Polycarbon instead of glass for collector glaze?

[Alexdr]

I'm trying to get a definitive take on whether I can use a polycarbon panel (UV treated Lexan) instead of glass as the glaze covering my hot water collector.
I keep seeing it being described as a good solution. And also that its a bad solution.
UV issues seem to be the main concern. But I'm in the tropics, so not worried about heat loss - the collector gets extremely hot during the day.
I do have concerns about the Lexan withstanding that heat and degrading quickly.
Any advice from pros or those in the know, would be very welcome. Thanks!

[J.P.M.]

I'm trying to get a definitive take on whether I can use a polycarbon panel (UV treated Lexan) instead of glass as the glaze covering my hot water collector.
I keep seeing it being described as a good solution. And also that its a bad solution.
UV issues seem to be the main concern. But I'm in the tropics, so not worried about heat loss - the collector gets extremely hot during the day.
I do have concerns about the Lexan withstanding that heat and degrading quickly.
Any advice from pros or those in the know, would be very welcome. Thanks!

If the collector(s) have a fair amount of life left in them, use glass. if not use poly. Just make sure it's UV inhibited and temp. rated.

As for the collectors getting very hot, that may be a (low) flow related problem or a small storage. But don't worry, if you change over to poly from glass, the collector loss coeff. will increase by maybe 20-30 % and your water temps. will be lower. For reasons you don't know about, plastics cannot compete with glass as the best collector glazing.

[Alexdr]

Thank you for your advice. The heat issue is actually not a problem, it’s just how things go as the day heats up In the tropics. ie people on northern climates need that glass to capture as much heat as possible from winter sun. Here, too much heat, every day! I am waiting to hear if the Lexan I can buy here is UV treated.
Otherwise, I go with glass.

[bcroe]

Thank you for your advice. The heat issue is actually not a problem, it’s just how things go as the day heats up In the tropics. ie people on northern climates need that glass to capture as much heat as possible from winter sun. Here, too much heat, every day! I am waiting to hear if the Lexan I can buy here is UV treated.
Otherwise, I go with glass.

How about, some of the unbuilt PV glass in frames, I have a few? Bruce Roe

[SunEagle]

Thank you for your advice. The heat issue is actually not a problem, it’s just how things go as the day heats up In the tropics. ie people on northern climates need that glass to capture as much heat as possible from winter sun. Here, too much heat, every day! I am waiting to hear if the Lexan I can buy here is UV treated.
Otherwise, I go with glass.

Most Lexan panels will yellow and can turn brittle because they are not UV treated. Just be careful what you purchase.

[J.P.M.]

Thank you for your advice. The heat issue is actually not a problem, it’s just how things go as the day heats up In the tropics. ie people on northern climates need that glass to capture as much heat as possible from winter sun. Here, too much heat, every day! I am waiting to hear if the Lexan I can buy here is UV treated.
Otherwise, I go with glass.

A reasonably well designed solar water heater will operate maybe 5 to 10 C. or so above the entering water temperature. The frames will get warmer but, depending on wind velocity, the glass will stay about the same or less than the absorber plate temp. and so probably within that 5 -10 C above inlet water temp. range.

If the flowrate is low, as in a thermosiphon type collector, the absorber and so the glass temp. will be higher. Still, depending on what you consider "hot" - that's a relative term - very "hot" collectors can indicate poor designs or off design low flow rates and if the latter, may mean a check of operating conditions might be in order.

In the end, IMO, you're better off with glass.

[khanh dam]

acrylic would be better it is more uv stable. it also cracks easily, but you don't have hail so should be fine.