How Hydroelectric Energy Works

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How Hydroelectric Energy WorksContents 1. The Hydropower Resource

2. Converting Moving Water to Electricity 3. Environmental Concerns

By taking advantage of the water cycle, we have tapped into one of nature's engines to create auseful form of energy. In fact, humans have been using the energy in moving water for thousandsof years. Today, exploiting the movement of water to generate electricity, known ashydroelectric power, is the largest source of renewable power in the United States andworldwide.

Unfortunately, hydroelectricity has its drawbacks. By blocking rivers with massive dams, wehave created a number of serious environmental and social problems, including habitat

destruction, prevention of fish passage, and displacement of local communities. Still, if it's doneright, hydropower can be a sustainable and nonpolluting power source that can help decrease ourdependence on fossil fuels and reduce the threat of global warming.

The Hydropower Resource On Earth, water is constantly moved around in various states, a process known as the hydrologiccycle. Water evaporates from the oceans, forming into clouds, falling out as rain and snow,gathering into streams and rivers, and flowing back to the sea. All this movement provides anenormous opportunity to harness useful energy.

The United Nations estimates that the total "technically exploitable" potential for hydropower is

15,090 terawatt-hours per year, or 15 trillion kilowatt-hours, equal to half of projected globalelectricity use in 2030 .[1] Only about 15 percent has been developed so far .[2] While much ofthe remaining potential may not be economically or environmentally suitable to develop, thereare still significant opportunities for new development in regions like the former Soviet Union,South Asia, and South America.

Hydropower provides one-fifth of the world's electricity, second only to fossil fuels. Worldwidecapacity is 776 gigawatts (GW), with 12 percent in the United States, nine percent in Canada,and eight percent in Brazil .[3] When completed, China's Three Gorges Dam, poised to becomethe largest hydroelectric project in the world with 18.2 GW of capacity, will move China aheadof Brazil. Globally, hydroelectric capacity has more than doubled since 1970, and another 100GW is currently under construction.

In the United States, hydropower has grown steadily, from 56 GW in 1970 to more than 95 GWtoday .[4] As a percentage of the U.S. electricity supply mix, however, it has fallen to 10 percent,down from 14 percent 20 years ago, largely as a result of the rapid growth in natural gas power

plants. In terms of electricity production, hydropower plants account for about seven percent ofAmerica's current power needs .[5]
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In some parts of the country, hydropower is even more important. For example, the Pacific Northwest generates more than two-thirds of its electricity from 55 hydroelectric dams .[6] TheGrand Coulee dam on the Columbia River is one of the largest dams in the world, with acapacity of nearly 6,500 megawatts (MW).

In addition to very large plants in the West, the United States has many smaller hydro plants. In1940 there were 3,100 hydropower plants across the country, but by 1980 that number had fallento 1,425. Since then, a number of these small plants have been restored; there are currently 2,378hydro plants (not including pumped storage) in operation .[7] These plants account for only a tinyfraction of the 80,000 dams that block and divert our rivers. As a result, there is a significantopportunity for growth according to the National Hydropower Association, which estimates thatmore than 4,300 MW of additional hydropower capacity can be brought online by upgradingexisting facilities .[8]

Worldwide there is a great deal of growth in small hydro projects. The World Energy Councilestimates that under current policies, installed capacity of small hydro will increase from about

48 GW today to 55 GW by 2010, with the largest increase coming from China .[9] More than halfof the current global small hydropower installed capacity is in China, with plans to develop afurther 10,000 MW in the next decade .[10]

An important issue now in the United States is the re-licensing of hydropower plants. Hydro plants have very long lives; the Grand Coulee dam, for example, has been in operation since1942. The federal government issues licenses for all dams for a 30- to 50-year period. In 1993,for instance, over 200 licenses were due for renewal, amounting to 2,000 MW of capacity. Re-licensing some of these dams should require dam owners to find ways to reduce environmentalimpacts. Unfortunately, in the 2005 Energy Policy Act, the hydropower licensing law wasamended as part of the Energy Policy Act of 2005, making it more difficult for the public to

participate in the re-licensing process .[11] Converting Moving Water to Electricity In order to generate electricity from the kinetic energy in moving water, the water has to bemoving with sufficient speed and volume to turn a generator. Roughly speaking, one gallon ofwater per second falling one hundred feet can generate one kilowatt of electrical power.

To increase the force of moving water, impoundments or dams are used to raise the water level,creating a "hydraulic head," or height differential. When water behind a dam is released, it runsthrough a pipe called a penstock, and is delivered to the turbine.
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An impoundment. Source: DOE Office of EERE

Hydroelectric generation can also work without dams, in a process known as diversion , or run-of-the-river. Portions of water from fast-flowing rivers, often at or near waterfalls, can bediverted through a penstock to a turbine set in the river or off to the side. The generating stationsat Niagara Falls are an example of diversion hydropower. Another run-of-the-river design uses atraditional water wheel on a floating platform to capture the kinetic force of the moving river.While this approach is inexpensive and easy to implement, it doesn't produce much power. Theentire Amazon River, if harnessed this way, would produce only 650 MW of power.

Another type of hydropower, though not a true energy source, is pumped storage. In a pumpedstorage plant, water is pumped from a lower reservoir to a higher reservoir during off-peak times,using electricity generated from other types of energy sources. When the power is needed, it isreleased back into the lower reservoir through turbines. Inevitably, some power is lost, but

pumped storage systems can be up to 80 percent efficient. There is currently more than 90 GWof pumped storage capacity worldwide, with about one-quarter of that in the United States.Future increases in pumped storage capacity could result from the integration of hydropower andwind power technologies. Researchers believe that hydropower may be able to act as a batteryfor wind power by storing water during high wind periods .[12] ,[13]

There are a variety of turbines employed at hydropower facilities, and their use depends on theamount of hydraulic head at the plant. The most common are Kaplan, Francis, and Pelton wheeldesigns. Some of these designs, called reaction and impulse wheels, use not just the kinetic forceof the moving water but also the water pressure.

