Frequently Asked Questions
- How do wind turbines create electricity?
- How big are wind turbines?
- How are wind farms laid out?
- How far out would offshore wind turbines be?
- How fast do the blades turn?
- What happens in a storm?
- How much energy does a wind turbine produce?
- How many turbines are in a typical wind farm?
- What are the local economic impacts of a wind farm?
- How does the cost of wind compare to other forms of electricity?
- How does the cost of offshore wind in the Southeast compare to other places?
- What is the impact of offshore wind on electricity rates?
- What are the longer term cost projections for offshore wind?
- What about subsidies?
- What is the impact on emissions?
- What about birds and bats?
- What is the impact on marine mammals?
- What about reefs and sensitive habitats?
- How does wind's water consumption compare to other energy sources?
- What about mining for rare earth minerals?
- What is the energy balance, or energy returned on energy invested, of wind turbines?
- How much energy do wind turbines produce?
- What is a capacity factor?
- So do capacity factors of 30-50% mean wind turbines are inefficient?
- So what is a "good" capacity factor for wind turbines?
- What about variability or intermittency?
- What about backup generation?
- How much land does a wind farm use?
- What is the impact of a wind farm on current land use?
- What about military training and activities?
- Are the turbines lit at night?
- Tourism and Offshore Wind
- What about shipping lanes?
- What is offshore wind's impact on commercial fishing?
- What is the impact on recreational fishing?
- How much land-based wind potential is there in the Southeast?
- How much offshore wind potential is there in the Southeast?
- Why is the Southeast's offshore resource so good?
- What about hurricanes?
- What about transmission?
- Why does the planned offshore transmission "backbone" by Google and others not come further south?
- What is happening with land-based wind technology?
- What new technologies are on the horizon for offshore wind?
A wind turbine functions like a very slow-motion fan, but in reverse. Instead of applying electricity to turn the blades and produce wind, a turbine uses wind to turn the blades, which are connected to a generator in the nacelle. The generator converts the mechanical rotation into electrical energy, which is then fed into the grid.
Land-based wind turbines can range from a 50kw turbine (about 100-200 feet tall) used to power an individual home to 2.5MW utility scale turbines that may reach heights in excess of 500 feet from the ground to the highest point of the blade's rotation. Offshore wind turbines are generally larger than onshore turbines in order to take advantage of the stronger, steadier winds typically located offshore. Current offshore wind turbines typically have a hub height of around 80-90 meters, or 260-300 feet. That is the distance from the water level to the nacelle at the top of the tower. Rotor diameters on the larger turbines can be up to 164 meters. That means the distance from the water level to the tip of a blade at its highest point could be around 175 meters, or 550-600 feet, for the larger turbines. The clearance between the water level and the lowest point of the blades is typically around 100 feet or more. The diameter of the tower at the water level is typically around 15 feet.
Land-based turbines are ideally laid out in a grid pattern perpendicular to the wind, although their placement is often constrained by structures, roads, bodies of water, etc. Offshore, turbines are typically arranged in a grid pattern, with turbines spaced about one-half mile to a mile or more apart. The turbines are connected together by transmission cables that are buried below the sea floor and those cables feed into one or more offshore substations. Energy is then transmitted from the offshore substation(s) to the onshore power grid.
The exact location of wind farms will depend on what areas are put up for lease and where projects are proposed. Virginia's wind energy area is 22 or more miles offshore, due largely to conflicts with military uses. In a state like North Carolina where tourism is such an important driver of the economy, we are likely to see projects proposed that avoid adverse effects on tourism or other industries. Recent proposals in other states have frequently been for projects ten or more miles offshore, which helps to minimize visual impacts.
Depending on the wind speed, offshore turbine blades will turn one revolution about every 4 to 8 seconds, or a rate of about 8 to 16 RPM.
Wind turbines are designed to withstand pretty rough weather. In a severe storm, when wind speeds get very high (typically around 55 miles per hour), the turbines are designed to automatically shut down in order to avoid damage. They do this by turning the nacelle and adjusting the blades to minimize wind forces and applying a brake to stop the rotor from turning. While there is 24-hour remote surveillance for offshore wind farms, all of these safety mechanisms are designed to occur without human intervention.
One 5 megawatt offshore turbine operating at a 40% average capacity factor would produce about 17.5 GWh (or 17.5 million kWh) of energy per year. In the Southeast, where we have pretty high per-capita electricity consumption, that would be equivalent to the annual usage of about 1,250 homes. In the Northeast, where they use less electricity per person, it would be about 2,500 homes. The design life of turbines is about 25 years, but it's possible we could see equipment upgrades or reuse of existing foundations near the end of that period that could extend the life.
