What Are the Environmental and Eco-logical Effects of Ocean Renewable Energy Development?

Boehlert and Gill (2010) aimed to answer that question in their synthesis, which blends and summarizes previous research on the environmental effects of specific ocean renewable energy technologies. In their synthesis, the researchers focused on offshore wind, thermal gradient, wave, tidal, and ocean current technologies, through all stages of development—construction, operation, and decommissioning. To classify the results in an intuitive way, Boehlert and Gill grouped environmental effects as either stressors or receptors and by level, from effect to impact to cumulative impact. Although the authors created a very organized system for evaluating the environmental effects of ocean renewable energy development (ORED) projects, their synthesizing did not give rise to definitive conclusions. Rather, the authors acknowledged that there is little research on the environmental effects of ORED, and that existing research is clouded in uncertainty. Therefore, the authors ultimately advise that additional baseline data be collected and that longer, more continuous research studies be undertaken. —Juliet Archer
Boehlert, G., Gill, A., 2010. Environmental and ecological effects of ocean renewable energy development: A current synthesis. Oceanography 23, 68–81.

G. Boehlert and A. Gill from Oregon State University and Cranfield University, respectively, compiled, summarized, and synthesized current scholarly research on the environmental effects of different ocean renewable energy technologies. The authors chose to limit their synthesis to five technologies: wave, wind, thermal gradient, tidal, and current energy conversion. The authors created a framework with six levels for the classification of their results. The first level is the type of marine renewable energy technology. The second level contains environmental stressors. Stressors are aspects of the environment which may be altered during the installation, operation or decommissioning of marine renewable energy technologies. In their definition of stressors, the authors include device presence, chemical, acoustic, electromagnetic field, energy removal, and dynamic effects. Environmental receptors, defined as “ecosystem elements with [the] potential for some form of response to the stressor,” are the third level of their framework. Boehlert and Gill include animals, such as fish and marine mammals and birds, the food chain, ecosystem, and physical environment, including benthic and pelagic habitats. The fourth level of their framework contains four potential environmental effects. These are given as combinations of length, long or short term, and magnitude, single or multiple effects. Environmental impacts, such as population change, community change, biotic process alteration, and physical structure or process alteration, comprise the fifth level. The authors distinguish between an “impact” and an “effect.” Specifically, an impact indicates the severity, direction, and duration of an effect. Effects are relegated to level four while impacts included in levels five and six. Lastly, cumulative impacts are presented on the sixth level. These impacts are analyzed separately from level five impacts because level six impacts consider the collective impact of all stressors caused by human impacts. Cumulative impacts are considered on spatial and temporal scales. This framework is used throughout the paper to classify and evaluate the environmental effects of marine renewable energy development.
After outlining their entire framework, Boehlert and Gill go on to give detailed explanations of the environmental stressors found in level two. The first, and arguably most obvious, stressor is the physical presence of renewable energy structures in the marine environment. The presence of these devices can result in a range of changes above and/or below the water surface. For instance, ocean wind energy devices have the highest vertical presence above the water. In contrast, ocean thermal energy conversion (OTEC), with its extensive pipe system along the ocean bottom, will have a greater presence below the water. The authors also note that some wave energy devices, like the Pelamis or Sea Dragon, have a significant presence on the ocean surface.
The authors also consider the dynamic effects of a device, as a stressor independent of its physical presence. The moving parts of devices, located above and below the water may have effects on the marine environment. One of the most common effects is “blade strike,” which typically describes either a migratory bird or fish colliding with a wind or current energy device, respectively. A less apparent effect of moving parts is the removal of energy from the air, water or waves. In the water, this may result in changes to turbulence, stratification, sediment transport and even changes in currents and tidal range. These changes may result in further changes such as disturbing the foraging activities of shorebirds or changing the distribution of intertidal organisms. Moving large amounts of water, such as the movement of deep cold and shallow warm water in OTEC processes, may entrap mobile species and redistribute nutrients to colder waters. The above environmental effects of moving parts show the importance of studying both short and long term and near and far field effects. 
The chemical effects of marine energy devices are not of paramount concern.  As Boehlert and Gill explain, the effects of chemicals utilized in marine renewable energy development and operations will be similar to the effects of any other ocean construction projects.  The small risk of chemical effects during installation, ordinary servicing, and decommissioning are expected to result from ocean vessel operations. However during ordinary operations, a risk of chemical spills exists, especially for devices which use hydraulic fluids. The effect of a spill from an OTEC could be very damaging because the working fluid would most likely be ammonia, which is extremely toxic to fish.  Leaching of chemicals may also occur if anti-fouling paints are used to deter organisms which would foul the device. The authors advocate for more research on the toxic compounds used in marine renewable energy development. In addition, the natural chemistry of ocean systems must be examined to determine whether the potential for negative ecological effects, including the outgassing of carbon dioxide and acidification<!–[if supportFields]> XE “acidification” <![endif]–><!–[if supportFields]><![endif]–> of upwelled waters, are high.
Acoustic effects of ORED may interfere with the natural acoustic environment, causing a disturbance to animal communication, orientation, reproduction and/or predator and prey sensing. For instance, it is widely known that acoustic changes impact fish and marine mammals. However, new research has shown that lobster and crab larvae may also be impacted. Therefore, acoustic effects must be examined during all phases of development, and on various temporal and spatial scales. For instance, the construction phase is usually considered noisiest and “most acoustically diverse.” These different noises may result from increased shipping surrounding the area, seismic surveys, pile driving and/or other construction activities. Currently, data to quantify the noise of ORED are deficient and therefore, hypotheses, such as that devices with underwater moving parts will be the nosiest, cannot be tested. Boehlert and Gill recommend that future research focus on determining the intensity, propagation, and acoustic profile of sounds emitted from various forms of ORED.
Since ORED are required to transmit electricity, all except shore-based OTEC or pressurized water pumps create electromagnetic effects in the marine environment. Industry standards currently require shielding on all cables that transmit electricity, to confine “directly emitted electric fields.” However, shielding does not restrict the magnetic part of an electromagnetic field (EMF). This can pose a problem for magneto-sensitive organisms, especially those which migrate long distances or orient using natural geomagnetic fields. Similarly, organisms which are electroreceptive, and use bioelectrical impulses to orient, feed, or mate may be severely impacted by the electromagnetic effects of ORED. However, scientists are uncertain as to the response of marine creatures to EMFs because the data needed to assess an impact does not exist. The authors suggest that “before-and-after baseline assessments” be completed and that the biological significance of effects as wells as possible thermal effects be examined.
The authors also list the possible impacts on the environmental receptors. The first receptors considered are the physical environment, and pelagic and benthic habitat. The physical environment may be changed by the removal of kinetic energy from the water, resulting in local acceleration, scouring, or altered sediment transport, deposition, or thermal regimes. Pelagic habitats will be most impacted by the creation of structures in previously vacant areas. This may increase fish populations which will probably attract more predators to the area. Pelagic organisms may also be impacted through impingement, collisions, or entanglement with ORED. Benthic habits will probably be the most impacted by ORED because of structural modifications and changes to water circulation and currents. Greater biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–> may result as devices create an “artificial reef,” but some species may benefit while others are negatively impacted. Other impacts have similar mixed effects. For instance, “shell mounds” may accrue on the ocean bottom as growth on lines, buoys, and anchors are sloughed off. This will alter the habitat but it may also create a productive habitat for fish. Therefore, research shows, albeit with much uncertainty, that ORED may have both positive and negative effects on the physical environment and various habitats.
Another important group of receptors includes organisms within the broad categories of fish, seabirds, and marine mammals. One surprisingly positive effect on fish is the creation of de facto reserves in areas where ORED are located, if fishing is banned. However, these reserves may result in increased mortality of resident fishes as new species and additional predators are attracted to the area. Migrating fishes, such as salmon<!–[if supportFields]> XE “salmon” <![endif]–><!–[if supportFields]><![endif]–>, elasmobranchs, and sturgeons, may also be affected by individual EMF, chemical, and acoustic stressors, or a combination of these stressors. Seabirds, on the other hand, will be primarily impacted by the above surface effects of ORED. For example, birds that are attracted to lights may collide with the above-water structures such as wind turbines. Furthermore, even if most seabirds are able to steer clear of turbines, the extra energy required to do so may have a negative impact, especially on local, diurnal migratory species. Since studies show that the impact of additional energy required intensifies as the time period of avoidance lengthens, cumulative impacts should be considered in future research. Seabirds may also be impacted by below surface structures to the extent that such devices increase fish populations, or present collision, entanglement, or blade strike risks for diving birds. Boehlert and Gill recommend that the effects on crucial areas of bird activity, migration patterns, and seabird prey be studied in the future.      
Marine mammals receive a disproportionate amount of attention among marine receptors in studies of the environmental effects of ORED. This is not surprising since the group is usually protected, captures more public interest and is more visible than other receptors. Concerns for cetaceans are similar to those for diving seabirds, and include risks of entanglement, collision, and blade strike, especially if fish populations increase near ORED. In addition, marine mammals may be attracted to or repelled by the acoustic emissions of ORED. Also, like fish, there is a potential that EMFs may disturb marine mammals’ natural orientation systems. The authors recommend more monitoring of cetaceans and pinnipeds, beginning at that same time as pilot and demonstration projects are launched. In addition, baseline data are needed for marine mammals and their prey species. Lastly, the authors urge that “special attention” be given to the migratory routes and important feeding grounds of marine mammals.
Although the number of studies on ORED has increased, the number that focuses on the environmental effects of these devices is relatively small. Currently, the development of devices and deployment of pilot projects and demonstrations outpaces the understanding of their effects. Thus, the need for more research is urgent and great. Boehlert and Gill advocate for simultaneous environmental research as these new technologies are deployed, in order to identify impacts for receptor and stressor groups and decrease uncertainty. Environmental standards for ORED are also needed, but stringent standards may inhibit new development. In contrast, lenient standards may lead to tremendous environmental damage. In light of these undesirable consequences, the authors recommend that balanced environmental standards be developed. At the end of their synthesis, Boehlert and Gill remind readers that the ultimate goal of ORED is to decrease our dependence on fossil fuels.  

