do his thing. Jimmy was the real deal. Less politician and more futurist. He’s still one of the few sane voices for true democracy (through a good cleansing of the electoral process) in the world today. In 1979 Jimmy sponsored and enacted a 40 percent federal tax rebate as an inducement to get Americans to buy solar water heating systems. Prior to this, the industry just hobbled along on innovation and the good will of a very small number of adventurous folks. 

Before I get into much more of the history of solar water heating, let me explain a little about what solar water heating is. 

Heating water using the sun’s energy is pretty much a no-brainer. It’s happening around us all the time. When the sun hits the ocean each day, it elevates the water temperature several degrees. The same happens with a pool or any body of water exposed to the sun. It seems natural to try to harness this effect, especially when we spend as much money as we do on domestic hot water (the hot water we shower or wash dishes with).  

Although there are a range of configurations for performing this task, all systems involve some type of solar collector as well as some form of storage. All the way back in the 1890s Clarence Kemp produced the first commercially manufactured solar water heater, dubbed the Climax. In 1897, 30 percent of the homes in Pasadena heated water using solar water heaters. 

These and most subsequent heaters employed large numbers of fine tubes (the early ones were nearly all copper) laid out in the sun and arranged so that water would flow through a very long thin passageway during which it would be heated up. Some of these were inside of boxes that helped to retain the heat. A combination of silvery or white surfaces for reflecting heat and black or dark covers helped to increase the temperature. That last part is an important passive heating concept and important in understanding many aspects of what one might dub “the secret life of houses.”  

Dark things not only get hotter, they also expand more than light colored materials exposed to the sun and thus move around more. Dark materials also wear out faster.  

In the case of the solar panel, black is the magic color since a black solar panel will heat water much faster than a white one. At least one popular panel is made of black butylene formed from two sheets into a labyrinth of tubules. Again, as water travels from one end to the other, water is raised to a high temperature. In addition to panels formed from great lengths of tubing, panels can also have shorter pipes that are heated to much higher temperatures using parabolic mirrors. One panel type has a short fat tank inside with a parabola built around it. The tank gets extremely hot and water can be heated inside the vessel very quickly.  

Once you have hot water, you need to store it and keep it hot, especially for night-time so the other critical component of a system like this is a well insulated tank. These tanks are often confused with water heaters since they tend to be pretty much the same size and shape and are connected to the water piping in the house. In systems I’ve inspected (almost all left over from the Carter administration), these are nearly always standing side by side with a gas water heater designed to heat water when the solar water heating system has gone cold. The smart systems have a small controller and an motor-driven valve that automatically switches back and forth between the gas and solar systems. The gas system runs at night after the solar tank has cooled below a reasonable bathing temperature and the solar runs during sunny days and as long as the heat holds out in the tank. 

Solar credits are back today and systems as I’ve just described can generate a federal tax credit of up to $2, 000 (or 30 percent of the installed cost) The government requires that at least half of the hot water demands of the house be provided for by the solar heating system in order to receive the credit. Payback for a system like this looks similar to photovoltaic system with about 8-10 years for a return on your investment (and free hotness thereafter) but it seems likely that a rise in energy costs (and hopefully, improved tax credits under future executive branch leadership) will bring these payback durations down somewhat. 

For years, the only systems I saw were ones with rusted out tanks and disconnected solar panels on the roof. The Regan administration killed the tax credit as soon as they took office and when the installation industry died, the service end died too. When the last installer has fled into plumbing or siding installation, there was no one left to keep these working for Dr. and Mrs. Jones and all that remained when I arrived was another system that had been completely disconnected and put back on the gas heater full time. 

This is definitely about global warming. I can’t think of a single alternative technology that has a deeper advantage over fuel burning than the heating of water. It’s a natural.  

If you’re looking at ways you can help the planet while upgrading your home, do yourself and your planet a favor by talking to your contractor about this most elegant of energy (and money) saving techniques. 



Got a question about home repairs and inspections? Send them to Matt Cantor at mgcantor@pacbell.net.