p>If your home has south-facing windows that recieve direct sun, then you are already benefitting from passive solar heat collection. I should make sure we are talking about the same thing here, since your comment about attaching something to your window is a bit confusing, here is our video guide page on passive solar basics –</p> <p><strong><a href="/guides/2260/how-to-build-passive-solar-homes-episode-1-of-the-ecohome-building-guide/" target="_blank">How to build a passive solar home</a></strong></p> <p>The short story is, that if the sun is coming in your window you are getting some passive heat, simple as that. The main design ‘features’ of passive solar heat collection are having a house oriented to the south, and ideally even triple pane windows, depending on where you live. That, and having <a href="/guides/2200/the-pros-and-cons-of-thermal-mass-in-buildings/" target="_blank">thermal mass in the path of the sun to absorb the heat</a> so it can later be released as the temperatures drops. If your house is built and your windows are in place, there isn’t a ton you can do at this point except perhaps have thermal mass in the path of the sun to collect heat, but that could be quite a bit of work for the benefit.</p> <p>If this does not address your actual question let us know. The only things that you would ‘attach’ to a window in this respect would be a <a href="/products/1076/sketch-nanotechnologies-inc-high-performance-clear-window-coatings-for-energy-savings-sketchnanogard-thermal/" target="_blank">window film to reduce heat transmission (see product here)</a>, or sunshades above the window to also prevent overheating. I hope that helps!</p