SKhy by alain monteiro from portugal

designer's own words:

This concept is an alternative to the infrastructures required for the electrolysis of large quantities of water to produce hydrogen. It's also inspired in plants because they produce their own food (and energy) and their byproduct (oxygen) is vital for us.
The top of the SKhy Bus is completely covered with solar cells for energy production, the brakes also generate extra energy, not for the bus's movement but for the production of hydrogen out of wastewater. Wastewater is rich in Urea, which is 300% more efficient than normal water. The processing of wastewater can be done even if the bus is parked, the same works for energy production, depending on the city's needs.
It possesses large air intakes to filter CO2 from the atmosphere thanks to ZIF materials (1l can hold up to 83l of CO2). The CO2 can then be used for the cooling and fire extinguishing systems or as substitute for other chemicals in wastewater treatment, or to make calcium carbonate to reduce the use of wood fibers in paper making.
The bus has an aluminum structure for lightweight and easy recycling. The seats and other components are made of recycled antimony free polyester from water bottles, this means it can be recycled endlessly. The braking system (and other components) are composed of piezoelectric ceramics, which reduce vibration and convert waste energy.
This would help clean municipal wastewaters, release oxygen and capture CO2, just like a plant. The clean water produced by the hydrogen engine is recollected for other purposes.
The outside surface is completely covered with tiny dimples, just like a golf ball, this reduces air resistance and drag force, consequently consuming less fuel.
Depending on the needs in large cities, the number of seats can be adjusted between 72 and 128. The windows can project information about the city, weather or useful to the passengers. The windows also get darker with the sun, to keep the interior fresh.
There is no driver, the bus is controlled via GPS and sensors, this reduces driving accidents, it also eliminates most of the traffic since space and movement can be coordinated far more efficiently through CPUs.

SKhy city bus

skhy_2.jpg info, fuel efficiency and materials

skhy_3.jpg bus as source of energy and as wastewater treatment station