The Podium, 20 August 1997

Contributed by Dan Price, Mechanical Engineer, Denver, USA
For the Zero Emissions Targeting Conference, The Commons, 6 August 1997.

Page Contents:

_Invitation
_Commentary and discussion of this paper
_Other presentations in this series

Conference Introduction:

CablePowerÔ technology is a system of energy conversion devices that will produce high-pressure (2000 psi+) hydraulic energy from the flowing energy of a river without the use of dams. Since dams represent up to 80% of the costs and most of construction complexity of conventional hydropower, the CablePower system will dramatically reduce costs and shorten engineering/construction cycles. Construction cycles of one year from ground breaking to first operation are feasible.

Traditional hydropower uses a dam to amplify water pressure ─ expressed in feet of head ─ to drive its turbines. Dams up to hundreds of feet high are required to create the head needed to generate sufficient power. CablePower technology, by contrast, has been shown through a simple laboratory model to be able to produce power for costs estimated between 4˘ and 8˘ per kilowatt hour. Optimization and mass production may result in system costs lower than initially estimated.

The company is currently on a research and development track to begin first commercial sales of complete power plants in the year 1999. The company is not currently soliciting commercial inquiries. Currently the company is seeking funding partners for a $250,000 prototype demonstration project during year 1998 in a water canal. Potential funding partners include various U.S. government agencies, U.S. based research organizations, & commercial enterprises. Other new sources are welcome and will be considered.

Hydrofoils held in tension by cables are mounted upon floating platforms moored in a river. The blades reciprocate, or translate in reversing directions, to convert the kinetic energy of the flow field to hydraulic pressure, which is then piped through a turbine connected to an electrical generator. In layman's terms; the blade strokes across the flow path. When the blade reaches the end of the path the cable tension and blade lift change to cause the blade to turn, then the blade strokes the other direction and turns at the end of that stroke. Properly rigged cables connected to a hydraulic piston are pulled by the blades thereby converting energy from the flowing water. We have a video of the test model to help in visualizing the process.

The significance of our laboratory success is that our limited investment has achieved a measure of economic success which has evaded solar and wind energy researchers who have had hundred's of millions of dollars in funding. The only success solar and wind researcher's can point to is success at providing power at the fringe of the energy marketplace.

Ultra-low head sources, which could not be developed heretofore, are abundant worldwide and located near population centers. Adoption of the CablePower technology will open this vast new hydropower marketplace.

Ultra-low head sources can be exploited because the CablePower system separates the energy extraction mechanism from the turbine generator. This decoupling allows the energy extraction mechanism to be constructed in large sizes to take advantage of large, diffuse energy fields.

The ultra-low head capability also permits considerable flexibility and cost savings in siting of the CablePower system: in urban centers, for example, where most of the population of a region resides, thus avoiding the capital costs and environmental impacts of long-range power transmission. Urban siting also minimizes the impacts upon natural flowing rivers. Urban river systems are highly channelized, dammed and otherwise controlled to minimize impacts due to flooding. Locating the system in these areas will cause scant impact upon natural river ecosystem.

Another advantage makes the CablePower technology highly adaptable: because it is mounted on floating platforms, it can be towed to location and maneuvered or adjusted to optimize production with changing conditions on site. Energy developers and investors will realize the value of being able to relocate substantial capital assets to new river regions when necessary. Platform mounting will allow the plants to be constructed in less time than with traditional hydropower, where the civil works can take a decade to complete. Construction of the platforms can proceed independently from construction of the civil works thereby reducing construction complexity.

Decoupling of the energy extraction mechanism also permits use of large high-speed synchronous generators. Low-speed small generators used in traditional hydropower can cost four times as much as generators used with CablePower technology.

In summary the technology makes less demands on capital resources such as concrete, steel, land, and copper than traditional hydropower. Minimizing resource utilization is not only makes for good economics (low cost) but also results in a system that will cause less total emissions than competing technologies. Less land for mines must be dug, less fuel to fire cement kilns is required, less land must be diverted from productively growing trees, and less electricity to make steel is required.

While CablePower technology is applicable to a wide range of low-head sites, including river and shallow tidal basins, the most economical size range for plants will be significantly affected by maintenance requirements and by economies of scale affecting construction and operation.

The first applications of the technology are likely those within water transmission canals. Canals offer a controlled channel into which small hydro plants can be inserted. Difficulties associated with flooding, large debris and navigation can be minimized at such sites. Additionally the water canals are often owned by public agencies which have a public mission to maximize economic gain from the projects.

In places where the canal must take more than approximately 1 foot of drop per 100 feet there are often times energy dissipation structures. The need for these structures is caused by a need to minimize forces on the canal liner. CablePower devices can be installed in these areas extracting energy from a water chute rather than allowing dissipation of the energy.

