Details on using a Prius as a backup generator for your house can be found in the Yahoo group "Prius_Technical_Stuff" message 2584. I won't post a link, because you would have to be signed into the group to read the message, but I have included the relevant sections of the message below.
Note: there is a current limitation, because the Prius' DC-DC convertor can pump a maximum of 60 A to the 12V battery (which is where this person wired in the inverter). If I am doing the math correctly, 60 A at 13.8 V is 828 W. Assuming the inverter is 100% efficient, 828 W gives you 6.9 A at 120 V. Inverters are not 100% efficient, so maybe you will have 5 A of power available in the extension cord running to your house. This is insufficient for major appliances (heater, AC, refrigerator), but it would run electronics and lights.
Douglas (2002 Silver, Wisconsin)
2002/05/03 ... This weekend I'm hoping to wire in my 1kw inverter and test using the car as a backup generator/power source for the house in the event of power outages. I expect that a twist of the key will have the quiet, low emission ICE run to recharge the NiMH pack that will keep the 12v battery charged via the 70a? dc/dc. Everyone will want one of these hybrids when they realize they can have backup power without the noisy, smelly, 500 hours to rebuild typical backup generator. In fact, short sell your generator manufacturer stock now!
2002/05/04 I wired in the 1kw inverter as a test, direct wired to the 28ah 12v battery in the trunk. Ran a few quick tests first, checked the resting voltage of the battery - 12.54v. Turned the ignition key to on, all controllable loads except for the ventilation fan was off, the voltage crept downwards into the 12.3's fairly quickly. Didn't expect that, thought the DC/DC would keep it up, but apparently it wasn't on. 'Started' the car, and the DC/DC switched on, the voltage climbed right up to approximately 13.8v, then to 13.84v when I switched the fan off. Guess I'll make sure we 'Start' the car before letting it sit with a radio or lights on. I noted that the 12v system battery negative cable was bolted to the chassis, with just a positive cable running elsewhere. I'll have to measure voltage at a few
points in the car just to see where it's at.
So, time for the real test. I plugged my Fair Radio 'charger' into the inverter, switched the inverter on, and dialed up about 5 amps into the Elec-trak's 36v battery pack. The inverter registered about 15amps, and the Prius 12v battery read 13.8v at the battery posts. So I dialed the Fair Radio unit up to 7, then 10, then 12amps, so that the inverter was drawing about 40amps from the Prius. The voltage held steady at about 13.8v, with about a 0.1v drop through the 6AWG cables I used to connect the inverter to bolted on screw terminals on the Prius battery -- yes, no fuse for this test. I plan to install either a fuse or a breaker after I determine maximum continuous current I want to draw from the Prius. On the fused connector next to the battery, it showed a 50A rating for the fuse, and a separate 5A rating for some 'other' fuse. Since I don't even have the owner's manual yet, I don't know the purpose of the 5A. So I limited my inverter draw to less than 50A.
I didn't watch the clock, but after a few minutes, the Prius traction pack depleted enough that the ICE started and began charging it. The 12v system voltage didn't change at 13.8v. The inverter and Fair Radio charger was left running at the approximately 40A draw. After a few minutes, the ICE shut down, while the traction pack via the DC/DC maintained the 12v system at 13.8v. Success! After I permanently mount the inverter, I'll have at least 600W continuous mobile and backup 120Vac power, with SULEV emissions, no noise or very little noise with the ICE running, and no generator to maintain.