Concealed Solar Hot Water

July 4, 2007

Image Credit: Dawn Solar

Solar hot water systems should be in use everywhere in the country. They are not terribly expensive to install, and the payback period on them is much shorter than it is for solar photovoltaic. Even in cold climates, it is possible to have a system with a heat exchanger and an antifreeze filled loop, so that the system can be run, even when nighttime temperatures are below freezing.

But the appearance of rooftop mounted panels is a drawback. Lots of people find solar panels, whether they are hot water or photovoltaic, to be unattractive. While it looses some efficiency by being out of direct sunlight, Dawn Solar offers a concealed solar hot water system. "The Dawn Solar System uses heat generated by the sun shining directly onto a roof. Solar energy is absorbed and transferred into a concealed, patent-pending collection system that is hidden just below the roof tiles. There is no ugly collector that is visible from the street."

The website offers few details about the configuration of the system, but presumably it uses some kind of pipe or tubing running just under the roof to collect heat from the attic space in the water for use in the building. The case study they offer is a distillery in New Hampshire (pictured) with the tubing running under the metal roof of the building. This is tied in with their other building systems and contributes to the radiant floor heating and the domestic hot water for the building.

The same week I came across this system, I also got an e-mail that included a suggestion of a similar system that someone had installed as a DIY project in his own attic.

Homeless Dave, who invented the Pedal Powered Washing Machine, is also a blogger who conducts interviews with a range of people on a teeter totter in his back yard. Most of the interviews are of local interest to Ann Arbor, though he has also hosted a former US president. A recent interview with the central power plant manager for the University of Michigan brought up some discussion of a couple of DIY projects that he had installed in his home, including one that struck me as being very similar to the Dawn Solar system. Homeless Dave sent me an e-mail about the interview and suggested it as material for possible DIY articles. There isn't enough information in their discussion to make a useful DIY article on its own, but if you are really inclined towards doing a DIY installation of this type, I think you may find some inspiration from this.

A few things occurred to me as a result of this that would make a DIY installation easier. For one, Wickboldt's system uses PVC pipe. While this can be installed fairly easily, there are joints that have to glued and pipe that has to be cut to do this. However, PEX tubing, which is also used in underfloor and in-slab radiant heating, is a continuous length of tubing, which could be pulled into the attic much like electrical wire and then threaded back and forth through the rafter spaces, much like the system described. Small diameter PEX would also have more surface area to diameter, so that it would potentially heat the water faster than the PVC version. There are also clips for installing underfloor radiant heating systems that would be equally appropriate for this application. And, again like an underfloor radiant system, efficiency of the system might be further improved by adding radiant foil insulation (as well as helping keep the attic cooler).

Let me know if you undertake a system like this. I'm interested in other examples of this and seeing how viable a possibility this would be for direct heating or even just pre-heating water for household use. This seems like a very viable possibility, and I'm interested in gathering more information to help make this a more useful system that more people can install and use in their own homes.