A Summary of Solar Water Heaters
Collected and prepared by: B Wu – Feb 2010
The following section is mainly based on the DOE’s website at:
http://www.energysavers.gov/your_home/water_heating/index.cfm?mytopic=12850
Solar Water Heater System
Solar water heaters—also called solar domestic hot water systems—can be a cost-effective way
to generate hot water for your home. They can be used in any climate, and the fuel they use—
sunshine—is free.
How They Work
Solar water heating systems include storage tanks and solar collectors. There are two types of
solar water heating systems: active, which have circulating pumps and controls, and passive,
which don't.
Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an
additional outlet and inlet connected to and from the collector. In two-tank systems, the solar
water heater preheats water before it enters the conventional water heater. In one-tank
systems, the back-up heater is combined with the solar storage in one tank.
Three types of solar collectors are used for residential applications:

Flat-plate collector
Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark
absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate
collectors—typically used for solar pool heating—have a dark absorber plate, made of
metal or polymer, without a cover or enclosure.

Integral collector-storage systems
Also known as ICS or batch systems, they feature one or more black tanks or tubes in an
insulated, glazed box. Cold water first passes through the solar collector, which preheats
the water. The water then continues on to the conventional backup water heater,
providing a reliable source of hot water. They should be installed only in mild-freeze
climates because the outdoor pipes could freeze in severe, cold weather.

Evacuated-tube solar collectors
They feature parallel rows of transparent glass tubes. Each tube contains a glass outer
tube and metal absorber tube attached to a fin. The fin's coating absorbs solar energy
but inhibits radioactive heat loss. These collectors are used more frequently for U.S.
commercial applications.
There are two types of active solar water heating systems:

Direct circulation systems
Pumps circulate household water through the collectors and into the home. They work
well in climates where it rarely freezes.

Indirect circulation systems
Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat
exchanger. This heats the water that then flows into the home. They are popular in
climates prone to freezing temperatures.
Passive solar water heating systems are typically less expensive than active systems, but they're
usually not as efficient. However, passive systems can be more reliable and may last longer.
There are two basic types of passive systems:

Integral collector-storage passive systems
These work best in areas where temperatures rarely fall below freezing. They also work
well in households with significant daytime and evening hot-water needs.

Thermo-siphon systems
Water flows through the system when warm water rises as cooler water sinks. The
collector must be installed below the storage tank so that warm water will rise into the
tank. These systems are reliable, but contractors must pay careful attention to the roof
design because of the heavy storage tank. They are usually more expensive than integral
collector-storage passive systems.
Solar water heating systems almost always require a backup system for cloudy days and times of
increased demand. Conventional storage water heaters usually provide backup and may already
be part of the solar system package. A backup system may also be part of the solar collector,
such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system
already stores hot water in addition to collecting solar heat, it may be packaged with a demand
(tank-less or instantaneous) water heater for backup.
For more information about solar water heating system components, see the following
information:


Heat Exchangers for Solar Water Heating Systems
Heat-Transfer Fluids for Solar Water Heating Systems
Selecting a Solar Water Heater
Before you purchase and install a solar water heating system, you want to do the following:



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
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Consider the economics of a solar water heating system
Evaluate your site's solar resource
Determine the correct system size
Determine the system's energy efficiency
Estimate and compare system costs
Investigate local codes, covenants, and regulations.
For information about specific solar water heater models and systems, see the Product
Information resources listed on the right side of this page (or below if you've printed the page).
Installing and Maintaining the System
The proper installation of solar water heaters depends on many factors. These factors include
solar resource, climate, local building code requirements, and safety issues; therefore, it's best
to have a qualified, solar thermal systems contractor install your system.
After installation, properly maintaining your system will keep it running smoothly. Passive
systems don't require much maintenance. For active systems, discuss the maintenance
requirements with your system provider, and consult the system's owner's manual. Plumbing
and other conventional water heating components require the same maintenance as
conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn't
provide a natural rinse.
Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by
a solar contractor. Systems with electrical components usually require a replacement part after
or two after 10 years. For more information about system maintenance, see the following:
 Solar Water Heating System Maintenance and Repair
 Solar Water Heating System Freeze Protection
 Scaling and Corrosion in Solar Water Heating Systems
When screening potential contractors for installation and/or maintenance, ask the following
questions:
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
Does your company have experience installing and maintaining solar water heating
systems?
Choose a company that has experience installing the type of system you want and
servicing the applications you select.
How many years of experience does your company have with solar heating installation
and maintenance?
The more experience the better. Request a list of past customers who can provide
references.
Is your company licensed or certified?
Having a valid plumber's and/or solar contractor's license is required in some states.
Contact your city and county for more information. Confirm licensing with your state's
contractor licensing board. The licensing board can also tell you about any complaints
against state-licensed contractors.
For contractor information, see the Professional Services resources listed on the right side of this
page (or below if you've printed it out).
Improving Energy Efficiency
After your water heater is properly installed and maintained, try some additional energy-saving
strategies to help lower your water heating bills, especially if you require a back-up system.
Some energy-saving devices and systems are more cost-effective to install with the water
heater.
Heat Exchangers for Solar Water Heating Systems
Solar water heating systems use heat exchangers to transfer solar energy absorbed in solar
collectors to the liquid or air used to heat water or a space.
Heat exchangers can be made of steel, copper, bronze, stainless steel, aluminum, or cast iron.
Solar heating systems usually use copper, because it is a good thermal conductor and has
greater resistance to corrosion.
Types of Heat Exchangers
Solar water heating systems use three types of heat exchangers:

