"Set Square" wrote in message
...

Actually, I'd like to be able to generate *all* my electricity from gas -
not just in an emergency. Bearing in mind that the marginal cost per kWHr of
(on peak) electricity is 3.6 times that of gas, I would save on fuel costs
as long as the overall conversion efficiency was more than about 27.5%

Which it isn't; and you'd want batteries to handle the peak loads.
Once you've got the batteries, you can store off-peak electricity.