Alternative Energy Solutions:Hydro-Electric and Tidal Energy

American University Professor Stephen Macavoy

Environmental Studies University Honors Capstone Neslihan Yildirim

Fall 2012

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Neslihan YildirimUniversity Honors in Environmental Studies Capstone Advisor: Professor Stephen MacAvoy and Albert Cheh CAS: Environmental Studies

Alternative Energy Solutions In Order To Address the Energy Demands of the World: Hydro-Electric and Tidal Energy

Over the last two centuries, industrial activities, deforestation and the burning of fossil fuels have released high concentrations of heat-trapping agents called greenhouse gases (GHGs) into the atmosphere. While a certain amount of greenhouse gas is important to keep our climate warm and livable, these higher concentrations are warming the Earth’s surface to temperatures that threaten life on our planet. Carbon dioxide (CO2) and methane are two GHGs that have increased dramatically due to human activity. With the challenges faced by global warming, the world is faced with the threat of energy demand. The purpose of this capstone is to encourage the use of renewable energy resources in order to best meet those challenges by providing detailed information on the scientific, economic and political backgrounds of two types of renewable energy resources: hydro-electric and tidal energy. The paper addresses several key topics including: How does the renewable energy function? Advantages/Disadvantages, Environmental Effects, Economic Feasibility, Current Electric Power Output/Capacity and Future Projections. Various mediums of research tools were used including energy reports published by the US Department of Energy (latest Annual Energy Outlook Reports) National Renewable Energy Laboratory, US Department of the Interior, and the Department of Energy and Climate Change. The research has indicated that tidal and hydroelectric energy have their advantages and disadvantages in terms of economic feasibility. Although both technologies can provide enough energy to sustain societies, they cannot address the energy demands of the world alone. A multifaceted approach needs to be taken to combine these energy resources with other renewables in order to sustain human lives on a global scale. Hydro-electric and wind energy should be used accordingly to best suit a country’s geographical location since each nation has its own unique natural resources to offer for total electricity output.

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Introduction

The amount of electricity a hydro-electric system can produce depends on the quantity of

water passing through a turbine (the volume of water flow) and the height from which the water

‘falls’ (head). The greater the flow and the head, the more electricity produced (Castaldi, 2003).

In order to harness the energy from flowing water, the water must first be controlled. Thus, a

large reservoir is created, usually by damming a river to create an artificial lake or a reservoir.

Water is then channelled through tunnels in the dam. The power of the water that flows through

the dam’s tunnels causes the turbines to turn and the turbines in turn make the generators move.

The generators are machines that produce the actual electricity. The transformer inside the actual

powerhouse takes the AC and converts it to higher voltage current. The engineers control the

water intake system. When there is a lot of energy that is needed, most of the tunnels to the

turbines are open and millions of gallons of water flow through them. When there is less energy

needed, then the engineers can slow down the intake system by closing some of the tunnels.

There are also outflow pipelines which carry the used water to re-enter the downstream river for

a second time use. Environmentally this is a great way of controlling how much energy is

produced since water, essentially does not get wasted. Only the actual amount that is needed is

used (US Department of the Interior). During floods, the intake system is helped by a spillway.

A spillway is basically a structure that allows water to flow directly into the river or other body

of water below the dam, bypassing all tunnels, turbines and generators. Spillways prevent the

dam and the community that surrounds the dams from being damaged. The spillways look like

long ramps and are generally empty and dry most of the time unless it is needed in case the

system is flooded (Water Encyclopedia). The water in the reservoir is considered potential

(stored) energy. When the gates open, the potential energy of water flowing through the penstock

becomes kinetic energy because it's in motion. The amount of electricity that is generated is

determined by several factors. Two of those factors are the volume of water flow and the amount

of hydraulic head. The head refers to the distance between the water surface and the turbines. As

the head and flow increase, so does the electricity generated. (Tribal Energy and Environmental

Energy).

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Hydro-electric power plants essentially capture the energy released by water falling

through a vertical distance, and transform this energy into useful electricity. In general, falling

water is channelled through a turbine which converts the water's energy into mechanical power.

The rotation of the water turbines is transferred to a generator which produces electricity. An

important calculation to consider when constructing and figuring out how much water flow is

needed to achieve a certain kW of electric power per hydroelectric power plant is in the

following equation/calculation:

Power Equation: P = eHQg

whereby P stands for the electric power output in KW, e stands for efficiency, H stands for head

in meters (how far the water drop is), Q stands for design flow (m^3/s) and g stands for the

gravitational constant, 9.81 m/s^2 (Castaldi, 2003).

