Larger dams can hold more water and can use more generators. However, they require much more land use. Low head generators must be placed where there is water flow. They need to be protected properly so that debris does not clog or obstruct the generator. Also, water needs to be channeled into it, so the current going through it is stronger and produces more energy.
Generators use no fuel and maintenance is minimal.
The heads can range from 3 to 10 meters with high efficiencies. One potential spot for low head generators is Alaska. It is ideal because of its southern coastline which has significant tidal ranges. The type of land that is conducive to building dams is an area with a decrease in elevation, a large area of land for a reservoir, and a large body of water with a strong current. There also needs to be plenty of land around the dam in case of flooding.