Congratulations to 2OE Class of 2009!

This year the MIT 2OE class consisted of 4 members. We asked each senior to fill out a short questionaire about their time at MIT and here are their responses:



Mike Smith-Bronstein

Plans: Nuclear Officer on a navy submarine

Favorite MIT Class: 2.005 (Thermal Fluids Engineering I) or Music of Africa

Favorite OE Memory: Watching the robotic kayak actually work in 2.017

Advice to Freshmen: Office Hours.

Kaitlyn McCartney

Plans:

Working for a small environmental and marine engineering consulting firm out of Falmouth MA and then going back to school for a Master's or PhD.. haven't decided yet! But the company will pay for it :-)

Favorite MIT Class:
Intro to Naval Arch. or Robotics

Favorite OE Memory:
Sinking our autonomous kayak in 2.017. Sad but funny.

Advice to Freshmen: Enjoy college, don't stress too much or work too hard. Its over before you know it.

Brooks Reed

Plans:

I'm entering the MIT/WHOI joint program next year, and plan to be co-advised by Franz Hover at MIT and Dana Yoerger at WHOI. I'm not sure which project I will be working on yet, but probably something related to navigation and control of AUVs. Eventually I think I'd like to be a research engineer somewhere, possibly at an oceanographic institution.

Favorite MIT Class:

Probably 2.005 or Popular Musics of the World (21M.294)

Favorite OE Memory:

I had a lot of fun with our 2.017 ROV project. Also, taking part in the first pool test of the Sea Grant Odyssey IV AUV.

Advice to Freshmen:

In terms of OE, classes aren't everything. Try to take opportunities to learn about the field from a broader perspective. It will help you stay interested, apply what you learn in class, and have good background knowledge for jobs and internships. Other than that, have fun.

Elizabeth Palmer

Plans: Working in the LNG Ships group at ExxonMobil.

Favorite MIT Class: 2.005

Favorite OE Memory: Testing the 2.011 ROV in Prof. Techet's class freshman year

Advice to Freshman: Don't take MIT too seriously.

Current Status of Tidal Power Generation Part V: Economic Analysis

Current Status of Tidal Power Generation

This is the fifth part of the first portion of a multi-part series featuring papers on OE-related topics by students from the 2.65 class. The series is intended to raise interest and awareness of ocean energy research at MIT and in the world. This portion is on Tidal Power generation and is written by James Modisette, a graduate student in course 16. His sources and the full-text with citations are available upon request.

Economic Analysis

The economics of tidal power generation are very complicated. The barrage style tidal power plants have gone through extensive testing and La Rance has demonstrated that it is an economically viable way of generating power. However, barrage style tidal power plants require massive initial capital and extensive construction time. Due to these limitations, there has been no significant interest in barrage tidal power since the early 1980s and it seems that nothing will disturb this trend.

On the other hand, tidal stream generators have the attraction of being small devices that can be installed on a piecemeal basis, thereby reducing their initial costs. This allowed for the creation of the first major tidal generation project in the U.S., Verdant Power. It also generated interest in tidal power throughout the north east and west of the U.S., as well as the U.K.. As studies of various designs, notably in the U.S., U.K., Canada, Japan, etc., are concluded, the long-term economic potential of stream turbines will become clearer. At this point, the cost of tidal stream power generation is a great unknown. Depending on which advocate is speaking, a very different conclusion can be drawn. For instance, a proposed 35 megawatts tidal stream facility beneath the Golden Gate Bridge in San Fransisco has user energy costs ranging from 6.6–7.6 cents per kilowatt hour from Electric Power Research Institute’s (EPRI’s) feasibility study [21] to 0.85–1.40 dollars per kilowatt hour from a feasibility study prepared by URS for the San Fransisco Public Utilities Commission.

One thing certainly undermines the value of the EPRI’s feasibility study, tidal power generation will be more expensive in the future than either wind or solar power, currently priced at 7 and 10–40 cents per kilowatt hour respectively. Tidal power is behind in development and a great deal of money and time needs to be spent on engineering and assuaging concerns about the environmental impact. Verdant Power claims it will spend more than five years and $2 million on environmental research, monitoring the impact of its turbines on fish and migratory birds before it will get to the final stages of obtaining the necessary permits to install more turbines and be capable of producingelectricity on a larger scale of ten megawatts. Wind and solar advocates have already spent much time on these issues, giving them a leg-up on development.

