Low head hydro power

Low head hydropower applications use tidal flows or rivers with a head of 20 metres (66 ft) or less to produce energy.[1] These applications may not need to dam or retain water to create hydraulic head. Using the drop in a river or tidal flows to create electricity may provide a renewable energy source that will have a minimal impact on the environment.

Comparison to conventional hydro

Most current hydroelectric projects use a large hydraulic head to power turbines to generate electricity. The hydraulic head either occurs naturally, such as a waterfall, or is created by constructing a dam in a river valley, creating a reservoir. Using a controlled release of water from the reservoir drives the turbines. The costs and environmental impacts of constructing a dam can make traditional hydroelectric projects unpopular in some countries.

Damless hydro captures the kinetic energy of rivers, channels, spillways, irrigation systems, tides and oceans without the use of dams.[2]

Construction of a dam and reservoir may have harmful environmental effects. For example, the damming of a river may “block the movement both of fish upstream to spawn and of silt downstream to fertilize fields”.[3] Where sites aren't cleared “the vegetation overwhelmed by the rising water decays to form methane – a far worse greenhouse gas than carbon dioxide”, particularly in the tropics.[3]

Since no dam is required, low-head hydro may dramatically reduce the following:

However, low-head units are necessarily much smaller in capacity than conventional large hydro turbines, requiring many more to be built for a given annual energy production, with some of the costs of small turbine/generator units being offset by lower civil construction costs. Just as for large hydro, not every site can be economically and ecologically developed; sites may be too far from customers to be worth installation of a transmission line, or may lie in areas particularly sensitive for wildlife.

Another potentially promising type of low head hydro power is dynamic tidal power, a novel and unapplied method to extract power from tidal movements. Although a dam-like structure is required, no area is enclosed, and therefore most of the benefits of 'damless hydro' are retained, while providing for vast amounts of power generation.

Hydrokinetic turbines

A "Hydrokinetic" turbine is an integrated turbine generator to produce electricity in a free flow environment. It does not need a dam or diversion. Instream Energy Systems has coined the phrase Instream Energy Generation Technology or IEGT places turbines in rivers, man made channels, tidal waters, or ocean currents. These turbines use the flow of water to turn them, thus generating electricity for the power grid on nearby land. In effect, IEGT is like planting windmills in the water and is environmentally friendly. While hydrokinetic includes generation from ocean tides, currents and waves, many researchers believe its most practical application in the near term is likely to be in rivers and streams.

Instream Energy Systems has deployed a 25 kilowatt hydrokinetic turbine in a canal just outside Yakima Washington. They have the ability to deploy multiple turbines along a river, canal, or aqueduct in order to maximize their energy harvest with minimal impact on the existing canals. Two major benefits of hydrokinetic deployment are the reliability and the predictability of the water delivery systems. Unlike wind, the water deliveries are planned well in advance and therefore utilities can accurately predict when more power will be coming online. A 35 kilowatt hydrokinetic turbine has been installed in the Mississippi River near Hastings, Minnesota. Underwater tidal turbines are propelled by tidal currents.[4] If the viable river and estuary turbine locations are made into hydroelectric power sites “researchers estimat[e] that [the United States’] rivers and estuaries could provide up to 130,000 gigawatt-hours per year — about half the yearly production of the country's dams”

Types of low head turbines

Main article: Water turbine

Turbines suitable for use in very low head applications are different from the Francis, propeller, Kaplan,or Pelton types used in more conventional large hydro.

Different types of low head application turbines are:

Installation of turbines in river current

The turbines can be installed in a variety of ways, multiple banks set on pilings driven into the river beds or mounted on existing river structures such as bridge piers. These turbines operate in a “free flow” environment that does not require the damming or diversion of rivers. This approach does not disrupt natural ecosystems or interfere with aquatic and marine life. The turbine generators can be attached to bridge abutments or pilings, which minimizes disruption to river beds.

Turbines are to be deployed in arrays of multiple units spaced no less than 15 metres (49 ft) apart where the site conditions, depth, and needed infrastructure are suitable. Exact depth and spacing is determined based on site conditions, including current flows and water depth. Since the turbines do not block waterways, and the water passing through the device is not subject to high pressure, these systems are designed to not impede or damage fish or other wildlife. This entire structure is installed at a depth that avoids any interference with recreational or navigational uses of a water resource. The power will be transmitted by cable to conversion equipment located on shore. The conversion equipment will convert the power from DC to AC, adjust the voltage and connect to the power grid. This approach will be better suited to river current where the flow is in one direction as opposed to ocean shore locations.

A competing idea is to suspend the turbines from a floating barge. The turbines suspended from the bottom of a floating barge can accommodate changes in flow. The barges can be deployed and have the generators come on line more quickly with fewer disturbances to the river bed. The obvious disadvantage to the barge system would be interference with navigation and recreational use of the waterway. This system does have some advantages, installation costs may be less depending on river bottom conditions and maintenance and repair would be somewhat easier. Concern over the impact on seasonal flooding and ice conditions also must be considered with the barge system.

