28'x15'= 420 sq. ft. Since you wanna do that massive killer crop (we'll figure 50 watts per sq. ft), you only need ~ 20 (1000 watt H.P.S.) for flowering, or 35 600 watt H.P.S.
Yeah, you NEED a generator. Drawing 20 kw's/hour x 12 hours= 240 kwh's a day= 7200 kwh's per month. You WILL get someones attention.
GIve each plant 3'x3', thats only ~45 plants. You'll be busy as a one armed paper hanger with crotch itch come trim time.
Better know an electrican, HVAC guy, or be both, seriously. And that 10,000 BTU AC you have you can smash. It will be just as effective when running that kind of light.
Who said weird:D:D
b0nger
P.S. Post pictures when you have it all set up. I will eagerly await them.