This chapter discusses ocean energy as renewable source of energy, wave energy, wave energy technologies, tidal power, ocean thermal energy conversion, ocean current energy, offshore wind energy, offshore wind energy technology, offshore solar energy, offshore solar energy technology, and concentrating solar power technology.

To replace fossil fuels and nuclear energy, a renewable energy source must meet four basic criteria.

1.Near limitless supply of energy: Energy that will not run out in the next 1,000 years and comes from a source that has existed for the last 1,000 years.

2.A constant even supply of energy: No periods of nonproduction, no spikes in production, no movement in energy location.

3.High energy density: Energy can be collected at one location with realistic commitment of technology and resources.

4.Survivability: Energy supply and collection is not disrupted by storms, natural disaster, war, etc.

Ocean current energy is the only form of renewable nonpolluting energy that meets all these requirements and it is the only energy source with the potential to replace fossil fuel and nuclear energy. Ocean energy is a term used to describe all forms of renewable energy derived from the sea. The ocean can produce two types of energy: thermal energy from the sun’s heat, and mechanical energy from tides and waves. Oceans cover more than 70% of Earth’s surface, making them the world’s largest solar collectors. The sun’s heat warms the surface water much more than the deep ocean water, and this temperature difference creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world. Ocean thermal energy is used for many applications, including electricity generation. There are three types of electricity conversion systems: closed cycle, open cycle, and hybrid.

Closed cycle systems: These use the ocean’s warm surface water to vaporize a working fluid with a low boiling point, such as ammonia. The vapor expands and turns a turbine. The turbine then activates a generator to produce electricity, as shown in Figure 7.1.

Pump warm surface sea water through a heat exchanger to vaporize a low boiling point fluid (such as ammonia) that then turns a generator

Cold deep sea water pumped through a second exchanger condenses the vapor back to liquid

Open cycle systems: Open cycle systems boil the sea water by operating at low pressures. This produces steam that passes through a turbine/generator.

Boil warm surface sea water to create steam that turns a low-pressure turbine

Steam is turned back to liquid by exposure to cold temperatures from deep-ocean water

Hybrid systems: Hybrid systems combine both closed cycle and open cycle systems.

Combine elements of open and closed cycle OTEC systems

Warm sea water is flash-evaporated into steam (open cycle)

Steam vaporizes a low-boiling-point fluid (closed cycle) that turns a turbine

A byproduct of open or hybrid cycle OTEC plants is the production of fresh water from sea water, known as desalinization.

Ocean mechanical energy is quite different from ocean thermal energy. Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the Moon, and waves are driven primarily by the winds. Thus, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices. A barrage (dam) is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. For wave energy conversion, there are three basic systems: channel systems that funnel the waves into reservoirs; float systems that drive hydraulic pumps; and oscillating water column systems that use the waves to compress air within a container. The mechanical power created from these systems either directly activates a generator or is transfered to a working fluid, water, or air, which then drives a turbine/generator. The world’s ocean may eventually provide us with energy to power our homes and businesses. Generating technologies for deriving electrical power from the ocean include tidal power, wave power, ocean thermal energy conversion, ocean currents, ocean winds and salinity gradients. Of these, the three most well-developed technologies are tidal power, wave power, and ocean thermal energy conversion.

Ocean wave energy is captured directly from surface waves or from pressure fluctuations below the surface. Waves are caused by the wind blowing over the surface of the ocean. In many areas of the world, the wind blows with enough consistency and force to provide continuous waves along the shoreline. Ocean waves contain tremendous energy potential. Wave power devices extract energy from the surface motion of ocean waves or from pressure fluctuations below the surface. Kinetic energy (movement) exists in the moving waves of the ocean. That energy can be used to power a turbine. In Figure 7.2, the wave rises into a chamber. The rising water forces the air out of the chamber. The moving air spins a turbine which can turn a generator. When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed. This is only one type of wave energy system. Others use the up-and-down motion of the wave to power a piston that moves up and down inside a cylinder. That piston can also turn a generator. Most wave energy systems are very small. But, they can be used to power a warning buoy or a small light house.