The Kaplan turbine is similar to a boat propeller, with a runner (the turning part of a turbine) thathas three to six blades, and can provide up to 400 MW of power .[14] The Kaplan turbine isdifferentiated from other kinds of hydropower turbines because its performance can be improved

by changing the pitch of the blades. The Francis turbine has a runner with nine or more fixedvanes. In this turbine design, which can be up to 800 MW in size, the runner blades direct thewater so that it moves in an axial flow .[15] The Pelton turbine consists of a set of speciallyshaped buckets that are mounted on the outside of a circular disc, making it look similar to a
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water wheel. Pelton turbines are typically used in high hydraulic head sites and can be as large as200 MW.

The ability to meet power demand fluctuations is an advantage of hydro plants with reservoirs.Unlike run-of-the-river plants, which produce power around the clock, hydro plants with dams

are typically used only when the power is most needed. Utilities save up the water, letting itloose only during peak times. Hydro plants, especially the large older plants built from the 1930sto the 1950s, are commonly the least-expensive source of electricity.

Environmental Concerns Although an inexpensive and nonpolluting energy resource, the environmental damage causedhydropower can be serious. The most obvious effect is that fish are blocked from moving up anddown the river, but there are many more problems.

When a dam is constructed, a river habitat is replaced by a lake habitat.While this may not sound so bad -- fish and birds like lakes, too -- it can cause a number ofenvironmental problems. In the Pacific Northwest, large federally owned dams have blocked themigration of coho, chinook, and sockeye salmon from the ocean to their upstream spawninggrounds. The number of salmon making the journey upstream has fallen 90 percent since theconstruction of four dams on the lower Snake River. Some steps are being taken to help the fisharound the dams, such as putting them in barges or building fish ladders, but this only helps somuch. Also, when young fish head downriver to the ocean, they can be chewed up in the turbinesof the dam. As of 2002, 71 percent of the area of Washington and 50 percent of Oregon containwatersheds with salmon and other related species that have been listed as threatened orendangered.

Dams can create large reservoirs submerging what used to be dry land, producing many problems. The Balbina dam in Brazil, for example, flooded 2,750 square kilometers (965 squaremiles), an area the size of Rhode Island. This land is often composed of wetlands, which areimportant wildlife habitats, and low-lying flood plains, usually the most fertile crop land in thearea. Population density is typically higher along rivers, leading to mass dislocation of urbancenters. The Three Gorges Dam in China is expected to dislocate up to 1.9 million people .[16]

Wildlife habitats destroyed by reservoirs can be especially valuable. In South America, 80 percent of the hydroelectric potential is located in rain forests, one of the most rich and diverseecosystems on Earth. The Rosana dam in Brazil destroyed one of the few remaining habitats ofthe black-lion tamarin, a rare and beautiful species of long-haired monkey.

Another problem can occur when the land area behind the dam is flooded without proper preparation. In Brazil, the Tucurui dam was built creating a reservoir in a rain forest region,without the forest first being cleared. Later, as the plants and trees that were submerged began to
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rot, they reduced the oxygen content of the water, killing off the plants and fish in the water.Moreover, the rotting plants gave off large quantities of methane, a powerful global warminggas.

A similar problem has occurred in Canada, in hydro projects built by Hydro Quebec. The stones

and soil in the flooded area contain naturally occurring mercury and other metals. When the landwas flooded, the mercury dissolved into the water, and then into the local fish populations. Thecreatures that eat the fish from bears and eagles, to the native Cree people are suffering frommercury poisoning. Mercury poisoning can cause brain damage, birth defects, liver disorders,and other ailments.

Impoundments used for hydropower can cause many other effects on water quality and aquaticlife. Rivers and lakes can be filled with sediment from erosion. Water falling over spillways canforce air bubbles into the water, which can be absorbed into fish tissue, ultimately killing thefish. By slowing down rivers, the water can become stratified, with warm water on top and coldwater on the bottom. Since the cold water is not exposed to the surface, it loses its oxygen and

becomes uninhabitable for fish. And as illustrated by the Colorado River in the Grand Canyon,fast-moving rivers can be filled up with sediment when they are slowed down. In an effort tomitigate this problem, the Department of Interior has flushed huge amounts of water out of damsin an attempt to clear away the sediment.

Another important habitat disruption comes from the operation of the dam to meet electricdemand. Water is stored up behind the dam and released through the turbines when powerdemand is greatest. This causes water levels to fluctuate widely on both sides of the dam,stranding fish in shallow waters and drying out the habitat. There are many competing pressureson dam operators -- to produce power, to provide water for recreational use both on the reservoirand downstream, to provide drinking and irrigation water, to allow Native Americans to carry

out traditional religious practices, and to preserve habitat for fish and plant species. In manycases, nature loses out to boaters, farmers, and electric customers.

The risk of a dam breaking should also not be ignored. The great Johnstown flood inPennsylvania was the result of a dam break (although not a hydroelectric dam); 2,000 peoplewere killed. In northern India and Nepal, in the Himalayas, huge hydroelectric projects are

planned that would create large reservoirs in a geographically unstable region. Frequentearthquakes make the dam a risky venture for heavily populated areas downstream. This iscompounded by the fear that large, heavy reservoirs would put additional pressure on the platesin the region, causing even more earthquakes. Finally, breakage could also result from war orterrorism, as dams have been considered potential military targets in the past. The environmentaland social effects of hydropower can be immense. But while hydropower has its problems, it canstill be a safe and sustainable source of electricity if proper measures are taken. By upgradingand improving the equipment at plants, by increasing fish-friendly efforts at dams, and byimproving run-of-the-river turbine technology, it may be possible to reduce the environmentaleffects of hydropower. Nonetheless, remediation may be impossible at some sites, and wildrivers should be unshackled.


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It is also important to compare the environmental effects of hydropower with alternatives. Thedamage to aquatic habitat from dams may be significant, but acid rain, nitrogen deposition, andthermal pollution from coal plants also lead to aquatic damage, as well as to air pollution andglobal warming. Provided we dismantle the worst hydropower facilities, and improve thesustainability of the others, we will be better off.

