Just Released! “Energy, Biology, Climate Change”

FrontCover6x9 white border 72dpi EBCC2015

Our newest book, published on May 6, 2015 and available at Amazon.com for $19.95.

The focus of this book is the interactions between energy, ecology, and climate change, as well as a few of the responses of humanity to these interactions. It is not a textbook, but a series of chapters discussing subtopics in which the authors were interested and wished to write about. The basic material is cutting-edge science; technical journal articles published within the last year, selected for their relevance and interest. Each author selected eight or so technical papers representing his or her view of the most interesting current research in the field, and wrote summaries of them in a journalistic style that is free of scientific jargon and understandable by lay readers. This is the sort of science writing that you might encounter in the New York Times, but concentrated in a way intended to give as broad an overview of the chapter topics as possible. None of this research will appear in textbooks for a few years, so there are not many ways that readers without access to a university library can get access to this information.

This book is intended be browsed—choose a chapter topic you like and read the individual sections in any order; each is intended to be largely stand-alone. Reading all of them will give you considerable insight into what climate scientists concerned with energy, ecology, and human effects are up to, and the challenges they face in understanding one of the most disruptive—if not very rapid—event in human history; anthropogenic climate change. The Table of Contents follows: Continue reading

Exploring the Reliability and Potential Climatic Impacts of Large-Scale Deployments of Offshore Wind Turbines

Wind power is widely available renewable energy source, but a large-scale deployment of several million wind turbines would be required to meet the estimated global energy demand in 2100 of 44 TW. Wang and Prinn sought to examine the environmental impacts and reliability of such an extensive use of offshore wind power (2011). The researchers had previously conducted a study to examine the effects of a similar large-scale deployment of wind turbines over land to meet about 10% of the predicted global energy needs in 2100. Their model suggested that such a significant use of wind turbines over land could lead to a significant temperature increase in the lower atmosphere over the installed regions. This model also predicted a significant disturbance in air circulation patterns as well as cloud and precipitation distribution. Unlike the previously modeled land-based wind turbine installations, the offshore wind turbine installations were found to cause a surface cooling over the installed regions. The disturbance to the global climate caused by offshore wind installations was calculated to be relatively small when compared to land-based installations. Yet there are significant concerns about the intermittent nature of power generation from offshore wind turbines caused by seasonal wind variations, so the operation of such a substantial offshore wind would demand significant measures taken on the part of system operators to cope with this variability. —Meredith Reisfield
Wang, C., Prinn, R. G., 2011. Potential climatic impacts and reliability of large-scale offshore wind farms. Environmental Research Letters. doi: 10.1088/1748-9326/6/2/025101.

