Frequently Asked Questions

Todd Hoitsma, owner of Liquid Solar answers some common questions below. He and his wife have a system at home and love it. With a 60-tube Apricus evacuated tube array and a 160-gallon storage tank they can turn off their on-demand backup water heater for months at a time. They also do limited space heating in their basement in the winter (October through April).

• Is there any difference between solar hot water and solar thermal?

  Same thing, different terms. Note that solar thermal should not be confused with electricity generated from photovoltaic (PV) panels.

• Is a solar thermal system the best way to reduce home energy consumption?

  Conservation always comes first. Before considering solar thermal, install low-flow faucets and showerheads (some actually are quite good!), insulate your water heater and pipes, and turn your water heater down to 120 degrees. Are you aware that Northwestern Energy customers can qualify for a free energy audit?

• Can I heat my house with solar thermal?

  Yes. We like to use these systems on well-insulated houses with radiant floors. See our discussion on space heating.

• How expensive is a solar thermal system?

  A fully-installed domestic hot water system for most homes averages $6,000 to $8,000 before tax credits (or $3,700 to $5,100 after credits). A larger system for space heating radiant floors typically starts at $8,000 to $15,000 before credits. Montana offers a $500 tax credit, while the federal credit is 30% of the total system cost. Costs are typically 20% lower for do-it-yourself-ers.

• What about payback?

  A solar thermal system generally assumes 7-12 years. Families with shower-loving teenagers see quicker payback than a frugal couple. We prefer to generate estimates using software on a case-by-case basis; those on propane or electric will see the quickest return on investment. Regardless, there are few home appliances that beat solar thermal's ability to recoup their cost and embodied energy over their lifetime.

• How does a solar thermal system work?

  As simply as I can put it, a solar thermal system either partially or fully pre-heats incoming city or well water before it gets to your water heater. A small pump circulates heated fluid from the collectors to the solar storage tank.

• What are better —evacuated tubes or flat-panel collectors?

  We use both types - it depends on the application, the roof layout, and personal aesthetics. But I generally prefer US-manufactured flat panel collectors. We have done a lot of testing and exhaustive data logging during extreme temps (I could bore most people with the details). In a March 2008 side-by-side test in Bozeman we found that flat panels outperformed evacuated tubes by 15%.

• What kind of maintenance do these systems need?

  It is good to check the gauges for pressure from time to time. A well-designed system should need very little maintenance. It is good to test the heat transfer fluid every 3-5 years.

• Do they work on cloudy days?

  There is some misleading information out there; even the best solar thermal system will not be able to capture any significant solar energy on the cloudiest days. Therefore, backup heating systems are needed.

• Do solar thermal systems work well with an on demand water heater?

  Perfectly. Both gas and electric units modulate. That means they heat incoming solar pre-heated water only as much as needed. Plus, they do not keep gallons of water at 130 degrees 24/7 like a tank water heater. We also install on-demand water heaters.

• Can I put a system on my existing house?

  Yes. Some houses allow for a much easier install than others. Factors that affect the difficulty of install include distance from roof to the backup water source, and the routing for copper supply lines. There also needs to be space for a storage tank.

• What if we have no good southern roof top exposure?

  Consider either a ground or wall-mounted collectors.

• Is it possible to use a photovoltaic-powered pump?

  Yes. We have one at home and they are pretty slick. Small and very efficient, DC-powered pumps work well with thermal systems because when there is enough sun on the small PV panel to fire up the solar pump, there is also enough sun to generate hot water.

• What is the biggest resistance to going solar?

  I think its the fact that we think about energy costs on a month-to-month basis. If we looked at energy costs over the long haul (duration of our mortgage?) nearly everyone would want solar.