Types of Hydroelectric Plants

As mentioned, Hydro-electric power plants can generally be divided into two categories.

"High head" and “Low head” power plants. The “High head” are the most common and

generally utilize a dam to store water at an increased elevation. The use of a dam also provides

the capability of storing water during rainy periods and releasing it during dry periods. This

results in a consistent and thus reliable production of electricity, able to meet larger demands.

Heads for this type of power plant may be greater than 1000 meters. High head plants with

storage are very valuable to electric utilities because they can be quickly adjusted to meet the

electrical demand on a distribution system. (RETScreen International)

"Low head" hydro-electric plants are power plants which generally utilize heads of only a

few meters or less. Power plants of this type may utilize a low dam to channel water, or no dam

and simply use the ‘run of the river.’ Run of the river generating stations cannot store water, thus

their electric output varies with seasonal flows of water in a river. A large volume of water must

pass through a low head hydro plant's turbines in order to produce a useful amount of power.

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Hydro-electric facilities with a capacity of less than about 25 Mega-Watts (1 MW = 1,000,000

Watts) are generally referred to as "small hydro," although hydro-electric technology is basically

the same regardless of generating capacity (RETScreen International).

An equation that best describes the “high head” versus “low head” relationship is Darcy’s

Law. Darcy’s law allows an estimate of the average time of travel from the head of the aquifer to

a point located downstream. It provides an accurate description of the flow of groundwater in

almost all hydro-geologic environments. Henry Darcy was a French engineer who studied the

movement of water through sand in 1856 (Division of Water Resources). He found that the rate

of water flow through a tube is proportional to the difference in the height of the water between

the two ends of the tube, and inversely proportional to the length of the tube. He also discovered

that flow was proportional to a coefficient, K, which is called hydraulic conductivity. Although

Darcy's Law was based only on slowly moving groundwater in confined aquifers, most of the

laws helped develop equations for other aquifer conditions we use today such as hydroelectric

energy. The equation for Darcy's Law is

Q = - KA[(hA - hB) / L] OR Q = - KA(dh/ dl)

where: 

Q=volume of water flow in ft3/day

K=hydraulic conductivity in ft/day

A=cross-sectional area in ft2

dh/dl=hydraulic gradient (change in head, dh with distance, dl)

The negative sign deals with the direction of flow that is toward the lower hydraulic head. The

idea is that groundwater flows or moves from areas of higher hydraulic head to areas of lower

hydraulic head as mentioned before (Pinder, 2006). It is based on Darcy’s work that we can

estimate the velocity of water or how fast the water is moving between points (as in the case with

hydroelectric turbines). Velocity is calculated by using hydraulic conductivity, porosity and

hydraulic gradient. The equation used for calculating the velocity of water is as follows:

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V= (K/n) (dh/dl)

where N = porosity, K is a constant of proportionality (a way to relate the reduced flow rate to

head loss and length of column) and dh/dl being the hydraulic gradient (Pinder, 2006)

"Pumped Storage" is another form of hydroelectric power. Pumped storage facilities use

excess electrical system capacity, generally available at night, to pump water from one reservoir

to another reservoir at a higher elevation. During periods of peak electrical demand, water from

the higher reservoir is released through turbines to the lower reservoir, and electricity is

produced. Although pumped storage sites are not net producers of electricity (it actually takes

more electricity to pump the water up than is recovered when it is released) they are a valuable

addition to electricity supply systems. Their value is in their ability to store electricity for use at a

later time when peak demands are occurring. Storage is even more valuable if irregular sources

of electricity such as solar or wind are hooked into the same system or electrical grid

(RETScreen International).

When designing a hydroelectric power plant, a number of elements and equipment need

to be taken into consideration. Dam size, basin size and depth, control gates, turbines, generators,

transformers ect. have to all be examined. A strategic location for hydro-electric power plants is

near waterfalls since water that crashes over the fall line is full of energy and can provide

electricity for millions of homes. A famous example of this is the hydroelectric plant at Niagara

Falls which spans the border between the US and Canada. The largest hydroelectric plant

however in the world is the Three Gorges Dam which spans the Yangtze River in China. It is 185

meters tall and 115 meters thick at its base (Division of Water Resources). It has a total of 26

turbines and a total generating capacity of 18,000 megawatts, which supplies energy to millions

of homes, businesses and schools across China. Although the Three Gorges Dam is operating,

engineers are still working to improve its efficiency. They are currently adding even more

turbines and generators to the project (National Geographic).

