Go Solar! Get Solar Hot Water from a Kit

The Sunward solar hot water kit is a proven system that takes most of the guess work out of setting up a solar water heater — and might even give you additional storage space!
By Bryan Welch and Dwight C. Purvis
December 2010/January 2011
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When finished, collectors for the solar hot water were mounted on a shed located away from the house.
PHOTO: BRYAN WELCH
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When the "Go Solar!" battle cry first went up decades ago, handy folks with a knack for plumbing and carpentry put their skills to work designing custom systems that fit their precise solar vision. That adventure — of creating and installing cutting-edge energy technology — remains a draw for some homeowners today. The rest of us would rather skip the adventure and opt for a proven system, such as the Sunward solar hot water kit that Country Home Products offers. With factory mounts and prefabricated components, this kit will allow you to enjoy long, hot, and solar-powered showers in just a few weeks — without the challenges of designing and building a system from scratch. If you’d like some expert help with installation, you can even hire a certified installer.

The solar collectors of the new Sunward system capture heat and transfer it to glycol-filled tubes. The glycol then circulates through a heat exchanger in the hot water storage tank. Some systems use water to carry heat from the collectors, but water would freeze in winter in some climates unless there were a mechanism to drain it each time the temperature fell below freezing. A glycol-based system can be used in a wider range of climates.

Country Home Products designed its Sunward system for versatile installation, too. Customers can choose to mount the collectors on the roof or on a ground-based frame. The roof-mounted frame lies flush with your roof, so you’ll need a south-facing slope, and your collectors will likely be a little less efficient than they would be on a ground-mounted frame (unless you have a steep roof ). The closer the angle of the roof matches the angle of the sun, the more effective the system will be.

If you want to mount your collectors in a frame, you have a choice between a weatherproof steel rack and a timber frame rack. We chose the timber frame option and enclosed it as a shed.

The first thing you’ll notice when the truck delivers your Sunward system is that it’s big. Packed on a wooden pallet about 9 feet long with a 4-foot-tall backstop, it can’t be safely unloaded in one piece. Pretty much everything you’ll need comes in the package, including the collectors, heat exchanger, mounting hardware, framing, connectors, and glycol. To protect the components, make sure to tell the delivery driver to disassemble the package and unload the components one at a time. Even with a pallet loader, the huge package is unwieldy. After it’s on the ground, you’re ready to start the installation.

How the Solar Hot Water System Works

The most complicated aspect of the system is probably circulating the hot glycol between your house and the collector. Like many solar hot water systems, Sunward’s system is designed to supplement your existing water heater, so the heat exchanger and the 80-gallon hot water tank that comes with the kit need to be located near your existing water heater and tied into the existing tank. If you’ve chosen a roof-mounted collector, this means you’ll need to run glycol lines to the tank through the roof and the house. If you go with the ground-mounted option, you’ll need to bury tubing from the collector to the storage tank inside your house. Because the lines contain only glycol, you can lay them in a relatively shallow trench without worrying that they’ll freeze. Just be careful next time you plant a tree!

The way this off-the-shelf system puts hot water in your pipes is simple, but it’s simple at the expense of efficiency. Sunward circulates water from its dedicated, 80-gallon tank through the heat exchanger. The tank Sunward provides is basically a water heater tank without energy hookups. In our experience, through spring and summer, the Sunward collectors kept 80 gallons of water piping hot. The dedicated Sunward tank is hooked into the existing water heater and refills it at the top of the tank with heated water when someone turns on a faucet. Your conventional heater will still use power to maintain its reservoir at the temperature you’ve set, even if you don’t use any hot water.

The basic system, including the timber-frame mounting kit, costs $7,650, but you can get a 30 percent federal tax credit, and your state may provide additional incentives (check the Database of State Incentives for Renewables & Efficiency for applicable state credits). Other mounting options (roof or steel rack) are less expensive. Sunward estimates that average homeowners can offset about 85 percent of their water-heating bills with solar hot water.

Annual savings and payback times will vary depending on numerous factors, such as local energy rates, family size, and the annual solar gain of the climate. We asked National Renewable Energy Laboratory engineer Jay Burch to help us with formulas to calculate best-case and worst-case examples. For sunny San Diego, where energy rates are high, we estimate you could save around $590 or more each year with this system if you’re currently using electricity to heat water. In Seattle, where both rates and sunshine levels are lower, the annual savings estimate is about $200.

Decisions and Revisions

A lot of people dislike the appearance of solar collectors on the roof of a home. In crowded or wooded areas, of course, homeowners may not have a better choice. On the prairie of eastern Kansas, where we live, it makes more sense to put the collectors on the ground — there’s plenty of room to put them behind the house and out of sight. It’s important to avoid positioning the collectors where they’ll be in the shade during part of the day.

In addition to holding the solar collectors, the timber frame rack serves as the frame for a multipurpose shed and doghouse. (The cost of enclosing the frame is not included in the package.) We debated whether to pour a concrete slab under it, but opted for a gravel footer instead, in case we ever want to move it. A shallow trench and a few yards of gravel later, we were ready to start building. The post-and-beam structure is easy to assemble.

