This is slightly embarrassing, but I recently put some foil on two windows that get morning sunlight. I taped the aluminum foil to the inside of the (double-paned) windows and completely covered them. They're in a spot where the neighbors can't see them. It seems to direct heat outward because the lawn below both windows got singed.
There's one more window I want to cover with aluminum to stop afternoon sunlight, but I'll consider a different method if someone will tell me what is better. I'd like it to be easily removable.
I was reading about someone doing this just yesterday... they got some cardboard, or plastic board, something like that, and taped the foil to that instead, making it easier to put the panel up and down in the window. They had a small bathroom window, so I don't know how effective that would be for you. If my apartment allowed aluminum foil on the windows I'd do this as well, but its in the lease saying I can't. Smart buggers....
Something else to try, that may not bust leases or burn grass is a thick satin finish sheet. The tight weave should stop light (if that's the need, I work nights, sleep days, so I need that) and the satin finish is semi-reflective, without being a direct mirror. It may not be as effective or cheap, but it is safer for all those outside your windows. You did mention the neighbors can't see the windows, so foil will probably work great for you.
there's a few more, but those have helped me bundles in understanding how to be ....greener? I hate that word, but for lack of a better description, there it is. How to use less energy and make a smaller impact upon the world around me. eh. You get the idea.
they make tint for windows that will do the same thing. it isn't easily removed but it looks better so you could potentially leave it up year round.
the tint comes with a warning to install on the outsied of the window so that it doesn't cause a temperature difference in the glass. it goes on to say that it could crack or shatter a double paned window because of this temperature difference.
I got mine from lowes home improvements near the window treatment section. I would direct you to their web page but I can never find anything using their site and search engine
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The key is to keep the heat out of the house in the first place. If yer foil isn't super up close and personal to the glass (no clearance) it will introduce a heat pocket. That heat pocket is inside yer house and it will still heat up the house some.
I put up some sun screens outside the window of my roommate's house and it did a wonderful job. I just used that thick poly sun screen stuff that you can find at most hardware/home improvement stores. It comes in green, black/charcoal, and off-white/cream/ivory. You can build a simple wood frame and attach the screen to it. Then you can attach that to the window frame on the outside with whatever you please fer easy access/removal. You can even paint the frame so it matches the house and protects the wood in the long run!
I have house window tint in my trucks back window and it works great. it's less of a tint and more of a 1 way mirror and blocks/reflects almost all IR and UV spectrum leaving most of the visible spectrum alone. there's moderate mirroring from the outside from certain angles but visibility inside is better than standard auto tinting. I found 4 boxes of it it in my grandparents basement when we cleaned their house out after they passed away. they had it in the front picture windows and it's GREAT. the room didn't get much warmer even with direct sun and curtains open. I'll find a pic of the box later.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"
We installed tint on a window last year, but needed to install an exterior shade from the eave as well this year. Even so, we still end up shutting the internal blinds on the hottest days.
One suggestion I read about in a book was to use rigid foam wrapped in cloth. Neatly done, the foam shades can be both attractive and very effective at blocking heat radiation in both the summer and winter. Even 2" of the foam is a better insulator than the glass itself. These same panels could be setup on sliding rails or hinged similar to exterior shutters (on the inside of course) for a semi-permanent installation.