I understand one therm has 100000btu's. Does that mean that if I use a internal combustion engine coupled to a generator (assuming 100% efficiency) I'm going to get 100000/3.14=31 Kwh? Where I live the gas costs $1 per therm (delivery and tax included) and electricity costs $.11/kwh. Even at 80% efficiency I'd generate my own electricity at half cost of what my electric company is charging. Something wrong with my math?