| Batteries by David Dietzler 2008 |
| Batteries have the advantage over fuel cells in that they can be recharged simply by plugging them into an electrical power source and they don't require large heavy tanks of compressed hydrogen and oxygen or even heavier insulated tanks of LH2 and LOX as fuel cells do. To recharge fuel cells the water generated by them must be electrolyzed and the hydrogen and oxygen compressed or liquefied with compressors and space radiators. This does not lend itself to mobile applications. Sodium-sulfur batteries are interesting because sodium and sulfur exist on the Moon and could be obtained by magma electrolysis. See: Magma Process and Na-K-P-KREEP |
| However, we find at http://en.wikipedia.org/wiki/Sodium-sulfur_battery NaS batteries run at 300-350 C. and the sodium is very corrosive. NaS batteries are not recommended for mobile applications but perhaps we can find a way to make them work in vehicles on the Moon. NIckel metal hydride batteries are another possibility. We can extract nickel from iron fines mined on the Moon. From 24,000 tons of iron fines we could get 1,200 tons of nickel. NiMH batteries are used effectively today in hybrid cars and trucks. See: NIckel and Cobalt |
| We also have some hydrogen on the Moon, but no cadmium so NiCad batteries are out and no lead although we can make sulfuric acid so conventional lead-acid batteries are out. There's no lithium on the Moon so lithium ion batteries are out too. We do have the basic materials for nickel metal hydride batteries. see: http://en.wikipedia.org/wiki/Nickel-metal_hydride_battery quote from above URL: The specific energy density for NiMH material is approximately 70 W·h/kg (250 kJ/kg), with a volumetric energy density of about 300 W·h/L (360 MJ/m³). Since one horsepower is 746 watts, an NiMH battery weighing 10.6 kg could generate one horsepower for an hour, not considering electric motor inefficiency. That's impressive. Battery packs on lunar vehicles might amass 1000 kg but weigh only 166 kg. on the Moon. A 1000 kg. NiMH battery would store 70,000 watt hours or enough energy ignoring inefficiency of electric motors to make one horsepower for 94 hours or ten horsepower for 9.4 hours ! That's impressive too. A mid-sized car traveling over level ground with no headwinds to fight at 25-30 mph only uses about ten horsepower. Acceleration from a stop requires major horsepower and so does highway travel. We will have no winds to fight or air friction and we will travel at slow speeds on the dusty Moon so we will be able to sustain a constant moderate speed while draining about 10 hp from the NiMH batteries for several hours before recharging is necessary. The 1000 kg battery would have a volume of 233 liters. That's only about a fourth of a cubic meter. Not bad at all. NiMH batteries could be the batteries of choice for lunar vehicles while fuel cells and sodium-sulfur batteries could be used for stationary applications like night span energy storage. From the wikipedia article about NaS batteries we find that a 6 MW, 48 MWh sodium-sulfur battery system has been built at Tsunashima, Japan. Several other utilities are considering such installations. |
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