Startup Idea : Let's save energy! (cheapest air con substitute)

I am renting a flat, so I can't improve conditions of this place as much as I want to. I am not an owner of this property I temporarily live in. The sun hits my window directly, so I found some eco solution to keep heat out of window for only 1 coin. It is working well (so I don't need to buy an air conditioner), but it looks worse than anything else (so that feature will have to be improved - but I've got an idea how to do it as well). The market for this idea will be huge, because lots of people: - suffer from direct sun light, - are renting flats; - can't afford air conditioner; - want to save energy, money. So I'm looking for sponsor or arbiter for this idea.