Before Scotland Increases Marine Re-newable Energy Capacity, It Must First Assess the Potential Impacts on Local Cetacean Species

The government of Scotland aims to increase renewable energy power to 50% of total electricity demand by 2020. To meet this goal, Scotland will likely to turn to marine renewable energy sources since it has commissioned or proposed United Kingdom Strategic Environmental Assessments (SEA) on wave, tidal, and marine wind energy, respectively. Additionally, the Crown Estate has announced that ten sites, within Scottish waters, will be available for marine wind energy development. However, the best methods for mitigating negative impacts on local cetaceans, including protected species, have not been determined. Thus, Scotland is conflicted. Should it increase its marine renewable energy capacity to the detriment of cetacean species? Or should it proceed with caution, in order to protect the cetaceans, and disregard its renewable energy goal? Dolman and Simmonds (2010) suggest that long term baseline research and real-time monitoring and mitigation methods be developed. Furthermore, they advise that the Scottish government employ adaptive management in all planning processes so that early learning can be incorporated into future plans. If Scotland is able to adopt some of Dolman and Simmonds’ recommendations, then perhaps it can have both –reliable marine renewable energy and healthy cetacean populations. —Juliet Archer
Dolman, S., Simmonds, M., 2010. Towards best environmental practice for cetacean conservation in developing Scotland’s marine renewable energy. Marine Policy 34, 1021–1027.

