Maybe you all should work backward. Check your electric bill. In the summer I average less than 10 kilowatt-hours per day, in the winter maybe up to 20. Thats over daytime hours so 1- 2 kilowatt-hours per hour. That means a box store 4000 watt gas generator is just fine for my needs (and most other households or they wouldn't be popular). My 20 HP (at the PTO) tractor gives me 10,000 watts hooked up to my 15,000 watt capable generator, but I really need only about 2000 of that on average (the other 8000 is wasted diesel but I have to run almost wide open to generate the RPMs up to stay at 60cpm), thus plenty to spare for surges. Take a look at your power bills. 15 kw generators were designed for dairy farmers who HAVE to milk (ie run their energy consuming milking machines).