I don't use any electricity to make my yogurt. I do have a store bought non-electric yogurt maker. It is a form fitted styrofoam cylinder that accepts a half gallon jug. Do you have a styrofoam cooler? Do you have a refrigerator? If you have either of these things, or any appliance that throws off heat, wrap your milk/yogurt in a towel and place in the cooler with a tight fitting lid, or on top of the refrigerator, or on top of a water heater. The yogurt should be kept at about 105*F ideally, undisturbed, for about 8 hours.
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. Margaret Mead