Use of Cast Acrylic sheets as glazing in a Flat Plate Collector for domestic water heating

I am designing a FPC for heating water. I was wondering about the feasibility of replacing the usual Low-iron tempered glass with Cast Acrylic sheets [owing to non-availability of the former where Im from].
I am concerned however, about its structural integrity under thermal loads. Will its optical performance remain satisfactory at the higher temperatures expected during service, or would it deform, or even melt.
If it would melt, I was considering adding 5mm ordinary glass glazing above the Absorber plate, and then add the acrylic after an air gap for protection, and added insulation. However this arrangement would lead to added costs and reduced transmittivity [and thus efficiency].
I’d appreciate any input regarding the problem, and suggestions regarding the design.