I often wished I could harness the power of methane.
If you are thinking of solar, be looking for a place to put 4-6 or more golf cart batteries as close to where you bring the wires from the roof panels down.
Some simple 120VAC/12VDC arithemetic. Ohm and Volta will roll over in their grave. A 120V device, like a fan, will draw about 2 amps. Powered by an inverter, the 12V Amp draw will be about 20A. Just move the decimal point over. People will jump in and say there are conversion losses, power factors, etc but its pretty close for rule of thumb. Figure out the DC amp draw and divide into Amp hour rating of batteries and you start getting a picture.
You size solar panels the same way you size solar panels for swimming pools; measure your roof space to determine how many of the biggest panels you can find to fit the space then buy as many as you can afford.
Great start.