Wang and Prinn, working at the Center for Global Change Science and the Joint Program of the Science and Policy of Global Change at the Massachusetts Institute of Technology, sought to compare the effects of deploying wind turbines over semi-arid grasslands to the effects of large-scale offshore wind installations. The land-based model found that using wind turbines on this scale could cause global surface warming exceeding 1 K over designated surface areas and alter global distributions of rainfall and clouds. To model the effects of large-scale deployment of offshore wind turbines, the researchers used the Community Atmospheric Model of the Community Climate System Model developed by the US National Center for Atmospheric Research. This model was coupled with a slab ocean model and the Community Land Model to simulate the long-term climate responses to large-scale offshore wind turbine use.
This three-dimensional climate model presented several advantages including a high spatial resolution of 2° by 2.5° along the latitudinal and longitudinal directions respectively, 26 vertical layers of atmospherics modeling, coverage of a large range of geographic areas, and consideration of multiple assumed strengths of wind turbine effects. To simulate the climate effect of offshore wind farms, Wang and Prinn modified the surface drag coefficient to represent the turbine-induced change to sea surface roughness.
The researchers conducted six simulations of offshore wind turbine effects. The wind turbines in each simulation were installed over regions between 60°S and 74°N in latitude, at depths of 200, 400, or 600 m and an assumed sea surface drag coefficient of either 0.007 or 0.001. The turbines were simulated to be in five regions free from sea ice that are likely to become actual offshore turbine installation sites, including the Southeast and East Asian coasts, the North American coast, the West European coast, the South American coast and Oceania. The higher drag coefficient was based on reported measurements over mesoscale wind farms, while the lower coefficient approximately doubles the average sea surface drag coeffient in areas without wind turbines. Each model was set up to run 60 years and take about 40 years to reach an annually repeating climatic steady state. These simulations utilized present day greenhouse gas levels to isolate the climatic effects of wind turbines from effects due to greenhouse gasses. The results compared the mean parameters of the last 20 years of each model used in analysis. Power gain from mean flow kinetic energy due to wind turbines was calculated by using the models with and without wind turbines, then subtracting. Raw wind power consumption increases proportionately with installation area and the sea surface drag coefficient assumed in the model. The researchers assumed a 25% conversion rate of raw wind power converted to electric power by wind turbines. The estimated output of electric power ranged from 6.8 to 11.9 TW with the higher drag coefficient, and from 1.7 to 3.1 TW with the lower drag coefficient. At most, these numbers would account for 25% of the predicted 44 TW of future global energy needs.
The climatic impacts of the simulated installations were significant. The surface air temperature over tropical and mid-latitude sites were reduced by nearly 1 K, with even greater cooling observed in the Arctic region and a slight warming in Antarctica. The cooling was due principally to enhanced latent heat flux from the sea surface to the lower atmosphere, driven by an increased turbulent mixing caused by the wind turbines, and extended vertically into the lower and middle troposphere through mixing. The annual averaged surface air temperature ranged from 0.4 to 0.6 K in models with a high surface drag coefficient and was about 0.2 K in the low drag coefficient cases. Cooling was also shown to be greater as a smaller fraction of the turbines were installed in tropical latitudes. Due to changes in the patterns of geographical locations of installed regions as turbines were modeled to be in depths of 200, 400, and 600 m. Though these turbines also create impacts on clouds, temperatures, precipitation and air circulation beyond the installation sites, the impacts were less significant then those observed with a similar deployment of turbines over land.
The large deployment of offshore wind turbines also presents concerns about intermittency and reliability, as well as the need to lower the high current unit wind power costs. Intermittency is especially serious over European coastal sites, where the potentially harvested with power could vary by a factor of 3 seasonally, and was generally found to be greater than a factor of 2 . The inconsistency of offshore wind as a power source would require solutions such as on-site energy storage, backup generation and long-distance power transmission for an electrical system dominated by offshore wind power.

Pricing Offshore Wind

Offshore wind power is an environmentally and economically beneficial energy source which significantly reduces harmful pollutants.  Though more expensive than land based wind power and conventional energy sources, it is one of the least costly renewable energy sources.  This large, clean resource is also the largest renewable energy source for many coastal states.  Based on these facts, it seems logical to invest in offshore wind power; however, its cost relative to conventional sources and fluctuating power output offer some obstacles to its implementation.  Regardless of these obstacles, the advantages of offshore wind power have spurred policymakers across the globe to prioritize offshore wind power, relative to other renewable sources, and begin to deploy it on a large scale.  Policy and investment decisions regarding this technology require an accurate cost analysis over time.  Levitt and his colleagues at Elsevier used two such cost models for their analysis.  The first, the Levelized Cost of Energy (LCOE), measures the total financial cost of produced energy without considering policy of financial structures.  The second measure, the Breakeven Price (BP), gives the minimum electricity sale price for financial viability given a particular policy, tax, and purchase contract structure.  These models can help decision-makers by giving the information needed to bring down costs and make offshore wind financially viable.—Donald Hamnett
Levitt, Andrew C., et al. 2011. Pricing offshore wind power. Elsevier. doi:10.1016/j.enpol.2011.07.044

