Solar Collector Glazing Materials

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:

• High temperature capability
   

• Transmit light very well
   

• Long life when exposed to UV and high temperatures
   

• Good impact resistant
   

• Light weight and easy to work
   

• Opaque to long IR to reduce heat loss
   

• Low cost

No single glazing material exhibits all of these properties, so picking the best material for your application is going to be a tradeoff.
 

Pros:  long life, good transmittance, high temperature capability, low transmittance in the long IR reduces heat loss, strong.

Cons: heavy, breakable, high cost.

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.
Many glass shops will offer blemished or pull-outs or miss-cuts at very low prices, but will not likely stock the highest transmittance glass.

www.palramamericas.com/Suntuf

www.palramamericas.com/Solar

Full Data Sheet ... (pdf)

Installation Guide... (pdf)

Examples:
My Solar Shop Collector...

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.

Pros: good transmittance, high impact resistance, good temperature capability (270F), light weight, low cost, good life, easy to cut, low transmittance in the long IR reduces heat loss, available at many home centers.

Cons: Have to seal corrugation ends, must be well supported, only 2 ft wide sheets commonly available, life and temperature capability not as good as glass (but good). The corrugations also add some surface area compared to flat glazing, and this increases heat loss a bit.

"Wiggle" strips are sold to seal the corrugations (see picture).
Polycarbonate (GE trade name LEXAN) is very tough -- its the football helmet stuff.
For use in collectors, it MUST have a coating or additives to resist UV.
It will not hold up to long time exposure to hot water vapor.
Nick reports that a 4 ft wide version called Dynaglas is available from Stuppy or Griffin greenhouse supply.

Examples:

My Solar Shed Collector...

Alain's Collector...

Specs... (pdf)

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.

Pros: good transmittance (but lower than single wall), high impact resistance, good temperature capability (270F), light weight, low cost, good life, very nice to work with, low transmittance in the long IR reduces heat loss, available in wide variety of widths, thicknesses, and nearly any length, available in many cities and from greenhouse suppliers, less heat loss due to the insulating effect of multiple layers.

Cons:   life and temperature capability not as good as glass (but good), more expensive than single wall, but still reasonable.

For use in collectors, it MUST have a coating or additives to resist UV.
It will not hold up to long time exposure to hot water vapor.

Examples:

Wayne's Collector...

The beer can collector...

http://www.cansolair.com/

This would include flat rigid sheets of polycarbonate in the 1/8 to 1/4 inch range.
This is a good glazing material.  It is used on some commercial collectors.

Pros: good transmittance, high impact resistance, good temperature capability (270F), light weight,  good life, easy to cut, good variety of sheet sizes and thicknesses available, low transmittance in the long IR reduces heat loss(?),
many glass shops stock it or can get it.

Cons:   life and temperature capability not as good as glass (but good), high cost.

These sheets are not as stiff as glass, and some collectors use  a gentle outward curve in the glazing to increase stiffness and rigidity.
For use in collectors, it MUST have a coating or additives to resist UV.
It will not hold up to long time exposure to hot water vapor

Data Sheet ... (pdf)

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:

"I've bought small pieces (e.g. 4'x8') of 0.010"-0.020" thick material from graphics suppliers, but it seems to me that the thinnest 0.007" stuff would make the best solar glazing, since it's the cheapest, about $1/ft2 in a 4'x100' 20-pound roll. IIRC, the min order is $300, with delivery in 2 weeks."

Pros: good transmittance, high impact resistance, good temperature capability (270F), light weight,  good life, easy to cut, available in 4 ft wide rolls, low cost, low transmittance in the long IR reduces heat loss(?).
 

Cons:   life and temperature capability not as good as glass (but good),  must be special ordered from GE plastics in rolls (although small quantities may be available from graphics or sign businesses).

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 support.
For use in collectors, it MUST have a coating or additives to resist UV -- be sure to choose the type of film rated for outdoor use.
It will not hold up to long time exposure to hot water vapor

Rigid PVC sheet (flat or corrugated)

Polyethylene film (greenhouse film)

Some good uses for these glazings:
Passive gain collector...

Sunspaces and Greenhouses ...

Acrylic Data Sheet...
 

http://www.solar-components.com/SUN.HTM

About $2.50 per sqft -- shipped in rolls.

SunLite Specs...

(Thanks to Paul for finding the spec sheet) 

http://www.coroplast.com

The upper temperature limit with no loading and good support is 180F, and the material melts at 324F.

(now if we could only convince politicians running for office to use this version for their signs, we would have a limitless supply of free glazing every 4 years)

(most of the above is from the Coroplast in response to an email questions)

www.warps.com/category.asp?section=windows

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.