CHAPTER 1

INTRODUCTION

I just did a Search here for "underwater" and "windmill" and it came up blank, so if this idea really has been posted here using some other verbiage,

Anyway, this Idea should be somewhat obvious in hindsight. We build ordinary windmills to extract useful power from wind energy. We put turbines in rivers (usually accompanied by dams) to extract useful power from downhill water flow. The second is more "energy intensive" than the first, which is why we all know that dams are great sources of electrical power, while electric-generator windmills spent decades in the economic doldrums (return on investment --ROI-- is relatively tiny, and only recently proved viable on a large scale).

Anyway, putting the equivalent of a windmill in a steady ocean current, say the Gulf Stream, should have an automatically-viable ROI that is intermediate between windmills and ordinary hydropower. This is because water is something like a thousand times denser than air, so a volume of flowing water contains a thousand times the energy of an equal volume of equally-flowing air.

Do note that the ocean has different currents at different depths. I once read somewhere that near the seafloor underneath the Gulf Stream is another current going the opposite direction. If true, then we can build towers on the seafloor, just like ordinary windmills, to extract power. Being so deep will protect them from ships, and most sea life is found at other depths, so they won't be bothered. Also, another thing that protects sea life is the fact that underwater windmills will have a SLOW rotation rate, due to that same greater density of water over air. This means we can also put windmills in the rich-life upper ocean currents; animals will have time to dodge the blades. (Some life forms, like barnacles, need to be discouraged; probably everything needs to be coated with Teflon or something even more slippery.)

Consider buoyant windmill modules can be anchored by cables to the bottom. They float up to perhaps fifty meters beneath the surface, in the midst of the ocean current. There they stay and generate power (which flows down those same anchor cables, and then toward shore).

Finally, it may be necessary to build all underwater windmill modules in counter rotating pairs. Again, this is because the water is denser than air; and for every unit of force that tries to rotate the blade, there will be reactive force against the generator assembly, Counter rotating blades will let such forces be canceled.

Tidal currents are being recognized as a resource to be exploited for the sustainablegeneration of electrical power. The high load factors resulting from the fluid proper-ties and the predictable resource characteristics make marine currents particularlyattractive for power generation. These two factors makes electricity generation frommarine currents much more appealing when compared to other renewables. Marinecurrent turbine (MCT) installations could also provide base grid power especially iftwo separate arrays had offset peak flow periods. This characteristic dispels the myththat renewable energy generation is unsuitable on a large scale.

The global strive to combat global warming will necessitate more reliance on cleanenergy production. This is particularly important for electricity generation which iscurrently heavily reliant on the use of fossil fuel. Both the UK Government and theEU have committed themselves to internationally negotiated agreements designed tocombat global warming. In order to achieve the target set by such agreements, largescale increase in electricity generation from renewable resources will be required.

Marine currents have the potential to supply a significant fraction of future electricityneeds. A study of 106 possible locations in the EU for tidal turbines showedthat these sites could generate power in the order of 50 TWh/year. If this resourceis to be successfully utilized, the technology required could form the basis of a majornew industry to produce clean power for the 21st century.

Although the energy in marine currents is generally diffuse it is concentrated ata number of sites. In the UK, for example, tidal races which exist in the waters around the Channel Islands and the ‘Sounds’ off the Scottish west coast are wellknown amongst sailors for their fast flowing waters and treacherous whirlpools. Theenergy density at such sites is high and arrays of turbines could generate as muchas 3000 MW in the spring tides.

In spite of the advantages offered by MCTs, it is rather surprising that such technologyhas not received much attention in terms of research and development. Thereare many fundamental issues of research and various key aspects of system designthat would require investigation. A major research effort is needed in order toexpedite the application of the marine current kinetic energy converters. Virtuallyno work has been done to determine the characteristics of turbines running in waterfor electricity production even though relevant work has been carried out on windturbines and on high speed ship’s propellers and hydro turbines. None of these threewell established areas of technology completely overlap with this new field so thatgaps remain in the state of knowledge. This paper reviews the fundamental issuesthat likely to play a major role in implementation of MCT systems. It also highlightsresearch areas to be encountered in this new area and reports on issues such asthe harsh marine environment, the phenomenon of cavitation and the high stresses encountered by such structures.

Fig.1 Consuming and harnessing the power generated under the oceans.