An attempt to compare the initial capital investments is presented in table 2. The numbers for tidal power are estimates, as only one “commercial” facility has been constructed and projecting unknown numbers into the megawatt scale is difficult. Table 2 indicates that with tidal power’s advantage of predictability over other renewable energy sources, it is not far from being an economically viable way to produce energy. Although, if a tax is not levied on carbon-dioxide and equivalents emissions, coal and natural gas will continue to be the only economic options.

Table 2: Estimated initial capital cost in dollars per peak kilowatts installed.










When considering renewable energy sources like tidal, solar, or wind, further economic consideration must be made. A variable power source affects the grid as a whole. There is an inherent inability for thermal energy sources to adjust their power output instantaneously when renewable energy becomes available or disappears. Either inefficiencies from the start-up costs of thermal energy sources will need to be accounted for in the grid or some form of storage will need to be added. Both of these options come with costs and consequences. Eventually someone will pay have to for this and it certainly won’t be the utility company. No plant built recently, all outside the U.S., has been built for less than $2, 000 per kilowatt of generating capacity.

An additional economic variable that must be addressed for any renewable energy is what form of subsidy is available to that energy source. Unfortunately, there are currently no U.S. federal subsidies available for tidal power, although it is a renewable energy source and one would hope that the government will begin to see it as a viable alternative. There are some states, MA, CA, RI, HI, etc., that have provided support for tidal power, either through low interest funding or subsidies and, therefore, they are the areas where development of tidal power plants is occurring. On the other side of the Atlantic, tidal power generation is receiving more significant support. SeaGen, for instance, is benefiting from U.K. support where it is receiving three times the subsidies or Renewable Obligation Certificates per megawatt hour than onshore wind farms. The extra incentives in the U.K. are helping tidal power catch up to the existing renewable energy developments.

Be sure to keep following this series, the next portion of this paper will focus on the future of tidal energy generation.

Current Status of Tidal Power Generation Part IV: Issues Surrounding Tidal Power Generation

Current Status of Tidal Power Generation

This is the fourth part of the first portion of a multi-part series featuring papers on OE-related topics by students from the 2.65 class. The series is intended to raise interest and awareness of ocean energy research at MIT and in the world. This portion is on Tidal Power generation and is written by James Modisette, a graduate student in course 16. His sources and the full-text with citations are available upon request.

Issues


Tidal-power generation, like all renewable energies, has its own set of limiting characteristics. Like wind and solar, tidal power cannot provide the constant power generation of a coal-fired power plant. A double-effect barrage or a tidal stream turbine will only produce peak power over four periods of several hours each day. There is also a variation, due to lunar and solar cycles, in the amplitude and period of the tides. However, these variations are predictable whereas wind and solar resources are at the whim of the weather. Scientists already know all the future variations in the tidal cycle. So a tidal power plant may add complexity to managing the power grid but it will not cause unexpected loss or creation of power.

Another limitation of tidal power plants is that along with the long construction times and massive amounts of capital necessary for installation of tidal barrages, they also require specific geographic coastal configurations. This leads to potentially large impacts on ports and shipping lanes and ends up with a case of NIMBY that may never be resolvable. Imagine if Jim Gordon had attempted to take over Nantucket Harbor for Cape Tidal as opposed to putting 130 turbines over thirteen miles away from Nantucket for Cape Wind. Even if they make environmental and economic sense, tidal barrages demand such a significant amount of coastal real estate that it is nearly impossible to conceive of having them in the U.S.

Tidal stream generators address this problem directly by being smaller, local units that can be placed underwater so that they are not visible and do not affect boat traffic. Tidal power generation has an environmental impact much like any other source of energy. There is no way that the construction of a tidal barrage will not alter the ecosystem of a living tidal basin, as demonstrated by La Rance. With the barrage tidal system there is a loss of seawater exchange. This loss leads to a change in the salinity of the water which can cause wholesale changes in ecosystems. The original ecosystem of the estuary where La Rance was installed was almost completely destroyed. It took the restocking of the estuary and ten to fifteen years before a new biological equilibrium
was reached.

Another environmental impact that both tidal barrages and tidal stream generators present, is a danger to fish. Tidal barrages benefit from existing hydro-power plants which also face this challenge and are being forced to develop new turbines that can operate without hurting fish. One possible solution for tidal barrages is to wait and allow standard hydro-power to solve the fish problem. Stream turbines, on the other hand, do not have that luxury. Verdant Power has already been delayed five years in the permitting process and has spent more than $2 million on environmental research.