Sarah Dolman and Mark Simmonds examined the negative effects of marine renewable energy technologies on cetacean species with regard to political drivers and cetacean conservation. They described the current legislative, political and legal situations in light of the urgent problems presented by climate change. The authors also presented the current research and understanding of how wind, wave and tidal renewable energies impact local cetacean species including harbor porpoises, bottlenose dolphins, baleen whales, and white beaked dolphins. Finally, after synthesizing the above information, Dolman and Simmonds presented their analysis of current best practices in marine renewable energy. Lastly, the authors presented key factors in Scotland’s attempt to implement best practices in marine renewable energy development.
Dolman and Simmonds found that both the UK and the Scottish government have ambitious plans to increase their renewable energy capacity. However, one challenge for developing Scottish marine renewable energy is that the UK parliament, not the Scottish government, has the authority to develop “within 200 nautical miles of the UK coastline.” Yet, the Scottish government is responsible for administering any developments. As the authority, the UK government has completed a SEA to consider the environmental implications of its plan to produce a total of 33 GW of offshore wind energy. Nonetheless, the UK government has not evaluated the environmental effects of wave or tidal power.
Another consideration in marine energy development is the legal protections of certain species. The authors reported that Scotland has 24 cetacean species that are “strictly protected” under the EU Habitats Directive. This law also requires that Special Areas of Conservation (SAC) be set aside for protected species. Currently, Scotland does not have adequate SACs for its protected species, such as small bottlenose dolphins and harbor porpoises. Scotland also has national laws aimed at protected vulnerable species. Scotland’s laws operate at the individual level, so that it is an offence to “deliberately or recklessly disturb or harass any cetacean… in a manner that is…likely to significantly affect its local distribution or local abundance.” Since this law includes “recklessly disturb[ing]” a cetacean as an offense, the authors predict that lawful activities, such as building wind turbines, may result in offenses. Lastly, Dolman and Simmonds explain that even though marine renewable energies may mitigate the threat of climate change, environmental laws must still be followed.
The numerous potential negative impacts from wind, tidal and wave energy are presented in the paper not as eventualities but as “conquerable” problems. With the construction of each energy system, pile driving has a significant impact because it results in noise and damage to the sea bed. In addition, increased vessel activities, habitat degradation, operational noise, and the method used to decommission plants are potential impacts for all three technologies. Some of these impacts have already been observed. For example, at a Danish wind farm, porpoise detections decreased over long ranges during pile driving. Most of the effects, including pile driving, are still being considered to determine the significant of their impact on cetacean species.

The authors conclude by presenting specific recommendations for the Scottish government. They advise that selecting an optimal location is a chief concern. To accomplish this, they recommend collecting data, on an appropriate scale, in order to determine habitats, species densities, distributions and population trends, among other things. Once a location has been selected, the Scottish government should then conduct a “full and transparent” Marine Spatial Planning. This Spatial Planning should be integrated with UK and Scottish SEAs to decrease important knowledge gaps and improve coordination. Monitoring should also be done in a coordinated way. The authors recommend that industry, the Crown Estate and the UK and Scottish governments work together to conduct baseline and continual monitoring of the chosen site. Lastly, the authors note that independent scientists and marine conservation groups are also needed to answer imperative questions and support industry best practices, respectively. The many considerations and connected factors show that developing marine renewable energy best practices in Scotland will not be easy. 

Maximizing the Efficiency of Offshore Wave Energy Converters: A Vital but Challenging Task

Although approximately 4 MW of wave energy have been installed worldwide, questions of how to maximize converter efficiency still exist (Bedard et al. 2010). Igic et al. (2011) explored this question by investigating how the overall performance of the Wave Dragon (WD) wave energy converter changed based on different control strategies and electrical system configurations. The authors modeled these dependencies using a computer simulation of one turbine<!–[if supportFields]> XE “turbine” <![endif]–><!–[if supportFields]><![endif]–>-generator connected to an AC/DC/AC converter and an infinite grid.  Results for torque, DC link voltage, power, speed, output voltage, and current were presented in relation to the height of the turbine head. Using a permanent magnet generator (PMG), Igic et al. found that the line to line voltage of their simulation was 690 V and the maximum current value was 50 A. In addition, their simulation was deemed appropriate for use in prospective studies of wave energy power take-off systems. Even though further research is still needed, the authors’ case study and simulation results should be considered in the design of future offshore wave energy converters. —Juliet Archer
Igic, P., Zhou, Z., Knapp, W., MacEnri, J., Sørensen, H., Friis-Madsen, E., 2011. Multi-megawatt offshore wave energy converters – electrical system configuration and generator control strategy. Renewable Power Generation, IET 5, 10–17.

Igic and colleagues examined various electrical system configurations and control strategies of the WD offshore wave energy converter in regards to overall system performance. First, Igic et al. presented a case study which thoroughly described the potential electrical systems, grid connections, and generators that could be used with the WD. Next, they described models and presented equations representing PMG and frequency converter control. In these models and equations, both generator and grid side control mechanisms were considered. Lastly, the team built a MATLAB simulation model by utilizing the “power system tool box” in order to investigate how the overall system performance was impacted by generator characteristics and control strategies. The authors made some minor assumptions while constructing their model. For example, the influence of converter harmonics and torque fluctuation was ignored. In addition, the AC/DC and DC/AC converters were both portrayed as voltage-controlled voltage sources (VCVS). Furthermore, the authors chose various parameters, such as stator resistance, inductance, and flux<!–[if supportFields]> XE “flux” <![endif]–><!–[if supportFields]><![endif]–> induced by magnet, for the PMG simulation. Finally, to focus solely on performance of the system control, Igic et al. assumed that the turbine<!–[if supportFields]> XE “turbine” <![endif]–><!–[if supportFields]><![endif]–> was connected to an infinite utility grid.
The simulation results of this paper pertain specifically to the WD wave energy converter. The WD is a floating barrage that creates electrical energy from wave power<!–[if supportFields]> XE “wave power” <![endif]–><!–[if supportFields]><![endif]–>. It is composed of three parts which are analogous to a human’s mouth, arms and stomach, which work together in the process of deriving energy from food.  The main part of the WD is a large floating reservoir that faces incoming waves. This part is analogous to the mouth because it is where the waves enter the system via a curved ramp. As the waves overtop the ramp and enter the reservoir, potential energy is created by the difference in relative elevation. The arm-like reflectors assist in directing waves towards the reservoir and typically increase the rate of energy capture by 70%. Finally, the 16–20 low-head water turbines are like the stomach because they are used to convert the hydraulic head[1] within the reservoir into the end product, electricity. The multiple small turbines provide the many advantages, such as efficient flow rate regulation, shorter draft tubes, higher speeds and allowing the performance of maintenance activities while production continues. In order to maximize efficiency and thereby performance, a control scheme of three phases is applied to the production process. The first phase is the careful regulation of the platform’s floating level in order to maximize the amount of power flowing over the ramp, given ocean conditions. The second phase is controlling the water level inside the reservoir in order to minimize energy loss from losses of pressure head and due to overflowed water. The last phase controls turbine<!–[if supportFields]> XE “turbine” <![endif]–><!–[if supportFields]><![endif]–> and generator speed in order to maximize turbine efficiency based on the instantaneous turbine head[2].
Results from the single turbine<!–[if supportFields]> XE “turbine” <![endif]–><!–[if supportFields]><![endif]–>-generator-frequency converter unit are shown in relation to turbine head height. When water head (m) is relatively high, torque (Nm), turbine speed (rpm), and the amount of power (W) delivered to the grid are also relatively high. The DC link voltage (V) does not have a similar positive correlation with the turbine head. Output phase voltage (V) is constant throughout the simulation and shows no relationship to turbine head. The output phase current (A) shows a pattern similar but not analogous to the height of the turbine head. The authors also found that torque quickly decreases to zero as the cylinder gate closes. This ensures that the WD will use the greatest amount of water potential energy within the system. Igic et al. conclude by recommending that the relationship between power fluctuation and voltage near the grid connection point be examined by incorporating a grid model into their simulation.