Liquid-to-liquid
This heat exchanger uses a heat-transfer fluid that circulates through the solar collector,
absorbs heat, and then flows through a heat exchanger to transfer its heat to water in a
storage tank. Heat-transfer fluids, such as antifreeze, protect the solar collector from
freezing in cold weather. Liquid-to-liquid heat exchangers have either one or two barriers
(single wall or double wall) between the heat-transfer fluid and the domestic water
supply.
A single-wall heat exchanger is a pipe or tube surrounded by a fluid. Either the fluid
passing through the tubing or the fluid surrounding the tubing can be the heat-transfer
fluid, while the other fluid is the potable water. Double-wall heat exchangers have two
walls between the two fluids. Two walls are often used when the heat-transfer fluid is
toxic, such as ethylene glycol (antifreeze). Double walls are often required as a safety
measure in case of leaks, helping ensure that the antifreeze does not mix with the
potable water supply. An example of a double-wall, liquid-to-liquid heat exchanger is the
"wrap-around heat exchanger," in which a tube is wrapped around and bonded to the
outside of a hot water tank. The tube must be adequately insulated to reduce heat losses.
While double-wall heat exchangers increase safety, they are less efficient because heat
must transfer through two surfaces rather than one. To transfer the same amount of
heat, a double-wall heat exchanger must be larger than a single-wall exchanger.

Air-to-liquid
Solar heating systems with air heater collectors usually do not need a heat exchanger
between the solar collector and the air distribution system. Those systems with air heater
collectors that heat water use air-to-liquid heat exchangers, which are similar to liquidto-air heat exchangers.
Heat Exchanger Designs
There are many heat exchanger designs. Here are some common ones:

Coil-in-tank
The heat exchanger is a coil of tubing in the storage tank. It can be a single tube (singlewall heat exchanger) or the thickness of two tubes (double-wall heat exchanger). A less
efficient alternative is to place the coil on the outside of the collector tank with a cover of
insulation.

Shell-and-tube
The heat exchanger is separate from (external to) the storage tank. It has two separate
fluid loops inside a case or shell. The fluids flow in opposite directions to each other
through the heat exchanger, maximizing heat transfer. In one loop, the fluid to be heated
(such as potable water) circulates through the inner tubes. In the second loop, the heattransfer fluid flows between the shell and the tubes of water. The tubes and shell should
be made of the same material. When the collector or heat-transfer fluid is toxic, doublewall tubes are used, and a non-toxic intermediary transfer fluid is placed between the
outer and inner walls of the tubes.