Tidal power

Main article: Tidal power

Tidal flow occurs due to the moving mass of water with speed and direction as caused by the gravitational forces of the sun and the moon, and centrifugal and inertial forces on the Earth's waters. Due to its proximity to the earth, the moon exerts roughly twice the tide raising force of the sun. The gravitational forces of the sun and moon and the centrifugal/inertial forces caused by the rotation of the earth around the center of mass of the earth-moon system create two "bulges" in the Earth's oceans: one closest to the moon, and the other on the opposite side of the globe.(CNW Group, 2008). This kind of energy is unique and different from traditional hydropower that has been around for centuries. There is no need to build a dam. Essentially a turbine is stuck in naturally flowing water. As the water flows, it turns a turbine. That is converted to electricity.

Tidal basin locations can also be developed using the low flow turbine technology as well. These areas are limited to ocean side locations and the difficulty associated with rotating the turbines to adjust to the direction of the tidal flow must also be accounted for. It would appear that the turbines suspended from under a floating barge would be better suited to the tidal application. The barge itself can be turned to face the direction of the tidal flow. It may also be more difficult to provide the areas for power conversion and connection to the power grid given the limited areas that can be developed to utilize tidal flows. Several demonstration projects are underway to study the feasibility of the tidal basin locations. Tidal turbines are a new technology used for tidal energy. They are similar to wind turbines and are arranged underwater in rows. They work best in areas with strong tides. They are also the least environmentally damaging of all the tidal power technologies, since they do not interfere with migration paths and the impact on basin bed is less as no construction is needed in the waterway itself.

In order for tidal power to work successfully it requires a tide difference of at least 5 metres (16 ft). Unfortunately there are only a few places where this occurs. This means tidal power plants cannot just be constructed anywhere. There are only a handful of sites on Earth with this type of tidal range. A demonstration project has begun in New York City. In the last four years, the federal commission has approved nearly a dozen permits to study tidal sites. Applications for about 40 others, all filed in 2006, are under review. No one has applied for a development license, Miller said. The site that is furthest along in testing lies in New York’s East River, between the boroughs of Manhattan and Queens, where Verdant Power plans to install two underwater turbines this month as part of a small pilot project.

Ocean and tidal currents can provide an indefinite supply of emission-free renewable energy. Since tidal and river currents exist everywhere in the world and are either constantly flowing or extremely predictable, converting the energy in these currents to electricity could provide a predictable, reliable and, in some cases, base load supply of electricity to the electric power systems or remote sites in many parts of the world. 70% of the world's population lives within 320 kilometres (200 mi) of an ocean. Accordingly, ocean current energy could become a vital part of the world's energy future.

Environmental impact of low head hydropower

A number of concerns have been raised about the environmental impacts of river current and tidal devices. Among the most important of these are:

Implementation and regulations

Government regulation

Most government regulation comes from the use of waterways. Most low head water turbine systems are smaller engineering projects than traditional water turbines. Even so, one needs to obtain permission from state and federal government institutions before implementing these systems . Some of the constraints faced with these systems in larger waterways are making sure waterways can still be used for boats and making sure that routes of migration of fish are not disturbed.

Government subsidies

US government subsidies can be obtained for implementation of small-scale hydro facilities most easily through federal grants, namely green energy grants . a specific example is the Renewable Electricity Production Tax Credit. This is a federal tax credit aimed at promoting renewable energy resources. To qualify, the hydro source must have a minimum capacity of 150 kW. This subsidy is given for the first ten years of production. Organizations receive $.011/kWh.

Public perception

Since these are sustainable energy source, are non detrimental to the water sources they utilize and are visually not an eyesore, they are well regarded within the public sphere . However, there is little public and industrial knowledge of these systems as they are still being tested to "answer real-world questions".[5] As such, proponents and manufacturers of these systems have tried to bring them into public knowledge

See also

References

  1. ↑ http://www.expertglossary.com/water/definition/low-head-hydroelectric
  2. ↑ I. I. Ivanov, G. A. Ivanova, V. N. Kondrat'ev and I. A. Polinkovskii (January 1991). "Increase of the efficiency of small hydroelectric stations" (PDF). Power Technology and Engineering. Springer New York. 25 (1): 1–4. doi:10.1007/BF01428128.
  3. 1 2 bruce (2008-03-11). "Hydroelectric power without the dam?" (Blog Online Posting).
  4. ↑ Erik Sofge (April 2007). "Underwater Wind Turbines Tap River Energy" (Magazine Website). Popular Mechanics.
  5. ↑ http://www.popularmechanics.com/science/green-tech/a1463/4213223/

Lam, Tina

Fairley, Peter

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