Wave energy conversion takes advantage of the ocean waves caused primarily by interaction of winds with the ocean surface. Wave energy is an irregular and oscillating low frequency energy source that must be converted to a 50 Hertz frequency before it can be added to the electric utility grid. Some systems extract energy from surface waves. Others extract energy from pressure fluctuations below the water surface or from the full wave. Some systems are fixed in position and let waves pass by them, while others follow the waves and move with them. Some systems concentrate and focus waves, which increases their height and their potential for conversion to electrical energy. A wave energy converter may be placed in the ocean in various possible situations and locations. It may be floating or submerged completely in the sea offshore or it may be located on the shore or on the sea bed in relatively shallow water. A converter on the sea bed may be completely submerged, it may extend above the sea surface, or it may be a converter system placed on an offshore platform. Apart from wave-powered navigation buoys, however, most of the prototypes have been placed at or near the shore. The visual impact of a wave energy conversion facility depends on the type of device as well as its distance from shore. In general, a floating buoy system or an offshore platform placed many kilometers from land is not likely to have much visual impact (nor will a submerged system). Onshore facilities and offshore platforms in shallow water could, however, change the visual landscape from one of natural scenery to industry. Many research and development goals remain to be accomplished, including cost reduction, efficiency and reliability improvements, identification of suitable sites, interconnection with the utility grid, and better understanding of the impacts of the technology on marine life and the shoreline. Also essential is a demonstration of the ability of the equipment to survive the salinity and pressure environments of the ocean as well as weather effects over the life of the facility.

Some of the issues that may be associated with permitting an ocean wave energy conversion facility include:

Disturbance or destruction of marine life (including changes in the distribution and types of marine life near the shore)

Possible threat to navigation from collisions due to the low profile of the wave energy devices above the water, making them undetectable either by direct sighting or by radar [Figure 7.3]. Also possible is the interference of mooring and anchorage lines with commercial and sport fishing.

Degradation of scenic oceanfront views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines.

Ocean waves are caused by the wind as it blows across the water. Waves are a powerful source of energy. The problem is that it is not easy to harness this energy and convert it into electricity in large amounts. Thus, wave power stations are rare. Waves passing across the top of the unit make a piston move, which pumps sea water to drive generators on land. They are also involved with wind power and biofuel. Renewable energy resources are ones that won’t run out. Wave power is renewable. Wave energy is generated by converting the energy of ocean waves (swells) into other forms of energy (currently only electricity). There are many different technologies that are being developed and tested to convert the energy in waves into electricity, as shown in Figure 7.4. Wave power varies considerably in different parts of the world, and whereas wind resource potential is typically given in gigawatts (GW), wave and tidal resource potential is typically given in terawatt-hours/year (TWh/yr).

Advantages:

The energy is free—no fuel needed, no waste produced

Inexpensive to operate and maintain

Can produce a great deal of energy

Disadvantages:

Depends on the waves—sometimes you’ll get loads of energy, sometimes almost nothing

Needs a suitable site, where waves are consistently strong

Some designs are noisy, but then again, so are waves, so any noise is unlikely to be a problem

Must be able to withstand very rough weather

Wave technologies have been designed to be installed in nearshore, offshore, and far offshore locations. While wave energy technologies are intended to be installed at or near the water’s surface, there can be major differences in their technical concept and design. For example, they may differ in their orientation to the waves or in the way they convert energy from the waves. Although wave power technologies are continuing to develop, there are four basic applications that may be suitable for deployment on the outer continental shelf (OCS): point absorbers, attenuators, overtopping devices, and terminators.

Terminators: Terminator devices extend perpendicular to the direction of the wave and capture or reflect the power of the wave. These devices are typically onshore or near shore, as seen in Figure 7.5; however, floating versions have been designed for offshore applications. The oscillating water column is a form of terminator in which water enters through a subsurface opening into a chamber, trapping air above. The wave action causes the captured water column to move up and down like a piston, forcing the air though an opening connected to a turbine to generate power. These devices generally have power ratings of 500 kW to 2 MW, depending on the wave climate and the device dimensions.