LOW IMPACT HYDROPOWER Hydroelectric facilities that meet certain standards to minimize their effect on rivers, fish, and

wildlife can now seek recognition as low impact under a voluntary certification programdeveloped by the Low Impact Hydropower Institute (LIHI). Criteria standards are based on themost recent and stringent mitigation measures recommended for the dam by state and federalagencies.

Worumbo hydroelectric facility, certified low-impactSource: Low Impact Hydro Institute

To be certified, a facility must adequately protect or mitigate its impacts in the following areas:river flows, water quality, fish passage and protection, watershed protection, threatened andendangered species protection, cultural resource protection, and recreation. The incentive forcertification is the ability to market a more sustainable energy source to consumers, especiallythose participating in voluntary green power programs. In addition, Pennsylvania requireshydroelectric projects to be LIHI certified in order to be eligible to count towards the state'srenewable electricity standard. Currently, more than twenty hydropower facilities have beenLIHI certified.

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Introduction to Hydroelectric TechnologyHydroelectric power is the generation of electric power from the movement of water flowingfrom a higher to a lower elevation. In contrast, hydrokinetic technology is a pre-commercialtechnology that uses river current to generate electric power. A hydroelectric facility requires a
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dependable flow of water and a reasonable height of fall of water, called the head. In a typicalinstallation, water is fed from a reservoir through a conduit called a penstock into a hydraulicturbine. The pressure of the flowing water on the turbine blades causes the shaft to rotate. Therotating shaft is connected to an electrical generator, which converts the shaft motion intoelectrical energy. After exiting the turbine, water is discharged to the river in a tailrace.

Before a hydroelectric power site is developed, engineers must assess how much power will be produced when the facility is complete. They also review the natural conditions that exist at eachsite: surface topography, geology, river flow, water quality, and annual rainfall and snowfallcycles. Extensive studies are conducted to evaluate the sites environmental conditions, landstatus and other factors that may influence the configuration of the hydro plant and theequipment selection.

A given amount of water falling a given distance will produce a certain amount of energy. Thehead and the discharge at the power site and the desired rotational speed of the generatordetermine the type of turbine to be used. The greater the head, the greater the potential energy to

drive turbines. More head or faster flowing water means more power .1

The steep mountains,abundant rain and snow, and relatively mild winter temperatures in Southeast and SouthcentralAlaska provide the ideal hydrologic conditions for hydroelectric power.

Cross section of hydraulic turbine generator.

Source: Army Corp of Engineers

Fold Table of ContentsIntroduction to Hydroelectric Technology Theoretical Horsepower Low-Head Hydropower Run-of-the-River Small, Mini, and Micro Hydropower Conventional Hydroelectric Storage Projects

Theoretical HorsepowerTo find the theoretical horsepower (the measure of mechanical energy) from a specific site, thisformula is used:

THP = (Q x H)/11.81where: THP = theoretical horsepowerQ = flow rate in cubic feet per second (cfs)H = head in feet
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11.81 = a constant

A more complicated formula is used to refine the calculations of this available power. It takesinto account losses in the amount of head due to friction in the penstock and variations due toefficiency levels of mechanical devices used to harness the power. To determine how much

electrical power can be produced, the mechanical measure (horsepower) must be converted intoelectrical terms (Watts). One horsepower is equal to 746 watts (U.S. measure).

South Fork Drainage, Prince of Wales Island,

Southeast Alaska.

Source: Alaska Energy Authority, 2008.

Impulse and reaction turbines are the two most commonly used types. Other types of turbinesinclude fixed pitch propeller and crossflow (also called the Ossberger or Banki turbines). Eachhas a specific operating range in terms of hydraulic head and power output. In order to optimizethe power output and reduce capital costs, the specific turbine to be used in a power plant is notselected until all operational studies and cost estimates are complete. The turbine selecteddepends largely on site conditions.

A reaction turbine is a horizontal or vertical wheel that operates with the wheel completelysubmerged, a feature that reduces turbulence. In theory, the reaction turbine works like a rotatinglawn sprinkler, where water at a central point is under pressure and escapes from the ends of the

blades causing rotation. Francis or Kaplan turbines are reaction machines that utilize both

hydraulic pressure and kinetic energy to create rotating shaft work. Reaction turbines are the typemost widely used in Alaska.

An impulse or Pelton- type turbine is a horizontal or vertical wheel that converts the fluidschange in potential energy (hydraulic head) into kinetic energy by water striking its buckets or

blades to make the extractable rotating shaft work. Pelton or Turgo impulse turbines may havesingle or multiple nozzles that accelerate flow to produce high velocity jets that impinge on a setof rotating turbine buckets to transfer their kinetic energy. The wheel is covered by a housing,and the buckets or blades are shaped so they turn the flow of water about 170 degrees inside thehousing. In contrast to a reaction turbine, the fluid contained in the impulse turbine does notcompletely fill all available void space, and the turbine operates at ambient pressure. After

turning the blades or buckets, the water falls to the bottom of the wheel housing and flows out.

Source: Bureau of Reclamation, 2005.
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Low-Head HydropowerA low-head dam is one with a water drop of less than 65 feet and a generating capacity less than

15,000 kW. Large, high-head dams can produce more power at lower cost than low-head dams, but construction of large dams may be limited by lack of suitable sites, by environmentalconsiderations, or by economic conditions . The key to the usefulness of low-head units is theirlower capital costs and the ability to satisfy local power needs with the available resource.

Run-of-the-RiverRun-of-the-river hydro facilities use the natural flow and elevation drop of a river to generate

electricity. Facilities of this type are optimally built on rivers with a consistent and steady flow.

Power stations on rivers with great seasonal fluctuations require a large reservoir in order tooperate during the dry season. In contrast, run-of-the-river projects do not require a largeimpoundment of water. Instead, some of the water is diverted from a river and sent into a pipecalled a penstock. The penstock feeds the water downhill to the power stations turbines.Because of the difference in elevation, potential energy from the water upriver is transformedinto kinetic energy and then to electrical energy. The water leaves the generating station and isreturned to the river with minimal alteration of the existing flow or water levels. With properdesign, natural habitats are preserved, reducing the environmental impact.