A utility scale offshore wind project would probably have between 60 and 200 turbines, each around 5 megawatts (MW) in size. That's about 75,000 to 250,000 "homes" worth of electricity in the Southeast. Double that in the Northeast.
Large wind farms are usually developed in rural or agricultural areas. For many lower-income counties, wind energy development represents a near-term economic opportunity that is often unparalleled in scale. Wind developments frequently become the largest taxpayer in a county while requiring very little in additional county services, which adds significant revenue to the county's bottom line, allowing for investment in schools, infrastructure, etc. In addition, wind farms provide a new source of revenue to landowners, which improves a farmer's bottom line. Finally, wind farms provide several high-paying, permanent local jobs to operate and maintain the facility in addition to the jobs required during construction and manufacturing.
Due to technology advancements, the cost of wind energy has dropped significantly in the past five years. In a land-based site with good wind resource, wind energy costs less per kilowatt-hour than almost any new conventional generation options, includeing new coal or nuclear. Natural gas prices are low right now, but as thos prices rise over time, so will electricity prices from natural gas. Wind energy has no fuel cost, so in addition to being a low-cost option today, it also provides a financial hedge against rising natural gas prices in the future.
According to a November 2010 report by the US Department of Energy's Energy Information Administration (EIA), North Carolina, Georgia, South Carolina, and Virginia have the lowest estimated construction costs of all East Coast states for new offshore wind. For a technology that has no fuel cost, that translates directly into lower offshore wind energy costs as compared to other states. The region's advantage is driven by low cost of living and highly competitive labor markets.
Offshore wind energy is currently more expensive than what we pay for electricity today. Because there is no fuel cost for wind, it can offer long-term, fixed-price contracts for energy, which helps to hedge against the volatility of fossil fuel prices and should save ratepayers money in the long run as fossil fuel prices rise. Justifying the near term cost impact of offshore wind is the major challenge in any state, but North Carolina has some competitive advantages in that regard. We have an enormous electricity market, using 91% as much electricity as New York State, which spreads the impact over a much wider base, resulting in lower ratepayer impact. We also have the lowest estimated construction costs in the country for offshore wind, which also lower the rate impact. So despite having relatively low electricity prices to begin with, it is estimated that the initial ratepayer impact for offshore wind in North Carolina would be among the lowest on the East Coast, just after New York and New Jersey. Initial ratepayer impacts for an early utility scale project in North Carolina are estimated to be less than $1 per month, but the best way to quantify that number is to put out a Request for Proposal (RFP) and solicit competitive bids from industry.
The cost of offshore wind (and many renewables) is trending down over time, while the costs of fossil fuels are generally trending up. The U.S. Department of Energy has long-term cost targets for offshore wind of 10 cents/kWh by 2020 and 7 cents/kWh by 2030. By comparison, the current average residential retail electricity rate in North Carolina is around 10 cents/kWh and some rates in the Northeast are already as high as 18 cents/kWh.
Wind energy projects are currently eligible for some state and federal tax credits, which is a non-permanent measure intended to help emerging industries reach scale and eventually compete without subsidies. A good summary of renewable energy incentives can be found here. (www.dsireusa.org) However, a key thing to understand is that all energy types are subsidized in some form. The well-established fossil fuel industries like oil & gas have been receiving subsidies for about 90 years and, in a total dollar amount, receive far more in subsidies than all renewable energies combined. There are also indirect subsidies like the public health costs of mining, transporting, and burning coal, for example. Those costs are real and are paid for by all of us through increased medical costs and elevated health insurance premiums, but they do not show up on our electricity bill. Nuclear energy receives significant subsidies in the form of insurance backing by the Federal Government, and thus, the taxpayers. If all subsidies were removed and all costs were honestly accounted for, it is likely that we would see a lot more renewables based solely on economics.
Because offshore wind energy displaces energy that would have been generated using fossil fuels, it reduces the amount of emissions that would have otherwise been created. There is often some additional cycling of fossil fuel plants required to accommodate wind's variability and emission reductions depend on what type of fossil fuel is being displaced, but overall offshore wind is estimated to result in annual reductions of more than 650,000 tons of carbon dioxide emissions for each utility scale wind farm.
