The bike would be more efficient if you hooked it directly to whatever mechanical appliance you might need to operate. A grain mill, ringer washer, meat grinder, water pump, etc. I tried hooking up a small 12 volt generator off a tractor and powering it by peddling. Wow. I'd rather bike uphill in the Himalayas. Alternators require even more power, so that's out. But, peddling would beat hand-cranking in a direct mechanical application such as the above-mentioned. What exactly are you wanting to power ?
Swampdweller