I have to monitor the existing alloy mirrors during the summer, and decide if they make a difference. If they do, and if I feel that making them clear would improve their performance, I might invest some of my earnings from the Feed in Tariff in some clear mirror!
This is Research, and the specific cost does not have to be met by strict payback targets. If these were ever to be produced commercially, the alloy is 1/6 the cost!
The 3mm polycarbonate would not be strong enough in itself to perform as my alloy sheets do now, but they could be cut to size and simply riveted to the existing aluminium sheets!
I have some spare aluminium alloy sheet and have a glass mirror and will spend time in the garden measuring the radiation from the reflection (shining the Sun in my face!) before spending more!