This was inspired by an article on BuildItSsolar.com
This is one method of a semi permanent fixing of bubble wrap to UPVC window units and my not be suitable for your style of window.
I have only done this on a frosted window as the reduction in visibility is not an issue.
Images show after & before.
Step 1: What you will need
A scraper to prise out glass retaining strips & rubber weather strips.
A clean window.
Bubble wrap - not shown but it needs to be measured so that it is slightly larger than the glass with an inch or so to spare.
Step 2: Remove internal retaining strips
Gently push the glass towards the outside, it will not fall out as the hole in the frame on the outside is smaller than the glass size (Check that you windows are like this before starting).
It only needs to move a bit to allow the removal of the internal retaining strips.
Using the scraper push one of the side retaining strip forward so it snaps out of it groove (2 of the strips would have been fitted last need to come out first - they should be the ones with the 45 degree mitered ends.
Step 3: Fit the bubblewrap
Trim any excess so that it covers the whole sheet of glass.
If you have any large gaps between the glass and the frame fill them with excess bubble warp but be sure not to have it showing on the out side of the glass.
Step 4: Re fiting process
Then re fit the external rubber weather strip to the top starting in the middle & working your way to the edges but leave about 1/4 loose from each end, this will hold the glass & bubble wrap in place at the top of the frame but also allow the side strips to go in later.
Then smooth the bubble wrap down & refit the lower retaining strip just like you did for the top & re fit the weather strip again leaving 1/4 loose at each end.
Next gently, using one of the side strips, comb the bubble wrap so it is smooth then snap it in just like the top & bottom ones, repeat this for the other side. once in place refit the external side rubber strips & finish off the top & bottom ones to secure the glass.