They could limit it to wind, water, and muscle power to provide the energy needed for their technology. So windmills, water wheels, and looms/spinning wheels are acceptable, but wood boiling water to make a steam engine would not. From there, you get ideas to use the power supplies better. I.e. if you need a constant power supply, you might use a water wheel. If the water is not that reliable, you can make a dam to store the water for release as needed. Another idea might be linking a windmill to a water lift, to move water back above the dam, so it can be reused.
Fire would be used to melt iron and harden various clays for the blacksmith and the buildings.
I wonder, what sort of technology they could develop under those limitations? Waterwheel pumping water up (
Pumped storage) for usage by a
Cam hammer (or few) to pound the metal, with another set of gears providing power to a set of bellows for the blacksmith. One blacksmith is all the labor that is needed to use the facility, but it will take a lot of work to set up.