            The LCOE is calculated based on two factors: energy production and costs from construction and operations.  For each year, the cost cash flows of the project’s operation, including construction, are compiled into nominal values.  The Net Present Value (NPV) of each year of the plants lifetime is assessed using the nominal values and nominal interest rates, thus not adjusting to inflation.  Next, the energy production for each year of the project is determined and each unit of energy is given a dollar value that is constant over the life of the project, in real terms.  Simply put, the LCOE is the NPV of costs (terms of currency) divided by NPV of energy produced (in terms of energy units).  LCOE and BP share four determining input factors, with BP encompassing an additional three.  The shared principal determinants are Capital Expenditure (CAPEX), the cost to buy and build the plant; Operating Expenditure (OPEX), ongoing costs to operate and maintain the plant; discount rate, the return on investment required to attract project investors; and net capacity factor, the fraction of power generated over the long-term dividend by nameplate power.  The further parameters covered in BP are tax and policy inputs as applicable to the scenario; price escalator, the price increases each year as determined by the power purchase contract; and financial structure (debt term, term of power purchase agreement, etc.).  BP is calculated similarly to LCOE, but with consideration of cost and benefits based on U.S. policies.
            In the analysis, LCOE and BP were calculated with consideration of four financial structures and three cost structures.  The financial structures used were Corporate, Tax Equity, Project Finance, and Government Ownership.  The three cost structures are First-Of-A-Kind (FOAK), a scenario under which the plant is the initial project in an underdeveloped market such as the United States; Global Average (GA), a scenario similar to Northern Europe in which the market is more mature; and Best Recent Value (BRV), the best case under the current European market and available technology.  Several patterns were learned in the analysis, of which the most pertinent to the aforementioned factors follow.  First, it was found that Project and Corporate structures yield similar results, while the Tax Equity structure prices are higher than the LCOE due to high required returns.  Second, BRV prices are between 2.1 and 3.8 times lower than FOAK due to different in many parameters.  The DOE loan guarantee program modestly positively impacts FOAK, but has no or an adverse effect on the other cost structures.  However, the program currently only applies to FOAK, so it is just as well.  Lastly, the BP is lowest for Government Ownership under the FOAK and GA structures.  This is due to the low cost of government buying, and the absence of high required returns for investors.  From the analysis, we have learned that the high current FOAK costs are not representative of the actual cost of offshore wind power.  To reduce costs to the GA, then BRV point, the policy must be to increase the industrialization and manufacture of offshore wind.  This policy, along with furthered research and development, has the potential to bring the costs of offshore wind below the BRV point.

Hybrid Wind-Tidal System Holds Potential to Guarantee Continuous Availability of Grid Power

Offshore wind power is subject to short-term fluctuations, limiting the potential for this technology to serve as a source of continuously available grid power. Scientists at the Graduate School of Energy Science in Kyoto have suggested a hybrid system that combines an offshore wind turbine with a corresponding tidal turbine to make offshore power available to the grid at a constant level (Rahman et al.2011). In the proposed system, tidal power is used to balance the variations in the load of offshore wind power by operating a flywheel motor/generator system. When wind power exceeds a specified level, the tidal system functions as a motor to store surplus power as rotational energy. When wind power falls below a certain level, the tidal system works as a generator to complement the wind power and counter large fluctuations in wind power that can affect the frequency and voltage of output. The hybrid system could enable the development and utilization of offshore renewable energy sources by proposing new load fluctuation control strategies. A laboratory performance analysis favorably evaluated the feasibility of this system. —Meredith Reisfield
Rahman, M., Shunsuke, O., Shirai, Y., 2011. Hybrid offshore wind and tidal turbine power system to compensate for fluctuation (HOTCF). Green Energy and Technology. doi: 10.1007/978-4-431-53910-0_24.

