Depend on a reputable local
dealer/installer for advice about
what systems and collectors
work best in your area.
needs for a family of four.
aLterNatiVe POwer eNterPrises iNc., ridgway, cOLO.
The most common types are open-loop
systems, which directly heat the water
that’s used in the house, and closed-loop
systems, which heat a fluid that then heats
the water used in the home. The most common working fluids are water and water/
antifreeze mixtures. Systems may use no
pumps, a single pump or two pumps. The
system consists of a set of solar collecting
panels to capture the sun’s heat, a transport
fluid to move the heat from the solar collector to the storage tank and a means to
move the heated fluid through the system.
The general types of systems are shown on
page 47, in rough order of cost from lowest to highest, assuming that all systems
use selective-absorber, single-glazed solar
collectors. All solar manufacturers must
submit their solar systems to the Solar Rating and Certification Corp.
for performance ratings and listings in order for the systems to be
eligible for federal tax credits. The SRCC’s Operating Guideline-300
ratings enable consumers and installers to compare how many therms
or kilowatt-hours a solar system will produce per year in any given
climate.
Systems are categorized by collector working fluid, means of circulation and system pressure, as shown on pages 44-47. Each type of system
has been developed for a specific market and climate zone. Some of the
systems in this table are no longer manufactured and sold in the United
States, such as the open-loop drain-down ( 4) and the percolator pump
Copper Cricket, though they remain in use. All of the other types work
well in their particular applications.
Knowing the advantages of each system type, and asking your
installer about which systems are preferred in your region, will help
you identify the best system for your needs. The schematics on pages
44-47 show basic elements of the most common system types (details
will vary). Let’s look at the pros and cons of each type.
In the integral collector storage system (schematic 1), city water
pressure drives the system. When a hot water tap is opened, preheated
water from the solar collector moves to the storage tank for final heating,
then into the house. There is no pump in the system, so the thermal mass
of the water is the only freeze protection. The thermosiphon system
( 2) is also pressurized by the city water line, but here cold water settles
to the bottom of the solar collector and as it is heated, it rises to the top
of the solar collector and then into the hot water tank. The system has
no pump. Freeze protection depends on a Dole-type thermostatic valve,
which automatically lets warm water run slowly through the collectors
and onto the roof during freezing periods.
The integrated collector with a storage tank installed above the
collectors ( 3) is common where hard freezes do not occur. In addition to the thermosiphon configuration shown in schematic 3, where
the pressurized water thermosiphons through the solar collector,
there are also evacuated-tube heat pipe systems. This configuration uses
a freeze-resistant alcohol-water mixture in the heat pipes, with the top of
As utility expenses spiral ever higher, wouldn’t we all like to draw
on the sun to heat our household
water?
The average 40-square-foot
( 3.7-square-meter) solar collector system
provides 38 gallons (144 liters) of hot
water daily, about 60 percent of the daily
water needs for a family of four. Virtually every U.S. location has adequate sun
for solar water heating. These systems
also benefit from what I like to call the
Four E’s: They save energy, create local
employment, reduce environmental
damage and empower energy security
— all necessary for life, liberty and the
pursuit of happiness. More than half of
your hot-water cost is fixed using solar
energy and will not rise with electric,
natural gas or heating oil prices. Solar energy is not taxed, and by using
less natural gas to heat water, we reduce demand for and hence the price
of natural gas. The first cost of a solar heating system may be higher than
that of a conventional system, but in the long run solar wins for our
society, the U.S. economy and your pocketbook.
In fact, solar water heating makes economic sense by any measure.
Compared to the national average price of $1.84 cents per therm for
natural gas, unsubsidized solar energy is $1.50 per therm amortized
over 35 years. A solar water-heating system that costs $6,600 installed
will produce about 125 therms per year in the Southwest, energy
valued at $325 — for an annual return on investment of 5 percent
before incentives. For those who benefit from the 30 percent federal
tax credit of $1,980, the cost per therm is just $1.05, with an annual
return on investment of 7 percent. The federal tax credit for solar
water heating is capped at $2,000 for residential installations. For a
system that replaces an electric water heater, the cost savings is $372
per year, based on the national average retail electricity cost of 10.97
cents per kilowatt-hour, providing a 5. 7 percent ROI without federal
tax credits, or a 7. 6 percent return with federal tax credits.
Here we examine the basic types of solar water-heating systems
and thermal collectors, how to find the best match for your location
and what to look for in a system and installer.
What System types Can I Choose From?
A solar water-heating system uses a solar collector to heat a working fluid that transfers the sun’s heat to a water-storage tank, as shown
in the figure on page 45. Household occupants use the water from the
storage tank to bathe, wash dishes and wash clothes. About 37 percent
of the sun’s heat makes it to your hot water faucets. The rest is lost
to the air surrounding the collector, piping and water-storage tank.
This efficiency is excellent compared to residential solar electricity-generating systems that may deliver only 12 percent of the sun’s
energy. A 40-square-foot solar water-heating system delivers about
1,400 watts of thermal energy for about eight hours a day. That, as
mentioned, is enough to meet about 60 percent of water-heating
HeLiOdyNe
Most systems will last well over 40 years with routine maintenance. above, a SUNDa evacuated-
tube solar water-heating system. Left, a Heliodyne system with flat-plate collectors.
