How to make single glazed windows more energy efficient?

[fadetoblack]

Hi All, 
I recently bought an old town house with predominantly west facing single-glazed windows and am now looking at adding an extra glaze to the windows to make it more energy efficient. 

Due to budget constraints, I'm looking at a DIY project using either acrylic and/or polycarbonate materials for the second glaze. 

I'm just writing to see if anyone has any recommendations on using the two materials?
Can both materials be pre-treated – maybe with a tint?– to block UV and mitigate direct sun?
Also, for the sake of better security, is it possible to install the polycarbonate panels on the outside (first floor anyway) effectively? 

Any tips on the subject would greatly appreciated. 

Thanks in advance, 

[fadetoblack]

Thanks Richard