[1] “The force exerted by a column of liquid expressed by the height of the liquid above the point at which the pressure is measured. Although head refers to a distance or height, it is used to express pressure, since the force of the liquid column is directly proportional to its height.” (Engineering Dictionary)
[2] “the level of difference between the reservoir level and the mean sea level”

Reverse Electrodialysis: Optimizing Per-formance in Up-Scaled Systems

Reverse Electrodialysis (RED)<!–[if supportFields]> XE “Reverse Electrodialysis (RED)” <![endif]–><!–[if supportFields]><![endif]–> is a salinity<!–[if supportFields]> XE “salinity” <![endif]–><!–[if supportFields]><![endif]–> gradient power (SGP) process whereby electrical power is produced from the reversible mixing of waters that have different salinity concentrations, such as river and sea water. This technology has promise as a future source of clean and sustainable energy, with an estimated global potential of 2.6 TW for all forms of SGP. However, previous research has been done on a relatively small scale. In order to create commercially viable RED power plants, researchers must first determine how to maximize the performance of large cell stacks. When trying to solve this problem, Veerman et al. 2010 found that there exists a tradeoff between the hydrodynamic and electrical requirements of spacers. In a RED system, spacers are open structures which separate alternately stacked cation (CEM) and anion exchange membranes (AEM), provide stack stability, and increase turbulence within the compartments. In attempting to maximize performance, Veerman et al. also considered other parameters such as, flow direction, residence time, flow velocity, and electrode segmentation. Their research is significant because it provides a “[f]irst [s]tep” towards the goal of producing commercial electricity from a RED power plant.—Juliet Archer

J. Veerman and colleagues, from Wetsus (Centre of Excellence for Sustainable Water Technology) and the University of Groningen, compared the performance of small and large laboratory RED stacks. In these stacks, power is generated by the potential difference between sea and fresh water over a membrane and the movement of ions through that membrane. The “large” stacks contained either 25 or 50 cells each, while the “small” stacks consisted of 50 cells each. Cell dimensions of the small stacks, which have been the focus of previous research, measure less than 10 by 10 cm2. These small stacks have a total active membrane area of 1 m2. In this study, Veerman et al. also utilized larger stacks with cell dimensions of 25 by 75 cm2 and total active membrane areas of either 9.4 or 18.75 m2. With these large RED stacks, the researchers also determined the impact of others parameters, when attempting to maximize performance at the lowest possible investment and operational costs. The researchers employed NaCl and hexacyanoferrate electrode rinse solutions, depending on which parameter they were testing. In using these applied electrode solutions, the study drifts from its focus on maximizing the performance of commercial SGP technology because these solutions are only used in laboratories. More advanced systems must be employed in RED power plants. For “sea water” they used a 30 g NaCl/L solution and for “river water” they used a 1 g NaCl/L solution. 
The authors found that hydrodynamic power losses are greatest at high flow rates. On the contrary, they also found that losses from co-ion transport and osmosis were significant at very low flow rates. Therefore, net power density (W/m2) and energy efficiency<!–[if supportFields]> XE “energy efficiency” <![endif]–><!–[if supportFields]><![endif]–> are maximized at optimal rather than maximal or minimal flow rates. In studying the effect of residence time on power density, Veerman et al. used Fumasep and Qianqiu membranes, cross-, co-, and counter-current flow directions, and 25 and 50 cell large stacks. The authors found that the generated electricity of stacks was mostly independent from the aforementioned parameters. Similarly, the number of cells had no effect on power density. This signifies that losses from shortcut currents, which increase as the number of cells increase, are minimal. Co-current and counter-current operations were also tested, to determine which mode is more efficient in RED stacks. In counter-current mode, river water flows downward and sea water flows upward.  However, in co-current mode both river and sea water flow upward. Contrary to evidence from other processes, the authors found that co-current mode resulted in a higher power density within the RED stacks. The researchers explained this surprising discovery based on the competing effects of a high potential difference near the inlet side and a high conductivity near the outlet side. Furthermore, the authors speculated that co-current operations minimize the pressure within the compartments and thus minimize leakage. Lastly, thin, delicate membranes and open spacers, both of which maximize power density, can be used with co-current operations.