The proposed system utilizes two types of power generation, the tidal motor/generator and the offshore wind turbine generator. While the tidal generator creates smooth output power, the output power of a wind turbine is directly dependent on wind velocity. Rahman and his colleagues built a laboratory scale prototype model of the hybrid system.
The offshore wind turbine generator component of this hybrid system consists of a coreless synchronous generator and a servo-motor. Servo-motors can be combined with encoders to provide an information feedback about position and speed and continuously correct performance. The servo-motor, controlled by a computer, simulated the rotation of an offshore wind turbine. The rpm (rotations per minute) of the motor determined the generation of electrical energy. A 6-pulse diode rectifier converts the AC power generated by the wind turbine to DC power. The tidal turbine component of the systems seeks to apply and control a two way energy flow scheme, so that energy can either be injected into the offshore wind turbine or stored as kinetic energy as wind power fluctuations demand. The tidal component combines a servo-motor with a generator/motor. The servo-motor serves as an input of tidal energy to the generator, which converts the mechanical energy from tides into electrical energy. The tidal turbine induction output is connected to a DC capacitator through a dual way converter. The researchers also placed several small controllers at both ends of the system to monitor operating conditions.
Tests of the system found that the tidal system turned to generator mode was successfully able to compensate for variations in wind generator output. Conversely, the tidal system could store rotational energy as a flywheel with small losses. The main challenge facing this model is to reduce the delay in recovering grid power to initial value after a drop in wind power generation, which suggests the control flexibility and overall stability of the system can be improved. This framework can produce a relatively stable power output when connected to a commercial grid, avoiding the inherent power fluctuations of traditional offshore wind technologies. The hybrid design makes the system stable, adaptable and easily scalable. Wind and tidal resources can complement each other to general large amounts of power in an economically feasible manner. Successful evaluation of load demands and resource forecasting could make the hybrid system method a successful technique for converting tidal energy and wind energy into electricity. 

The Feasibility of Powering the World with Wind, Water, and Solar Power

Jacobson and Delucchi (2011) address the pressing problem of climate change by proposing to produce all new power worldwide from wind, water and sunlight (WWS) by 2030 and to replace pre-existing energy sources with WWS by 2050. In this Part I of their two-part study, they assess the feasibility of doing so by calculating global end-use energy demand in a WWS world and comparing it to that of a world powered by fossil fuels as projected by the Energy Information Administration. They also examined worldwide capacity for WWS energy production and the limitations of materials used for the construction of WWS infrastructure. They estimated that about 3,800,000 5 MW wind turbines, 49,000 300 MW concentrated solar plants, 40,000 300 MW solar PV power plants, 1.7 billion 3kW rooftop PV systems, 5350 100 MW geothermal power plants, 270 new 1300 MW hydroelectric power plants, 720000 0.75 MW wave devices, and 490,000 1 MW tidal turbines can meet global energy demand in 2030 with a 1.0% increase in land use, and found that barriers are primarily social and political rather than technical or economic. —Lucinda Block
Jacobson, M. Z., Delucchi, M. A., 2011. Providing all global energy with wind, water and solar power, Part I: Technologies, energy resources, quantities and areas of infrastructure, and materials. Energy Policy 39, 1154–1169.