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Below is a picture of what the inside of a hydropower plant looks like:

Ontario Power Association

Hydroelectric power provides almost all the energy for some nations. Norway, Brazil, and

the Democratic Republic of Congo all get more than 90% of their electricity from hydroelectric

power plants. The largest U.S. hydropower plant is the 6,800-megawatt Grand Coulee power

station on the Columbia River in Washington State. Completed in 1942, the Grand Coulee today

is one of the world's largest hydropower plants, behind the 13,320-megawatt Itaipu hydroelectric

plant on the Paraná River between Paraguay and Brazil. It generated almost 58 million

megawatts of hydroelectricity in 2009. Furthermore, the Hoover Dam, which is one of the

biggest dams was built during the Great Depression. The Hoover Dam is still in use, providing

power to 1.7 million people in Arizona, California, and Nevada. It is often considered a great

engineering construction and is named after Herbert Hoover, the U.S. president who helped

make the project happen. In terms of how much energy the system can produce hydroelectric

power plants generally range in size from several hundred kilowatts to several hundred

megawatts, but a few enormous plants have capacities near 10,000 megawatts in order to supply

electricity to millions of people. According to the National Renewable Energy Laboratory, world

hydroelectric power plants have a combined capacity of 675,000 megawatts that produces over

2.3 trillion kilowatt-hours of electricity each year; supplying 24% of the world's electricity

(National Renewable Energy Laboratory).

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Advantages

There are many advantages as to why we should use and invest in hydro-electric power.

The first advantage is that once a dam is constructed, electricity can be produced at a constant

rate. If the electricity is not needed, then the ‘sluice’ gates can be shut in order to stop electricity

generation. This is also an advantage since the water can be saved for use another time when

electricity demand is high. The lake that forms behind the dam can be used for water sports and

other leisurely activities. Often large dams have become tourist attraction sites. Another

advantage is that when in use, electricity that is produced by dam systems do not produce

greenhouse gases nor do they pollute the atmosphere in any way as gas, coal or oil power plants

do. Today hydroelectricity prevents the emission of GHG corresponding to the burning of 4.4

million barrels of petroleum per day worldwide, which is a very significant amount.

Hydroelectricity also contributes to the storage of drinking water since the power plant reservoirs

collect rainwater which can then be used for consumption or for irrigation. In storing water, they

protect the water tables against depletion and reduce our vulnerability to floods and droughts.

Hydro-electricity also promotes guaranteed energy and price stability. River water is a domestic

resource which, contrary to fuel or natural gas, is not subject to market fluctuations. Furthermore,

with an average lifetime of 50 to 100 years, hydroelectric developments are long-term

investments that can benefit various generations. They can be easily upgraded to incorporate

more recent technologies and have very low operating and maintenance costs (US Department of

the Interior)

Disadvantages

As with any renewable energy technology, there are also various disadvantages to hydro-

electric power. The first disadvantage is that it disrupts the aquatic ecosystems. The dams

developed across the rivers can disturb aquatic life and lead to their large scale destruction. There

is a chance that fish and other water animals may enter the penstock and ultimately the power

generation turbines where they will be killed. Dams can also disturb the mating seasons and

mating areas of the water animals. In some cases water animals have to swim against the water

stream during breeding seasons. If a dam is built in the path of migrating fish they could be stuck

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there and killed, never reaching their destination. This could devastate a population of fish.

Another disadvantage of hydroelectric dams are the disruption that it causes in the surrounding

areas. Plant and animal life around rivers thrive due to continuous fresh flowing water in the

river. Due to the construction of dams, lots of areas have to be cleared that disrupt the plant and

animal life. In many cases, trees have to be cut, which destroys not only the plant life but also the

animals dependent on them. Even changing the course of the flow of water in the river due to the

construction of the dam disrupts the plants and animal life. The third disadvantage is that it

requires large land areas since power generation unit and transformers are needed to connect

them to the national grid. This requires forests to be cleared disrupting many local, natural

ecosystems. Finally, because the dams are built on such a large scale, it is often necessary for

humans to relocate. This becomes fairly inconvenient for a lot of people and thus causes large

scale oppositions and revolts against the construction of dams. In India for example, there has

been a large opposition to the one of the biggest hydroelectric power projects named “Sardar

Sarovar.” Though millions of people are to benefit from the project, the government didn’t

manage the important issue of the resettlement of people who were displaced from the adjoining

areas of project. This led to one of biggest protests in Indian history, which saw a number of

hunger strikes, protest marches and even police attacks on the protesters (National Renewable

Energy Laboratory).

Environmental Effects

In terms of environmental effects/ waste, hydro-electric has its fair share of drawbacks.

