There are some really good ideas here. There are also some I just can't see working before the population reaches 20 billion+. The vertical farm for instance I just can't see working.<p>Using salt solutions to heat and cool a building is an interesting idea. I'm not sure how a thermostat would work in that situation though. I would suspect the temperature is controlled by the mix of salts in the solution and once that is set it would be a pain to change.