Efficient energy extraction from tides, estuaries, rivers, and other shallow water movement has not yet been feasible. Also, a system for this application should be fish friendly. The machine planned uses a 4 blade horizontal turbine impeller which has the flow entering from the side at any radial direction, exiting from the other side of the rotor in the same general direction.

As the water encounters the blade it carries the blade with it with a maximum arc of 180 degrees. The other sector of the horizontal blades automatically fold along a split line located radially along the spine of each blade, such that drag is minimal. At any given moment, half the blades are unfolded and are slowly rotating with the fluid flow, while the other half of the flat blade array are folded, offering a narrow streamlined profile to the flow as they advance into it.

By fitting trigger vanes to the main impellers, the folding and unfolding is automatic, entirely actuated by natural flow. Also, since all motion of impeller blades is coincident with natural flow, fish are auto directed from being injured or killed by impeller contact.

The system promises energy conversion far exceeding tide energy extractors relying on surface wave motion, as well as shallow water impellers relying on axial flow into the impeller, with very small diameters limiting energy transfer.

The provision of large diameter flat turbines capable of side flow energy extraction opens up the opportunity of small floating anchored generators which could range from 4 feet to 30 feet in diameter, easily parked, with power cables going onshore. The main generator would likely be DC with invertors and phase control electronics to feed into the local network or grid. The units would generate with water flowing in any direction. They would auto adjust to incoming and outgoing tides.