Although hydropower makes it possible to produce electricity without using or emitting fossil

fuels, there are various environmental consequences that come with this technology. The first

environmental impact is that since large reservoirs are required for the operation of hydroelectric

power stations, this can create flooding of river banks which can destroy biologically rich areas

such as wetland habitats. Another environmental impact is in the tropical regions, the reservoirs

of power plants may produce substantial amounts of methane due to plant material decay in

flooded areas (anaerobic environments), which is a GHG. Reservoirs can collect sediments

which concentrates nutrients as well as pollutants. When these sediments build up, then this

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causes the reservoirs to become shallower. According to the World Commission on Dams report,

“where the reservoir is large compared to the generating capacity (less than 100 watts per square

metre of surface area) and no clearing of the forests in the area was undertaken prior to

impoundment of the reservoir, greenhouse gas emissions from the reservoir may be higher than

those of a conventional oil-fired thermal generation plant.” Thus, this would cause much more

damage and release of methane than it occurring through the natural forest decay. Some key

factors that influence reservoir emissions are degassing (removal of gases from water for

example), methane bubbles, plankton growth and decay, decomposition of flooded biomass and

soils, carbon inputs from watershed, growth and decay of aquatic plants, length of annual ice

cover, CO2 diffusion, water level fluctuation and drawdown of vegetation (Window On State

Government Energy Report).

Operating the power plant may also raise the temperatures of the water in the reservoir

which can lead the plants and animals near the dam to migrate elsewhere, thus changing the local

natural habitats of the region. Another impact is that hydroelectric projects can disrupt the

aquatic ecosystems both upstream and downstream of the plant site. For example, some studies

have shown that dams that are along the Atlantic and Pacific coasts of North America have

reduced salmon populations since it prevents them from moving upstream. Some dams however

such as the Bonneville Dam have installed ‘fish ladders’ to help fish migrate (especially those

that try to swim upstream). Fish ladders are a series of wide steps built on the side of the river

and dam and it allows the fish to slowly swim upstream instead of being completely blocked by

the dam. Another drawback is that hydropower often entails changes to the natural variations in

the water in a given natural watercourse (Renewableenery.no). The changes in the water level

throughout the year can cause erosion and other problems in the surrounding land areas (such as

the loss of riverbanks). Lastly, power lines that are built for the hydroelectric dams can affect

bird populations through collision or by short circuit due to contact of the birds with these man

made structures (National Geographic).

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Economic Feasibility

Hydroelectric electricity has various factors that contribute to its overall cost structure

and economics. These costs include investment expenses (buying the land, building the dam,

purchasing turbines, AC generators and other electrical equipment, ect.) and operating expenses

throughout the facility’s lifetime (e.g. maintenance and salary costs). Approximately 75% of the

hydroelectric kWh costs are made up of investment costs (initial capital and interest) which

makes the overall costs stable during the electrical production stages (as compared to gas

turbines, coal thermal, or pressurized water nuclear reactors). Today, the world’s hydroelectric

plants have a total capacity of 675,000 megawatts that produce over 2.3 trillion kilowatt-hours of

energy per year. This is providing roughly one quarter of the world’s electricity. Many countries

outside of North America have the majority of their electricity coming from hydroelectric power

plants. For instance, nearly a decade ago, 99% of Norway’s electricity was provided via

hydroelectric power plants. The United States produced about 159.74 gigawatts in 2010

according to the Energy Information Agency, and that is approximately 6.67% of total U.S.

production.

In terms of its cost structure, hydro-electric power has high initial costs. The average

initial cost to set up a dam or a hydroelectric power plant is around $1.2 million while the annual

costs for maintenance are around $12,368. However the initial costs are all dependent on the size

and power generation capacity of the dam. For example, the Hoover Dam has a power generating

capacity of 2.8 million kW and cost around $49 million to build which is almost the cost of a

nuclear energy power plant (US Department of Energy). The Three Gorges Dam on the other

hand, according to BBC News, cost around estimated $25-75 billion with power output of around

49 million kW hours (BBC News). Although a hydropower plant has a high capital cost,

maintenance costs are minimal when looking at some other sources of energy production. The

plant life can be extended economically by relatively cheap maintenance and the periodic

replacement of equipment (replacement of turbine runners, rewinding generators, etc). Typically

a hydro-power plant in service for 40 - 50 years can have its operating life doubled.

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Comparing the cost of electricity with the initial investment of a hydropower system, the

pay back period is short. Theoretically, a hydro plant should be able to produce electricity for a

fixed amount during the life span of the unit. The operating costs should not change because

there is no associated price to the water. Unlike in fossil fuel plants, the price of natural gas, coal,

etc. fluctuates depending on what the market is doing. In terms of its fuel, hydro-energy does not

require any fuel like most other sources of energy. This is a huge advantage over other fossil

fuels whose costs are increasing at a drastic rate every year (US Department of the Interior). In

terms of transportation, countries without big rivers are unable to get hydroelectric power.

