Learn about how to heat your water with solar power. These questions cover the basics of how solar thermal technology works, the costs and available rebates and the many other FAQ's. These questions were answered by Noah of Affinity Solar and Franz of Vaillent Solar.

1. 08/10/2011: Clean Energy Series
Solar Thermal (hot water) Workshop
Preliminary
1. What characteristics should a house have to be considered a good solar candidate?
A roof that is south facing is the ideal spot for solar. Other directions can work and in the case
with solar hot water (as opposed to electric) you do not need constant direct sun on the
system. Also, make sure the roof is in good condition and does not need to be replaced.
2. Are solar thermal and solar hot water heating the same thing?
Solar hot water refers to domestic hot water (shower, sink) and thermal is not only domestic
hot water, but space heating and pool heating also.
3. Does Sonoma County have the correct climate for solar thermal?
Yes. While Sonoma County may receive some morning fog or have rainy days the overall
sunny climate is suitable for solar hot water systems.
4. Even if some of my system is shaded, will the unshaded parts still work?
The system will still work. Unlike string electric systems, which go down if one panel is
shaded, solar hot water systems will still continue to heat your water; it just may not happen
as fast.
5. Should an energy assessment of the home be done before solar is installed?
It is always a good idea. While it is not required before installing a solar hot water system
there are rebates available through the Sonoma County Energy Independence Program which
cover 75% of a home assessment. www.sonomacountyenergy.org
6. Should the hot water pipes be insulated before a domestic solar water heating system is
installed?
Yes, insulation of pipes is important. If you do not have insulated pipes the temperature drop
from your water storage tank to the faucet will be greater. Insulation in this case is assisting
with heat transfer as opposed to the insulation you might have on your pipes outside to
prevent them from freezing.
Functionality
1. How does solar thermal work?
Energy is absorbed from the sun in collector panels located on your roof or ground. The
energy in the form of heat is then transferred to water that is stored in the system. There are
different types of solar hot water systems, which are installed depending on your usage,
climate and water quality. The collectors also differ as do ways in which you store the water.
Disclaimer: The information provided by the City of Santa Rosa and Solar Sonoma County through its Clean Energy Advocate program (CEA) is
limited to an unofficial overview of energy efficiency and solar upgrades, available rebates, incentives, and other related information. It does not
constitute professional advice or other professional financial guidance, and it should not be relied upon as such or used as the only source of
information when making purchasing decisions, investment decisions, tax decisions, or when executing other binding agreements. While the CEA
strives to provide the best information possible, the CEA makes no representations or warranties as to the accuracy of the information provided
or arising out of your use of the information provided by the CEA.

2. Flat plate collector panel (above)
Evacuated tube solar collector
2. Can solar hot water heating be used for pool heating, radiant heating systems and domestic
hot water heating?
Some panels can be used for all. The easiest heating is domestic hot water. An average system
will provide enough hot water for a family of 3-5.
1. What’s the difference between a direct and indirect water heating system?
Direct = Open-loop system, where you allow water to circulate through the system
Indirect = Closed-loop system, which is more common and allows for a heat transfer fluid
(glycol usually) to circulate to help transfer heat more effectively.
2. Should you have a back-up system to heat your domestic water supply?
Yes. Solar hot water is expected to cover 70-80% of your usage year round. To heat the
remaining 20% a backup system is needed. You can hook up your existing water heater to a
solar hot water system, with minimal additions to complete the install.
3. Is it better to have water filled tubes or heat transfer fluid filled tubes?
This is specific to your site and where you live. For example, if you have poor water quality
you would want a heat transfer fluid so that you do not have scale build up in your solar
tubes. Heat transfer fluid is also applicable if you live in an area with frequent freezing
temperatures.
4. Can a solar thermal system be ground mounted?
You can put a system on the ground, it usually requires additional work to lay pipes to and
from the house versus on the roof.
Disclaimer: The information provided by the City of Santa Rosa and Solar Sonoma County through its Clean Energy Advocate program (CEA) is
limited to an unofficial overview of energy efficiency and solar upgrades, available rebates, incentives, and other related information. It does not
constitute professional advice or other professional financial guidance, and it should not be relied upon as such or used as the only source of
information when making purchasing decisions, investment decisions, tax decisions, or when executing other binding agreements. While the CEA
strives to provide the best information possible, the CEA makes no representations or warranties as to the accuracy of the information provided
or arising out of your use of the information provided by the CEA.