Run-of-the-river power plants typically have a weir or diversion structure across the width of theriver. This weir contains an intake structure, often consisting of a trash rack, an intake screen,and de-sanding elements to conduct the water into the penstock. These installations have a smallreservoir behind the diversion to keep the intake flooded and reduce icing problems.

The output of the power plant is highly dependent on the drainage basin hydrology. Spring breakup will create a lot of energy, while flow diminishment during winter and dry seasons willcreate relatively little energy. A run-of-the-river power plant has little or no capacity for energystorage, and so cannot coordinate the output of electricity generation to match consumer demand.Most run-of-the-river applications are small hydro.

Small, Mini, and Micro HydropowerSmall hydro is the development of hydroelectric power on a scale that serves a community or anindustrial plant. The definition of a small hydro project varies, but a generating capacity of up to10 MW is generally accepted as the upper limit of what is termed small hydro. Small hydro can
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dams and reservoirs of larger hydroelectric projects provide for energy storage, holding water to be used to generate electricity when flows are lower. Unfortunately, most Alaska electric loadsare highest during the winter, the same time that river flow (and the electric power generationcapability of small and run-of the-river hydro) is at its lowest. This lowers the amount of run-of-the-river hydro capacity that can be installed without significant amounts of excess capacity in

the summer.

Conventional Hydroelectric Storage ProjectsWhen suitable hydraulic heads are not present or when power needs are substantial, dams areconstructed across rivers to store water and create hydraulic head to drive the turbo machinery.Dams typically last for 50 to 100 years and so, are constructed of durable materials likereinforced concrete, roller-compacted concrete, earth, and crushed rock. Smaller dams may be

constructed of steel or timber crib design. They vary substantially in terms of height and storagevolume, depending upon local topography. There are several design approaches used forconcrete dams, including solid and hollow, gravity and arch geometries.

In addition to the actual dam structure, there are a number of other major design considerations.For example, the penstock inlet manifold (usually with screens to keep debris and fish fromentering the turbine) and the discharge or tailrace system must be designed to maintain thehydraulic head and minimize the effects of sedimentation, silt, and ice build-up. Substantialeffort goes into the design of the dam spillway to safely direct extreme flows downstream of thedam when the available reservoir storage is inadequate to contain it.

Power Creek H ydro proj ect

Where the topography allows, several successful design concepts are available to help mitigatethe environmental impacts of conventional storage hydropower projects. In regions with high-elevation natural lakes, lake taps may be utilized to feed a power tunnel bored in rock to carrywater to the downstream powerhouse. This approach reduces the need to construct a dam; thetunnel serves in place of the penstock; and the lake is utilized as a natural storage reservoir. Atother sites, natural barrier waterfalls can facilitate licensing of upstream hydro developmentthrough their function as fish migration barriers. Fish protection and passage facilities and eco-friendly turbines can also be designed to mitigate fisheries impacts of hydroelectric facilityconstruction. In order to be constructible, all hydro projects must pass rigorous assessment.Environmental effects must be determined. Mitigation measures, compliance monitoring, andenvironmental follow-up programs must be established.

A strong attribute of conventional hydropower is the dispatchability that results from the abilityto control the rate of power production through storage and release of water contained behind the
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dam. Given the general increase in electrification that is occurring worldwide, the demand forusing hydropower reservoirs for both base-load and peaking applications is rising. Other factorsmay also lead to increased interest in conventional hydropower. The variable nature of otherrenewable energy sources like wind and solar makes pairing with hydro energy storage anattractive option for integrated supply systems.

Additionally, the scale of energy production attainable with hydroelectric storage lends it toconnection with large electrical grids to displace conventional fossil fuel-based power sourceswith clean, non-carbon-based power. Fuel switching to inexpensive hydropower may be possiblein some situations for home heating and (someday) for plugin hybrid cars.

http://energy-alaska.wikidot.com/hydro-power-technology-overview

HYDROKINETIC ENERGY (In-River, Tidal, and Ocean Current)

Introduction to Hydrokinetic Energy Unfold

Table of Contents

Hydrokinetic devices are powered by moving water and are different from traditionalhydropower turbines in that they are placed directly in a river, ocean or tidal current. Theygenerate power only from the kinetic energy of moving water (current). This power is a functionof the density of the water and the speed of the current cubed. The available hydrokinetic powerdepends on the speed of the river, ocean , or tidal current. In contrast, traditional hydropower usesa dam or diversion structure to supply a combination of hydraulic head and water volume to aturbine to generate power. In order to operate, hydrokinetic devices require a minimum currentand water depth.

How Does Hydrokinetic Energy Work?

As water flows through a turbine or other device, the kinetic energy of the flowing river, tidalfluctuations, or waves is converted into electricity by the device.

As mentioned in the above introduction, hydrokinetic devices require a minimum current andwater depth. The minimum current required to operate a hydrokinetic device is typically 2-4knots. Optimum currents are in the 5-7 knot range. Water depth is an important factor in the totalenergy that can be extracted from a site, since rotor diameter is dependent on adequate water
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level above the installed device. Hydrokinetic devices are ideally installed in locations withrelatively steady flow throughout the year, locations not prone to serious flood events,turbulence, or extended periods of low water level.