Veerman et al. also considered the effect of electrode segmentation on generated power (W). The power of a segmented stack was found to be 11% more than that of an unsegmented stack. However, segmentation may not be practical in actual RED power plants because it is probable that segmentation’s small advantage disappears at high flow rates. Furthermore, segmentation requires the use of complicated and costly electronics, which may reduce its theoretical benefits.  The authors also measured the pressure from fluid resistance in the manifolds, bore holes, and compartments—around the supply and drain holes and where uniform flow exists—in order to calculate hydrodynamic losses. Fluid resistance in the manifolds and bore holes resulted in negligible and very low losses, respectively. Around the outlet and inlet holes, on the other hand, resistance was very high and these areas accounted for the majority of fluid resistance within the system. When graphed against flow velocity (cm/s), uniform spacer resistance for horizontal and vertical operation in co-current mode had approximately equal slopes.  To decrease fluid resistance, the authors recommend that more inlet and outlet places be created and that very open spacers be used around supply and drain holes. The researchers conclude by recommending that future RED designs utilize very open spacers, co-current operation, and very thin membranes.

Designing Prototype Tidal Current Turbines in Taiwan

Since the island has limited energy resources, developing renewable energy projects is an imperative for the government of Taiwan.  Although it has a few on-shore wind turbines, ocean-based renewable energies are an obvious alternative since the country is surrounded by the Pacific Ocean.  This line of thinking has secured National Science Council funding for Tsai et al. (2010) to begin the design and testing of prototype tidal current turbines.  The team plans to conduct field tests between Keelung Harbor and Keelung Island because of the high speeds that currents achieve while traveling over Keelung Sill.  Tsai et al. are primarily focused on designing blades, with an ideal camber and pitch, and turbines, which will move automatically to take advantage of the changing direction of currents.  Once a prototype is designed, the will test for the design’s dynamic response to irregular waves and winds, non-uniform currents and typhoon conditions.  If they are successful, Taiwan will be closer to its goal of increasing renewable energy to 10% of total capacity by 2025.—Juliet Archer
          Tsai, C., Doong, D., Kehr, Y., Li, H., Ho, C., Kuo, N., Huang, S., Lo, Y., Lee, H., 2010.  A pilot project on ocean energy generation by tidal currents on the northern coast of Taiwan.  Oceans 2010 IEEE – Sydney, 1–5.

     

          Cheng-Han Tsai and colleagues at the National Taiwan Ocean University and Minghsin University of Science and Technology have undertaken five related projects in order to install a 3 kW current generator on Keelung Sill and to better understand the dynamic responses of tidal energy converters.  The first three projects aim to simulate and assess the tidal current power surrounding Taiwan and especially that of the Keelung Sill area.  To accomplish this challenging task, Tsai et al. use a numerical model, in situ measurements and satellite images.  In order to simulate tides numerically, the model used a finite difference method[1] to solve control equations.  In addition, a vertically integrated continuity equation and equations of motion in x and y directions were used along with a hydrostatic equation[2] that determined pressure at depth z.  To measure water velocity, the model averaged volume transport over depth.  The numerical model shows that strong currents are present at Keelung Sill.  However, the model is likely an underestimation of current velocity because it shows a maximum velocity of only 1.0 m/s in a 24-hour cycle. 
          In order to verify their model, the Tsai et al. are conducting in-situ measurements of the currents at Keelung sill three times, for at least one month each.  The velocity is measured by deploying Aquadopp Profilers (at depths of 10m, 15m, and 20m) in addition to an Aquadopp (at 5m) and a RCM-7 current meter (at 20m).  These instruments are deployed at five different sites on Keelung Sill during each testing period.  Preliminary measured results show that the current speed in this area can be as high as 2.2–2.4 m/s depending on the depth, 15–20 m, respectively.  These early results confirm the team’s suspicion that the numerical model underestimated current speed.  From these measurements the power (in Watts) of the current can be calculated, using velocity, an efficiency coefficient, the water density and the blade sweep area. 
          The third project of Tsai et al. is to determine water depth, tidal elevation, and tidal energy around Keelung Sill using high frequency satellite images.  The scientists will use a Formosa-2 satellite that has a sun-synchronous orbit.  The images will be used to calculate temporal-variable water depth, which can then be compared to the in-situ data.  This information will also be used to estimate tidal elevation and energy.  Developing a tidal current turbine is the fourth project presented in this paper.  The team’s objective is to find the ideal configuration of blade camber and pitch so that the turbine will produce the maximum power output, based on the current speed.  The team also plans on designing a turbine that moves, on its own, in response to a current’s change in direction.  If Tsai et al. succeed, the turbine will always face into the current and therefore maximize its power production.  Before testing on-site, the power generation capacity of the design will be tested at the National Taiwan Ocean University’s cavitation tunnel. 
          The last project planned is the assessment of the dynamic response behavior of the new turbine.  This project will begin with the installation of the team’s 3 kW turbine design at Keelung Sill.  The scientists are interested in this topic because there are few data available on the response of turbines to the forces of winds, waves, and currents.  Their hypothesis is that the blade will experience the most load variations.  The team is especially interested in the effect of extreme forces, present during typhoon conditions, on the blades and structure of turbines.  This information is pertinent because of their government’s goal of increasing renewable energy production and its emphasis on ocean-based renewable energies.  If ocean current energy production is to be a viable option for Taiwan, then turbine designs must withstand typhoon conditions[3].  Although these on-going projects are not complete, significant results are expected based on the ambitious goals and detailed plans that have been laid out in this paper.     
Other Sources
American Meteorological Society.  “Glossary of Meteorology.”  Accessed February 12, 2011.  http://amsglossary.allenpress.com/glossary/browse?s=h&p=36
Central Weather Bureau of Taiwan.  “Meterology Encyclopedia.”  Accessed February 13, 2011.  http://www.cwb.gov.tw/V6e/education/encyclopedia/ty015.html
Wikipedia. “Finite difference method.” Last modified December 31, 2010.  Accessed February 12, 2011.  http://en.wikipedia.org/wiki/Finite_difference_method


