F.4 Role and Importance of Energy

Energy is the backbone of any mobility artifact. A cyclist spends around 0.2 kWh for normal cycling, and a car driver spends 30 kWh for the same displacement. The gross weight and maximum speed of a vehicle are directly proportional to engine specifications. The important elements related to energy when urban mobility is considered are as follows:

• The usage of energy and other material resources by a mobility mode in its lifetime is the most important and deciding factor for assessing the impact and its mere existence. For example, the environmental impact of the lithium battery used in BEVs is small. The operation phase of the car, mostly recharging the batteries, is the dominant contributor to the environmental burden caused by the transport service. The contribution of the lithium within the battery has a share of about 2% of the environmental impact of the total transport service.
• The energy source or carrier will basically dictate the typology and functionality of a mobility mode. The safety and precautionary steps needed to be taken for the energy carrier for any unnecessary collisions or impact will decide the necessary active and passive safety features. The time taken to refill, swap, or recharge the carrier will decide the form and functionality of the mobility artifact. Size and weight matter for any mobile product, so any aspect of the energy source that will improve the power-to-weight ratio is a winner.
• The shape and safety requirements of energy sources decide the context in which the vehicle will operate. For example, the photovoltaic cells applied on a vehicle for energy production need to have more open flat vehicle surface, and hydrogen storage has specific safety requirements.
• Tank-to-wheel efficiency and emissions are also important, especially in the case of urban mobility, for reducing the local emissions. For example, BEVs are 30–40% greener than ICE cars when life cycle efficiency is considered. The same are almost 90% greener when only tank-to-wheel efficiencies are considered.

The maturity of the application and capacity in supply of an energy source plays an important role when pursuing a political agenda and consumer acceptance. The availability of a particular energy source in abundance for a lifetime of a vehicle system is also very important.