Flowing water carries more than 800 times as much energy as a comparable volume of air, which makes water power an appealing method for producing electricity. Even before the advent of electricity, water mills were some of the earliest systems that went beyond human- or animal-power to do work. In the electrical age, hydropower has typically been associated with big dams and correspondingly large infrastructures. Capturing the power of enormous volumes of water behind a dam allows hydropower stations to produce billions of killowatt-hours of electricity annually, comparable to other base load power plants. But like other base load plants, there is also a strong downside to big dams that makes them less than environmentally preferable. However, new hydrodynamic systems are coming along that draw power from moving water and are able to produce energy with far less environmental impact.

While pent up artificial lakes are easy to turn into massive power plants, the environmental devastation that comes from the flooding of millions of acres of land, and the disruption of the ecosystem of the river make large-scale hydropower a second-class form of green power, at best. From a carbon perspective, hydropower is certainly preferable to burning fossil fuels. But the associated damages caused by building large-scale hydropower plants — including turning flowing water into lakes and blocking the migration of fish — is such that new dams for generating electrical power are mostly off the table.There are alternatives to creating an enormous lake in order to constantly feed the turbines.

Small-scale turbines that can sit in flowing bodies of water and generate electricity could now be poised to bring a new face to hydropower. These turbines are greener since they don’t require the blockage of waterways and the destruction and flooding of land in order to be able to produce power. Hydrodynamic power works with the energy in moving water, rather than closing off waterways to build up huge reserves of potential energy stored in the water held behind giant dams. Developmental systems from several companies are now exploring the production of more modest amounts of power, but with far lower cost and with much less environmental destruction than that from the creation of dammed hydropower. Companies such as Hydrovolts Inc., Free Flow Power and Verdant Power have different systems to make use of this power, which they are testing in different parts of the country. There are also researchers who are working on other systems that can potentially take advantage of more energy available in slower moving water.

The federal government in the United States has identified this as an as-yet untapped source of power. The existing water infrastructure of the American West offers a great deal of hydropower potential, with the greatest amount found in the states of Colorado, Oregon and Wyoming. A study by the U.S. Department of the Interior’s Bureau of Reclamation found that 1.5 million megawatt-hours of renewable energy could be generated through hydropower without needing to construct new — and environmentally questionable — large-scale dams. Instead, existing waterways and reservoirs can be used to provide electricity in addition to serving water needs of the region. (For comparison, the Hoover Dam power station produces about 4 million megawatt-hours of electricity annually. Think of this as another one-third of a Hoover Dam spread out through the existing water infrastructure.)

Aqueducts and canals represent an available source of power for additional electrical generation. Particularly in the western U.S., where water management is carried out through an extensive infrastructure of constructed canals and waterways, it may be possible to provide power for tens of thousands of additional homes. Existing dams that were built for water management rather than for power generation may be able to be tapped for power production as well, through the installation of smaller scale equipment that can efficiently and cost-effectively produce power from dams that may have previously been thought too small to be useful for power generation.

To make use of this hydrodynamic power, small, in-line turbines can be installed that generate electricity from the flow of water through aqueducts and canals. The turbine sits directly in the waterway, without a dam, which means that the negative impacts to the environment, as well as the infrastructure costs to install this equipment, are greatly reduced.

Because these waterways already constrict the flow of water moving through them, a greater proportion of the energy from the water flow can be captured with this equipment. In a canal, where most of the water flow must go through the turbine, the efficiency can be as high as 60 percent. Depending on the size of the waterway and the flow rate of the water moving through it, turbines can provide electrical output ranging from 1.5 kW to 30 kW. Because many of these waterways have continuous flows of water moving through them, they are well suited to provide additional, continuous power generation for the grid.

The Bureau of Reclamation has over 47,000 miles of canals, laterals, drains, pipelines and tunnels. To find places with hydropower potential, the government study identified those locations where there was at least a 5-foot drop and where the waterway was in operation for at least four months out of the year and where the power generation potential was at least 50 kW (based upon flow rate of canal and the drop height).

One manufacturer producing turbines for in-line uses is Hydrovolts, Inc. These are reasonably small pieces of equipment. Turbines for canals and waterways are about the size of a car or small truck. Waterfall turbines can be even smaller, and will still produce a significant amount of power. They are also fairly inexpensive, with the cost of the smallest portable model starting at just $2,000. The canal-sized turbines cost from $20,000 to $40,000. While wholesale electrical rates are not great, since their output will be fairly consistent, these turbines can potentially repay their investment cost in just a few years. Initial tests of the Hydrovolts turbine were carried out in the Roza Canal in Washington State earlier this year.