3. 5. How long does it take to install a solar thermal system on the roof?
Two to five days is typical. The location of the system and if there is a need to re-plumb can
affect the time frame.
6. How reliable is solar hot water heating?
It is very reliable. The technology has been used for over 100 years. In the 70’s and 80’s there
was a big boom for solar hot water systems and many of those are still in operation today.
Maintenance is important to keep your system running however.
7. What is the life expectancy of the system?
All systems should have at least a 10 year warranty. Anything less than that will not qualify for
the PG&E rebate currently available. A 10 year warranty is recommended but systems are
lasting for 20-30+ years with proper maintenance.
8. Are some systems better than others?
There is a quality difference. In the case of solar hot water there are “solar fractions.” One
may show annual production at 50%, but a stronger model will show 80% which will be more
expensive but that is tied in with quality of the system.
Batch heater – These hot water systems are not as efficient but they are simpler in design and
therefore less expensive.
9. Will my contractor take care of permitting with the city for me?
Yes, your contractor should take care of this. Make sure to review the proposal from your
contractor to see if the permitting fees have been included. If they are not included this is
something you will want to ask your contractor about. If the contractor is uninformed about
permitting you may wish to get a second proposal to compare expertise and confidence in the
process and install. A permit is required for all solar hot water (and solar electric) systems.
Financing
1. How much does a system cost?
On average a system can cost between $4,000 to $9,000. Keep in mind PG&E offers a rebate
up to $1800 and there is a 30% federal tax credit available.
2. Are there tax credits or rebates available to help finance my project?
Yes. A federal tax credit (30% of the system) and PG&E offers a rebate up t o$1800.
3. Can you lease a solar hot water system?
In Sonoma County that option is not currently available.
After installation
1. What maintenance do solar hot water systems require once they’re installed?
Every 2-5 years you will need to replace your *glycol (heat transfer fluid) which should be
done by your installer because they have the proper tools and pumps. Your storage tank (just
Disclaimer: The information provided by the City of Santa Rosa and Solar Sonoma County through its Clean Energy Advocate program (CEA) is
limited to an unofficial overview of energy efficiency and solar upgrades, available rebates, incentives, and other related information. It does not
constitute professional advice or other professional financial guidance, and it should not be relied upon as such or used as the only source of
information when making purchasing decisions, investment decisions, tax decisions, or when executing other binding agreements. While the CEA
strives to provide the best information possible, the CEA makes no representations or warranties as to the accuracy of the information provided
or arising out of your use of the information provided by the CEA.

4. like a normal water heater) should also be drained, as well as checking the anode for
corrosion.
*Glycol is a non-toxic substance and is different from anti-freeze that is used in vehicles.
2. What if my water is hard, do maintenance concerns change?
It is recommended that you use an indirect/closed-loop system so there isn’t build up in your
pipes. The City of Santa Rosa has moderately hard water and is sufficient for solar hot water
systems.
3. What is the usual warranty for solar hot water systems?
10 years is standard for both workmanship and the hardware of the system.
Do-It-Yourself
1. Any tips for do it yourselfers?
While is it possible to build your own system and purchase the items wholesale, it is quite
complicated and not recommended. There are additional issues with plumbing and heat
exchangers which should be handled by a professional.
Disclaimer: The information provided by the City of Santa Rosa and Solar Sonoma County through its Clean Energy Advocate program (CEA) is
limited to an unofficial overview of energy efficiency and solar upgrades, available rebates, incentives, and other related information. It does not
constitute professional advice or other professional financial guidance, and it should not be relied upon as such or used as the only source of
information when making purchasing decisions, investment decisions, tax decisions, or when executing other binding agreements. While the CEA
strives to provide the best information possible, the CEA makes no representations or warranties as to the accuracy of the information provided
or arising out of your use of the information provided by the CEA.