Wind turbines represent a relatively low risk to birds when compared to buildings, cell towers, cars, and housecats (to name just a few). Many birds have also demonstrated the ability to avoid offshore turbines or windfarms altogether. Despite these lower relative risks, wind farms should obviously not be placed in areas of particularly high risk, like common migratory paths along the shoreline for example. UNC researchers recently completed a year-long offshore bird survey that identified a relatively low density of birds in the range of 10km to 40km from the coast, which coincides well with areas that are under consideration for offshore wind development.
Based on experience and studies in Europe, marine mammals are most affected by the sounds generated during construction, particularly when pile driving monopole turbine foundations. Animals have been observed leaving the area during construction activities and then generally returning after construction noises cease. Care is often taken to avoid construction during sensitive whale migration seasons or temporarily halt construction if certain animals are sited within the vicinity.
Sensitive marine habitats are currently not considered for offshore wind development. For example, the area off the NC coast know as "the Point", where the Gulf Stream and Labrador Current converge, creating a rich and diverse marine ecosystem, is off limits to offshore wind development. Once wind farms are constructed in appropriate locations, the rock scour protection around the base of the tower acts as an artificial reef, creating new habitat and attracting a diversity of marine life where it would have otherwise not been present.
Many fossil fuel plants burn fuel to create steam which drives generators, meaning that significant quantities of water are required to cool equipment and generate electricity. Wind energy uses no water in the production of electricity, thus preserving an increasingly scarce resource. By contrast, combined cycle coal and natural gas generators can use hundreds or thousands of liters of water per megawatt-hour (MWh) of electricity generated. Nuclear uses close to one thousand liters per MWh in a "closed loop" configuration and one hundred thousand or more liters per MWh in an "open loop" configuration.
Rare earth elements are used in a number of applications, including to make large magnets inside wind turbine generators. Despite their name, rare earth elements are relatively plentiful in the earth's crust, with some having a similar abundance to copper. Anti-wind propogandists often try to claim that wind energy is environmentally unfriendly because of the mining and processing for rare earth ore. While every energy resource has its pros and cons, the fact is that the environmental damage caused by mining to support wind energy is miniscule when compared to mining and extracting of fossil fuels. This interesting infographic does a good job of putting this issue into perspective.
Various studies have shown that it takes somewhere around 3-8 months of operation for a wind turbine to generate the same amount of energy that it takes to manufacture, install, operate, and decommission the turbine.
A single 5 MW offshore wind turbine operating at a 40% average capacity factor would generate enough electricity for about 1,250 typical North Carolina households. A 500 MW wind farm would generate enough for 125,000 NC homes. If that electricity was exported to, say, New York, it would serve about 250,000 homes. North Carolina and other Southern states have significantly higher per-capita electricity consumption than Northeastern states.
A capacity factor is the average output of a wind turbine over the course of a year as a percentage of its rated output. Capacity factor is a function of both the turbine and the average wind speed. For example, if a 5 MW offshore wind turbine was in an area where it operated at a 40% capacity factor, that means over the course of a year it would produce, on average, 2 MW of power. (2 MW average output / 5 MW rated output = 40%)
No. If all we cared about was maximizing capacity factor, it would be possible to put a tiny wind turbine in a very windy environment and get very high capacity factors since it would run at its small rated capacity almost all the time. But that would neither maximize production nor minimize energy cost and would also place unnecessary wear on the turbine. The right turbine for an area is one that generates the most energy at the lowest cost, which means it should be sized to generate energy over the range of expected wind speeds. So ideally, the turbine would generate its rated capacity on the windiest days while still generating some electricity on lower wind-speed days. That means over the course of a year, the right turbine for an area will usually produce less than its rated capacity and will operate at full capacity on the very windy days.
It depends on a number of factors, but 30% has been described as reasonable, 35% very good, and over 40% outstanding. North Carolina has extensive areas offshore with estimated capacity factors greater than 35% and 40%
Based on historical wind measurements at three offshore buoys off the coast of North Carolina, wind turbines in those locations would have been producing some energy almost all of the time - between 92-97% of the time during the winter (January) and over 90% of the time during Summer (August). Wind is a variable resource and the energy output does change with the wind speed. However, our electricity grid is already built to handle significant variability in order to match supply and demand. Compared to land-based wind, offshore wind is stronger, steadier, and tends to be more coincident with daily demand patterns. Forecasting of wind, particularly day-ahead, is also generally very accurate.