Attenuators: Attenuators are long multi-segment floating structures oriented parallel to the direction of the waves, as seen in Figure 7.6. They ride the waves like a ship, extracting energy by using restraints at the bow of the device and along its length. The differing height of waves along the length of the device causes flexing where the segments connect. The segments are connected to hydraulic pumps or other converters to generate power as the waves move across. A transformer in the nose of the unit steps up the power-to-line voltage for transmission to shore. Power is fed down an umbilical cable to a junction box in the seabed, connecting it and other machines via a common subsea cable to shore.

Point absorber: A point absorber is a floating structure with components that move relative to each other due to wave action (e.g., a floating buoy inside a fixed cylinder) as in Figure 7.7. Point absorbers often look like floating oceanographic buoys. They utilize the rise and fall of the wave height at a single point for energy conversion. The relative up-and-down bobbing motion caused by passing waves is used to drive electromechanical or hydraulic energy converters to generate power.

Overtopping devices: Overtopping devices have reservoirs that are filled by incoming waves, causing a slight buildup of water pressure like a dam, as in Figure 7.8. The water is then released, and gravity causes it to flow back into the ocean. The energy of the falling water is used to turn hydroturbines to generate power. Specially built floating platforms can also create electricity by funneling waves through internal turbines and then back into the sea.

Another form of ocean energy is called tidal energy. When tides come into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant. Tidal energy has been used since about the 11th century, when small dams were built along ocean estuaries and small streams. The tidal water behind these dams was used to turn water wheels to mill grains. For tidal energy to work well, you need large increases in tides. An increase of at least 16 ft in height between low tide to high tide is needed. There are only a few places where this tide change occurs around the earth. Some power plants are already operating using this idea. Tidal power or current power systems capture the energy of ocean currents below the wave surface and convert them into electricity. Typically, these systems rely on underwater turbines, either horizontal or vertical, which rotate in either the ocean current or changing tide (either one way or bidirectionally), almost like an underwater windmill. These technologies can be sized or adapted for ocean or for use in lakes or nonimpounded river sites.

Tidal barrages work rather like hydroelectric schemes, except that the dam is much bigger. A huge dam called a barrage is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam. The ebb and flow of the tides can be used to turn a turbine, or push air through a pipe, which then turns a turbine. Large lock gates, like the ones used on canals, allow ships to pass. A major drawback of tidal power stations is that they can only generate when the tide is flowing in or out—in other words, only for 10 hours each day. However, tides are totally predictable, so we can plan to have other power stations generating at those times when the tidal station is out of action. Tidal energy is generated from tidal movements. Tides contain both potential energy, related to the vertical fluctuations in sea level, and kinetic energy, related to the horizontal motion of the water. It can be harnessed using technologies using energy from the rise and fall of the tides or by technologies using energy from tidal or marine currents, as seen in Figure 7.9.

The temperature of water can be used to create energy. This ocean energy idea uses temperature differences in the ocean. It’s warmer on the surface because sunlight warms the water. But below the surface, the ocean gets very cold. That’s why scuba divers wear wet suits when they dive down deep. Their wet suits trap their body heat to keep them warm. Power plants can be built that use this difference in temperature to make energy. A difference of at least 38° Fahrenheit is needed between the warmer surface water and the colder deep ocean water. This type of energy source is called ocean thermal energy conversion (OTEC); its plants may be land-based, floating, or grazing. Renewable ocean energy can help diversify our energy portfolio and improve our environment. With the proper support, these resources will become a robust part of a reliable, affordable, clean electric supply infrastructure.