Another limiting characteristic is that tides aren’t always close to urban populations where there is a high demand for power. For instance, there are large tides in Newfoundland but the population density is negligible. Transferring tidal power generated in Newfoundland to the urban regions of southern Canada or the Northeastern U.S. is infeasible. The capital to create the power lines to transfer the power is outrageous and by the time the power reached the cities a significant amount of energy will have been wasted in transit canceling out any benefits of generating the renewable energy.

Be sure to keep following this series, the next portion of this paper will focus on an economic analysis of tidal power generation..

Ongoing Series: Current Status of Tidal Power Generation, Part 3

Current Status of Tidal Power Generation

This is the third part of the first portion of a multi-part series featuring papers on OE-related topics by students from the 2.65 class. The series is intended to raise interest and awareness of ocean energy research at MIT and in the world. This first section is on Tidal Power generation and is written by James Modisette, a graduate student in course 16. His sources and the full-text with citations are available upon request.

Current Installations

Current tidal power installations utilize one of two generation schemes: the barrage style, built mostly around the 60’s, and the stream generator, deployed over the past ten years. A large number of “prototype” barrage style tidal power generators are installed around the world. The main characteristics of the four largest tidal barrages are shown in table 1.

Table 1: Main characteristics of large barrage tidal power plants.

The most successful barrage style tidal power generator is La Rance, in France, shown in figure 5. It was built during the mid-60’s and other than a seven-year period in the late 70’s it has been consistently generating 240 megawatts from 24 turbines. Although it is only a single-basin scheme, the generators are reversible bulb turbines capable of turbining or pumping in both directions. This added complexity was included in the prototype plan to increase flexibility and provide as much data as possible for the development of tidal technology. The La Rance location has a maximum head of eleven meters, a minimum head of three meters, and an average tide of eight and a half meters. It also benefits from having no major seasonal changes in the tides, just a standard fourteen day recurring cycle.

Figure 5: Area view of the La Rance power plant.

La Rance has had only one major mechanical issue in its 40 years of operation which,an impressive feat for a prototype facility. In 1975 it was discovered that the stresses from the start-up for pumping had been underestimated and that every stator had to be rebuilt. This was concluded by 1982 with little loss (<>
were used. In 1979, after thirteen years of use, all of the blades were still in excellent condition with some of the original paint still on them.

Although La Rance has been generating “clean power” since 1969, it has caused environmental damage to the estuary closed off by the barrages. The closing of the estuary with the cofferdam caused almost complete destruction of the marine flora and fauna. The estuary had to be re-stocked with aquatic life, and after fifteen years it flourished again, but not with the same ecosystem. The basin was smaller and the tidal flow was broken up between the sluice gates and the turbines. These changes led to the survival of different species. While the original ecosystem was essentially replaced, it does not appear that the barrages accelerated silt growth in the estuary, but it has led to simple sedimentary redistribution. La Rance also came with some unforeseen advantages. Tourism in the Bretagne region received a major boost and maintains a level that never existed before the power plant was constructed. Additionally, the most positive outcome of La Rance is that the average cost of tidal energy generated in 1976 was equal to the average cost of nuclear kilowatt hour and also equal to the average system thermal kilowatt hour cost. Other than operation and maintenance costs there have never been any fuel costs at La Rance.

Other barrage style tidal generators include a facility in the Annopolis River in Novia Scotia generating (20 megawatts), the Kislaya Bay in the Russian Arctic (400 kilowatts), and more than a hundred Chinese plants (total capacity of 7.5 megawatts). All of these facilities were much smaller than La Rance and were trial facilities for proposed larger tidal generation installations. Different turbine technologies, pumping strategies, and construction techniques were tested and a great deal of information about barrage style tidal power generation developed. For the most part, all of the prototype facilities have been successful and yet none of them have led to large-scale commercial barrage style tidal power generation. The necessary capital costs and extremely slow start up times continue to scare away politicians and investors.

More recently, following the advances in technology for wind turbines, kinetic energy turbines have started to emerge around the world. The stream turbines benefit from the fact that they are significantly smaller installations, can be fully submerged in a tidal stream without disrupting shipping traffic, and do not require the same massive initial capital investment.

There are many new tidal stream turbines around the world that have been set up to test capabilities in preparation for larger developments. Two of particular interest are Verdant Power and SeaGen. Verdant Power has six turbines in the East River between Manhattan and Roosevelt Island. SeaGen has a Marine Current Turbine off of Northern Ireland capable of generating what they claim as the first “commercial” amount of power. Verdant Power is the first major tidal-power generation project in the U.S.. The project was initiated in 2002 and by December 2006 two turbines had been installed in the East River. One of the turbines has been delivering a maximum of 35 kilowatts to the grocery store and parking garage on Roosevelt Island while the other one has been delivering performance data. In May 2007 another four turbines were installed. The six turbines will need to be monitored for eighteen months to address environmental concerns.

