I would dare say you are focusing on the wrong side of the glass.
A solar screen would probably be the best option and could easily be removed during the winter period. If you have dealt with previous versions, don't forget they have come a long way since then.
If that doesn't work for you, look for solar shades or wooden shutters that fully operate.
For more information:
Read "In a west-facing room, what is the most effective way to stay comfortable in summer and winter: replace windows or add shades?" a Q&A answered by Polly Osborne.