200kWh is a lot for a bus-roof sized solar array. It can be done, but it'll take up a good chunk of the space on the roof.
200kWh = 200000Wh
200000Wh per month / 30 days = 6666.67 Wh per day
I'm just guessing here, but I would say that at a suitable North American latitude you may get a couple hours of peak solar charging plus a reduced amount in the morning and evening. For simplicity's sake, let's just say you'll have 5 hours of peak solar charging.
6666.67 Wh / 5 hours = 1333.33 watts
So a solar array of 1333.33 watts could potentially provide you with around 200kWh of electricity, but (as you know) you would also need an appropriate battery bank. Also, this isn't taking into account seriously cloudy/rainy/snowy days.
100kWh a month is reasonable, though. 666.67 watts is easy. 2 or 3 good sized panels can provide that, though I wouldn't expect to be using electric heaters and the like off of this small of a system. The battery chemistry probably wouldn't like it (serious voltage drop) which would also add more heat to the wires.
These are largely made up numbers, but it may give you an idea of how solar panels translate into the type of electricity we use on any given day in a typical house. We use LOADS of electricity in our daily lives without even realizing it.
I have a 600 watt solar array on my roof and a 455Ah battery bank. The system works wonderfully for all the things I do with it: water pump, laptops, phone chargers, lights, fans, tools (even bigger ones like table saws), small 12v refrigerator, stereo. I tried a tiny space heater through the inverter for the fun of it some time back, though, and it imparts a pretty harsh voltage drop. I wouldn't want to run that for long.
Originally Posted by Zephod_beeblebrox2
if I have a backup generator running on diesel that should do a lot.
Do you have any particular aversion to propane? Nobody is trying to force it down your throat, but my suspicion is that a diesel generator creating electricity to run a resistive device that creates heat would be more expensive (and loud) than a gas that, when ignited, instantly and silently creates heat. There are also some neat little propane on-demand water heaters out there...