Four 130 watt lights: 4 * 130 = 520 watts.
Watts = Volts * Amps
520 = 13.5 * Amps
520 = 12.6 * Amps
Amps = 38.5 ~ 41.6 Amps
This is a simple approximation... but it's true in principal. As others have said, you'll want to consider what the requirements of the total vehicle are first... that way, you know that you'll be okay while on the trail.
Remember that the alternator output is normally rated at the 'typical' driving level, not at idle. At lower RPM's, the alternator isn't putting out as much power as it would at a higher RPM. (It has to do with the way that an alternator makes power via an AC sine wave and rectifier bridge.) Just something to keep in mind if you're sitting on the trail for an extended period of time.
As others have said, LED's are low power devices, but they can be a bit expensive for the quality units. Granted, upgrading to a high output alternator isn't cheap either... so you'll want to plan your upgrades accordingly. Another way to get a lot more light is to go with HID vs. Halogen. A typical 35 watt HID will dump a lot more light than a 35 watt halogen will.
Hope this helps.