As the frame went up, we realized that with a long, flat wall on one side and the long slope of the collectors on the other, the shed formed a pretty effective sail and would bear the brunt of our prairie winds. The cable-and-arrowhead anchors supplied in the kit didn’t inspire our confidence, especially considering the dubious clay ground we set the shed on.

Our soil expands and contracts dramatically, so the cables would have been slack all the time. We decided to drive 48-inch lengths of rebar through each corner of the sills. With the wind in mind, we thought the three collar ties in the kit might also be insufficient, so we added collar ties on each of the five roof beams.

The only real disappointment in the kit was the vinyl elbows and tubing designed to hide the glycol tubing between the collectors and the ground. The vinyl pieces didn’t fit well and looked clumsy. We hired a gutter contractor to bend a few pieces of metal spout that matched the bronze color of the collectors. They look nicer and should protect the tubing from the mower. The gutter guy also made end caps for the roof ridge, which looked a little crude straight out of the kit.

We wanted an insulated shed, so we added stud walls inside the timber frame. We sheathed the structure with cedar and painted it to match the house. When it was done, we were gratified by (and maybe a little surprised at) how cute it was!

The instructions for mounting the collectors are excellent, and the collectors are surprisingly easy to mount and plumb. However, because of their size and the angle of the roof, plan to have at least three people around to line up the collectors and mount them.

The theory and practice of installing the mixing valve and the anti-scald device are the most complicated and unusual facets of the system. We found a loose connection in the recirculation pump after we had filled the system with glycol. We realized the pump was so quiet that we wouldn’t have known about the loose connection if we hadn’t checked the signal lights on the heat exchanger that turn on when the pump is running.

The system went right to work as soon as we attached the photovoltaic panel that powers the circulating pump, but it took us a while to determine that it was working. Supply pipes between the solar tank and the original water heater come with thermometers. One shows the water temperature in the pipe from the solar water tank to the old water heater. The other shows the temperature of the water leaving the old water heater. We didn’t immediately understand whether the readings were influenced by water flowing through the pipes. When no hot water is being used, for example, the water in the pipes gradually approaches the temperature of the air. After we had figured out how the thermometers worked, we could see that we were drawing 140-degree-Fahrenheit water out of the solar system 12 hours after installation.

Sunward’s system is well-designed and quietly competent, but we’re curious just how much energy it will save over time. We’re considering meters to measure the comparative temperatures between the solar tank and our original water heater tank to check whether a circulating pump between the two tanks could save a lot more energy. Stay tuned.


Bryan Welch is the publisher and editorial director of MOTHER EARTH NEWS. He recruited his friend Dwight Purvis to help with this solar water project.

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Post a comment below.

 

Bryan
1/5/2011 2:43:57 PM
If the solar heat exchanger were connected to the main tank, then you would never use non-solar energy to keep the tank warm. As this simple system is configured, you only draw the solar-heated water into the main tank when you are utilizing hot water in the house. If you go very long without running hot water, your conventional tank uses conventional energy to keep that water warm. We turned down our thermostat, which worked while the solar hot water was more than sufficient for the house, but when the short, cloudy days of winter arrived we needed to turn up the hot-water thermostat, which resulted in some unnecessary propane consumption on sunny days when we're not home. If the main tank were hooked to the exchanger, that the solar system would be keeping the water supply warm.

Dave M.
1/5/2011 2:15:47 PM
One sentence in this article could use a little more explanation: "The way this off-the-shelf system puts hot water in your pipes is simple, but it’s simple at the expense of efficiency." I take this to mean that this thermosiphon dump from an external heat exchanger into the top of the tank is not efficient? What would be the hot setup (pun intended)? An internal heat exchanger or some kind of pressurized delivery system for the heated water? A little more clarification, please, Bryan.

Bryan
12/9/2010 2:53:01 PM
Yes, it would probably be more efficient to put it on the roof. We have a shake roof we didn't want to disturb, that's the long and short of it. So it went in the yard. - Bryan

Mark
12/2/2010 10:47:29 AM
I am interested in further exploration of the considerations that went into the author decision to go with an outbuilding mount rather than a roof mount on his house. While the lower pitch of a typical roof is somewhat less effective for winter water heating, it seems like heat losses in the pipe run from outbuilding to home would be much larger than the slight efficiency loss.

Farmerboy
11/28/2010 8:26:06 PM
I just finished reading the article. I think this system would be great coupled with a tankless water heater. It would be a little more expensive to start with but you would not use energy to heat the water stored in a standard tank type water heater. I have been a long time subscriber, and look forward to every issue, keep up the great work!

Connie Kenny
11/18/2010 5:21:55 AM
Here's another way to look at Renewable Energy vs Conventional Energy....You NEVER have a payback with conventional Energy, because if you don't pay the monthly bill (look at it like rent)for your heat, hot water, or electricity you will not recieve it. At least with renewable there will be a time when it WILL be paid back and you don't have to shell out that monthly expenditure.

Tam
11/17/2010 2:29:30 PM
I love the concept of ideas like this - but has anyone stopped to do the math on this? Depending on what your specific savings are, it would take anywhere from 13 to 38 years just to get your money back on this system. Until they find a less expensive way to do something like this, it certainly doesn't help the average person.








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