Gravity water wheels as a micro hydropower energy source: A review based on historic data, design methods, efficiencies and modern optimizations

Nowadays, due to the need for clean energy and sustainable electricity production, hydropower plays a central role in satisfying the energy demand. Particularly, use of low head micro hydropower plants is spreading worldwide, due to their low payback periods and good environmental sustainability. Gravity water wheels are micro hydropower converters typically used in sites with heads less than 6 m and discharges of a few cubic meters per second. Although water wheels were scientifically investigated as far back as the eighteenth century, they were largely ignored throughout the twentieth century, and only in the last two decades has there been a renewed interest in their use among the scientific community.