Musings

In the ‘Green Energy’ world, much is being made of solar thermal & electric, wind power, tidal power, and so forth, and yet a terrific technology has been commercialized and as yet, has received little attention.

A Hydrokinetic turbine is simply a wind generator that is submerged in a flowing stream, and turns the water current into electricity. Water however, is much more productive of power than the wind. Water has almost 900 times the energy density of air, and therefore can produce an exceptional amount of power in a small space. And, water flows at predictable rates, 24/7, unlike the wind. Furthermore, the turbine blades are harmless to fish and other aquatic life.

Fast-flowing water has great power. The energy (kW/m2) increases as the cube of the velocity (V3) in meters per second (m/s). Faster currents have much more power. A current of 3 m/s or 6 mph has about 13 kW/m2 of energy. In this stream a hydrokinetic turbine that is 40% efficient can make about 5 kW of power from one square meter (about 3x3 ft) of flow. This is enough power for two modern American homes, from a device the size of an office desk.


Market Size
A 1986 study by New York University of free-flow river power in the USA estimated conservatively that there is 12,500 MW of undeveloped capacity for energy. This is worth about $10 billion in electricity sales today. The study criteria were:
• Only rivers with mean flow rate > 4000 cfs and velocities > 4.3 ft/s
• Only 25% of width is available
• Only 25% of the length of a river reach
• Turbine diameter = 80% of mean depth
• Turbine spacing of ½ diameter and row spacing = 5 diameters
• 40% turbine efficiency
The study did not consider smaller rivers and canals where Hydrokinetic turbines can also generate renewable energy. The market just in the USA is thus many thousands of megawatts larger that the NYU estimate. Suitably fast flows are found in regions with high altitudes and snow packs, large rainstorms or significant rainy seasons such as monsoons, or where large flows go through narrow channels. In the latter case, it is where there are high tides or seasonal rainfall or timed releases of water from reservoirs and dams into irrigation canals.

These commercial units come in all sizes