Basically In hydro power to generate power you can go for a small amount of water falling a long distance or a large amount of water falling a small distance
Its a classic high head low flow pelton wheel installation.
He wouldn't need such large pipe for a penstock if he was using a pelton wheel, but he also doesn't have the head to drive a pelton efficiently - the more the better for one of those.
I've seen systems that put 2kw of energy through 2" pipe! 350+ feet of vertical head will do that.
Yeah it's basically a modification of a pelton wheel, sort of adapted for higher flow and lower pressure. Technically a turgo wheel IS a pelton wheel, but they serve sort of separate purposes.
Its a classic high head low flow pelton wheel installation.