Tube-in-tube
In this very efficient design, the tubes of water and the heat-transfer fluid are in direct
thermal contact with each other. The water and the heat-transfer fluid flow in opposite
directions to each other. This type of heat exchanger has two loops similar to those
described in the shell-and-tube heat exchanger.
Sizing
A heat exchanger must be sized correctly to be effective. There are many factors to consider for
proper sizing, including the following:
 Type of heat exchanger
 Characteristics of the heat-transfer fluid (specific heat, viscosity, and density)
 Flow rate
 Inlet and outlet temperatures for each fluid.
Usually, manufacturers will supply heat transfer ratings for their heat exchangers (in Btu/hour)
for various fluid temperatures and flow rates. Also, the size of a heat exchanger's surface area
affects its speed and efficiency: a large surface area transfers heat faster and more efficiently.
Installation
For the best performance, always follow the manufacturer's installation recommendations for the
heat exchanger. Be sure to choose a heat-transfer fluid that is compatible with the type of heat
exchanger you will be using. If you want to build your own heat exchanger, be aware that using
different metals in heat exchanger construction may cause corrosion. Also, because dissimilar
metals have different thermal expansion and contraction characteristics, leaks or cracks may
develop. Either of these conditions may reduce the life span of your heat exchanger.
Heat-Transfer Fluids for Solar Water Heating Systems
Heat-transfer fluids carry heat through solar collectors and a heat exchanger to the heat storage
tanks in solar water heating systems. When selecting a heat-transfer fluid, you and your solar
heating contractor should consider the following criteria:

Coefficient of expansion – the fractional change in length (or sometimes in volume, when
specified) of a material for a unit change in temperature
 Viscosity – resistance of a liquid to sheer forces (and hence to flow)
 Thermal capacity – the ability of matter to store heat
 Freezing point – the temperature below which a liquid turns into a solid
 Boiling point – the temperature at which a liquid boils
 Flash point – the lowest temperature at which the vapor above a liquid can be ignited in
air.
For example, in a cold climate, solar water heating systems require fluids with low freezing
points. Fluids exposed to high temperatures, as in a desert climate, should have a high boiling
point. Viscosity and thermal capacity determine the amount of pumping energy required. A fluid
with low viscosity and high specific heat is easier to pump, because it is less resistant to flow and
transfers more heat. Other properties that help determine the effectiveness of a fluid are its
corrosiveness and stability.
Types of Heat-Transfer Fluids
The following are some of the most commonly used heat-transfer fluids and their properties:

Air
Air will not freeze or boil, and is non-corrosive. However, it has a very low heat capacity,
and tends to leak out of collectors, ducts, and dampers.

Water
Water is nontoxic and inexpensive. With a high specific heat, and a very low viscosity, it's
easy to pump. Unfortunately, water has a relatively low boiling point and a high freezing
point. It can also be corrosive if the pH (acidity/alkalinity level) is not maintained at a
neutral level. Water with a high mineral content (i.e., "hard" water) can cause mineral
deposits to form in collector tubing and system plumbing.

Glycol/water mixtures
Glycol/water mixtures have a 50/50 or 60/40 glycol-to-water ratio. Ethylene and
propylene glycol are "antifreezes." Ethylene glycol is extremely toxic and should only be
used in a double-walled, closed-loop system. You can use food-grade propylene
glycol/water mixtures in a single-walled heat exchanger, as long as the mixture has been
certified as nontoxic. Make sure that no toxic dyes or inhibitors have been added to it.
Most glycols deteriorate at very high temperatures. You must check the pH value,
freezing point, and concentration of inhibitors annually to determine whether the mixture
needs any adjustments or replacements to maintain its stability and effectiveness.

Hydrocarbon oils
Hydrocarbon oils have a higher viscosity and lower specific heat than water. They require
more energy to pump. These oils are relatively inexpensive and have a low freezing
point. The basic categories of hydrocarbon oils are synthetic hydrocarbons, paraffin
hydrocarbons, and aromatic refined mineral oils. Synthetic hydrocarbons are relatively
nontoxic and require little maintenance. Paraffin hydrocarbons have a wider temperature
range between freezing and boiling points than water, but they are toxic and require a
double-walled, closed-loop heat exchanger. Aromatic oils are the least viscous of the
hydrocarbon oils.