          Mark Z. Jacobson and Mark A. Delucchi found a decrease in global end-use energy demand in 2030 compared to the Energy Information Administration’s projections, which predicted demand will increase from 12.5 trillion watts (TW) to 17 TW in the year 2030 given an energy supply similar to today’s, constituted by 35% oil, 27% coal, 23% natural gas, 6% nuclear, and the rest from biomass, sunlight, wind, and geothermal. In the WWS scenario proposed by the authors, all end uses that can be electrified would use WWS power directly, and end uses that require combustion (like industrial processes) would use electrolytic hydrogen produced with WWS. Heating and cooling processes would employ electric heat pumps, and batteries, fuel cells, or a hybrid of the two would replace liquid fuels in non-aviation transportation. Aviation would use liquefied hydrogen to then be combusted. Jacobson and Delucchi calculated that an all WWS world would require approximately 30% less end-use power than the EIA projections for our current heavily fossil fuel-powered world. This is due to some increases in efficiency, for example, in the case of using electricity directly for heating or electric motors, as well as modest conservation measures (increases in efficiency through better insulation, more efficient lighting and heating, passive heating and cooling in buildings, and large-scale planning to reduce energy demand) and subtracting the energy requirements of petroleum refining.
          The authors investigated the availability of renewable resources that could potentially be exploited for power production in order to evaluate whether these could meet global energy demands in 2030. They found that wind and solar power in likely-developable locations could each provide enough power by themselves to meet global demands, with wind power potentially providing 3–5 times global demand and solar power potentially providing 15–20 times global demand. Concentrated solar power (CSP) could also meet global demand and has the ability to store energy for night usage, but it requires more land than PV and can use about 8 gal/kWh of water in a water-cooled plant, compared to almost no water for PV or wind. At the same time, air-cooled plants could be a viable alternative to water-cooled plants in areas of scarce water resources. Although other WWS technologies like wave power, geothermal and hydropower have much less energy potential (between 0.02 TW for tidal power and 1.6 TW for hydroelectric), Jacobson and Delucchi say they will be more abundant and economical than wind or solar in many locations and that since wind and solar power are variable, these other technologies could help stabilize electric power supply.
          In the WWS power generation scenario created by the authors, 50% of power will come from wind, 20% from CSP plants, 14% from solar PV plants, 6% from rooftop PV, 4% each from hydrothermal and geothermal plants, and 1% each from wave and tidal energy. Calculating combined footprint and spacing areas required for these technologies led Jacobson and Delucchi to the conclusion that their WWS scheme will require an additional 1.0% of global land area.
          The authors found that resource availability of bulk materials like steel and concrete is unlikely to constrain the development of WWS power systems. Some of the rarer materials used for WWS technologies include neodymium for electric motors and generators, platinum for fuel cells, and lithium in batteries, however, could present problems. Wind power is currently limited by neodymium requirements for permanent magnets in generators. Solar power is limited by silver reserves, although research suggests that opportunities exist to produce PV power with low cost and commonly available materials. Current neodymium requirements for electric motors similarly imply a need to develop alternative motors that do not use rare-earth elements. Global reserves of lithium are limited and in order to satisfy requirements for electric vehicles and other uses, a global recycling program is needed. Similarly, a platinum recycling program would be required in a scenario of producing 20 million hydrogen fuel cell vehicles per year, which could easily deplete platinum reserves in less than 100 years. Although Jacobson and Deluccchi expect the cost of recycling or replacing neodymium or platinum to be negligible, this is dependent on a drastic improvement in worldwide recycling infrastructure and in many cases finding viable alternatives to existing technologies.
          Jacobson and Delucchi find a world powered entirely by wind, water and solar power to be feasible, with a marked decrease in global end-use energy demand, a 1.0% increase in land use, and some need for technological substitutions and/or recycling programs for materials used in renewable energy construction. The authors recommend replacing all new energy with WWS by 2030 and all existing energy with WWS by 2050. The study does not provide a life-cycle analysis of implementation of the proposed WWS technologies. This would potentially be useful, as it would require a measured analysis of all environmental impacts, including impacts of natural resource extraction for new infrastructure. Interestingly, Jacobson and Delucchi neglect to consider factors like the CO2 emissions from the chemical process of making cement, which would be required on a large scale for the production of wind turbines in their scenario.
The authors have published Part II to this study, in which they consider reliability, system and transmission costs, and policies needed to implement worldwide WWS infrastructure. 

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.   

The Potential for Offshore Wind Farms in California

In order to take advantage of the many benefits of wind power, it is important to first identify which regions could viably harness the technology. Without a clear picture of the extent of wind resources it would be impossible to know their potential impact on the grid, and therefore, the environment. Dvorak et al. (2009) modeled the average wind speeds off the coast of California to measure the total available offshore wind power for the state. Remarkably, 17–31% of California’s electricity demand could be met using current offshore turbine technology. Factoring in floating turbines (which are still in prototype stages, but could be constructed in deeper waters) offshore wind power could provide 174–224% of the state’s energy needs. Clearly, not all of this energy capacity can be harnessed; however, there is still an enormous renewable energy resource to be developed off the coast of California. — Noah Proser 
Dvorak, M.J., Archer, C.L., Jacobson, M.Z., 2009. California offshore wind energy potential. Renewable Energy 35, 1244–1254.

