Seite - 53 - in Our Car as Power Plant

53 Natural gas can be converted with a much larger effi ciency, currently 72%, by a process called methane steam reform- ing. In this process high-temperature steam produces a synthetic gas containing CO plus H2 from CH4 and H2O in a fi rst step. In a second step the carbon monoxide CO is converted to CO2 and H2 (24). Nowadays, most of the hy- drogen for industrial purposes is produced by steam reforming, due to easy availability and low prices of natural gas. Currently 30 million kg of hydrogen is produced daily, in refi neries and large industrial plants (24). Production from electricity, by a process called ‘electrolysis’ has at present an effi ciency of 67%. This process is carbon- free, as the only component used is water. A voltage applied over water splits it into H2 and O2. A novel, but promising route is direct conversion from sun- light, inside a solar photo-electrochemical panel. The electrons liberated by photons are immediately used to separate hydrogen atoms from oxygen atoms in the water mole- cules. A solar-to-hydrogen effi ciency of 4.9% has been reached in laboratory based on a metal oxide photo-anode (29). OUR CAR AS POWER PLANT HYDROGEN CONVERSION TECHNOLOGIES ENERGY SOURCE PROCESS EFFICIENCY Natural gas Steam reforming 72% Coal/Oil Gasifi cation 56% Biomass Gasifi cation 44% Electricity Electrolysis 67% Sunlight Photo-electrochemical 4.9% (lab)