Science Forums 2

[CraigD]

Originally Posted by freeztar

I know little to nothing of the tech behind fuel cells, but I have read that they can be built to be as safe as traditional fuel tanks.

The major issue with various kinds of fuel cells (the term is a bit of a misnomer, as these devices are not containers for fuel, but generators of electricity that take fuel consisting of hydrogen and oxygen, and produce waste heat and water) is not safety – they and fuel containers they require have existed since the 19th century, been used without major incident in most manned spaceflight (with the exception of Apollo 13, which suffered a crippling explosion in one of its 2 oxygen tanks due to wiring that had been unknowingly damaged prior to launch, not anything related to its fuel cells) – but energy density. Compared to petroleum and alcohol-burning motors and their fuel systems, fuel cell-electric motor and their traditional fuel systems weigh 3 or more times as much. (the 4/2007 Scientific American article “Gassing Up with Hydrogen” (subscription or purchase requires for full article text) has a good discussion of these issue)

From an emissions perpective, hydrogen fuel cells are wonderful. The Apollo missions used their fuel cell exhausts for the crew’s water supply – it was nearly completely pure.

Another very major obstacle with fuel cells is cost. Currently, they cost about US $5/watt, about 3-6 times the cost of a diesel-powered electric generator. The sort of low-mass systems best suited for application such as vehicles cost about $10/watt for the fuel cell alone, ignoring the cost of the fuel storage and other systems. For comparison purposes, note that 1 horsepower equals 750 watts. A typical lawnmower engine (3.5 HP, or 2625 W), would thus currently cost about $26,250 for a fuel cell equivalent – though this comparison is likely somewhat exaggerated, as such systems would almost certainly use hybrid battery systems (like those used in current hybrid autos) to reduce the required power of the fuel cell.