The girls tell me that their granny is growing green curtains outside the windows of the bedroom and living room in Yokohama. They are a combination of goya and morning glory. Goya is a bitter gourd, it looks like a knobbly cucumber and it IS very bitter. Both it and the morning glory are climbers and are trained up a trellis to provide shade and to keep the indoor temperature down. Since the tsunami there have been rotating power cuts to save energy and people are being encouraged not to use their air conditioners as much and at a higher temperature.
Another benefit is, if so inclined, one can pick the goya and cook them. A traditional Okinawan food, they are supposed to be ideal to eat in hot weather. I have to admit, try as I might, it was pretty impossible to acquire a taste for them. Regardless, having a soft green curtain outside the window is a lovely idea, don't you think?