Challenges in Hydrokinetic Energy

Among the challenges in hydrokinetic energy is the presence of glacial silt in Alaska waters,especially Cook Inlet. Over time, silt and other sediments in the water flowing throughhydrokinetic turbines can erode the machinery. In addition to this, the migration of fish andmarine mammals, ice and other debris, as well as river and ocean bed stability, must be takeninto careful consideration

Hydrokinetic Energy in Alaska

Alaskas first in -stream hydrokinetic turbine, located in Ruby

Alaska has significant potential for hydrokinetic development in both rivers and tidal basins.Most inland communities in Alaska are situated along navigable waterways that could hosthydrokinetic installations, and Alaska, with 90% of the total U.S. tidal energy resource, is hometo some of the best tidal energy resources in the world. While there are obvious opportunities,there are also significant environmental and technical challenges (see below) related to thedeployment of hydrokinetic devices in Alaskas rivers and tidal passages. Some of these arecommon to installations in any location. Other concerns are more specific to Alaskan waters. Asof 2008, hydrokinetic devices are considered pre-commercial. The Yukon River Inter-TribalWatershed Council installed a 5 kW New Energy Encurrent turbine in the Yukon River at thecommunity of Ruby for one month in 2008. A 100 kW UEK turbine is planned for installation inthe Yukon River at Eagle in 2009. The New Energy EnCurrent machine, in 5 and 10 kW size, isavailable for purchase from ABS Alaska in Fairbanks, and New Energy Corporation isdeveloping 25kW, 125kW, and 250kW devices as well. This technology is still being refined forAlaskan applications. Its performance is unproven.

EETG: Yukon Hydrokinetic Project
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EETG: Nenana Hydrokinetic Turbine

Technology Introduction

Hydrokinetic devices typically use vertical or horizontal axis turbines similar to those developedfor wind generation; however, because water is approximately 850 times denser than air, theamount of energy generated by a hydrokinetic device is much greater than that produced by awind turbine of equal diameter. In addition, river and tidal flow do not fluctuate as dramaticallyfrom moment to moment as wind does. This predictability benefit is particularly true for tidal

energy. It can be predicted years in advance and is not affected by precipitation or evapo-transpiration.

ORPC's Beta TidGen Power System. Photo: ORPC

Hydrokinetic Technology in Alaska

In Alaskas riverine environments, water flow fluctuates, often dramatically, on a seasonal basis.Snowmelt from glaciers and seasonal snow accumulation contributes significantly to the totalwater volume in Alaska s waterways. Generally, flow rates are the highest during springsnowmelt, but this higher flow is associated with significant debris flowing within the water
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channel. Debris is often directed to the fastest area of flow (the thalwag) and is not necessarilyconfined to the surface. In the winter, river flow often drops off dramatically and is largelysupplied by local groundwater. This fact coupled with challenges associated with ice/turbineinteractions leaves open to question whether hydrokinetic devices would be cost effective duringwinter months in most Alaskan rivers. If hydrokinetic devices are only deployed seasonally in

riverine environments, an imbalance between resource availability and electricity demand (whichis often highest in the winter months) will result.

It is possible that in dealing with resource and load fluctuations on short time periods, energystorage could be utilized or excess energy could be dissipated for heating purposes (see theEnergy Storage section for more information).

The hydrokinetic working group agreed that commercial projects will likely be operating in thestate in the next three to five years. The group was not ready to make specific recommendations(see below) for hydrokinetic projects for specific villages in Alaska. Recommendations from theworking group are less project specific. They are tipped toward finding appropriate ways to

move forward with this technology. The members of the working group stressed that its successis tied to not overestimating the maturity level of the technology by skipping over beta testingand demonstration phases.

Hydrokinetic energy represents a real opportunity for power generation using local resources atselect locations in Alaska; however, there are still numerous environmental and technicalchallenges associated with this technology. For example, there are concerns related tointeractions between turbines and both adult and juvenile fish, since most communities withhydrokinetic resources are heavily dependent on local subsistence and commercial fisheries.Additional concerns include ice interaction with infrastructure, silt abrasion, submerged debriswhich could damage turbines, navigation hazards, and impacts on marine life.

The actual construction and operation of a pilot device or devices will result in a more completeunderstanding of technical, environmental, and cost factors associated with hydrokinetic energy.This would provide a solid starting point for additional cost and economic analysis for specificsites around the state.

SnapshotTECHNOLOGY SNAPSHOT: HYDROKINETIC

Installed Capacity(Worldwide)

1500 kW worldwide, all demonstration projects

Installed Capacity(Alaska )

0 kW installed

Number of Potentially available to communities in all regions of Alaska located near a major
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communitiesimpacted

waterway or tidal basin, excluding the North Slope

Technology Readiness Pre-commercial to early commercial

Environmental ImpactImpacts on local hydrology and aquatic species must be assessed on a case bycase basis. AEA anticipates that these impacts can be minimized by appropriatesiting, design and operation.

Economic StatusA 2008 EPRI study calculates paybacks in the 3-9 year range for three proposedhydrokinetic sites in Alaska, however this has not been verified by a commercialinstallation.

Case Studies Igiugig In-River Hydrokinetic Site , Cairn Point at Knik Arm Tidal Energy Site , Nenana , Eagle

Systems

Alaska Specific Technology Challenges Environmental concerns , especially with regard toimpacts on fish must be addressed. Fisheryresources in Alaska have unparalleled value forsubsistence, sport, and commercial use. It is criticalthat hydrokinetic energy development be fullyevaluated for impacts on these resources.

Survivability and performance issues must beexamined. Alaskan waters have many hazards forhydrokinetic devices, including high rates ofsediment transfer in river beds, debris, and ice.These issues also complicate the design ofanchoring and cabling systems.

Resource assessment is necessary. There is ashortage of river velocity and depth data,particularly for winter months.

Effects on navigation are important. Many of thefast flowing rivers in Alaska with potential forhydrokinetic development are also majorwaterways for barge delivery of bulk materials toisolated communities. A major consideration isthat these devices not impede river traffic
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HYDROELECTRIC POWER GENERATION

Introduction to Hydroelectric Power

Alaska has enjoyed a long and rich history with hydroelectric power. By 1908, southeast Alaskaalone had over 30 developed water power sites with a capacity of 11,500 kW. The vast majority, built by private developers, provided power for industrial operations, mainly for the gold miningworks in Juneau and on Douglas Island. Today hydropower in Alaska provides 24% 1 of thestatewide electrical power. Major developers include the State of Alaska and public and privatelyowned utilities. These power plants have proven to be long-term, reliable, and relativelyinexpensive sources of power. Hydropower installations have the reputation for being robust anddurable, operating successfully at some sites for more than a century. Hydropowers lowoperation and maintenance costs coupled with long lifetimes result in stable power rates. InAlaska, hydropower is currently the largest and most important producer of electricity from arenewable energy source. With increased interest in replacing fossil-fuel-powered generation

with renewable energy resources, the statewide inventory of installed hydropower capacity willcontinue to expand.