Wind power, whether onshore or offshore, does not require an equal capacity of dispatchable backup generation to be built with it. There is a cost to cycling other plants to accommodate wind's variability, but those costs are well documented and low, generally less than one half cent per kWh. The first several wind projects in the Southeast will likely be integrated into the grid without any new backup generation being built. As wind becomes a higher percentage of the energy mix, many industry experts estimate that it will require an additional 10-20% of its nameplate capacity in backup generation to accommodate variability. Natural gas is a common choice for load-following plants and Southeastern utilities are already actively expanding the fleet of natural gas plants to replace retiring coal plants.
Even though a land-based wind farm may be spread out over a very large area, the amount of land actually used for wind farm purposes, including turbine locations, service roads, and electrical equipment, is usually about one acre per turbine or roughly 1% of the total land area of the wind farm. The actual footprint of each wind turbine is about 0.25 to 0.5 acres. Much of the land used for a wind farm is for service roads, which often times enhances the accesibility for uses like farming and ranching.
Some of the best sites for land-based wind farms are often farms, ranches, or even timberland. While a large wind farm could be spread out over several thousand acres, the amount of land that is actually removed from its original service because of turbine foundations and service roads is usually about one percent (1%) of the total land area. That means that about 99% of the land area is still used for farming, ranching, timber growth, or other uses. At the same time, a wind farm provides the land owner with additional income from lease payments and often improves four season access to the land through upgraded service roads. In many ways, wind farms can help preserve family farms by providing a new source of reliable income while still allowing the land to be used as it was before.
The US military has a very active presence in the Southeast, both onshore and offshore. As such, the Department of Defense has requested about 40% of the total offshore area within 40 meters of water depth in NC to be off limits to offshore wind development and even larger percentages of the potential areas in VA were removed at DoD's request. The states and the Department of Interior have been very accommodating to military requests and we are not likely to see offshore wind developments in those areas until new mitigating factors become available that make offshore wind farms more compatible with certain military operations. On land, developers are working closely with military bases to ensure any impacts to military operations are either avoided or sufficiently mitigated.
The short answer is yes. The longer answer is yes, but exactly how they are lit may vary from project to project based on the location and what the Federal Aviation Administration (FAA) sees as most appropriate. As one example, the Final Environmental Impact Statement for the proposed Cape Wind project in Massachusetts requires the following lighting. Requirements in the Southeast are expected to be similar. The corner turbines will be equipped with medium intensity red lights at the top of the tower to increase nighttime visibility. The other perimeter turbines will have low-intensity red lights, which should be visible from 1.2 to 1.7 miles away. Aviation lights will flash synchronously every few seconds and the interior turbines will not be lit at night. In addition to red beacons for aviation, U.S. Coast Guard amber navigation warning lights will be installed on each turbine's access platform approximately 32 feet (9.8 meters) above the surface. These amber warning lights will be visible to nearby ocean vessels, but will not be visible from shore.
Travel and tourism is a major economic driver in many parts of the Southeast. For example, in North Carolina alone, tourism generated $17 billion in revenue in 2010 and supported jobs for 185,000 NC residents, with much of that taking place on the coast. Offshore wind farms can be sited far enough offshore to minimize any visual impacts in sensitive areas, and most developers in the US are proposing projects around ten or more miles offshore. In some areas, the presence of offshore wind farms can enhance recreational boating and fishing opportunities and in other areas, turbines should be placed further offshore or not at all. Bottom line: tourism is a hugely important industry in the Southeast. Engaging stakeholders and protecting and enhancing that industry will be a major focus of successful offshore wind developers.
There is a lot of maritime shipping traffic up and down the East Coast. Turbine towers are likely to be spaced 1/2 mile to 1 mile apart but despite that wide spacing, very large shipping vessels will likely avoid the wind farms. The Bureau of Ocean Energy Management is actively looking at high-traffic areas to determine what areas are appropriate for potential wind development. Similar analysis has been done in Mid-Atlantic states with even higher shipping traffic, like New York and New Jersey, so there is some precedent for criteria to identify areas that are suitable for wind development.
If we do this right, there will be no impact or a positive impact. In a 2009 study by the University of North Carolina, members of the study team interviewed several NC commercial fishermen in order to identify areas off the coast where commercial fishing practices would not be compatible with offshore wind farms. Those areas identified have been excluded from consideration for development of offshore wind. At the same time, by creating new structures in the water that can act as artificial reefs, fishing opportunities may be enhanced in some areas. Outreach to fishing communities has also taken place in Virginia and is currently underway in South Carolina.
Offshore wind turbine foundations create new structures in the water that can act as an artificial reef, greatly enhancing opportunities for recreational fishing. Offshore wind farms are likely to become popular destinations for recreational fishing trips off the Southeast coast.