Fig.2 Turbine placed under water to consume ocean power.

CHAPTER 2

HISTORY

Two British consultants have developed an underwater pump that can irrigate riverside fields without using fuel or causing pollution. The prize-winning turbine is easy to construct and can work continuously

Originally designed to harness the energy of the Nile to irrigate the desert areas of Sudan, the pump has a three-blade rotor that utilizes the energy of moving water, just as a windmill uses wind. The underwater pump can be operated by a single person with little training.

Fig.3 Two blade fins placed under water and generating energy.

Fig. 4 Turbines running under water without harming the water animals.

Fig.5 huge turbine placed under the sea and rotating in the direction of flow.

Researchers launched the first offshore tidal energy turbine on Monday. The rotor on the English coast uses the power of the tides to generate electricity. Just the beginning: The first "farm" of tidal turbines could spring up off the English coast within years.

Imagine taking a windmill, turning it on its side and sinking it in the ocean. That, in effect, is what engineers have done in the Bristol Channel in England. The aim is to harness the energy the tide produces day in, day out. On Monday, the world's first prototype tidal energy turbine was launched.

The "Sea flow" installation was built into the seabed about one and a half kilometers (one mile) off the Devon coast. Above the surface, only a white and red-striped tower is visible. Beneath, 20 meters down, the single 11-meter long rotor turns up to 17 and a half times a minute at a maximum speed of 12 meters per second, drawing energy from the water's current.

The €6 million ($7 million) project's supporters -- which include the British and German governments and the European Union -- hope that tidal turbines may one day be a further source of energy. Unlike sun and wind energy, tidal energy is reliable, since it's not affected by the weather.

"As long as the earth turns and the moon circles it, this energy is a sure thing," Jochen Bard from ISET, a German solar energy institute involved in the project, told the dpa news agency.

The red dots show locations where tidal energy turbines could be employed in Britain and northern France.

Sea flow can generate around 300 kilowatts, while rotors developed in the future should be able to produce a megawatt. The new facility is pegged to be linked to Britain's national grid in August, and a second rotor is to be added by the end of 2004. Marine Current Turbines (MCT), which operates Seaflow, estimates that 20 to 30 percent of British electricity needs could be provided by the new technology.

CHAPTER 3

Renewable Energy

We can divide renewable energy sources into two main categories: traditional renewable energy sources like biomass and large hydropower installations, and the "new renewable energy sources" like solar energy, wind energy, geothermal energy, etc. Renewable energy sources provide 18% of overall world energy (2006), but most of this energy is energy from traditional use of biomass for cooking and heating - 13 of 18%. In large hydropower installations is another three percent. So, when we exclude conventional biomass and large hydropower installations it is easy to calculate that so called "new renewable energy sources" produce only 2.4% of overall world energy. 1.3% are water heating solutions, 0.8% are different power generation methods, and 0.3% are biofuels. In the future this portion should be significantly increased because the availability of non-renewable sources is decreasing with time, and their damaging influence has significantly increased in the last couple of decades. Sun delivers 15 thousand times more energy to Earth than humanity really needs in this stage, but despite this some people on Earth are still freezing. This fact shows us that we should exploit renewable sources much more and that we do not have to worry about the energy after fossil fuels cease to exist. Development of renewable energy sources (especially from wind, water, sun and biomass) is important because a couple of reasons:

  • Renewable energy sources have major role in decreasing of emissions of the carbon dioxide (CO2) into atmosphere.
  • Increased proportion of renewable energy sources enhances energetic viability of the energy system. It also helps to enhance energy delivery security by decreasing dependency on importing energetic raw materials and electrical energy.
  • It is expected that renewable energy sources will become economically competitive to conventional energy sources in middle till longer period.

Fig.6 Different types of renewable energy.

Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally replenished). About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity. New renewables (small hydro, modern biomass, wind, solar, geothermal, and biofuels) accounted for another 3% and are growing very rapidly. The share of renewables in electricity generation is around 19%, with 16% of global electricity coming from hydroelectricity and 3% from new renewables.

3.1SOLAR ENERGY

Solar energy is the energy derived from the sun through the form of solar radiation. Solar powered electrical generation relies on photovoltaic and heat engines. A partial list of other solar applications includes space heating and cooling through solar architecture, day lighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes.

Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.

Fig.7 Nellis Solar Power Plant, 14 MW power plant installed 2007 in Nevada, USA.

3.2 BIO MASS

Biomass (plant material) is a renewable energy source because the energy it contains comes from the sun. Through the process of photosynthesis, plants capture the sun's energy. When the plants are burnt, they release the sun's energy they contain. In this way, biomass functions as a sort of natural battery for storing solar energy. As long as biomass is produced sustainably, with only as much used as is grown, the battery will last indefinitely.

In general there are two main approaches to using plants for energy production: growing plants specifically for energy use (known as first and third-generation biomass), and using the residues (known as second-generation biomass) from plants that are used for other things. See bio based economy. The best approaches vary from region to region according to climate, soils and geography.

3.3 BIO FUEL

Biofuels include a wide range of fuels which are derived from biomass. The term covers solid biomass, liquid fuels and various biogases. Liquid biofuels include bio alcohols, such as bioethanol, and oils, such as biodiesel. Gaseous biofuels include biogas, landfill gas and synthetic gas.

Bioethanol is an alcohol made by fermenting the sugar components of plant materials and it is made mostly from sugar and starch crops. With advanced technology being developed, cellulosic biomass, such as trees and grasses, are also used as feedstock’s for ethanol production. Ethanol can be used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive to increase octane and improve vehicle emissions. Bioethanol is widely used in the USA and in Brazil.

Biodiesel is made from vegetable oils, animal fats or recycled greases. Biodiesel can be used as a fuel for vehicles in its pure form, but it is usually used as a diesel additive to reduce levels of particulates, carbon monoxide, and hydrocarbons from diesel-powered vehicles. Biodiesel is produced from oils or fats using trans esterification and is the most common biofuel in Europe.

Biofuels provided 2.7% of the world's transport fuel in 2010.

3.4 GEOTHERMAL ENERGY

Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth's geothermal energy originates from the original formation of the planet (20%) and from radioactive decay of minerals (80%). The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. The adjective geothermal originates from the Greek roots geo, meaning earth, and thermos, meaning heat.

The heat that is used for geothermal energy can be stored deep within the Earth, all the way down to Earth’s core – 4,000 miles down. At the core, temperatures may reach over 9,000 degrees Fahrenheit. Heat conducts from the core to surrounding rock. Extremely high temperature and pressure cause some rock to melt, which is commonly known as magma. Magma convicts upward since it is lighter than the solid rock. This magma then heats rock and water in the crust, sometimes up to 700 degrees Fahrenheit

From hot springs, geothermal energy has been used for bathing since Paleolithic times and for space heating since ancient Roman times, but it is now better known for electricity generation.

Fig. 8 Steam rising from the Nesjavellir Geothermal Power Station in Iceland.

3.5 WIND ENERGY

Airflows can be used to run wind turbines. Modern wind turbines range from around 600kW to 5 MW of rated power, although turbines with rated output of 1.5–3 MW have become the most common for commercial use; the power output of a turbine is a function of the cube of the wind speed, so as wind speed increases, power output increases dramatically. Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms. Typical capacity factors are 20-40%, with values at the upper end of the range in particularly favorable sites.

Globally, the long-term technical potential of wind energy is believed to be five times total current global energy production, or 40 times current electricity demand. This could require wind turbines to be installed over large areas, particularly in areas of higher wind resources. Offshore resources experience average wind speeds of ~90% greater than that of land, so offshore resources could contribute substantially more energy.

Fig.9 Wave power principle. You can see from this picture that huge wave amplitude is needed in order to achieve efficient transformation.

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3.6 HYDRO ENERGY

Energy in water can be harnessed and used. Since water is about 800 times denser than air, even a slow flowing stream of water, or moderate sea swell, can yield considerable amounts of energy. There are many forms of water energy:

  • Hydroelectric energy is a term usually reserved for large-scale hydroelectric dams. Examples are the Grand Coulee Dam in WashingtonState and the Akosombo Dam in Ghana.
  • Micro hydro systems are hydroelectric power installations that typically produce up to 100kW of power. They are often used in water rich areas as a remote-area power supply (RAPS).
  • Run-of-the-river hydroelectricity systems derive kinetic energy from rivers and oceans without using a dam.

3.7 TIDAL ENERGY