How Does Hydroelectric Power Work?

Hydroelectric power uses the gravitational force of water falling falling or flowing water togenerate electricity. Most hydroelectric power comes through the use of dams: the potentialenergy of dammed water drives a water turbine and generator. The power that is generated at ahydroelectric facility depends upon the volume of water moving through the dam and the heightdifference between the water's source and outflow.

Challenges of Hydroelectric Power

Impoundment hydroelectric projects are some of the cheapest and largest producing forms ofrenewable energy; however, they can have serious damaging impacts on the surroundenvironment, oftentimes making smaller "run-of-the-river" projects more attractive. Althoughthese smaller devices produce less electricity, they can be less detrimental to salmon runs anddecrease likelihood of inundating riparian valleys .2


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>> Facilities in AK


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Cross section of hydraulic turbine generator.

Source: Army Corp of Engineers

Theoretical Horsepower

To find the theoretical horsepower (the measure of mechanical energy) from a specific site, thisformula is used:

THP = (Q x H)/11.81where: THP = theoretical horsepowerQ = flow rate in cubic feet per second (cfs)H = head in feet

11.81 = a constant

A more complicated formula is used to refine the calculations of this available power. It takesinto account losses in the amount of head due to friction in the penstock and variations due toefficiency levels of mechanical devices used to harness the power. To determine how muchelectrical power can be produced, the mechanical measure (horsepower) must be converted intoelectrical terms (Watts). One horsepower is equal to 746 watts (U.S. measure).

Snapshot

TECHNOLOGY SNAPSHOT: HYDROELECTRIC

Installed Capacity(Worldwide)

654,000 MW

Installed Capacity(Alaska)

Approximately 423 MW
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Resource Distribution

Resource potential exists throughout many areas of the state, with mostdeveloped projects in the southeast and southcentral portions of the state;Alaska has 40% of U.S. untapped hydropower (192 billion Kwh energypotential)

Number ofcommunities /

population impacted 100+ (potentially +80% of Alaskas population)

Technology Readiness Commercial (mature)

Environmental Impact Requires proper design to mitigate impacts to downstream aquatic life,downstream water quality, and recreational uses

Economic StatusUnit costs are variable and site specific. Where found to be economic,

hydroelectric installations provide reliable, inexpensive renewable energy

Case Studies Bradley Lake , Four Dam Pool , Southeast Alaska , South Fork Prince of WalesIsland , New Hydro Projects

Wind Working Group Recommendations , References

News DOE Hydro News

--

Systems

Impulse and reaction turbines are the two most commonly used types. Other types of turbinesinclude fixed pitch propeller and crossflow (also called the Ossberger or Banki turbines). Eachhas a specific operating range in terms of hydraulic head and power output. In order to optimizethe power output and reduce capital costs, the specific turbine to be used in a power plant is notselected until all operational studies and cost estimates are complete. The turbine selecteddepends largely on site conditions.

A reaction turbine is a horizontal or vertical wheel that operates with the wheel completelysubmerged, a feature that reduces turbulence. In theory, the reaction turbine works like a rotatinglawn sprinkler, where water at a central point is under pressure and escapes from the ends of the

blades causing rotation. Francis or Kaplan turbines are reaction machines that utilize bothhydraulic pressure and kinetic energy to create rotating shaft work. Reaction turbines are the typemost widely used in Alaska.
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An impulse or Pelton- type turbine is a horizontal or vertical wheel that converts the fluidschange in potential energy (hydraulic head) into kinetic energy by water striking its buckets or

blades to make the extractable rotating shaft work. Pelton or Turgo impulse turbines may havesingle or multiple nozzles that accelerate flow to produce high velocity jets that impinge on a setof rotating turbine buckets to transfer their kinetic energy. The wheel is covered by a housing,

and the buckets or blades are shaped so they turn the flow of water about 170 degrees inside thehousing. In contrast to a reaction turbine, the fluid contained in the impulse turbine does notcompletely fill all available void space, and the turbine operates at ambient pressure. Afterturning the blades or buckets, the water falls to the bottom of the wheel housing and flows out.

Source: Bureau of Reclamation, 2005.

Low-Head Hydropower

A low-head dam is one with a water drop of less than 65 feet and a generating capacity less than15,000 kW. Large, high-head dams can produce more power at lower cost than low-head dams,

but construction of large dams may be limited by lack of suitable sites, by environmentalconsiderations, or by economic conditions . The key to the usefulness of low-head units is theirlower capital costs and the ability to satisfy local power needs with the available resource.
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Run-of-the-River

South Fork Drainage, Prince of Wales Island,

Southeast Alaska.

Source: Alaska Energy Authority, 2008.

Run-of-the-river hydro facilities use the natural flow and elevation drop of a river to generateelectricity. Facilities of this type are optimally built on rivers with a consistent and steady flow.

Power stations on rivers with great seasonal fluctuations require a large reservoir in order tooperate during the dry season. In contrast, run-of-the-river projects do not require a largeimpoundment of water. Instead, some of the water is diverted from a river and sent into a pipecalled a penstock. The penstock feeds the water downhill to the power stations turbines.Because of the difference in elevation, potential energy from the water upriver is transformedinto kinetic energy and then to electrical energy. The water leaves the generating station and isreturned to the river with minimal alteration of the existing flow or water levels. With properdesign, natural habitats are preserved, reducing the environmental impact.

Run-of-the-river power plants typically have a weir or diversion structure across the width of theriver. This weir contains an intake structure, often consisting of a trash rack, an intake screen,and de-sanding elements to conduct the water into the penstock. These installations have a smallreservoir behind the diversion to keep the intake flooded and reduce icing problems.

