I have a kitchen windowsill that faces south and has a brick wall jutting out about a foot and a half on both sides. Given the cost of materials and the upkeep expenses during the winter for a normal greenhouse, I was wondering how difficult it would be to build a "windowsill" greenhouse that extends from the end of the brick walls into the window, the window being the opening. I'm thinking that this way there wouldn't be 200 dollar a month heating costs in the winter, because of house heat, plus the heat trapped by the sun. Is this plausible? I imagine it couldn't hold too many plants, but if it worked it seems easy to maintain (accepting the possibility I'm totally wrong).
I can't find anything with plans on how to do it, so I was wondering if you have ever heard of this, or know of any plans?