we operate a mobile pet grooming business that requires portable power. We have 3 Onan 3.6 KW propane fueled generators. we use them about 1000 hours per year, and have a pretty steady diet of breakdowns. The propane keeps them clean, but its a lawn mower engine spinning the electronics. Expected life is about 4-5 thousand hours. We also have a system that consists of the trucks engine spinning the alternator, charging a bank of marine 12v batteries and a 3 kw inverter. this seems like a better system to me-no lawn mower engine, solar and manual options for charging the 12v batteries, and reasonably reliable inverter units. Then there is the 5kw generac generator at home, piped in to the municipal gas system with automatic transfer switch, which has functioned well in occasional blackouts for 6 years now. You can determine the load by adding up the requirements of each electrical component: 5kw runs my furnace, assorted lights, fridge, freezer, gas stove.