Refrigerants/phase change fluids
These are commonly used as the heat transfer fluid in refrigerators, air conditioners, and
heat pumps. They generally have a low boiling point and a high heat capacity. This
enables a small amount of the refrigerant to transfer a large amount of heat very
efficiently. Refrigerants respond quickly to solar heat, making them more effective on
cloudy days than other transfer fluids. Heat absorption occurs when the refrigerant boils
(changes phase from liquid to gas) in the solar collector. Release of the collected heat
takes place when the now-gaseous refrigerant condenses to a liquid again in a heat
exchanger or condenser.
For years chlorofluorocarbon (CFC) refrigerants, such as Freon, were the primary fluids
used by refrigerator, air-conditioner, and heat pump manufacturers because they are
nonflammable, low in toxicity, stable, noncorrosive, and do not freeze. However, due the
negative effect that CFCs have on the earth's ozone layer, CFC production is being
phased out, as is the production of hydrochlorofluorocarbons (HCFC). The few companies
that produced refrigerant-charged solar systems have either stopped manufacturing the
systems entirely, or are currently seeking alternative refrigerants. Some companies have
investigated methyl alcohol as a replacement for refrigerants.
If you currently own a refrigerant-charged solar system and it needs servicing, you
should contact your local solar or refrigeration service professional. Since July 1, 1992,
intentional venting of CFCs and HCFCs during service and maintenance or disposal of the
equipment containing these compounds is illegal and punishable by stiff fines. Although
production of CFCs ceased in the U.S. 1996, a licensed refrigeration technician can still
service your system. You may wish to contact your service professional to discuss the
possible replacement of the CFC refrigerant with methyl alcohol or some other heat
transfer fluid.
Ammonia can also be used as a refrigerant. It's commonly used in industrial applications.
Due to safety considerations it's not used in residential systems. The refrigerants can be
aqueous ammonia or a calcium chloride ammonia mixture.

Silicones
Silicones have a very low freezing point, and a very high boiling point. They are
noncorrosive and long-lasting. Because silicones have a high viscosity and low heat
capacities, they require more energy to pump. Silicones also leak easily, even through
microscopic holes in a solar loop.
The Economics of a Solar Water Heater
Solar water heating systems usually cost more to purchase and install than conventional water
heating systems. However, a solar water heater can usually save you money in the long run.
How much money you save depends on the following:
 The amount of hot water you use
 Your system's performance
 Your geographic location and solar resource
 Available financing and incentives
 The cost of conventional fuels (natural gas, oil, and electricity)
 The cost of the fuel you use for your backup water heating system, if you have one.
On average, if you install a solar water heater, your water heating bills should drop 50%–80%.
Also, because the sun is free, you're protected from future fuel shortages and price hikes.
If you're building a new home or refinancing, the economics are even more attractive. Including
the price of a solar water heater in a new 30-year mortgage usually amounts to between $13
and $20 per month. The federal income tax deduction for mortgage interest attributable to the
solar system reduces that by about $3–$5 per month. So if your fuel savings are more than $15
per month, the solar investment is profitable immediately. On a monthly basis, you're saving
more than you're paying.
Estimating a Solar Water Heater System's Cost
Before purchasing a solar water heating system, you can estimate its annual operating cost and
compare it with other more and/or less efficient systems. This will help you determine the energy
savings and payback period of investing in a more energy-efficient system, which will probably
have a higher purchase price.
Before you can choose and compare the costs of various systems, you need to know the system
size required for your home.
Calculating Annual Operating Cost
To estimate the annual operating cost of a solar water heating system, you need the following:
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
The system's solar energy factor (SEF)
The auxiliary tank fuel type (gas or electric) and costs (your local utility can provide
current rates).
Then, use the following calculations.
With a gas auxiliary tank system:
You need to know the unit cost of fuel by Btu (British thermal unit) or therm. (1 therm =
100,000 Btu)
365 × 41,045/SEF × Fuel Cost (Btu) = estimated annual cost of operation
OR
365 × 0.4105/SEF × Fuel Cost (therm) = estimated annual operating cost
Example: Assuming the SEF is 1.1 and the gas costs $1.10/therm
365 × 0.4105/1.1 × $1.10 = $149.83
With an electric auxiliary tank system:
You need to know or convert the unit cost of electricity by kilowatt-hour (kWh).
365 × 12.03/SEF × Electricity Cost (kWh)= estimated annual operating cost
Example: Assuming the SEF is 2.0 and the electricity costs $0.08/kWh
365 X 12.03/2.0 X $0.08 = $175.64
Comparing Costs and Determining Payback
Once you know the purchase and annual operating costs of the solar water heating systems you
want to compare, you can find the costs associated with conventional water heating systems and
compare the two.
Use the table and calculations below to compare two solar water heating systems and determine
the cost savings and payback of the more energy-efficient system model.
System Models
System
Price
SEF
Estimated Annual Operating Cost
System Model A
System Model B (higher SEF)
Additional cost of more
efficient system model
(Model B)
Price of System Model B - Price of System Model A =
$Additional Cost of Model B
Estimated annual operating
cost savings (System Model
B)
System Model B Annual Operating Cost - System Model
A Annual Operating Cost = $Model B's Cost Savings
Per Year
Payback period for Model B
$Additional Cost of Model B/$Model B's Cost Savings
Per Year = Payback period/years
Example:
Comparison of two solar water heating system models with electric backup systems and
electricity costs of $0.08/kWh.
System
Price
SEF
Estimated Annual Operating
Cost
System Model A
$1,060
2.0
$176
System Model B
$1,145
2.9
$121
System Models
Additional cost of more efficient model
(Model B)
Estimated annual operating cost savings
(Model B)
$1,145-$1,060 = $85
$176-$120 = $56 per year
Payback period for Model B
$85/$56 per year = 1.5 years
Other Costs
When comparing solar water heating systems, you should also consider installation and
maintenance costs. Some systems might cost more to install and maintain.
Consult the manufacturer(s) and a qualified contractor to help estimate these costs. These costs
will vary among system types and sometimes even from model to model.
Solar Swimming Pool Heaters
You can significantly reduce swimming pool heating costs by installing a solar pool heater.
They're cost competitive with both gas and heat pump pool heaters, and they have very low
annual operating costs. Actually, solar pool heating is the most cost-effective use of solar energy
in many climates.
How They Work
Most solar pool heating systems include the following:

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A solar collector — the device through which pool water is circulated to be heated by the
sun
A filter — removes debris before water is pumped through the collector
A pump — circulates water through the filter and collector and back to the pool
A flow control valve — automatic or manual device that diverts pool water through the
solar collector.
Example of a solar pool heating system.
Pool water is pumped through the filter and then through the solar collector(s), where it is
heated before it is returned to the pool. In hot climates, the collector(s) can also be used to cool
the pool during peak summer months by circulating the water through the collector(s) at night.
Some systems include sensors and an automatic or manual valve to divert water through the
collector(s) when the collector temperature is sufficiently greater than the pool temperature.
When the collector temperature is similar to the pool temperature, filtered water simply bypasses
the collector(s) and is returned to the pool.
Solar pool collectors are made out of different materials. The type you'll need depends on your
climate and how you intend to use the collector. If you'll only be using your pool when
temperatures are above freezing, then you'll probably only need an unglazed collector system.
Unglazed collectors don't include a glass covering (glazing). They are generally made of heavyduty rubber or plastic treated with an ultraviolet (UV) light inhibitor to extend the life of the
panels. Because of their inexpensive parts and simple design, unglazed collectors are usually less
expensive than glazed collectors. These unglazed systems can even work for indoor pools in cold
climates if the system is designed to drain back to the pool when not in use. Even if you have to
shut the system down during cold weather, unglazed collectors may be more cost effective than
installing a more expensive glazed collector system.
Example of how a solar collector works.
Glazed collector systems are generally made of copper tubing on an aluminum plate with an
iron-tempered glass covering, which increases their cost. In colder weather, glazed collector
systems—with heat exchangers and transfer fluids—capture solar heat more efficiently than
unglazed systems. Therefore, they can be used year-round in many climates. Glazed collectors
also can be used to heat domestic hot water year-round.
Both glazed and unglazed collector systems should include freeze protection if they'll be used in
colder conditions.
Selecting a Solar Pool Heater
A solar pool heating system usually costs between $3,000 and $4,000 to buy and install. This
provides a payback of between 1.5 and 7 years, depending on your local fuel costs. They also
typically last longer than gas and heat pump pool heaters. Your actual cost and payback depend
on many factors. Therefore, before you purchase and install a solar pool heating system, you
should do the following:




Evaluate your site's solar resource
Determine the correct system size
Determine the system's efficiency
Compare system costs

Investigate local codes, covenants, and regulations.
Installation and Maintenance
The proper installation of a solar pool heating system depends on many factors. These factors
include solar resource, climate, local building code requirements, and safety issues. Therefore,
it's best to have a qualified solar thermal systems contractor install your system.
After installation, properly maintaining your system will keep it running smoothly for 10–20
years. Consult your contractor and read your owner's manual for maintenance requirements.
Your collector should require little maintenance if the pool's chemical balance and filtering
system are checked regularly. Glazed collectors may need to be cleaned in dry climates where
rainwater doesn't provide a natural rinse.
When screening potential contractors for installation and/or maintenance, ask the following
questions:

Does your company have experience installing and maintaining solar pool
heating systems?
Choose a company that has experience installing the type of system you want and
servicing the applications you select.

