This page gives my take on glazing material candidates for solar collectors.
Solar collectors are a fairly tough test of glazing materials. Collectors glazing is exposed to high temperatures, long time outdoor exposure, impacts from hail and/or vandals, while also requiring high light transmission and reasonable cost.
The ideal glazing material for solar collectors would have these properties:
No single glazing material
exhibits all of these properties, so picking the best material for your
application is going to be a tradeoff.
Here is a table of glazing candidates and the pros and cons as I see them.
|Collector Glazing Materials|
Glass is a good glazing material for solar collectors.
High transmission (low iron) tempered glass is used on the majority of commercial solar collectors.
Tempered glass with a low iron content is preferred. Non-tempered
glass in collectors can crack from the heat, and glass with a high iron
content transmits less light.
|Polycarbonate -- Corrugated
This is a thin sheet of polycarbonate shaped into a corrugated pattern. It is commonly used for greenhouses, porch roofs, ... It makes a good glazing for solar collectors.
"Wiggle" strips are sold to seal the corrugations (see picture).
|Polycarbonate -- Multiwall
This is an extruded polycarbonate glazing material that consists of multiple panes connected by ribs. Commonly there are two panes, but there can be up to 5 panes. It is commonly used for greenhouse and sunspace glazing.
For use in collectors, it MUST have a coating or additives to resist UV.
|Polycarbonate -- Rigid sheet
This would include flat rigid sheets of polycarbonate in the 1/8 to 1/4 inch
These sheets are not as stiff as glass, and some collectors use a
gentle outward curve in the glazing to increase stiffness and rigidity.
|Polycarbonate -- Rigid film
Data Sheet ... (pdf)
A rigid polycarbonate thin sheet material that is in the 0.007 to
0.03 inch thick range.
It has the advantages over corrugated polycarbonate that it comes in 4 ft widths, and does not require sealing the corrugation ends.
I've have zero experience with this material, but it was suggest by solar guru Nick Pine as a good choice, and it looks promising. From Nick:
Order directly from GE Structured Products -- contact information is in the Data Sheet.
Its not clear to me exactly how much support this material will require.
If the glazing frame applies tension to the film, it may need little
|Rigid Acrylic Sheet
Rigid PVC sheet (flat or corrugated)
Polyethylene film (greenhouse film)
Some good uses for these glazings:
|These materials can be good choices when the glazing is not exposed to high temperatures (e.g. sunspace glazing), but they will not stand up to the temperatures seen in solar collectors -- trust me on this -- they melt :)|
|Sun-Lite Fiberglass Glazing
is a fiberglass reinforced plastic glazing made for solar glazing
applications by KalWall. I don't have any experience with this material.
About $2.50 per sqft -- shipped in rolls.
(Thanks to Paul for finding the spec sheet)
|Coroplast -- Horticultural grade
is the corrugated plastic the material that is commonly used for sign
boards. This material is made in a Horticultural grade which has some
UV inhibitor, and comes in "natural", which is the color of the
polypropylene resin used to make it. This material has been used as a
glazing for greenhouses. The greenhouse grade is translucent, and has
73.5% transmittance. It is guaranteed for 3 years.
temperature limit with no loading and good support is 180F, and the material
melts at 324F.
(most of the above is from the Coroplast in response to an email questions)
Vinyl does not have a high enough temperature capability for use in most
solar collector applications.
It can be good for things like enclosing a porch to make a sunspace.
Richard reports that that Flex-O-Glass has done well in in a vertical air heating collector that is protected from summer sun by an overhang.
Must be UV treated and formulated for your coldest winter temperatures.
More information on glazing suppliers here...
Gary June 8, 2008