However, in countries that have big rivers, the transport of hydroelectric power is not an issue.

Electricity is generated at the dam itself, and then transported to cities through electric cables.

Therefore, as long as a country has rivers suitable for building dams, the electricity generated

will be accessible to everyone connected to the energy grid. Essentially, the main costs of

hydroelectric plants are largely the construction of the plant, with no further costs for fuel and its

transportation. Hydropower is one of the cheapest ways to generate electricity. On average it

costs about seven cents per kilowatt-hour to produce electricity from a hydroelectric plant. By

refurbishing the equipment on the hydro equipment, you can increase its efficiency. An

improvement of only 1% would supply electricity to an additional 300,000 households (Energy

Information Agency). It is also important to note that the government subsidizes the costs and the

power that is associated with hydroelectric power. The ownership and distribution of electricity

is owned by various power marketing administrations. The role of these administrations is to

market hydroelectric power at the lowest possible rates to consumers while adhering to business

principles. These administrations, which are all a part of the US Department of Energy are the

Bonneville Power Administration, Southeastern Power Administration, Southwestern Power

Administration and the Western Area Power Administration.

When compared to other renewable energy methods, hydroelectricity remains quite

competitive since it does not release GHG emissions from fossil fuel combustion such as sulfur

dioxide, nitric oxide, carbon monoxide and mercury. It also avoids the hazards and

environmental and human health impacts of coal mining. Compared to nuclear power, it

generates no nuclear waste (so there is no drawback of finding solutions to store waste) and has

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no dangers that are associated with uranium mining. Compared to wind and solar farms for

example, hydroelectricity power plants are more predictable since it has a storage reservoir and

can be generated to create power when it is needed. They can also be easily regulated to follow

the demands and variations of power. Furthermore, in terms of meeting the energy demands of

the world, hydroelectric power plants have the capacity to do so. For example, in 1998, the

hydroelectric plants of Norway and the Democratic Republic of the Congo provided 99% of each

country's power and hydroelectric plants in Brazil provided 91% of total used electricity. In the

US, more than 2,000 hydropower plants make hydro-electric power the country's largest

renewable energy source (at 49%) (US Department of Energy). The US has overall increased its

hydroelectric power generation from about 16 billion kilowatt-hours in 1920 to nearly 306

billion kilowatt-hours in 1999. Canada however is by far the world's largest hydroelectric power

producer. In 1999, it generated more than 340 billion kilowatt-hours of power, or 60% of its

electric power, far outdistancing the U.S. hydropower percentage. The former Soviet Union,

Brazil, China, and Norway are among the other top hydroelectric-generating countries (National

Renewable Energy Laboratory).

Current Electric Power Output and Capacity

Policies related to development of hydropower facilities vary by country and, in some

cases, have a significant effect on these plants contributions in meeting needs for electricity.

Each year, the U.S. Energy Information Administration (EIA) develops an outlook for the

international energy markets, including electricity. The International Energy Outlook 2012

(IEO2012) projects markets through 2035. According to the IEO2012 renewable energy is the

fastest growing source of electricity. Total generation from renewable resources will increase by

3% annually, and the renewable share of world electricity generation will grow from 18% in

2007 to 23% in 2035. According to their predictions, Hydroelectricity leads the field accounting

for 35% of the total renewable energy in the US. Of the 4.5 million GWh of new renewables

added over the projection period, 2.4 million GWh are attributed to hydroelectric power.

However the types of renewable fuels used differ between the OECD and non- OECD regions. In

non-OECD countries, hydropower is expected to be the predominant source of renewable

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electricity growth. Strong growth in hydro is expected in China, India, Brazil, and many nations

in Southeast Asia, including Malaysia and Vietnam. The United States currently has more than

2,000 hydroelectric power plants which account for more than half of the country’s renewable

energy sources. China, Canada and Brazil are the only countries producing more hydroelectric

power than the United States. However there is still unused capacity in hydroelectric power

plants and a lot of power potential yet to be developed. According to a research done by the

Idaho National Laboratory (INL), only 10% of the natural stream energy resources have been

developed in the US and there are still 60% of the power available that is yet to be developed.

The West is home to many of this undeveloped or untapped energy and there is a lot of potential

there. The good news is that the majority of these potential energies can be harnessed without

constructing new dams. They can be harnessed with existing technologies (United States Energy

Information Administration Report).