Advances in wind turbine technology that allow efficient capture of even lower wind speeds have greatly increased the number of areas where wind energy can be deployed cost effectively. There are curently around a few thousand megawatts of commercially viable wind energy potential in coastal areas of the Southeast (excluding mountain ridgetop wind). That amount would provide power equivalent to the consumption of several hundres thousand homes.
According to the National Renewable Energy Laboratory (NREL), just four states (VA, NC, SC, and GA) have about 63% of the total East Coast offshore wind resource in less than 30 meters of water. If we look at resource greater than 12 miles offshore and in less than 30 meters of water, those same four states have 82% of the East Coast resource. NREL estimates the technical potential within 50 miles of the coast of VA, NC, SC, and GA to be about 583 gigawatts, which which is equal to about two times the electricity demand of every coastal state from Maine to Florida. This region has the potential to be a significant exporter of offshore wind energy.
There are a few factors that contribute to the Southeast having very good offshore wind resource. 1) The region has a very long coastline, so there is a lot of windy area. 2) The continental shelf slopes more gently in the Southeast, providing ample shallow water area in which to erect turbine arrays. 3) The proximity of the Gulf Stream flowing from the South and its convergence with the Labrador Current flowing from the North create a unique and energetic microclimate, resulting in impressive estimated capacity factors for offshore wind energy off the NC coast.
The North Sea, where many offshore wind turbines operate today, has very rough weather. But they don't have hurricanes. Current turbines are designed to a IEC Class 1A specification, which means they can handle sustained wind speeds of about 112 miles per hour and gusts up to 156 mile per hour. Turbine manufacturers are aware that additional design changes will be forthcoming when projects are proposed in areas with hurricane risk. Also, early indications from industry are that insurance companies will be willing to insure projects in the Southeast. Finally, according to the national hurricane center's data, there have been only five Category 4 hurricanes (Diana-1984, Gracie-1959, Helene-1958, Hazel-1954, Able-1950) and one Category 5 (Hugo-1989) hurricanes that have come within 75 miles of the Virginia, North Carolina, or South Carolina coasts since the earliest available data in 1842. Hurricanes are a real issue for offshore wind in the Southeast, but industry is aware of the challeneges and does not expect any of them to be show-stoppers.
Access to adequate transmission capacity is a key siting consideration for land-based wind development, and projects proposed in the Southeast have generally factored that in. For offshore wind projects, taking a regional approach to transmission solutions can greatly reduce the overall cost. For example, There is a very robust interconnection point in Hampton Roads, VA that could be used as an interconnection pont for projects near the border in North Carolina. Similarly, a project near the NC/SC border could connect in either NC or SC, depending on which was the most cost-effective option. Southeastern utilities have studied various offshore wind transmission scenarios and are now starting to conduct joint, multi-state studies to find the best regional solutions. The cost of any transmission upgrades will need to be factored in to the cost-benefit analysis as the state looks at offshore wind development options.
The offshore transmission backbone that was announced in 2010 is planned to cover areas where there are significant offshore wind development activities taking place. At the time the project was announced, Southeastern states had not announced any concrete plans for offshore wind development, so it is not surprising that their plan did not extend further south. (It currently is planned to stop at the VA/NC border.) If a significant amount of offshore wind development is eventually planned in the Southeast, it is reasonable to assume that an offshore backbone could be extended further south, either by the same group of companies or by a different group.
Technology improvements in wind energy have driven major cost reductions over the last several years. Improvements in turbine and blade technolgy that enhance performance in lower wind speed sites have increased the number of commercially viable wind energy projects. There are also major improvements happening in forecasting of wind speeds through meteorological data collection & analysis and other technologies like look-ahead LIDAR, which uses lasers to read the wind speed as it approaches a turbine. We will continue to see exciting innovations in wind energy that keep reducing wind energy cost and increasing wind farm performance.
Floating turbine platforms are being tested at full-scale now and offer the ability to install windfarms further offshore in even stronger winds with potentially lower installation costs. Combining wind installations with other ocean energy generation is another possibility for the future. That would include things like current, wave, and ocean thermal gradient energy generation. Offshore energy storage is another technology that has potentially "game changing" implications for offshore wind. Measurement of hub-height wind speeds from floating buoys using technologies like LIDAR are increasing our understanding of energy potential while reducing the need for more expensive fixed towers. The offshore wind industry is a dynamic and rapidly improving industry with a lot of exciting things happening.