Hot water
solar panels
Solar hot water heater panels and important
specifications
Hot water solar panels, or collectors, are the
heart and soul of
any solar water
heater. With that said, the panels' orientation, performance
specifications as well as physical specifications
can determine the panels' efficiency and application.
Panel or collector orientation
With either an integrated
collector storage unit , a flat
plate collector as well as an evacuated
tube collector, it will be important to maximize a site's solar
resource. The position the hot water solar panels
are installed in is commonly referred to as the collector orientation.
The collector (or panel) orientation will determine if the
sun's
radiant heat is being efficiently maximized or not.
Panel
or collector mount
The panel or collector mount is simply the
physical from of installation chosen by the professional solar installer.
With all hot water solar panels there
are three collector mounting options to consider; a roof mount, a
ground mount
and an awning mount.
Roof
Mount
- The most common mount used in residential
applications.
- Horizontal brackets are used for positioning.
- The surface area and weight
of the solar water panel must be considered.
Awning
Mount
- Attaches the collector to the top of an outside
wall.
- Horizontal brackets are used for positioning.
- Overall surface area and weight of the
panel is somewhat of a concern.
Ground
Mount
- Installation is usually as simple as placing
support poles in the ground.
- In most instances, brackets can be used for
positioning.
- The hot water solar panels' size and
weight is much less a concern.
Panel
or collector tilt
The panel (or collector) tilt is simply the angle
at which the collector is installed. A proper tilt, or angle,
has to be pre determined in order to maximize a site's solar resource.
The tilt can be influenced by the collector mount. A particular mount
can (to some extent) limit the solar water panels' tilt.
Both the cold and warm climate seasons' must be
factored in when determining an advantageous year round tilt or angle.
Professional solar panel
installers strongly recommend using an angle close or
equal to your site's global latitude.
For all locations in the Northern Hemisphere, the
solar water panel should face south or southwest at an angle close or
equal to the locations' global latitude.
Panel
or collector headers
The headers are the large tubes that are bonded to
the risers of hot water solar panels. The headers circulate inlet fluid
through the collector and circulate heated fluid from the
collector
as well. The position of the panels' headers have important
installation
ramifications.
Internal Headers
Internal headers are positioned on the inside of
the
hot water solar panels' frame or plate. Hot water solar panels with
internal headers have two separate inlet points and two separate outlet
points.
The purpose of having two sets of inlets as well
as outlets is to connect two or more hot water solar
panels to one
another. In fact, these panels are designed for applications that
require two or more collectors for greater hot water output.
External
Headers
External headers are positioned inside of the
solar water panels' frame or plate. These headers have a single inlet
and a single outlet, one at the top and one at the bottom. Hot water
solar panels with external headers are designed for those heating
systems that only require a single panel or collector.
Hot water solar panels with external headers can
be installed together in larger applications, if it's required, but
additional plumbing parts will be needed.
Important
physical specifications
Surface
Area
The panel (or collector) surface area is the total
size of the panel, including the outer frame. The overall size of the
panel is important because the surface area in some cases can determine
if a certain model or mount is unfit for a site.
Net Aperture Area
The net aperture area is the surface area of the
collector that actually absorbs the sun's thermal radiation. The
collector net
aperture area is an important physical specification to consider when
sizing a solar water heating panel.
Absorber Plate
Material
The absorber plate is responsible for capturing
the sun's radiant heat. So the material it is made out of is important.
Copper is generally the most trusted absorber plate material,
but other metals are commonly used.
Absorber Coatings
Coatings are used to assist the absorber plate in
collecting solar heat. Black paint is often used, as well as more
complex coatings referred to as selective surfaces. Both are effective
at absorbing heat but selective surfaces generally retain heat better
than black paint, especially low E selective surfaces.
Manufacturers use selective surface absorber plate
coatings with descriptive names such as black chrome, metallic
oxide and titanium oxide, and some just simply identify that a
selective surface is used to coat the absorber plate.
Panel Insulation
In flat plate collectors a sheet of
polyisocyanurate
foam is often used to further insulate the frame. Polyisocyanurate foam
is
very effective at reducing heat loss. Some models use fiberglass
insulation instead, and fiberglass is effective, but not as effective
as polyisocyanurate foam.
Panel or
Collector Glazing
The glass or plastic material used to cover the
panels' frame is important as well. With flat plate collectors, low
iron tempered glass is quickly becoming the new glazing standard. Low
iron tempered glass is essentially window glass that's chemically
altered to reduce the iron content.
This allows about 90% of the sun's rays to
penetrate through the glass. The low iron glass is then tempered, or
toughened. This is important because tempering the glass enables flat
plate collectors to withstand the toughest hailstorms.
Some less expensive flat plate hot water solar
panels use special plastic glazing. The plastics used generally allow
just about the same amount of solar radiation inward, but these
plastics don't insulated as well as low iron tempered glass.
In evacuated tube solar collectors, more times
than not, the glass tubes are made up of either borosilicate
glass
or soda lime glass. While both are very durable, borosilicate glass is
more resistant to extreme thermal temperatures.
Evacuated tube collectors with
borosilicate glass tubes are generally slightly more expensive than
models with soda lime glass tubes.
Important
performance specifications
Thousands
of BTU
Thousands of BTU, or thousands of British thermal
units, is the unit
the industry uses to measure the thermal output of hot water solar
panels. This
performance specification is always found on the collector
thermal performance
rating label of SRCC certified and rated hot water solar
panels.
Knowing how much solar thermal output a particular
water heating system will require is an important part of sizing
a solar water panel.
Y -
Intercept
This rating specification is found on the
thermal performance rating label of all SRCC certified and rated hot
water solar
panels also. It's a measurement of the effectiveness of a panel when
the
circulating fluid temperature is equal to the outside climate
temperature. Y - intercept is usually provided in the form of a decimal
or a percentage.
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