i have personally installed 600 amp service equipment for residential customers, in several locations. also quite a few 400 amp services.
600 amp @ 240 = 115,200 watts
400 amps @ 240 = 76,800 watts
200 amps @ 240 = 38,400 watts
100 amps @ 240 = 19,200 watts
as you can see, even a small, 100 amp panel will provide enough power for most grows, and a 200, definitely. with a 200 amp panel, a grower could very easily run 25 1000w fixtures, with room to spare for hvac....
the key to having enough power, is money talks.... the combination of the proper electrical equipment and wiring, and 240v fixtures.
keep your bills paid, and dont even think about trying to 'tap' or find a way to beat the meter, and the power company doesnt give a shit what you do, all they want is $$$. for all they know you like to metal fab work and have welders out the ass in your basement, they really dont care. tho in some states, you wouldnt want to really go nuts, the rates are astronomical if the local power utillity uses a tier/usage based billing system.
however, i will caution this, serious power requires a serious investment in both time, money, material, planning, engineering, and hiring professionals to get the job done right, or to, at least, oversee your work and ensure its integrity as a system.