(Quick back-of-the-napkin math: A turbine costing $40,000 and generating an average of 25kW over a year of operation will produce almost 220 MWh of power and earn over $10,000 at a wholesale electrical rate of $0.05/kWh. That could mean that the equipment could be paid off in four years.)

Hydrovolts turbine in the Roza Canal in Washington State:

Hydrovolts turbines also can be outfitted with different kinds of blades, depending on the flow rate of the water. This makes the system more versatile, and the same equipment can be used in different locations, with just a change of blades in order to produce the optimal yield from a given location.

While many of these channels being discussed for use are artificial waterways used for irrigation, the same technology can be used in open water rivers and streams with a sufficient flow rate. In those cases, having the waterway open to fish migration and movement is another benefit from this technology.

While the Hydrovolts turbines are being developed for very small waterways, the opposite end of the hydrokinetic power scale is also being explored with a project set in the world’s largest river. Free Flow Power is a company that is developing river flow turbines to be placed along a length of the lower part of the Mississippi River.

The Free Flow Power turbine is a 3-meter diameter multi-bladed propeller inside a housing that makes it look very much like a large jet engine. The turbine has a 40 kW rating. The first array of these turbines will be installed at a total of 25 locations along the Mississippi River and will provide a total generating capacity of 3,303 MW. Given the size of the river and the volume of water that flows through it, there is a great potential for much more energy production if this technology turns out to be effective and cost-competitive.

Unlike wind farms, these turbines are out of sight below the surface of the water. Despite their size, since these turbines will be installed below the water’s surface, they will present very little obstacle to navigation, so that the Mississippi will also continue to serve as an efficient highway for barge traffic moving goods up and down the river. This project may be just the beginning for harnessing the vast power of so much water moving through the middle of the country.

In New York City’s East River, the Roosevelt Island Tidal Energy Project (RITE) being run by Verdant Power Inc. will eventually have 30 turbines installed underwater and generating as much as 1,050 kW of electricity when the pilot project is fully installed in 2015. These turbines are considerably larger than the Hydrovolts equipment. Rather than drawing power from the narrow flow of water in a channel, these units are instead powered by the tidal flows from the ocean.

Verdant Power has another project that builds on some of the work done for the RITE project. The Cornwall Ontario River Energy Project (CORE) is installing turbines in the St. Lawrence River near Cornwall, Ontario to study how the turbines work in a river flow situation.

The turbines Verdant is developing are three-bladed, without an enclosure, and look quite similar to the now familiar three-bladed wind turbines, except for their comparatively much smaller size. The Verdant turbines are larger than those being developed by Free Flow Power; for the CORE project they are using turbines with a blade diameter of 5 meters and with a generating capacity of 60-80 kilowatts. These turbines, too, would sit out of the way of surface vessels on the bottom of the waterway. An animation from Verdant shows what a large-scale farm of these turbines might look like.

Along with these developmental systems, researchers are working on other low-velocity technologies for hydrokinetic power generation. One system, being explored by researchers at the University of Michigan is called VIVACE, which stands for Vortex Induced Vibrations for Aquatic Clean Energy. VIVACE is especially interesting because it promises to work with slow moving river flows as slow as 2 knots. Most river currents in the United States are slower than 3 knots.

The VIVACE system works with horizontal cylinders placed across the flow of the water to create a vortex as the water flows past the cylinder. “Vortex Induced Vibration (VIV) is an extensively studied phenomenon where vortices are formed and shed on the downstream side of bluff bodies (rounded objects) in a fluid current. The vortex shedding alternates from one side of a body to the other, thereby creating a pressure imbalance resulting in an oscillatory lift.” This motion of the cylinder can, in turn, be used to move a magnetic field in order to produce electricity.

The turning blades of hydrokinetic turbines are a potential concern, just as wind turbines are with birds. Part of the reporting being done with these early projects is to study potential problems with this kind of equipment. Although its development is lagging behind some of the other systems, VIVACE may turn out to be a preferable technology because it has less impact on marine wildlife. The cylinders used in this system are very slow moving (only about 1 cycle per second), and the risk of harm to any fish is therefore extremely low.

Hydrokinetic projects are appealing because the power generation is more constant than some other sustainable systems. Waterway flows can be more regular and dependable than intermittent sources like wind. Hydrokinetic power is presently an underutilized resource, but as these companies develop their technology, it is likely to become another part of the energy mix.

Main, second and third photo credits: Hydrovolts Inc.

Video credit: Hydrovolts Inc.

Fourth photo credit: Free Flow Power

Fifth photo credit: Kris Unger/Verdant Power, Inc.