The turbine is composed of three sets of blades, as in Figure 7.10. The blades close when they are moving in the same direction as the flow of water, creating an obstacle that the water has to push out of its path of flow. When water pushes on the closed blades it causes the main shaft and generator to rotate. This rotational energy is collected in the form of electricity from the generator. When the blades are moving in the opposite direction as the flow of water, they open, creating minimal drag in the oncoming flow of water. This design creates very high surface area and drag on the power stroke side of the turbine while creating very low surface area and drag on the returning side. This design has proven to be the most efficient for collecting energy from ocean currents.

Benefits of ocean turbines:

Energy output of 13.5 MW/hour

100% reliable energy—not dependent upon wind or sun, ocean currents are always flowing

Doesn’t add heat to environment

No emissions

Water safe materials and paints

Antifouling, anticorrosive, won’t rust, won’t grow sea life

Can’t see it, hear it, or smell it

Huge survivability in storms (unlike other free energy devices)

Can provide energy and clean water to hurricane/tsunami victims

Components in the utility scale turbines are noncorrosive, nontoxic metals and high performance composite fiber

Design of turbine has large acoustic signature so marine animals can echolocate it, moves slowly enough for them to move around it, will not harm marine life

Less susceptible target for terrorism

Doesn’t take up high value land; places that need power have high population density, usually can’t support large wind turbines or solar projects because the demand is too high for the available area for those projects

The relatively constant flow of ocean currents carries large amounts of water across the Earth’s oceans. Technologies are being developed so that energy that can be extracted from ocean currents and converted to usable power. Ocean waters are constantly on the move. Ocean currents flow in complex patterns affected by wind, water salinity, temperature, topography of the ocean floor, and the Earth’s rotation, as shown in Figure 7.11. Most ocean currents are driven by wind and the solar heating of surface waters near the equator, while some currents result from density and salinity variations of the water column. Ocean currents are relatively constant and flow in one direction, in contrast to tidal currents along the shore. While ocean currents move slowly relative to typical wind speeds, they carry a great deal of energy because of the density of water. Water is more than 800 times denser than air, so for the same surface area, water moving 12 mph exerts the same amount of force as a constant 110 mph wind. Because of this physical property, ocean currents contain an enormous amount of energy that can be captured and converted to a usable form.

Wind energy has been utilized by humans for more than 2,000 years. For example, windmills were often used by farmers and ranchers for pumping water or grinding grain. In modern times, wind energy is mainly used to generate electricity, primarily through wind turbines. All wind turbines operate in the same basic manner. As the wind blows, it flows over the airfoilshaped turbine blades, causing them to spin. The blades are connected to a drive shaft that turns an electric generator to produce electricity. The newest wind turbines are highly technologically advanced and include many engineering and mechanical innovations to help maximize efficiency and increase the production of electricity. Offshore winds tend to blow harder and more uniformly than on land. The potential energy produced from wind is directly proportional to the cube of the wind speed. Thus, increased wind speeds of only a few miles per hour can produce a significantly larger amount of electricity. For instance, a turbine at a site with an average wind speed of 16 mph would produce 50% more electricity than at a site with the same turbine and average wind speeds of 14 mph. This is one reason that developers are interested in pursuing offshore wind energy resources. Commercial-scale offshore wind facilities are similar to onshore wind facilities. The wind turbine generators used in offshore environments include modifications to prevent corrosion, and their foundations must be designed to withstand the harsh environment of the ocean, including storm waves, hurricane-force winds, and even ice flows. New technologies, such as innovative foundations and floating wind turbines that will transition wind power development into the harsher conditions associated with deeper waters, are shown in the Figure 7.12.

The engineering and design of offshore wind facilities depends on site-specific conditions, particularly water depth, geology of the seabed, and wave loading. In shallow areas, mono piles are the preferable foundation type. A steel pile is driven into the seabed, supporting the tower and nacelle. The nacelle is a shell that encloses the gearbox, generator, and blade hub (generally a three-bladed rotor connected through the drive train to the generator) and the remaining electronic components, as in Figure 7.13. Once the turbine is operational, wind sensors connected to a yaw drive system turn the nacelle to face into the wind, thereby maximizing the amount of electricity produced.

