This time of year here it's more use to keep the heat in. I wonder if it will stay up when flipped upside down.
Come to think of it get two and sandwich them would be ideal with an extra air pocket. The mags would hopefully stick two as good as one?
I am using a product called EVglass from EVinsulate. I use it year-round. If I didn't need help installing it then I might swap it out for an opaque screen in the summer but the EVglass helps a lot in the summer too. One of the reasons to swap it out for an opaque screen is to make it easier to sleep-in while sleeping in the car. But I plan to start using a tent this summer to accommodate my dog.
EVglass is made from clear polycarbonate and makes the roof double pane. It's made in Canada and is designed to insulate the cabin in the cold winter. They say that when combined with extra insulation for the battery, their products cut winter-time range loss in half. I think this is true.
EVglass also helps keep the cabin cooler in the summer. The OEM roof already blocks most of the sunlight but this makes it get hot. The air gap helps prevent this heat from getting into the cabin. Ideally we'd be able to combine the EVglass with an opaque screen but I haven't figured out how to do that. There is a screen that attaches with suction cups (NOT TO BE USED WHILE DRIVING) but the suction cups didn't seem to stick to the polycarbonate.
BTW: the two-piece wire-frame screens are pretty easy to install and uninstall. Only takes a few minutes (after you figure it out). The mag stuff seems very cool but if you're only changing the screen seasonally it may not be worth it. If you are changing it daily or even weekly then mag is the way to go IMO.
I don't know if the benefit of a 2nd screen would be worth the hassle. Of course, your watt-hours/km may vary.
I live in the high desert at an elevation of 1.8 km. The sun is absolutely brutal here. I have a set of
insulated window shades (made from something like Reflectix). They attach with suction cups. I keep the one for the driver's door in the car and use it to block the window when I'm sitting in the car for more then a few minutes and the sun comes in through that tinted window. I don't feel the same need to block the roof when I'm using the EVglass. Of course, this is somewhat subjective.