Cars that run on compressed air:
Great on the surface, and excellent if compressed air is generated by using renewables, or even by hydrolysis of water to generate 2 fuels: hydrogen fuel and compressed oxygen for air cars? If renewable biomass is used as fuel to drive compression, it is more efficient to use the fuel directly in a combustion engine to run a car. A case can be made for renewable charcoal biomass as a sustainable fuel wherever biomass is abundant. But the qeustion is - should we make compost for soil or burn the biomass? If biomass is missing in soil, we should compost biomass.
Comment on MDI by MJ - Great potential. What issues does it solve? 1. Fuel storage via air. 2. Clean burn. Disadvantage: Air is not so efficient - they are claiming 70% expansion efficiency, with compression up to 60% efficiency - so at best about ~40% efficient. If compressor is driven by a 30% fuel engine, that is about 10% overall efficiency.
Comparison from the accessibility perspective: renewable char gas from coppiced permaculture plantings appears to be more sustainable in terms of local energy production from a living ecosystem. If energy is obtained from renewables such as wind, the air engine would be a great case for the car.
We should encourage them to opensource the air engine?Another question: how difficult is it to fabricate efficient air engines?
Summary of air cars: simply removing the point of fuel production to another place, while losing efficiency due to low efficiency of air conversion to motor power, at the benefit of a 'clean burn.'
Best case scenario: photovoltaics and wind power are found everywhere - and they are used to run compressors for air cars. Fueling stations would have to be available everywhere.