Alternative Vehicle Drives
Alternative Vehicle Drives
What technical options do we have beyond the battery-powered electric vehicles (BEV)? Electric vehicles with hydrogen fuel cells would be such an option. But it is also worth a closer look here:
Hydrogen is produced by electrolysis from water using electricity, then enormously compressed, transported, stored and finally converted back into water in a fuel cell with the release of electricity. This electricity can then e.g. drive an electric vehicle. So this process involves many transformation processes that reduce the overall efficiency. The highest efficiencies of fuel cells currently achieved are about 60% . In the production of hydrogen by electrolysis, one can assume an efficiency of about 70 %. The problem is:
In the calculation of the overall efficiency you have to multiply the individual efficiencies, so in the above figures, the 0.6 times 0.7 is 0.42 or just a total efficiency of 42%. For a kilowatt-hour of electricity from a hydrogen-powered fuel cell, therefore, you must initially spend almost 2.5 kWh of electrical energy. The compression, transport and storage worsen the efficiency again. So if we change vehicles not to battery-powered ones but to hydrogen fuel cell electric vehicles, we would need more than two and a half times the amount of electricity in the transport sector. The grid stabilization by recharging from the vehicles into the electricity grid, which is fundamentally important for the success of the energy turnaround, would not be so readily possible. Another significant disadvantage of these vehicles is the lack of recuperation, so the return of kinetic energy in the battery. It is precisely this feature that makes electric vehicles in the city so efficient, since accelerating and braking at the next traffic light makes even large and heavy vehicles, converted into diesel fuel, consume just over a liter. To at least compensate for this disadvantage, there are developments, in addition to the fuel cell still a battery to install, as it was implemented for example in the Toyota Mirai. However, this leads to even more technology on board and drives the costs up considerably. The safety aspect of sitting on a 700 bar hydrogen pressurized tank, which can form an extremely explosive oxyhydrogen gas mixture with the surrounding oxygen, is another point to consider in the discussion.
Fuel cells, such as those used today in vehicles, contain platinum as an important material. For a fuel cell with 100 KW power today you need about 43g of platinum. The problem is: platinum is extremely rare. Globally, only about 200 tons of it are produced per year and the production of platinum is anything but an environmentally friendly and clean thing. For the 65 million German vehicles alone, 43g per vehicle would require 2,795 tonnes. If we were to move globally to fuel cell vehicles, with 1.2 billion vehicles estimated globally, well over 50,000 tons would simply need 250 times the current annual world production of platinum. Even if it succeeds in reducing the platinum content in fuel cells to only 25% of today's value, it would still be more than 60 times as much as we can produce today.
 Alexander Stubinitzky: Ökoeffizienzanalyse technischer Pfade für die regenerative Bereitstellung von Wasserstoff als Kraftstoff. In: Fortschritt-Berichte VDI. 6: Energietechnik, Nr. 588. VDI Verlag, 2009, ISBN 978-3-18-358806-0, ISSN 0178-9414.