 In order to measure the total wind power available, Dvorak et al. used data from offshore buoys to create a weather model. Unfortunately, data from the buoys could not be used directly since there are too few to create a useful map of wind speed; however, when the buoy data were compared to the weather model the variance between the two was relatively low. The researchers also examined bathymetry (water depth) data to determine the type of turbine foundation that could be constructed in each area. Typically, monopile foundations can be used in waters up to 20 m in depth; multi-leg foundations are used up to 50 m in depth, and floating turbines would be used in deeper waters.
Though the authors discounted the power available in deeper waters somewhat, floating turbine technology will soon be a reality. Currently, a 2.3 MW floating turbine is operating in the North Sea off the coast of Norway. As more research is conducted on this technology, the wind resources available to California and many other coastal states will greatly increase.
Overall, California has an abundant wind power resource that should not be ignored. The offshore wind capacity in Northern California is particularly impressive, potentially providing 2.2 GW of average output. Furthermore, offshore wind is relatively consistent throughout the day unlike land-based wind power. Though only a fraction of this resource is likely to be utilized, it can still have a substantial impact on California’s energy independence and greenhouse gas emissions.

Urban Wind Power: Another Source of Renewable Energy

Wind power can also be used on a small scale to reduce greenhouse gas emissions and household energy costs. While roof-top wind turbines are not as efficient as those used for large-scale wind farms, they have the advantage of not being subject to energy losses from transmission and distribution. Nalanie Mithraratne (2009) performed a life cycle assessment of 1.5 kW Swift wind turbines in New Zealand to determine their net energy savings and emissions reductions. She found that, for households in New Zealand, a roof-top turbine would take 7–11 years to make returns on energy, and 10–16 years to compensate for the CO2 emitted in its manufacture, transport, and maintenance. — Noah Proser 
Mithraratne, N., 2009. Roof-top wind turbines for microgeneration in urban house in New Zealand. Energy and Buildings 41, 1013–1018.

 First, Mithraratne had to determine what locations and turbines would be viable for micro-scale wind power production. In the urban environments being considered, wind resources are affected by nearby buildings and trees as well as the architecture of the building the turbine is mounted on. These obstacles can significantly reduce wind energy production. Additionally, the turbines cannot exceed community noise standards and must be light enough to be installed on an average household’s roof. The inherent difficulties involved with urban wind power effectively limit turbines to areas with average wind speeds of at least 5.5 m/s. Mithraratne also suggests that turbines should only be installed on buildings that are 50% higher than the surrounding structures.
The life cycle analysis of the turbines revealed that the manufacturing process accounts for nearly 80% of the energy used and roughly 70% of the greenhouse gases emitted in the turbine’s life. The author also evaluated the energy costs of transporting, installing, maintaining, and, finally, decommissioning the turbines. Overall, one turbine can be expected to emit 2312 kg of CO2, while generating 10520–16820 kWh of electricity during its 20-year lifespan. Thus, using urban wind power can create a net reduction of 539–2246 kg of CO2. The wide range of this statistic is due to the different scenarios Mithraratne considered, which involved different maintenance regimes and disposal techniques.
It is important to note that the life cycle analysis presented here was focused on urban wind power in New Zealand. Transportation of the turbines from the UK was a large factor in the energy costs and emissions in this scenario (roughly 18%). Clearly, less remote locations would have lesser transportation costs, and, correspondingly, higher net CO2 reductions with quicker returns on investments. Though urban wind power is unlikely to make up any large portion of worldwide energy production, it could be a useful and practical addition to the grid.