When looking at hydroelectricity globally, the use of hydroelectricity and other grid-

connected renewable energy sources is expected to grow slowly over the next couple of decades,

increasing at a rate of 2.9% per year until 2035, according to the Energy Information

Administration (EIA). Most of that growth will come from the construction of new hydropower

and wind generating facilities and increased biofuels production. In 2010 for example,

hydropower accounted for 2.51 quadrillion BTu of energy and the EIA projects that to rise to

3.06 quadrillion BTu by 2035. Therefore, the future of hydropower looks promising and is

projected to increase in the non-OECD countries (Institute for Energy Research).

Future Projections

Despite its ‘expected growth,’ the future of hydroelectric power in the US, as well as

worldwide, is complicated. As we know, the capabilities of hydroelectric power have been

maxed out here in the United States, however this is not the case in most other countries. There

are a range of large scale hydro electric construction projects in the works in the developing

industrial nations. The true future of hydroelectric power worldwide depends on the abilities of

scientists to make technological breakthroughs. Although the IEO2012 projects a growth in

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hydroelectricity, there also some contradictory evidence that in fact argue that figuring out how

much hydropower will be available in the future is becoming more and more difficult. The

reason is because the old way of predicting stream flow by taking records of past flow and

designing dams based on those amounts is becoming complicated due to climate change. Already

we can see water flow flowing less and even drying in many tropical regions. Shrinking rivers

have already reduced or even shut down power generation in existing dams. For example, Kenya

is developing geothermal and wind power to compensate for unreliable hydropower since they

have been hit hard by drought. According to the report “Projected Changes in Hydropower

Generation 2050” completed by scientists at the Norwegian University of Science and

Technology have found that while mid-latitude areas will experience reductions in river flow

(thus hydropower reductions) some areas such as Northern Europe, East Africa and Southeast

Asia will probably see a boost. Therefore, the predictions made by IEO2012 are accurate but

considerations of where there will be future water shortages in various geographical regions will

need to be taken into account when discussing hydropower as a renewable source in meeting the

energy demands of the world.

Tidal Energy

Besides the construction of dams, there are also other types of Hydroelectric plants where

energy can be captured such as tidal power. Tidal Energy uses the natural ebb and the flow of

coastal tidal waters (which are created mainly by the relative motion of the Earth, moon, sun and

the gravitational interactions between them) in order to instigate tidal power plants to produce

electricity. The coastal water levels change twice on a daily basis, which fills and empties natural

basins along the shorelines. It is these currents that flow in and out of the basins that interacts

with the mechanical devices. Since there are about two high and two low tides each day, the

electrical generation from tidal power plants goes through periods of maximum electricity

generation every six hours or so (Department of Energy and Climate Change). Essentially, the

tides contain the energy that can be harnessed for this electricity production through tidal energy

generators (underwater turbines). The two types of energy that can be harnessed are kinetic and

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potential energy. Kinetic energy can be harnessed from the ebbing and surging tides while the

potential energy can be harnessed from differences in the high and low tides (EWTEC).

Tidal energy can be harnessed and generated through various methods. Traditional tidal

electricity generation involves the construction of a barrage across an estuary to block the

incoming and outgoing tides. Tidal fences for example block a channel, which forces water to go

through it and turn its turbines to generate electricity. One way to harness tidal energy is through

tidal streams. Tidal stream generators make use of the kinetic energy of moving water to power

turbines in a similar way that wind turbines use wind to power turbines. With barrage tidal

plants, they make use of the potential energy in the difference in height between high and low

tides. Basically, a dam or barrage is installed, usually where there is a narrow water channel with

gates and turbines at certain points. As water flows through the turbines, they turn a generator

that produces electricity. Tidal turbines work like an underwater wind turbines. They use the

tides to turn blades and to essentially create electricity. The barrage tidal plants, which are the

most commonly used today have three main parts to them. These include the barrage, sluice

gates and a turbine. The barrage acts much like a dam by holding back water to be later released.

The sluice gates allow water to flow through the turbine. The turbine in turn spins as the water

flows through it which rotates an electricity producing generator. The turbines in the barrage can

be used to pump extra water into the basin at periods of low demand. This usually coincides with

cheap electricity prices, generally at night when demand is low. A company will therefore buy

the electricity to pump the extra water in, and then generate power at times of high demand when

prices are high so as to make a profit. In order for tidal energy to be economical, a tidal range of

at least 7 meters is required and the overall magnitude of these effects is essentially dependent

upon the gravitational pull from the sun and moon and the local coastal habitat interactions

(Energy World).