In particular, the fear exists that the rotor blades could chew up the river’s fish as the rotor tips travel up to nine meters per second. As with any new technology Verdant Power has suffered some set backs. In September 2008 it had to replace all of the original rotor blades because the design was faulty and some had broken off. The original rotors were made from fiberglass with a steel skeleton while the new rotors were made from aluminum and magnesium. Although they have suffered some set backs, Verdant Power is optimistic and plans on installing enough turbines to produce 10 megawatts.

Marine Current Turbines of Bristol, England, has also tested an eleven meter turbine capable of producing 300 kilowatts off the coast of Devon, England, for four years. After the success of Marine Current Turbines’ test, SeaGen [3] selected them to produce what it is calling the world’s first tidal turbine capable of generating “commercial” amounts of energy or 1.2 megawatts. As seen in figure 3 (b), the SeaGen installation works by using two rotating blades that turn nominally at fourteen revolutions per minute. The two blades drive a gear box before the power reaches the generator. SeaGen was built at Belfast’s Harland and Wolff’s shipyards and is bolted to the sea floor. The process of bolting it to the sea floor encountered unexpected complications and it took fourteen days as the installation team had to fight the very tides that they hoped to harness. But, the ability to manufacture the stream generators on-shore, as SeaGen was, will go a long way to ensuring their economic viability.

Currently, the SeaGen power generation unit is designed to break the surface of the water with a column structure. This allows for the rotor assembly to be lifted out of the water for maintenance and inspection without the need for divers swimming in tricky fast-moving water. This characteristic may only be desirable in some locations and Marine Current Turbines has already conceptualized a fully submerged second generation design.

Be sure to keep following this series, the next portion of this paper will focus on the challenges facing tidal power generation..

Current Status of Tidal Power Generation


This is the second part of the first portion of a multi-part series featuring papers on OE-related topics by students from the 2.65 class. The series is intended to raise interest and awareness of ocean energy research at MIT and in the world. This first section is on Tidal Power generation and is written by James Modisette, a graduate student in course 16. His sources and the full-text with citations are available upon request.

Kinetic Energy Turbines - Tidal Steam Generators
Some consider the phrase “fast moving currents” to be an overstatement as the fastest currents in the world are only about 10mph, but it is the density difference between water and air that makes tidal kinetic energy turbines possible. The density of water is about 850 times larger than the density of air, so it is easy to see that the energy in the tidal current, 1/2pv^2, can be comparable or better than that of wind power, which has already been harnessed and deemed economically feasible.

Using tidal stream generators to generate power is a fairly new technology. These generators fall into the second category of tidal power generators using the kinetic energy in fast moving tidal streams. Most of their development has been aided by the 35 year history of wind turbines. Stream generators can be broken down into several different design types. There are turbines, with either vertical or horizontal axes, with or without shrouds, and then oscillating devices. There are different benefits with each design. The vertical axis turbine has the potential to have fewer moving parts underwater and shrouds can be used to increase the flow rate.

Aided by wind turbine technology, horizontal turbines currently dominate the market. Due to this, horizontal turbines at times can be hard to distinguish from their wind turbine cousins, as shown in figure 3. The prominent difference is that they are not as large or as sleek as wind turbines. Bulking up the hub and blades is necessary to withstand larger stress loads produced by tidal currents.

Figure 3: Diagram of horizontal tidal stream turbines. These generators use the kinetic energy in tidal streams to drive rotors. The rotational motion passes through a gearbox and then drives a generator. a) Verdant turbine being tested in the East River between Manhattan and Roosevelt Island b) SeaGen installed in the Strangford Lough off Northern Ireland

Another design option is the oscillating device shown in figure 4. These devices are newer and have been designed to have a minimum of underwater moving parts. Instead of rotating parts they feature fins or wings that are at an angle of attack relative to the tidal stream. The angle of attack causes lift to be generated which can be used to force a hydraulic cylinder to extend or retract. As the fin reaches the top/bottom of its swing the angle of attack changes so that the cycle can continue.

Figure 4: Representation of an oscillating style stream generator. The
oscillating device uses the kinetic energy in tidal streams to create lift
on a wing which is converted to linear motion to drive a piston.
Although oscillating devices have some inherent benefits, the technology is too recent to have broken into the market in the same way as rotor driven turbines.

Be sure to keep following this series, the next portion of this paper will feature current installations of the technologies which have been discussed..

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