Today’s offshore turbines have technical modifications and substantial system upgrades for adaptation to the marine environment. These modifications include strengthening the tower to cope with loading forces from waves or ice flows, pressurizing nacelles to keep corrosive sea spray from critical electrical components, and adding brightly colored access platforms for navigation safety and maintenance access. Offshore turbines are typically equipped with extensive corrosion protection, internal climate control systems, high-grade exterior paint, and built-in service cranes. To minimize the expense of everyday servicing, offshore turbines may have automatic greasing systems to lubricate bearings and blades as well as heating and cooling systems to maintain gear oil temperature within a specified range.

Lightning protection systems help minimize the risk of damage from lightning strikes that occur frequently in some offshore locations. There are also navigation and aviation warning lights. Turbines and towers are typically painted light grey or off-white to help them blend into the sky, reducing visual impacts from the shore. The lower section of the support towers may be painted bright colors to increase navigational safety for passing vessels. To take advantage of the steadier winds, offshore turbines are also bigger than onshore turbines and have an increased generation capacity. Offshore turbines generally have nameplate capacities between 2 MW and 5 MW, with tower heights greater than 200 ft and rotor diameters of 250–430 ft. The maximum height of the structure, at the very tips of the blades, can easily approach 500 ft, and turbines even larger than 5 MW are being designed. While the tower, turbine, and blades of offshore turbines are generally similar to onshore turbines, the substructure and foundation systems differ considerably.

Monopiles with diameters of up to 20 ft are typically used in water depths ranging from 15–100 ft. The piles are driven into the seabed at depths of 80–100 ft below the mud line, ensuring the structure is stable. A transition piece protrudes above the waterline, which provides a level flange to fasten the tower. In even shallower environments with firm seabed substrates, gravity-based systems can be used, which avoids the need to use a large pile driving hammer. Tripods and jackets foundations have been deployed in areas where the water depth starts to exceed the practical limit for monopiles.

Offshore wind turbines have a considerably larger power output than their land-based counterparts. Previously, offshore turbines were restricted to shallow waters; however, they are now mounted on semi-submersible structures, allowing access to even better wind patterns further from the shore. Offshore wind turbines as shown in Figure 7.14 have a much higher capacity than the conventional turbines employed in land wind farms, mainly due to the enhanced wind patterns experienced offshore. Offshore turbines previously were mounted on structures fixed to the seabed, which restricted them to relatively shallow water at a maximum depth of 150 ft. However, offshore wind turbines can be mounted on floating structures, allowing them to operate in deeper waters further out to sea. This considers renewable energy from offshore wind turbines and from turbines mounted on a floating structure.

Over the last 40 years or so, the offshore oil and gas industry has designed and developed various floating structures as in Figure 7.15 to support hydrocarbon production platforms. Most of these designs are suitable as support structures for offshore wind turbines; the more popular types are:

Semi-submersibles: These structures comprise hulls fabricated from large horizontal pontoons onto which vertical steel columns are welded, as in Figure 7.16. The columns and horizontal pontoons are interconnected and braced by a lattice of tubular steel supports. The structures are held to the seabed by anchors, whose chains are maintained in a catenary mooring mode by winches situated on the main deck. Various structures have been examined for potential use as floating supports for offshore wind turbines, including a multi-wind turbine support. However, this type of semi-submersible would require automatic weathervaning, controlled by satellite navigation that would turn the structure into the wind without interfering with the mooring system. Semi-submersibles can be self-propelled by their own marine diesel engines; the nonpropulsion type is towed to the required location. The offshore oil and gas industry has used semi-submersible floating structures for many years both as drilling rigs and production platforms, operating in depths of water of up to 6,000 ft.

Tension leg platform (TLP): This is a floating platform fixed by high-tensile solid steel round tie rods, attached to a specially designed template piled and grouted onto the subsea bedrock. The tie rods are kept in tension by overhead winches located under the main deck. TLPs can operate in depths of 6,000 ft.

