The beverly clock has an ingenious power source. It has a sealed container of air that expands and contracts with temperature differences throughout the day. I'm envisioning a sealed plastic box with a hole cut in the top, and a flexible material over the hole (like a balloon). This material would be connected to a toothed bar interlocking with a gear, connected to a pulley over which the weight and chain that normally run these clocks hangs. The toothed bar only grips the gear in one direction, and when it does it turns the gear/pulley and winds the chain. When the temperature and therefore the pressure of the air in the box fluctuates, it moves the toothed bar up and down, winding the chain. This means that the natural behavior of the environment winds this clock.
It would be difficult to get much productive power out of this setup, but it's a novel approach to the problem and might be worth keeping in mind.