Hydroelectric power is the generation of electric power from the movement of water. A hydroelectric facility requires a dependable flow of water and a reasonable height of fall of water, called the head. In a typical installation, water is fed from a reservoir through a channel or pipe into a turbine. The pressure of the flowing water on the turbine blades causes the shaft to rotate. The rotating shaft is connected to an electrical generator which converts the motion of the shaft into electrical energy.
Small hydro is often developed using existing dams or through development of new dams whose primary purpose is river and lake water-level control, or irrigation. Occasionally old, abandoned hydro sites may be purchased and re-developed, sometimes salvaging substantial parts of the installation such as penstocks and turbines, or sometimes just re-using the water rights associated with an abandoned site. Either of these cost saving advantages can make the ROI for a small hydro site well worth the use of existing site infrastructure & water rights.
Since small hydro projects usually have minimal environmental and licensing procedures, and since the equipment is usually in serial production, standardized and simplified, and since the civil works construction is also small, small hydro projects may be developed very rapidly. The physically small size of equipment makes it easier to transport to remote areas without good road or rail access.
Micro-hydro installations can also provide multiple uses. For instance, micro-hydro projects in rural Asia have incorporated agro-processing facilities such as rice mills – alongside standard electrification – into the project design.
Low head hydro power applications use river current or tidal flows of 40 meters (approximately 131 feet) or less to produce energy. These applications do not need to dam or retain water to create hydraulic head; the head is only a few metres. Using the current of a river or the naturally occurring tidal flow to create electricity may provide a renewable energy source that will have a minimal impact on the environment.
According to a report by REN21, during 2008 small hydro installations grew by 28% over year 2005 to raise the total world small hydro capacity to 85 gigawatts (GW). Over 70% of this was in China (with 65 GW), followed by Japan (3.5 GW), the United States (3 GW) and India (2 GW). China plans to electrify a further 10,000 villages by 2010 under their China Village Electrification Program using renewable energy, including further investments in small hydro and photovoltaic’s.
A 2013 report by the International Center on Small Hydro Power and UNIDO found that installed small hydro power around the globe was estimated at 75 GW and potential small hydro power was approximately 173 GW. Over 50% of the world’s potential small hydro power was found in Asia however the report noted “It is possible in the future that more small hydropower potential might be identified both on the African and American continents”
Low head hydro power
Low head hydro power applications use river current or tidal flows of 40 meters (approximately 131 feet) or less to produce energy. These applications do not need to dam or retain water to create hydraulic head; the head is only a few metres. Using the current of a river or the naturally occurring tidal flow to create electricity may provide a renewable energy source that will have a minimal impact on the environment.
A low-head hydro project generally describes an installation with a fall of water less than 5 metres (16 ft). Most current hydroelectric projects require 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 bed, creating a reservoir. Using a controlled release of water from the reservoir creates the head required to turn the turbines. The costs and environmental impacts of constructing a dam make traditional hydroelectric projects difficult to construct.
Damless hydro captures the kinetic energy of rivers, channels, spillways, irrigation systems, tides and oceans without the use of dams.
Construction of a dam and reservoir has many environmental effects. For example, the damming of a river “blocks the movement both of fish upstream to spawn and of silt downstream to fertilize fields”. In addition, “the vegetation overwhelmed by the rising water decays to form methane – a far worse greenhouse gas than carbon dioxide”.
Since no dam is required, low-head hydro may dramatically reduce the following:
- The safety risks (of having a dam), avoiding the risk of a flash flood caused by a breached dam
- Environmental and ecological complications – Need for fish ladders and Silt accumulation in basin
- Regulatory issues
- The initial cost of dam engineering and construction
- Maintenance – Removing silt accumulation.
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.
Types of low head turbines – 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:
- Axial Flow Rotor Turbine: This type of turbine consists of a concentric hub with radial blades, resembling a wind mill. Either a built in electrical generator or a hydraulic pump which turns an electrical generator on land provides the electricity.
- Open Center Fan Turbine: These turbines consists of two donut shaped turbines which rotate in the opposite direction of the current. This in turn runs a hydraulic pump that in turn drives a standard electrical generator.
- Helical Turbine: This type of turbine has hydrofoil sections that keep the turbine oriented to the flow of the water. The leader edge of the blades turns in the direction of the water.
- Cycloidic Turbine: The cycloidic turbine resembles a paddle wheel, where the flow of the water turns the wheel with lift and drag being optimized. Lift or flutter vanes looks like a huge Venetian blind.
- Hydroplane blades: They are made to oscillate by the flowing water, thus generating electricity.
- FFP Turbine Generator: This type of turbine uses a rim-mounted, permanent magnet, direct-drive generator with front and rear diffusers and one moving part (the rotor) to maximize efficiency.
- Gravitation Water Vortex Power Plant: This type of hydro power plant use the power of a gravitation water vortex, which only exists at low head.
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:
- Marine life. Concerns have been raised about the danger to marine animals, such as seals and fish, from wave and tidal devices. There is no evidence that this is a significant problem. Such devices may actually benefit the local fauna by creating non-fishing ‘havens’ and structures such as anchoring devices may create new reefs for fish colonization.
- Sea bed. By altering wave patterns and tidal streams, devices will undoubtedly have an effect, for example, upon the deposition of sediment. Research carried out to date would seem to indicate that the effects would not be significant, and may even be positive, for example by helping to slow down coastal erosion. (This is particularly pertinent in light of evidence that waves have steadily increased in size in the recent past.) The sea in the lee of devices would almost certainly be calmer than normal, but, it has been suggested, this would help in creating more areas for activities such as water sports or yachting.
- Most wave and tidal energy devices would be invisible from the shore. They would have none of the problems of visual and noise pollution that older versions of wind turbines engender. The main impact would probably be from the extensive transmission lines needed to take the energy from the shoreline to final users. This problem would have to be addressed, possibly by using underground transmission lines.
- Fishing and shipping activities. Offshore wave and tidal devices would almost certainly require areas to be closed to fishing and shipping activities. The siting of such devices would have to be negotiated, therefore, with relevant local groups (for example, fishermen), as well as with national and international bodies. (Science and Technology,2001)
