I can suggest the simple and reversible fix at the link below using bubble wrap on your windows for insulation in the winter. We added bubble wrap to all our windows 7-years ago and have seen a HUGE difference -- even in a new-built home with energy-efficient windows. Secondary benefit - no more moisture accumulating on windows in the winter.

Tips:
-cut the bubble wrap slightly smaller than the window
-use distilled water since minerals in tap water can etch glass

We also have insulated Levolor blinds on our windows.

For summer, it's my experience it takes more coverage than bubble wrap only. In fact, the more layers of protection, the more effective. On our west windows we have these layers of protection.
-UV blocking glass AND UV blocking screens (they are thick and black)
-awnings
-bubble wrap is left on windows that aren't "seen" and normally covered with blinds
-a few windows I also add room-darkening insulated drapes under the Levolor blinds for additional protection. I use a tension rod for easy installation and removal.

Other options and ideas....

--The townhouse we lived in before moving here, I made multi-layer "Window Quilts" for all the windows, but it's a lot of work and expense to do it properly. You can Google information for making your own.

--We use this method on the egress windows in the basement, but the downside, it blocks all the light along with the heat and cold. We cut rigid insulation to fit our windows. I covered the sheets of foam insulation with decorative material (spray-on adhesive and decorative trim at the seams) so it looks nice inside and outside.

--You could also add heat control plastic film to your windows, but it does fade and needs removed and replaced occasionally (a task that is a pain somewhere lower than the neck - LOL). We added this to our storm door on the west side of the house. The brand we used was Gila - found at Lowe's.

Check your library for these books. Even though they are a bit out of date (remember the Energy Crisis during the Carter Administration), they still have a lot of good ideas in them. The nice thing -- we have new materials we can adapt to the ideas.

-Movable Insulation - by William K. Langdon (1980)
-Better Homes and Gardens Energy-Saving Projects You Can Build (1979)

-Grainlady

Here is a link that might be useful: Bubblewrap window insulation