The output of the power plant is highly dependent on the drainage basin hydrology. Spring breakup will create a lot of energy, while flow diminishment during winter and dry seasons willcreate relatively little energy. A run-of-the-river power plant has little or no capacity for energystorage, and so cannot coordinate the output of electricity generation to match consumer demand.Most run-of-the-river applications are small hydro.
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Small, Mini, and Micro Hydropower

Small hydro is the development of hydroelectric power on a scale that serves a community or anindustrial plant. The definition of a small hydro project varies, but a generating capacity of up to10 MW is generally accepted as the upper limit of what is termed small hydro. Small hydro can

be further subdivided into mini hydro, usually defined as less than 1,000 kW, and micro hydro,which is less than 100 kW. Micro hydro applications might serve for single families or smallenterprises, while mini hydros might be appropriate for small communities.

A small hydro plant might be connected to a conventional electrical distribution network as asupplemental source of renewable energy. Alternatively, a small hydro project might be built inan isolated area that would be uneconomic to serve from a network, or in areas where there is noelectrical distribution network. Small hydro projects usually have minimal reservoirs and civilconstruction work, consequently a relatively low environmental impact.

A large and growing number of companies offer standardized turbine generator packages in the

approximate size range of 200 kW to 10 MW. These water-to-wire packages simplify the planning and development of the site, since one vendor looks after most of the equipment supply.

Non-recurring engineering costs are minimized, and development cost is spread over multipleunits, so the cost of such systems is improved. While synchronous generators capable of isolated

plant operation are often used, small hydro plants connected to an electrical grid system can useeconomical induction generators to further reduce installation cost and to simplify control andoperation.

Micro hydro plants may use purpose-designed turbines or industrial centrifugal pumps connectedin reverse to act as turbines. While these machines rarely have optimum hydraulic characteristics

when operated as turbines, their low purchase cost makes them attractive for micro hydro classinstallations.

Regulation of small hydro generating units may require water to be spilled at the diversion tomaintain the downstream stream habitat. Spilling will also happen when the natural flow exceedsthe hydroelectric system capacity, since the project will generally have no reservoir to storeunused water. For micro hydro schemes feeding only a few loads, a resistor bank may be used todissipate excess electrical energy as heat during periods of low demand. In a sense this energy iswasted, but the incremental fuel cost is negligible so economic loss is minor.

Since small hydro projects may have minimal environmental and licensing procedures, the

equipment is usually in serial production. Civil works construction is also limited. The small sizeof equipment also makes it easier to transport to remote areas. Fore these reasons, small hydro projects may reduce development time.

Small hydro and mini hydro can be used as alternative energy sources in off-grid communitieswith small loads. Small hydro tends to depend on small water turbines fed directly by rivers andstreams. When compared with other renewable energy alternatives like wind and solar, run-of-
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the river hydroelectric generators are able to deliver a relatively consistent electric supplythroughout the day.

Run-of-the-river hydroelectric generators in Alaska do not provide the same seasonallyconsistent electric supply that larger hydroelectric projects do. This is a result of the seasonal

changes in the flows of Alaska rivers, with diminished flow rates during the winter months. Thedams and reservoirs of larger hydroelectric projects provide for energy storage, holding water to be used to generate electricity when flows are lower. Unfortunately, most Alaska electric loadsare highest during the winter, the same time that river flow (and the electric power generationcapability of small and run-of the-river hydro) is at its lowest. This lowers the amount of run-of-the-river hydro capacity that can be installed without significant amounts of excess capacity inthe summer.

Manufacturers

Projects Introduction

Conventional Hydroelectric Storage Projects

When suitable hydraulic heads are not present or when power needs are substantial, dams areconstructed across rivers to store water and create hydraulic head to drive the turbo machinery.Dams typically last for 50 to 100 years and so, are constructed of durable materials likereinforced concrete, roller-compacted concrete, earth, and crushed rock. Smaller dams may beconstructed of steel or timber crib design. They vary substantially in terms of height and storagevolume, depending upon local topography. There are several design approaches used for

concrete dams, including solid and hollow, gravity and arch geometries.

In addition to the actual dam structure, there are a number of other major design considerations.For example, the penstock inlet manifold (usually with screens to keep debris and fish fromentering the turbine) and the discharge or tailrace system must be designed to maintain thehydraulic head and minimize the effects of sedimentation, silt, and ice build-up. Substantialeffort goes into the design of the dam spillway to safely direct extreme flows downstream of thedam when the available reservoir storage is inadequate to contain it.


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Power Creek H ydro proj ect

Where the topography allows, several successful design concepts are available to help mitigatethe environmental impacts of conventional storage hydropower projects. In regions with high-elevation natural lakes, lake taps may be utilized to feed a power tunnel bored in rock to carry

water to the downstream powerhouse. This approach reduces the need to construct a dam; thetunnel serves in place of the penstock; and the lake is utilized as a natural storage reservoir. Atother sites, natural barrier waterfalls can facilitate licensing of upstream hydro developmentthrough their function as fish migration barriers. Fish protection and passage facilities and eco-friendly turbines can also be designed to mitigate fisheries impacts of hydroelectric facilityconstruction. In order to be constructible, all hydro projects must pass rigorous assessment.Environmental effects must be determined. Mitigation measures, compliance monitoring, andenvironmental follow-up programs must be established.

A strong attribute of conventional hydropower is the dispatchability that results from the abilityto control the rate of power production through storage and release of water contained behind the

dam. Given the general increase in electrification that is occurring worldwide, the demand forusing hydropower reservoirs for both base-load and peaking applications is rising. Other factorsmay also lead to increased interest in conventional hydropower. The variable nature of otherrenewable energy sources like wind and solar makes pairing with hydro energy storage anattractive option for integrated supply systems.Additionally, the scale of energy production attainable with hydroelectric storage lends it toconnection with large electrical grids to displace conventional fossil fuel-based power sourceswith clean, non-carbon-based power. Fuel switching to inexpensive hydropower may be possiblein some situations for home heating and (someday) for plugin hybrid cars.