[1] “Finite-difference methods approximate the solutions to differential equations using finite difference equations to approximate derivatives” (Wikipedia)
[2] “The form assumed by the vertical component of the vector equation of motion when all Coriolis, earth curvature, frictional, and vertical acceleration terms are considered negligible compared with those involving the vertical pressure force and the force of gravity” (American Meteorological Society)
[3] An average of three to four typhoons hit Taiwan each year. (Central Weather Bureau of Taiwan)

Offshore Wind Farms: Environmental Impacts Are Not Benign

As is with other relatively new industries, the environmental effects of offshore wind energy have not been fully examined.  In their comprehensive review, Wilson et al. (2010) find that although many gaps in knowledge exist, overall, offshore wind generation does result in adverse ecosystem effects.  These effects were generally minor, but their magnitudes are dependent on the sensitivity, migration patterns, mating and feeding habits of the specific fish, benthic invertebrates, birds, marine mammals, and other creatures which inhabit potential wind energy sites.  Negative environmental effects during the exploration, installation, operation and decommissioning of wind farms result from increased noise, the presence of electromagnetic fields, habitat loss and degradation, and the potential for collision with turbines.  There is also evidence that environmental benefits may result from offshore wind energy generation.  For instance, the towers and foundations of offshore wind turbines have been found to act as artificial reefs which may increase fish and benthic populations.  Furthermore, wind farms may deter commercial fishing, especially the use of beam-trawling, creating, in effect, wildlife protection areas.  The authors caution that the magnitude and direction of environmental consequences, especially long term, are not well examined and thus additional research is needed.—Juliet Archer
Wilson, J., Elliott, M., Cutts, N., Mander, L., Mendão, V., Perez-Dominguez, R., Phelps, A., 2010.  Coastal and offshore wind energy generation: Is it environmentally benign?  Energies 3, 1383–1422.

          Wilson and colleagues at the Institute of Estuarine and Costal Studies at University of Hull (Hull, United Kingdom) determined the potential environmental effects of an offshore wind farm using a conceptual model or “horrendogram” and then analyzed these effects relative to an undeveloped offshore site.  The authors separately analyzed environmental effects during the different phases of a project, such as exploration, construction, operation and decommissioning.  They further classified their findings based on whether the impact was likely to have a major, moderate, minor, negligible, nonexistent or beneficial interaction.  Wilson et al. also considered the persistence (days, weeks, months, etc.) and spatial extent (nearfield, far-field) of an impact.  The classification of impacts was based on historic data, recent studies, reports, and expert judgment. 
          In regards to the seabed, Wilson et al. determined that when utilizing current monopile foundations, disturbance and possible alteration of the sediment structure is unavoidable.  The alteration of sediment structures occurs when fine particles are released from the drilling of monopiles into hard chalk or other bedrock.  Drill cuttings may also smother benthic[1] and other creatures.  The installation can also cause scour or erosion of the seabed around the base of the new turbine as the flow of currents in the immediate area changes.  To minimize current, wake, and habitat changes, turbines can be spaced further apart so that the affected area is small compared to the size of the entire wind farm.  To minimize erosion of the seabed, scour protection can be installed.  Depending on the type of material and design used, such as rocky substratum adjoining to sandy substrata, scour protection can also increase the surface area available for colonization.
          The authors noted that habitat increases can be especially beneficial for juvenile benthic creatures, such as crabs.  This impact would therefore be beneficial to both the benthic ecosystem and commercial fisheries as populations are protected within a certain area yet increase overall.  Fish populations have also been shown to increase when wind farms are located in nursery areas, as juvenile mortality decreases and spawning biomass increases.  Furthermore, scour protection design considerations that increase complexity, like holes and artificial seagrass beds, can increase the number of fish in an area.  Again, increased fish populations would benefit commercial fisheries as larger populations spill out into fishing grounds.  However, it is unclear whether habitat creation would offset habitat loss for native organisms and so the overall direction of the impact is unknown.  Also, the magnitude of the impact may be dependent on the location of the wind farm and the specific aquatic populations with which it interacts. 
Wind farms also have negative impacts on fish communities.  For instance, electromagnetic (EM) fields, created by export cable routes and connecting cables, may cause a significant moderate impact, especially on sensitive species like elasmobranchs[2], and teleosts[3], and on other demersal[4], and benthic organisms.  Potential EM field impacts include decreased hunting performance and incomplete migrations.  The significance of these EM field effects is dependent on the type and magnitude of current, insulation type, conductor core geometry, particulars of the seabed, and the depth of the cable (if buried).  In addition, noise and increased turbidity during the construction phases may have moderate to minor impacts on hearing specialists and visual predators, respectively.  Noise pollution can also occur during operation and may lead to sublethal effects like disturbances in fishes’ gathering of information about other fish (prey, predators, competitors, and mates) and locations (migration routes and feeding grounds).  Overall the many potential feedback loops make it difficult to predict precisely how wind farms will impact fish and benthic organisms.
          The effect on mammals and coastal and sea birds is, on the other hand, overwhelmingly negative.  For instance, the probability of collision with turbine blades is especially high if species pass through often.  This impact can be mitigated by proper placement of wind farms in regards to wind currents and birds’ foraging and breeding areas.  However, the probability of collision for large birds, which cannot easily maneuver may be unavoidable.  Times of low visibility and/or high winds are likely to exacerbate the problem.  Bats are also especially susceptible to collisions because of their curiosity and attraction to the turbines’ artificial lighting and high insect populations.  In the long run, habituation to wind farms has been shown to decrease avian mortalities as birds learn to recognize the wind turbines as dangerous.  Improving turbine technology, by using larger blades that rotate more slowly, for instance, may also decrease the collision rates of birds and bats. 
Another potential impact on avian creatures is habitat loss and resulting displacement as birds avoid the turbine structures.  If the required diversions, and thus extra energy expenditures, are large enough, then the wind farm can become a barrier and may reduce the breeding and survival rates of the population.  As with fish populations, the impact of habitat loss on bird populations is dependent on location.  For example, if the farm is located near an estuary or on a coast, then it may decrease the area available for feeding or roosting.  Furthermore, if a wind farm is poorly located in regards to adjacent developments then cumulative effects may be detrimental to bird populations.  Cumulative effects may occur if a chain of wind farms is located in a flyway corridor for a rare species.  More information via improved predictive and observational models is needed in order to determine the significance of the above impacts on birds and mammals.
Marine mammals like cetaceans (dolphins, whales, and porpoises) and pinnipeds (seals and sealions) may be significantly impacted by the noise produced by wind farms.  These marine mammals are extremely vocal and some also use echolocation to communicate, navigate, avoid predators, forage, and locate other individuals.  The noise interference with these activities would be greatest during exploration and construction.  Noise interference would also occur, at minimal levels, during operation.  The results of this interference may include displacement (temporary or permanent), changes to feeding and social behaviors, reductions in breeding success, stress, and death.  The magnitude of these effects is dependent on the mammals’ habituation to noise, low-frequency hearing abilities of specific species, sound-propagation conditions, and ambient noise levels.  To decrease the cumulative effects of a proposed wind farm, location decisions should give consideration to the breeding and migration patterns of marine mammals in relation to existing offshore activities.       
Wilson et al. recommend a number of improvements to the technologies and processes of determining and measuring the environmental effects of proposed offshore wind farm sites.  The technologies recommended are very specific to each affected organism, while some of the processes are in the form of general guidelines.  For example, the authors recommend that future research distinguish between real and perceived impacts of offshore wind farms.  Additionally, they advise that monitoring be in proportion to the actual effects and not to the publics’ perceived effects.  They also advise monitoring programs for endangered, protected, and ecosystem key organisms.  Lastly, the authors emphasize the many gaps in knowledge and the need for studies focusing on long term effects.  Wilson and colleagues conclude by acknowledging that offshore wind farms are not entirely environmentally benign.  Yet the authors remind readers to weigh the costs with the environmental benefits, including the creation of renewable energy. 
Other sources:
Merriam-Webster. “demersal,” “teleost,” “elasmobranch,” “benthic.” Last modified 2011.  Accessed February 6, 2011.  http://www.merriam-webster.com/