Spar floating structure: The spar is just a large floating round hull that can be fabricated from steel or concrete. It has several sections built inside the hull which serve as ballast and oil storage tanks, being tethered to the seabed with conventional chains and winches. Spars can also operate in water depths of 6,000 ft. The Petronius Spar hydrocarbons production platform, weighing 45,000 tons, is currently operating at a depth of 1,750 ft in the Gulf of Mexico.

Offshore semi-submersible wind turbines in production: Hywind Statoil was the first company to produce electricity from a wind turbine mounted on a floating structure. In this case the structure was a steel fabricated spar type which was fabricated and towed in the horizontal position to an inshore assembly fiord. Here it was ballasted with sea water and brought to the vertical position, and further permanently ballasted with concrete. The tower was fitted onto the top of the spar, followed by the nacelle and rotor, and then the structure was towed to the offshore location where it was further ballasted and moored to the seabed. The wind turbine has a capacity of 2.6 MW, and there are plans to add more floating turbines, eventually constructing an offshore floating wind farm.

It is proposed to transmit power ashore through conventional subsea cabling, but also utilizing an innovative process known as high voltage direct current (HVDC). The units will be mounted on conventional bottom fixed structures such as steel jackets or monopods. The AC current produced by the wind turbine is converted to DC current before being transmitted ashore. This has several advantages over transmitting high voltage AC current:

Less power loss giving greater efficiency

Better control of distribution, less effects of land network faults

Instant determination of power being generated and distributed ashore

Transport of wind-generated energy: All the power generated by wind turbines needs to be transmitted to shore and connected to the power grid. Each turbine is connected to an electric service platform (ESP) by a power cable. The ESP is typically located somewhere within the turbine array, and it serves as a common electrical collection point for all the wind turbines and as a substation. In addition, ESPs can be outfitted to function as a central service facility and may include a helicopter landing pad, communications station, crew quarters, and emergency backup equipment. After collecting the power from the wind turbines, high voltage cables running from the ESP transmit the power to an onshore substation, where the power is integrated into the grid. The cables used for these projects are typically buried beneath the seabed, where they are safe from damage caused by anchors or fishing gear and to reduce their exposure to the marine environment. These types of cables are expensive and are a major capital cost to the developer. The amount of cable used depends on many factors, including how far offshore the project is located, the spacing between turbines, the presence of obstacles that require cables to be routed in certain directions, and other considerations.

Solar energy technologies [Figure 7.17] potentially suitable for use in ocean environments include concentrating solar power technology and photonic technology. Every minute the Sun bathes the Earth in as much energy as the world consumes in an entire year. Since oceans cover more than 70% of the Earth’s surface, they receive an enormous amount of solar energy. Deep ocean currents, waves, and winds all are a result of the Sun’s radiant energy and differential heating of the Earth’s surface and oceans.

Solar radiation can be converted directly to usable energy through a variety of technologies. While there are no commercial solar energy facilities operating offshore at this time, solar energy technologies potentially suitable for use in offshore ocean environments include concentrating solar power (CSP) technology and photonic technology. CSP is a thermal solar technology that concentrates the Sun’s rays to heat fluids or solids, and the heat is used to drive steam turbines or other devices to generate power. Photonic technologies convert the Sun’s radiant energy directly to electricity or other useful forms of energy. Selection of the appropriate solar technology for a given situation depends in part on the intended use of the energy to be generated. CSP technologies might be more appropriate for generating and delivering electricity to shore, while photonic technology might be more appropriate for generation of electricity to be used on-site (such as on offshore platforms) and for supplying energy for activities such as hydrogen production or desalinization.

Concentrating solar power (CSP) technology: CSP plants generate electric power by using mirrors to concentrate (focus) the Sun’s energy and convert it into high-temperature heat. That heat is then channeled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity. This approach requires large areas for solar radiation collection to produce electricity at commercial scale. CSP utilizes three technological approaches: trough systems, power tower systems, and dish/engine systems.