Hydropower Technology DevelopmentHydroelectric power is the largest source of renewable electricity in the United States, producingabout 7% of the nation's total electricity throughout the last decade. Even after a century of

proven experience with this reliable renewable resource, significant opportunities still exist toexpand the nation's hydropower resources through non-powered dams, water conveyance
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systems, pumped storage hydropower, and new site development. The Water Power Programsupports the hydropower industry and complements existing investments through thedevelopment and deployment of new technologies and key components, and by identifying keyopportunity areas through which hydropower generation can be enhanced.

The Water Power Program aims to provide 15% of the nation's electricity needs by 2030 withwater power (hydropower plus marine and hydrokinetic technologies), with hydropower makingthe largest contribution to this goal. With more than 2,500 U.S. companies supporting thehydropower industry, adding additional hydropower generation will create a large and enduringeconomic benefit here at home by revitalizing the domestic manufacturing and hydropowerindustry.

Learn more about the Water Power Program's work in the following areas of hydropowertechnology development:

Advanced Turbines Materials and Manufacturing Hydropower Systems Hydropower Technology Accomplishments

Advanced Turbines

The Alden Turbine, model seen above, allows fish passage without sacrificing performance.Credit: Alden

The Water Power Program supports the development of more efficient and environmentallyfriendly hydropower turbines that can compete with traditional designs. One such project is theAlden Turbine, which is designed to reduce fish mortality while generating at efficiencies equalto or better than conventional Francis turbines. This turbine will allow downstream fish passageand optimal hydropower generation. After extensive testing and demonstration, the Alden
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Turbine can be deployed in areas that are otherwise unused for hydropower because of fish populations.

Materials and Manufacturing

The Water Power Program funds R&D to identify and test new materials and manufacturingtechniques that improve the performance and lower the costs of hydropower. Areas of program-funded research focus include materials or coatings that reduce the life-cycle cost of turbinerunners, draft tubes, and penstocks, and identification and testing of ways to improve generatorefficiency and reliability.

Hydropower Systems

The Water Power Program works to develop, demonstrate, and test new technologies andtechniques that can improve the energy efficiency and environmental performance ofhydropower. The program's activities support industry by reducing capital and operations andmaintenance costs, increasing unit availability and plant capacity factors, reducing risk throughenhanced system reliability, and improving the quality environmental performance attributes aswell as ancillary power benefits and quantity of the energy produced. Areas of focus includewater-use optimization, the application of advanced materials and manufacturing methods, andmodeling and prediction of water power grid services.

Technology Development Accomplishments

The program has numerous accomplishments in hydropower technology development. The projects described below highlight just a few of the program's new opportunities and recentsuccesses in water-use optimization, facility upgrades, and environmental mitigationtechnologies.

New Opportunities for Advanced Hydropower R&D

Having revamped its hydropower technology efforts, in 2011 the Water Power Program releasedits first major solicitation for hydropower R&D in more than a decade. These projects, which areunderway and scheduled for completion in 2014, aim to reduce costs of hydropower technologiesand demonstrate the dynamic grid benefits of advanced hydropower and pumped storagetechnologies.


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The Oroville Complex in California serves as one demonstration site for the Water-UseOptimization Toolset.Credit: California Department of Water Resources

Optimizing Hydropower Systems for Power and Environment

The Water Power Program sponsored a team of DOE national laboratories to develop anddemonstrate a suite of advanced, integrated analytical tools, known as the Water-UseOptimization Toolset (WUOT). WUOT will assist managers and operators in operatinghydropower plants more efficiently, resulting in more energy and grid services from availablewater resources while enhancing the environmental benefits from improved hydropoweroperations and planning. WUOT includes tools for hydrologic forecasting, seasonal hydro-systems analysis, day-ahead scheduling and real-time operations, and environmental

performance operations, in addition to a graphical user interface and a shared database. WUOT is

being deployed for demonstration at the Oroville Complex on the Feather River in California, theupper Colorado River portion of the Colorado River Storage Project, and the Conowingo Damcomplex on the Susquehanna River in Maryland.

Revitalizing American Infrastructure

The new turbine/generator unit in Boulder, Colorado, was funded through the AmericanRecovery and Reinvestment Act of 2009 to increase generation and turbine efficiency.Credit: City of Boulder


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Three of the Water Power Program's hydropower efficiency projects sponsored through theAmerican Recovery and Reinvestment Act of 2009 have been completed with overwhelmingsuccess, resulting in an increase of more than 3,000 megawatt-hours per year.

The Los Alamos County Department of Public Utilities installed a low-flow turbine to its Abiquiu

Hydroelectric Facility in New Mexico. The new turbine boosts overall facility output from 13.8megawatts to 16.8 megawatts. The City of Boulder, Colorado completed a modernization project to its Boulder Canyon

Hydroelectric Project by installing a new turbine/generator unit. The new unit resulted in a 30%increase in generation and an 18 48% increase in turbine efficiency.

The City of Tacoma installed two Francis turbine/generator units to the Cushman Dam inWashington. The new units add approximately 3.6 megawatts of annual electrical generation.

DOE-funded researchers developed a small "sensor fish" device to understand the physicalstresses fish experience as they pass through a dam which is now being updated for wider use bythe industry.

Technology Development for Fish Passage

Using funding from the Water Power Program, DOE's Pacific Northwest National Laboratory(PNNL) has initiated a redesign of their Sensor Fish, a device filled with sensors to measure theconditions that real fish experience when passing through a hydropower turbine. The device hasalready proven very valuable, providing information that is otherwise unobtainable in order toensure the safe fish passage. Throughout the redesign, PNNL will expand the types of tests theSensor Fish can assist with, reduce the overall cost of producing the Sensor Fish, improve itsdata storage capacity, and improve its realistic representation in a set of new conditions. Theultimate goal is to make the Sensor Fish commercially available so that industry personnel can

buy and use one right off the shelf.

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Documents

How Hydroelectric Energy Works