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Solar Hot Water

Building and Site Assessment

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Answering these questions will help you determine if a solar hot water system will work for your building or site.

1. Do you have a south-facing roof?

Because Montana and Wyoming are in the northern hemisphere, solar hot water collectors need to face south for maximum performance. This placement allows collectors to take full advantage of the sun’s path in the sky. The sun shines longest on a building’s south side. A slightly southeast or southwest placement will not result in significant loss in system performance.

Yes! — Move to Question #2
No — A solar hot water system may not work well. You can add a south-facing roof extension or other structure if it can safely support collectors. Collectors can be mounted on a wall or the ground, but consider possible shading, snow drifts, lawn care, and vandalism. Collectors can be mounted on east- or west-facing roofs to face south, but they stick-up, are highly visible, and can be viewed as unattractive. Architects and builders can address this by designing “solar ready” buildings and integrating solar technology components
into the design.

2. Does your roof have enough space for collectors?

For a residential system, the rule of thumb is that 20 square feet of collector roof/surface area is needed per person for the first two people in a household. Add 12-14 square feet of collector area for each additional hot water user.

Yes! — Move to Question #3
No — If your roof is not large enough for the collectors, consider a smaller system, extending your roof, or mounting collectors on a wall or the ground.

3. Is your roof unshaded?

Solar hot water systems are most efficient when collectors receive direct sun and are not shaded. Thus, consider possible shading from nearby buildings and the mature height of landscape plants such as trees.

Yes! — Move to Question #4
No — If the shade is from landscaping, consider removing the plants. If a structure is to be built that will shade any solar system you are considering, check local and state codes to see if you have “solar access” rights. Refer to Step 6‘s Pre-Installation Considerations section. www.solarworks.co.uk

4. What’s the angle of your roof?

If possible, use your latitude (46° for Helena, Mont.; 41° for Cheyenne, Wyo.) as the collector tilt angle to maximize the annual sun energy collected. Collectors can be installed at various angles depending on your hot water needs. Installers can mount collectors directly (flush) on an existing roof or tilt at an angle that sheds snow easier or that produces more hot water in a particular season.

Flat Roofs

Collectors can be angled on flat roofs, but should not be placed flat (horizontal) because they will not receive enough sun (especially in winter) to make installation cost-effective. Plus, snow will not slide off and will block the sun making the building more dependent on the back-up system that is typically powered by natural gas, electricity, or propane.

5. Is your roof in good condition?

Most roofs can safely support collector weight (about 160 pounds for two residential scale collectors). While innovative roof flashing can make collector removal easy, it’s less expensive and less labor intensive to make roof repairs before collectors are installed.

Yes! — Move to What’s Next
No — If your roof needs to be replaced or repaired, complete that first and make sure it can handle the collectors’ weight. If considering a new roof, contact a solar hot water company for roof recommendations that might make system installation easier or less expensive.

What’s Next?

If you answered yes to every question or can make adjustments where you answered no, your building or site may be a good solar hot water system candidate. A system supplier or installer can provide a detailed assessment. Next, consider how conservation and efficiency measures can result in a more efficient and affordable system; then, learn about
systems that work well in Montana and Wyoming.