One of the nifty ideas I ran into when I was doing my science degree all those years ago was that of creating synthetic (and thus mass producible) versions of the plant molecule chlorophyll.
The reason this is cool is that the chlorophyll molecule is able to catch light and use the energy to split water into oxygen and hydrogen. This in turn is useful for us, because if we can build synthetic systems to harness this process we can use the sun to directly produce hydrogen, which we can later burn to power cars, and run power plants, and possibly in the future create electricity directly via fuel cells, thus bypassing the thermal energy losses of combustion systems. And it would be completely green and renewable, because it would use only water, and when eventually use, the hydrogen would create only water.
So it was cool to read the other day that Aussie scientists had taken another step towards getting this up and going.