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Here is a picture of the daily distribution of tidal phases that occur:

Source: Energy World

When looking at the power available from these kinetic systems in a turbine at any particular

time mathematically, engineers use the following formula:

where:

Cp = the turbine power coefficient

P = the power generated (in watts)

p = the density of the water (seawater is 1027 kg/m³)

A = the sweep area of the turbine (in m²)

V = the velocity of the flow

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Advantages

There are various advantages of tidal energy. One big advantage is its predictability. The

size and the time of tides can be predicted very efficiently. In order to harness tidal waves, we

just need to follow tidal cycles. Strong tidal waves are very much capable of generating a high

amount of electricity with 80% more efficiency than coal or oil and 30% more than solar power

according to the US Department of Energy. Furthermore, another advantage is that once the tidal

power plant structures are built, the energy is free, clean (does not generate emissions or wastes)

and renewable. This is a huge benefit especially when considering this type of energy in the long

run and running its cost- benefit analysis. Another advantage is that its maintenance is cheap and

the efficiency of the technology increases with better and stronger waves, thus the energy does

not fluctuate much if its at this level. Furthermore, tidal energy can also be effective at low

speeds (unlike wind energy for example). Water has 1000 times higher density than air which

makes it possible to generate electricity at low speeds. Calculations show that power can be

generated even at 1 m/s (equivalent to a little over 3 ft/s). Tidal plants also use a source that is

abundant in nature (ocean water) which is another advantage since there is no threat of ocean

water depletion (at least anytime soon). Lastly, tidal power plants have long lifespans. This

ultimately reduces the cost these power plants can sell their electricity, making tidal energy more

cost- competitive with other renewable as well as fossil fuel sources (Ocean Energy Council).

Disadvantages

Tidal energy also has some disadvantages. One of the major drawbacks that are holding

investors and dealers back from moving towards tidal energy is the cost incurred to develop

powerful plants and devices. Most people are looking at the short term costs and neglecting the

long term maintenance costs of tidal energy. Another disadvantage is its availability for everyone

across the globe. The only cities or countries that can benefit from this technology are the ones

that are surrounded by strong tidal waves. Places that don't have strong tidal waves or are far

from tidal energy do not have facilities to generate this power (which in that case we would need

to develop ways to transfer these energies from one country or city to another, leading to more

costs). Even when the electricity is generated, it would average to around 10 hours a day

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(depending on how strong and how high the tides are) which tidal energy alone would not be

enough to cover a full 24 hour day energy demands without another complimentary renewable

energy such as wind or solar power. Another disadvantage is that the barrages may also affect

tidal levels. The change in tidal levels may cause flooding of the shoreline and thus affect the

coastal beach areas which are used by people for swimming and recreation. Another

disadvantage is that salt water causes corrosion in metal parts of the tidal power plant. It can be

difficult to maintain tidal stream generators due to their size and depth in the water. Finally,

another disadvantage is that tidal power plants need to be constructed close to land (as opposed

to wind energy which can be located far out in the sea). This is an area where various

technological solutions are being worked on. If engineers can come up with a technology that

can exploit weaker tidal currents at locations further out in the sea, then this would be very

beneficial (Ocean Energy Council).

Environmental Effects

In terms of environmental effects, tidal power plants can affect the ecosystem of marine

life. Turbine barrages disturb the migration routes of fishes, movement of marine animals and

thus reduce fish populations, which would be a huge controversy amongst environmentalists. In

terms of waste, mechanical fluids such as lubricants can leak out, which may be harmful to the

marine life nearby. In order to make sure that this doesn't happen, proper maintenance can

minimize the amount of harmful chemicals that may enter the environment. The quality of the

water in the basin/estuary and a change in sediment levels can also occur due to tidal turbines

which would affect the turbidity of the water and animals that live and depend upon it (such as

fish and birds) (Department of Energy and Climate Change).

Economic Feasibility

When looking at tidal energy from an economics perspective, the cost of setting up a tidal

power station can be very high, although once in place the operating costs are low. The cost of

building a Tidal Power Plant can have a high capital cost. In the United States, the estimated total

cost of installing a tidal energy turbine is $4,715,000. The estimated commercial plant capital

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cost of a tidal energy farm is $23,630,000 (assuming there are on average 12 turbines).