The low cost of modifying the canal structure to be suitable for the technology will allow construction of small economical hydropower plants. Since many of these canal structures are similar throughout the world the technology developed will have application throughout the world in canal or water transmission projects. We envision application in water supply and waste water applications.

CablePower technology has the greatest potential when applied to large hydro sites, with 100 MW capacity and larger. For these sites, economies of scale will benefit consideration of costs for plant construction, maintenance, and power transmission.

Large sites will also be better able to justify enhancements such as locks, bypass channels, inflatable weirs, alternate anchor points, and backup power. Each of these elements are capital items that can enhance the economics or application of the CablePower technology. The relative cost of the turbine-generator system is also reduced significantly when larger generators are considered.

Tidal power has been pursued in the past because of the inherently huge development potential located very near to world population centers. In most cases, however, tidal power has not proven to be economical due to the need for constructing a dam. Because pressure-head dams are not required, the high costs and environmental impacts associated with dams can be avoided. Suitable sites include bays where jetties have been constructed or where the tidal flows naturally narrow.

Adoption of CablePower technology will bring about a dramatic reduction in environmental impacts associated with hydropower technology as it has been traditionally applied.

With CablePower systems there is no need to build dams. The pitfalls of dam construction and operation are entirely circumvented. No real estate is lost. No human or wildlife populations are dislocated. No long-distance power transmission towers are required. Power plants producing clean energy can be located near population centers.

High rates of fish mortality, a significant concern with high-head dams, are not an issue with the CablePower system. Indications are that the technology will not increase rates of kill or gradual die-off of the fish population. Analysis of the design parameters of the technology indicates why this should prove to be the case. Two major categories of effect are addressed: effects caused by the damming structure; effects caused by the turbine system.

The effects caused by the damming structure include increased predation, temperature effects, habitat destruction, and delayed progress of migrating fish. The effects caused by a turbine system include pressure effects, mechanical strike by blades, water shear, and concentration of predators. The CablePower system will mitigate or eliminate all of these effects.

The most important factor to consider in assessing the environmental consequences of a dam is the head height of the dam. [Gleick, 1992] Facilities that minimize or eliminate the need for a dam have significant environmental advantages over those that require a dam.

High-head dams flood the river channel, resulting in serious ecological consequences. Significant habitat for mammal, avian, and aquatic species is lost. Increased access to the area results in increased encroachment by man. Animal migration routes can be disturbed. New opportunistic species can invade the area and disrupt members of the native ecology. The natural sediment transport capacity of a river can be disturbed.

Fish passage through conventional turbines has been the subject of significant research interest over the last 40 years. Most of the research has been focused on salmon production in the Pacific Northwest ─ specifically, the problems associated with the transport of juvenile fish downstream past turbines. Through study and experimentation, many problems have been solved, yet the solution for some significant problems remains elusive.

The adverse effects on downstream migration of juvenile fish involve several factors:

1. Unacceptable retention time within the reservoir.

2. Exposure to reservoir predators.

3. Pressure effects within the turbine.

4. Physical contact with the turbine components.

5. Fluid shear damage.

6. Cavitation damage.

7. Downstream concentration of predators.

8. Stress from passage through this foreign device.

We can summarize our analysis of fish survivability by the consideration of a few factors. Fish can be damaged when passing through a turbine by hitting the turbine blades or walls, by pressure changes within the turbine, by shear forces in the water, and by cavitation. Of these, cavitation has been the least problematic, as owners have minimized cavitation in order to minimize turbine damage.

Because the CablePower concept greatly minimizes reservoirs or stagnant pools, the effects created by an artificial reservoir are eliminated. With the open-channel energy conversion mechanism of the CablePower system, changes in pressure in the water along a stream line do not occur. Damage from the blades and shear forces in the water are the only mechanisms that could potentially harm fish with the CablePower system.

The following expanded analysis of fish passage survivability through CablePower mechanisms demonstrates the advantage of the technology as compared to traditional turbine technology.

Pressure Effects ─ One tidal low-head Straflo turbine installation study [Stokesbury, 1991] indicates that 64.5% of damaged fish were damaged by pressure effects. Elimination of this factor should result in significant improvement in downstream fish survivability through a hydroelectric plant. Due to the open channel design proposed for the CablePower system, fish will not experience this pressure effect.

Shear Forces ─ Shear forces in the CablePower system are equivalent to those occurring with water flowing over a natural low-head drop and striking obstructions in the flow path. Fish have evolved to navigate naturally occurring turbulence. Shear forces in the CablePower system should be within the range normally encountered by fish navigating a river.

Mechanical Impact of Fish with Mechanism Components ─A formula used since 1957 [Cada, 1990] in estimating the probability of turbine blade fish contact is:

P=l*n*R*a*cosa/f.

