A beautifully simple way of reducing air conditioning costs

Glass buildings can suffer from quite significant overheating due to solar gain. The obvious answer is to crank up the air conditioning to 'solve' the problem.

Office workers usually need hot water to make their cups of tea. The obvious answer is to install furnaces to boil water.

But wait... what would happen if you were to pour water into the windows to make a huge great solar kettle? Well, I for one, probably wouldn't make my tea with the water, but researchers at the Polytechnic University in Madrid, have been working on this, and have found that they can reduce air conditioning costs by up to 70%. The story was reported by Treehugger and can be read here.

This strikes me as one of those wonderful - how come we didn't do this before - ideas. And, my question for the day is "what other obvious synergies are we missing?"