Essentially, the cost of tidal energy is very site specific, and influenced by geography, distance to

grid, and speed and volume of the current. As an example of the cost of setting up, a proposed

8000 MW tidal power plant and barrage system on the Severn Estuary in the UK has been

estimated to cost $15 billion, while another in the San Bernadino strait which would produce

2,200 MW as a tidal fence in the Philippines will cost an estimated $3 billion (Australian

Institute of Energy). There are currently two large commercial scale tidal power sites in

operation around the world. The first is a 240 MW bulb turbine at the mouth of La Rance estuary

in France. That site powers a city of 300,000 people. The second is the Bay of Fundy plant in

Canada which generates 16 MW powering around 4,500 houses in the area. In terms of its

operation and maintenance, since tidal power plants do not require any fuel, its operation and

maintenance costs are very low. The only maintenance it would really need is to make sure that

its metal parts are in tact and that there are no harmful chemicals that are being released into the

water during its operation. In general, this technology is still not cost effective and more

technological advancements are required to make it commercially viable (Department of Energy

and Climate Change). Furthermore, the transportation of tidal energy as well as setting up the

actual plants within the oceans can be quite cumbersome and expensive. Moving and placing

these big physical structures in the water can require the use of heavy machinery to lift and place

it in the water, thus leading to high initial transportation costs (Denny, 2009)

Future Projections

Wave, tidal and ocean energy technologies are just beginning to reach viability as

potential commercial power sources. While just a few small projects currently exist, the

technology is advancing rapidly and has huge potential for generating power. The Northwest

could become a world leader in this new arena if we invest now. Thus, in terms of meeting the

global energy demands, tidal stream technology alone cannot currently play a big role in meeting

the global energy demands. However, tidal energy along with other marine technologies can help

meet government targets for CO2 and other fossil fuel reductions. Although no commercial wave

or tidal projects have yet been developed in the United States, several projects are planned for

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the near future, including projects in the Northwest. AquaEnergy Group, Ltd is currently

designing and permitting a one-megawatt demonstration wave power plant at Makah Bay,

Washington. Furthermore, Ocean Power Technologies has received a “preliminary permit” to

explore construction of North America’s first utility-scale wave energy facility off the coast of

Reedsport, Oregon. With the support of the Oregon Department of Energy, Oregon State

University is also seeking funding to build a national wave and tidal energy research facility near

Newport, Oregon. Several tidal power projects are also being explored in the region. Tacoma

Power has secured a “preliminary permit” to explore a tidal power project at the Tacoma

Narrows, one of the best locations for tidal power in the country, and Snohomish County Public

Utility District has received “preliminary permits” for seven other potential tidal power sites in

the Puget Sound. Therefore, in order to have a strong grasp on future projections on this

technology, we need to start with these projects and see how much electricity they generate.

Once we can get several data and compare the different regions with one another, then we can

begin to determine how feasible tidal energy will be (Renewable Northwest Project). The United

States receives a lot of wave energy along its coastlines each year, and tapping just one quarter of

this potential could produce as much energy as the entire U.S. hydropower system. Oregon and

Washington have some of the strongest wave energy resources and could eventually generate

several thousand megawatts of electricity using wave or tidal resources.

Although the US has not yet developed in tidal energy, according to the Carbon Trust,

tidal energy is ready to become a significant provider of clean energy for the UK and the globe.

For example, in the UK alone some 15-20% of the its electricity demand could come from

marine renewables such as wave and tidal technologies. This is very significant considering how

many types of renewable energy technologies that are out there (The Guardian). Furthermore, if

we combine tidal energy with solar and wind technologies, then this could further lead us to meet

greater energy demands of the world.

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Conclusion

Hydro-electric energy is a great renewable energy source with new constructions and

technological advancements rapidly on the rise. There are currently 14 large scale projects that

are being developed and scheduled to completed between 2012 and 2022 in China, India,

Venezuela and Berma (with most being in China). Some hydropower stations such as the Hoover

Dam in the US are considering changing their turbines with new ones that will work more

efficiently at lower water levels (IEEE). Although hydroelectric will be a big part of our future

electricity generation, a country cannot rely on hydroelectricity alone for its electricity supply.

Therefore it is of interest to countries to combine this technology with other forms of

technologies.

Furthermore, although tidal power is not yet widely used, it has a great potential for

future electricity generation since they are more predictable than most other renewable

technologies such as wind energy and solar power. Since oceans cover almost two thirds of

earth's surface, they truly present renewable energy source with extreme potential and one worth

of further exploration. Some ocean techniques that are being developed are wave energy (kinetic

energy that exists in the moving waves of the ocean caused by winds) and ocean thermal energy

conversion (OTEC) which is a method for generating electricity that uses the temperature

difference between deep and shallow waters (since the water gets colder the deeper you go

further). However current technologies aren't at the right level to capture this potential.

Problems such as ecological, size and cost of the power plants remain to be an issue that needs

addressing (UNICEF). All that ocean or tidal energy needs now is the technology that will be

capable of exploiting its high potential of energy. If we can manage to do that then these

renewable energies can have a huge impact on how we address moving sustainably into the

future.

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