P = Probability of blade contact (%)

l = fish length (cm)

n = number of runner blades

R = revolutions per second

a = cross sectional area of water passage (m²)

a = blade angle at the front of the blade

f = discharge rate (m³/s).

A similar fish contact equation that should be proportionally correct for the CablePower systems:

P=l*n*L*C*A*D_h*cosa/f.

P = Probability of blade contact (%)

l = fish length (cm)

n = number of runner blades

L = length of runner blades (m)

C = Cycles per second

a = Aspect ratio of channel

D_h = Hydraulic diameter of channel

a = blade angle at the front of the blade

f = discharge rate (m³/s).

We think neither equation rigorously calculates probability, but each is proportionally correct for its respective geometry. To compute probabilities from each equation and to then compare the results could result in significant error. It is correct to note that the general trend of the CablePower system is equivalent to the observed trends in turbine systems, and that a reduced speed should result in greatly reduced fish mortality.

Fish navigate natural rivers, with high survivability. It is postulated that as the CablePower mechanism speed is slowed, the fish are able to use a combination of senses and locomotion to navigate through the mechanism. Therefore, if the head of the device is low enough, the above equations of probability of impact would no longer be applicable.

Injuries to Fish Due to Impact with Turbine Components ─When fish impact an object, the damage to the fish is related to the speed of impact and to the place on its body that the fish is struck. Researchers have suggested that there must be a threshold velocity below which no injuries occur. ^[Von Raben, date] This suggests that, if the mechanism speed were slow enough, injuries to fish could be entirely eliminated.

Figure 8 shows the relationship between blade speed and fish mortality when applying the theories of probability of impact and threshold of injury. The sloped line is the fish mortality as predicted by the equations first proposed by Von Raben. Zero mortality below a certain speed is shown as the "Threshold of Mortality."

The CablePower blades can move much slower than a conventional turbine blade, and if the force of impact is low enough, the fish will be able to survive an impact. And with the mechanism moving laterally, the fish may be able to simply dodge the blades. Due to the location of scales, the surface area presented for contact, and the ability of fish to bend laterally, fish are generally less likely to be killed by a hit along the side.

These factors ─ summarized as low impact energy, perceptual avoidance, and natural resistance to lateral damage ─ favor CablePower mechanisms over conventional turbines.

Fish Passage Around the CablePower System Fish will be able to navigate through the CablePower mechanism by passing either through the blades or around the blades. The slow moving nature of the device will result in designs where the fish will simply move directly though the device. In addition, because CablePower is a velocity-head system, it is not necessary to totally enclose the flow passage with moving blades to efficiently extract the energy of the flow stream. Near the walls and floor, the velocity is slower and not as usable in power production. With baffles and screens, the fish can be directed to navigate upstream through alternate channels without coming into contact with the blades.

Bell, Milo C., Fisheries Handbook of Engineering Requirements & Biological Criteria, Fish Passage Development and Evaluation Program, Corps of Engineers, North Pacific Division, Portland, Oregon.

Cada, Glenn F., "A Review of Studies Relating to the Effects of Propeller-Type Turbine Passage on Fish Early Life Stages," North American Journal of Fisheries Management, Vol. 10, 1990, pp. 418-426.

De Camp, R.E. , "Current Motor," U.S. Patent No. 830,973, Sept. 11, 1906.

Gleick, P. H., "Environmental Consequences of Hydroelectric Development: The Role of Facility Size and Type," Energy, Vol. 17, No., 1992, pp. 735-747.

Goldsmith, K., "Future Prospects for Hydropower," based on a background document used at the United Nations Inter-Governmental Expert Group Meeting on New and Renewable Energy Sources, August 1991, in International Water Power and Dam Construction, August 1992, Volume 44, pp. 14-16.

Grose, David L., "Wind Powered Apparatus," U.S. Patent No. 4,470,770, Sept. 11, 1984.

Lee, William S., "Energy for our Globe's People," Environment, September 1990, Volume 32, pp. 12-15, 33-35.

Makovich, Larry and Gregg Smalley, "Forecast: The Electric Power Industry 1993-2010," Electrical World, Nov. 1, 1993, Vol. 207, pp. 17-24.

Stokesbury, Kevin D. E. and Michael J. Dadswell, "Mortality of Juvenile Clupeids During Passage through a Tidal, Low-Head Hydroelectric Turbine at Annapolis Royal, Nova Scotia," North American Journal of Fisheries Management, Vol. 11, 1991, pp. 149-154.

Symons, J. E., and E. B. Symons, "Current Motor," U.S. Patent No. 1,000,351, Aug. 8, 1911.

Von Raben, K., "Regarding the problem of mutilation of fishes by hydraulic turbines," Fisheries Research Board of Canada Translation Series.

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