How many years of experience does your company have with solar heating
installation and maintenance?
The more experience the better. Request a list of past customers who can provide
references.

Is your company licensed or certified?
Having a valid plumber's and/or solar contractor's license is required in some states.
Contact your city and county for more information. Confirm licensing with your state's
contractor licensing board. The licensing board can also tell you about any complaints
against state-licensed contractors.
Comparing Solar Swimming Pool Heating System Costs
Solar pool heaters represent one of the most cost-effective uses of solar energy today.
Photo credit: Heliocol.
Before purchasing a solar pool heating system, you can estimate and compare the costs of using
different solar collector models. This will help you determine the potential cost savings of
investing in a more efficient type of collector, which may require fewer panels for the collector
area needed to heat your pool.
To estimate and compare costs, you need to know the following:
 A collector's thermal performance rating (Btu/day)
 Total number of collector panels or piping for the area needed to heat your pool
 Total installed cost of system.
You can then calculate a collector's energy output per dollar spent or invested using this formula:
(Btu/day X # of collector panels/piping modules) ÷ total installed cost of system = Btu/$ per
dollar spent
Example:
(27,900 X 4) Btu ÷ $3,000 = 37.20 Btu/day per dollar spent
If you just know the prices and thermal performance ratings (Btu/day) of collectors, you can use
the following formula to calculate the energy output for each dollar spent or invested for different
collectors:
Btu/day ÷ collector price = Btu/day per dollar spent
Example:
21,000 Btu ÷ $387 = 54.26 Btu/day per dollar spent
Don't choose a solar pool heating system or collector based solely on its estimated costs. When
selecting a solar pool heater, it's also important to consider all of the factors involved in the
system's sizing and quality of the design and installation.
Determining the Efficiency of Solar Swimming Pool Heating
System
You can determine the efficiency of a solar swimming pool heating system based on the
collector's thermal performance rating if available.
A solar collector's thermal performance rating is measured by Btu (British thermal unit) per
square foot per day:
Btu/(ft2day)
Or, the rating can be measured by megajoules (MJ) per square meter per day:
MJ/(M2day)
It can also be measured by Btu per day, which is simply the rating in Btu/(ft2day) multiplied by
the area in ft2. Also used is MJ per day, which is the rating in MJ/(M2day) multiplied by the area
in M2.
The higher the number, the greater the solar energy collection efficiency. However, because
weather conditions, instrumentation accuracies, and other test condition constraints can vary,
the thermal performance of any two collectors should be considered approximately the same if
their ratings are within 25 Btu/(ft2day) of each other.
High efficiency solar collectors not only will reduce your annual operating costs, but may also
require fewer square feet of collector area to heat the pool.
Don't choose a solar pool heating system based solely on its collector efficiency. When selecting
a solar pool heater, it's also important to consider the following:
Sizing a Solar Swimming Pool Heating System
In general, the surface area of your collector should be equal to at least 50 percent of the pool's surface
area.
Photo credit: Aquatherm Industries.
Sizing a solar swimming pool heating system involves many factors:
 Pool size
 Length of swimming season
 Average regional temperatures
 Desired pool temperature
 Site's solar resource
 Collector orientation and tilt
 Collector efficiency
 Use of a pool cover.
Solar system contractors use worksheets and computer programs to help determine system
requirements and collector sizing.
Basically, the surface area of your solar collector should equal 50%–100% of the surface area of
your pool. In cooler and cloudier areas, you may need to increase the ratio between the collector
area and the pool surface area. Adding collector square footage also lengthens the swimming
season.
For example, a 15-by-30-foot outdoor swimming pool in Florida typically requires a collector that
equals 100% of the pool's square footage to accommodate year-round use. This equals 450
square feet of collectors. In northern California, most people use outdoor pools 6–8 months per
year, so they typically size their systems at 60%–70% of the pool's surface area.
In any climate, you can usually decrease the required collector area by using a pool cover.
You'll also want a properly sized pool pump for a solar system. If you're replacing a conventional
pool heating system with a solar system, you may need a pump larger than your current one or
a separate, smaller pump to move the pool's water to and through the collectors.
Sample Pictures of Roof Mounting Solutions (for both Solar
collectors and PV)
Sample Pictures of Collector manufacturing processes