[1] benthic –adj.: of, relating to, or occurring in the depths of the ocean
[2] elasmobranch –noun: any of a subclass (Elasmobranchii) of cartilaginous fishes that have five to seven lateral to ventral gill openings on each side and that comprise the sharks, rays, skates and extinct related fishes
[3] teleost –noun: bony fish
[4] demersal –adj.: living near, deposited on, or sinking to the bottom of the sea

Offshore Wind Energy: A Viable Option for California?

In the future, offshore wind energy could provide 174–224% of California’s (CA) current electricity needs (Dvorak et al. 2010).  This estimate is based on the development of floating and other turbine tower support technologies that will enable the placement of turbines in deep water (50–200 m).  The advancement of these technologies is critical to the viability of offshore wind energy in CA since approximately 90% of wind resources are located in deep water.  Utilizing only existing technologies, for depths up to 50 m, the estimate decreases to wind energy providing 17–31% of the state’s electricity needs.  Compared to Southern (SCA) and Central CA (CCA), the Northern coast (NCA) has the greatest potential for immediate development.  NCA’s potential annual delivered energy by turbines at depths of 0–50 m, utilizing winds speeds ≥ 7.0 ms-1 is 63.1 terawatt hours (TWh).  This potential delivered energy would offset approximately 36% of CA’s current carbon electricity sources.  Although NCA has the most shallow water wind resources, it has limited transmission capacity compared to the other regions.  At the time of writing, the potential for offshore wind energy has not yet been developed in CA or elsewhere in the United States.—Juliet Archer

          Dvorak, M., Archer, C., Jacobson, M., 2010. California offshore wind energy potential. Renewable Energy 35, 1244–1254.

          M. J. Dvorak and his colleagues quantified CA’s potential for offshore wind energy by locating potential turbine sites using bathymetry data, modeling multiple years of mesoscale weather data and then calculating the potential energy and power provided by offshore turbines.  To give context, the CA coast was divided into three areas, NCA, CCA, and SCA.  Within these regions, potential sites were classified by depth using high-resolution bathymetry data.  To determine average offshore wind speed, a mesoscale model version 5 (MM5) weather model was run for all of 2007 and for the months of January, April, July, and October of 2005 and 2006.  This modeling allowed the calculation of annual and seasonal average wind speeds at turbine hub height (80 m) as well as the average power density of the wind resource.  The modeling data were validated using offshore weather buoy data from the National Oceanic and Atmospheric Administration (NOAA) National Data Buoy Center (NDBC) for years 1998–2008.  The MM5 data very closely matched the NDBC buoy data. 
          To estimate the energy production potential, the number of turbines that could be built and the potential production capacity of each site was calculated.  The REpower 5M, 5 MW wind turbine, requiring 0.442 km of area, was used for all calculations.  In calculating turbine density, the authors accounted for surface area that could not be utilized due to shipping lanes, wildlife areas, viewshed considerations, etc., by including a conservative 33% exclusionary factor.  The turbine capacity factor (CF) is defined as the ratio of actual output over a period of time and maximum output at nameplate capacity over that time.  It was calculated for each site using the relationship between average wind speed, rated power and rotor diameter of the REpower 5M turbine.  This calculation allowed annual energy and average power output to be calculated for each site.  In all calculations, winds were assumed to follow a Rayleigh probability distribution over time. 
          The results show that the potential for wind energy in CA is significant, but not currently feasible, in all regions.  The relatively shallow waters of NCA have the most potential using current turbine foundation technology.  The development of sites in CCA is limited because most resources exist far from San Francisco and in deep waters.  The Farallon Islands is one such site whose development is dependent on lengthy undersea transmission cables and a study of the environmental effects of wind turbines on nearby bird, marine mammal, and fish populations.  SCA has similar problems since the CA Bight shields the Los Angeles coast and sends most winds to sites 50 km or farther from shore.  These distant sites include Point Conception, San Miguel Island and Santa Rosa Island.  If technologies for deepwater resources are developed, then the combination of SCA’s high demand and many grid interconnection points will make it an ideal region for offshore wind energy development.
          A hypothetical, but currently feasible, wind farm near Cape Mendocino in NCA is proposed by the authors.  The farm would be located in water that is less than 50 m deep and therefore could utilize current monopole or multi-leg turbine foundations.  It would occupy about 138 km2 in area and contain 300 REpower 5M turbines.  The farm could be connected to the local electrical grid via an existing power plant in Humboldt Bay.  The authors predicted that it would be most productive in summer months and that its hourly activity would be consistent throughout daytime hours.  This represents a significant advantage over onshore wind farms which peak at night and thus do not match the high daytime summer demand.  Using the aforementioned exclusionary factor, the proposed farm could replace 4% of CA’s current carbon electricity generation.  This great potential to offset carbon energy sources suggests that offshore wind energy sites should be seriously considered in CA.   

