We have a retractable on our south-facing patio door/window near San Jose and it's made a huge difference in terms of heat rejection after we installed it. On hot summer days it makes a noticeable difference. And since it's retractable it doesn't make the back room permanently dark. It's one of the major items that lets us survive a south bay summer without air conditioning. We'll probably upgrade our gas furnace to a heat pump eventually and get AC "free" but in the meantime this was a much cheaper stopgap.
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