Trough systems: Trough systems use large, U-shaped (parabolic) reflectors (focusing mirrors) that have oil-filled pipes running along their center, or focal point, as shown in Figure 7.18. The mirrored reflectors focus sunlight onto the pipes and heat the oil inside to temperatures as high as 750°F. The hot oil is used to boil water, which produces steam to run conventional steam turbines and generators.

Power tower systems: Power tower systems, also called central receivers, use many large, flat heliostats (mirrors) to track the Sun and focus its rays onto a receiver. As shown in Figure 7.19, the receiver sits on top of a tall tower in which concentrated sunlight heats a fluid, such as molten salt, to temperatures as high as 1,050°F. The hot fluid can be used to boil water, which produces steam to run conventional steam turbines and generators. Or the thermal energy can be effectively stored for hours, if desired, to allow for electricity production during periods of peak demand, even when the Sun is not shining.

Dish/engine systems: Dish/engine systems use mirrored dishes (about 10 times larger than a backyard satellite dish) to focus and concentrate sunlight onto a receiver, as shown in Figure 7.20. The receiver is mounted at the focal point of the dish. To capture the maximum amount of solar energy, the dish assembly tracks the sun across the sky. The receiver is integrated into a high efficiency “external” combustion engine. The engine has thin tubes containing hydrogen or helium gas that run along the outside of the engine’s four piston cylinders and open into the cylinders. As concentrated sunlight falls on the receiver, it heats the gas in the tubes to very high temperatures, which causes hot gas to expand inside the cylinders. The expanding gas drives the pistons. The pistons turn a crankshaft, which drives an electric generator. The receiver, engine, and generator comprise a single, integrated assembly mounted at the focus of the mirrored dish.

Solar photonic technology: Solar photonic technology absorbs solar photons (particles of light that act as individual units of energy), and converts the energy to electricity (as in a photovoltaic [PV] cell) or stores part of the energy in a chemical reaction (as in the conversion of water to hydrogen and oxygen). PV technology converts sunlight directly to electricity. Concentrated PV (CPV) systems, which must track the Sun to keep the light focused on the PV cells, use various methods to concentrate sunlight such as mirrors or lenses. The primary advantages of CPV systems are high efficiency, low system cost, and low capital investment to facilitate rapid scale-up; reliability, however, is an important technical challenge for this emerging technological approach.

Currently, most ocean power technologies are not economically competitive with conventional fossil fuel power. They tend to have low operating costs but high construction costs with a long payback period. Careful site selection is also extremely important to keep the environmental impacts of ocean power technologies to a minimum. Protecting shorefronts, keeping sea life migration patterns and habitat intact, and preventing alterations in ocean temperature or sedimentation processes must all be considered. In addition, water and geographic conditions must be right for the technologies to work.

1.Define “ocean energy.”

2.What are the two different types of energy produced from the ocean?

3.What are the three types of electricity conversion for ocean thermal energy?

4.What is desalinization?

5.How is ocean wave energy captured?

6.Define “wave energy.”

7.What are the advantages of wave energy?

8.What are the disadvantages of wave energy?

1.What are the basic criteria for a renewable energy source?

2.Write about closed cycle systems of electricity generation.

3.Write briefly about ocean mechanical energy.

4.What are the methods used to convert wave energy into electricity?

5.What is a terminator device?

6.Explain an attenuator.

7.What is a point absorber?

8.What are overtopping devices?

9.Explain briefly tidal energy.

10.Write about ocean thermal energy conversion.

11.Explain the operation of ocean turbines.

12.What are the benefits of ocean turbines?

13.Write in short about ocean current energy.

14.Write in short about offshore wind turbines.

1.Write in detail about wave energy to electricity conversion.

2.Explain in detail the different wave energy technologies.

3.Explain offshore wind energy and its technologies.

4.Explain offshore solar energy and its technologies.

http://www.energy-without-carbon.org/OceanThermal

http://www.darvill.clara.net/altenerg/wave.htm

http://www.boem.gov/