An Overview of Ocean Renewable Energy Technologies

          The untapped potential of ocean renewable energy is vast like the ocean’s uncharted depths.  And like the deep ocean, it is also mysterious —since most technologies that capitalize on the sea as an energy resource are still in the early stages of development and testing.  Therefore, Bedard et al. (2010) state that it is unclear which technologies will be the most cost efficient and reliable while producing the fewest environmental effects.  The technologies currently being developed include ocean wave, thermal, tidal/open-ocean current, tidal barrage, salinity gradient and shallow/deepwater offshore wind energy.  Among these, only shallow water offshore wind energy has reached the status of a fully-deployed commercial technology.  Part of the reason the other technologies are not yet commercial is because of the time it takes for development and testing.  This process, from initial concept to deployment of a full-scale model in natural waters is estimated by Bedard et al. to take at least 5 to 10 years. Consequently, the future for ocean energy technology is bright since only a glimmer of its potential impact has been seen. —Juliet Archer
Bedard, R., Jacobson, P., Previsic, M., Musial W., Varley, R., 2010. An overview of ocean renewable energy technologies. Oceanography 23, 22–31.

In their review, Bedard et al. explain the history, current status and different concepts or designs of each of the above mentioned ocean energy technologies.  As of their writing, only 4 mega-watts (MW) of wave energy have been installed worldwide.  Most of the deployments of concepts such as point absorbers, overtopping terminators, linear absorbers, and oscillating water column terminators (OWC) have been small-scale prototypes.  In the United States, further installation of wave energy technology has been hindered by a lack of standardized facilities in which to test wave energy devices in the open ocean.  However, these and other challenges are recognized and are being met by private and public groups, such as the Northwest National Marine Renewable Energy Center (NNMREC) funded by the United States Department of Energy (DOE), and Pacific Gas and Electric (PG&E).  In Portugal these problems have already been confronted, resulting in the first commercial wave energy plant being deployed in 2008.  Furthermore, demonstration projects are continuing and planned at other sites around the world, including Australia and Ireland.  If these early projects are successful, Bedard et al. predict that wave energy technologies with a total of 100 MW of capacity will be deployed in five to ten years. 
Tidal current or hydrokinetic ocean energy technologies have only been installed in rivers or less than one kilometer from coasts.  The three types of water turbines that exploit the kinetic energy of moving water are axial, cross-flow and combination axial and cross-flow turbines.  In addition there are also non-turbine designs such as oscillatory hydrofoils, hydro venturi and vortex induced motion devices.  In the United States, hydrokinetic technology has been tested in New York’s East River but like wave energy, hydrokinetic technologies lack proper infrastructure to deploy and test devices in tidal passages.  However, in-stream demonstrations in rivers continue around the world.   If results are successful, the authors expect that tidal energy capacity will increase by 1–10 MW within five to ten years.  Despite studies in the 1970s determining minimal adverse environmental effects, technology has not yet been developed to harness the power of open-ocean currents, like the Gulf Stream. 
Offshore wind energy is a promising resource because of the location of high-wind areas near some of the world’s largest cities.  In comparison to onshore wind energy technology, offshore technology does not suffer from the same transportation and installation restrictions.  However, the cost of infrastructure and logistical support for offshore units is significant and capital costs are typically double those of onshore turbines.  Therefore, offshore units tend to be larger in order to maximize the value of the infrastructure.  In 2008, the worldwide capacity of offshore wind energy was 1,471 MW.  This is insignificant in comparison to the almost 121,000 MW of total installed wind power in the same year.[1]  Overall, the industry is challenged by high costs, especially of operation and maintenance, in comparison to mature land-based wind technology.  However, Germany, China and the United States, among other countries, are all in processes of adding new capacity.  Furthermore, the first full-scale floating turbine was deployed in 2009 and exemplifies the infancy and potential growth of the industry.
Ocean thermal energy conversion technologies (OTEC) extract energy from the difference in temperature between cold deep ocean water (less than 40°F) and warm surface water (more than 80°F).  The challenge of developing commercially viable OTEC energy technologies is currently being undertaken by a number of small companies, some of which are funded by the DOE.  The major difficulties in the commercialization of OTEC are that the capital costs are high and the resource has a low-energy density.  At the time of writing, no major commercial OTEC technologies have been installed. 
Salinity gradient energy conversion technology, like OTEC, extracts energy from a physical gradient.  Salinity gradient power or osmotic power exploits the differing salt concentrations in fresh and sea water.   The methods for this process are reverse electro dialysis (RED) and pressure-retarded osmosis (PRO).  Currently, the Netherlands and Norway are the only countries developing salinity gradient technologies for commercial use.  In the Netherlands, plans have been proposed to exploit the salinity differential between the Afsluitdijk dike and the ocean with RED technology.  In 2009, Norway installed the world’s first salinity gradient power plant using PRO technology, designed for 10 kW of capacity.  If this plant is successful, then the construction of commercial osmotic power plants is probable in the next few years.  Based on the current state of ocean renewable energy technologies, rapid growth in the use of ocean–based renewable energy can be expected. 


[1] “Global Wind 2008 Report,” Global Wind Energy Council, accessed January 23, 2011, http://www.gwec.net/index.php?id=153&L=0.