It takes power to make power. Constructing offshore wind farms will need standby power from auxiliary generators for a range of functions. When provided reliably, the project is more likely to complete on time
Bill Cook / Strategic Account Manager, North America, Aggreko Americas
Alf Scambler / Renewables Sector Development Manager, Northern Europe, Aggreko UK Ltd
The wind industry has grown to the point where it is now the fourth largest source of electrical power in North America after natural gas, coal and nuclear. Industry reports indicate that global electricity generation from wind energy reached 60 GW in 2016. The U.S. Department of Energy’s Wind Vision report says the United States may be able to meet 10% of its electricity needs through wind power by 2020, 20% by 2030, and 35% by 2050.
That growth will be possible because the cost of producing electricity from wind energy on a per kilowatt-hour (kWh) basis is approaching the costs of other forms of conventional electricity generation, such as that from coal and natural gas. More recently, growth is driven by favorable cost factors and market drivers such as corporate purchasers. In that U.S., federal wind energy Production Tax Credit (PTC) and Investment Tax Credit (ITC) programs have been extended until December 31, 2019, so that wind projects that begin construction in 2017 will receive an ITC or PTC of 24% or 1.84 cents/kWh. This is an important advantage when considering that the general cost of a wind energy project is around $2 million per MW.
Incentives only partly explain why wind driven power surpassed hydroelectric power capacity in 2016 (wind power: 82,000 MW vs. hydroelectric: 80,000 MW). While federal tax credits have encouraged wind farm development, state incentives, such as guaranteed markets and exemption from property taxes, could pay for another 10%.
Compelling market drivers and declining project costs must continue if wind energy markets, such as in North America, are to expand the wind power industry’s capacity seen in other regions, such as Europe. Fortunately, wind energy installation costs have declined by 40% over the last three years, according to a recent Union of Concerned Scientists (www.ucsusa.org) report, making it logical to assume that the pace of the last few years could continue.
One recent development has been the energy focus of private industries. For example, energy giant Enbridge Inc., primarily focused on oil and gas pipelines, recently announced it was investing $1.7 billion for 50% of the Hohe See wind energy project off the coast of Germany, which follows Enbridge’s $282 million purchase in 2016 of a 50% stake in a group of French offshore wind projects. The Calgary-based company’s CEO, Al Monaco recently said to the effect that the political landscape in North America has shifted. “Let’s call it a more balanced tone for energy and infrastructure and development,” he said, seemingly paving the way for North American onshore and offshore wind energy projects.
Aside from reduced installation costs, issues around the variability from electricity generated by wind power and challenges with grid interconnections are steadily being resolved. Improved technology and infrastructure and the growth offshore favors the growth of wind industry capacity.
For example, 2016 saw the official launch of operations for the Block Island Wind Farm, a 30MW installation off the coast of Rhode Island. Additional and larger offshore development projects are in the works.
Against this backdrop, wind energy developers are realizing the need for a wider and more flexible temporary power capability throughout the offshore and onshore wind farm lifecycle. Each of these phases has special needs:
- Operations and maintenance.
Compared to onshore wind energy projects, offshore wind farm projects present a new learning curve. Much of the offshore wind turbine, related testing, and additional power supplies can be done at the manufacturing facility on both high and low voltage systems. Additional temporary power is often required more frequently than expected because the manufacturer may not have sufficient power on site. In addition, the new manufacturing facilities will require supplemental power or contingency plans for loss of power during production. In the manufacturing realm, there is also the real possibility for climate control during winter and summer months for the blades and electrical.
As an example of the additional scope of testing required for offshore projects, there is a remote 100% reliable power requirement for the light detection and ranging (LIDAR) system situated on a metmast, if the project is to progress from the planning phase into the construction phase. In the planning phase, the operation cannot lose power. The purpose of the LIDAR is to ensure the collection of a constant stream of information on the wind, birds, and other wildlife. The planning phase also calls for the ground work testing of the cables for routes and boring survey holes will also need temporary power support.
Throughout the wind farm construction phase, temporary power for large and small loads can be supplied with a wide range of generators. With onshore projects, the substation benefits from smart generators for civil engineering works that can synch together and be placed on load demand. For example, two 125 kVA generators may be working in tandem during the day, whereas only one is required to operate in the evening, therefore saving fuel.
For onshore and offshore applications, one of the available support services includes testing the HV (high voltage) cable and substation. An HV cable soak test is available for construction of the offshore substation so that the developer can test all relays and transformers on the substation prior to floating out. This prevents potential failures that will be costly to rectify offshore.
Meanwhile, temporary generators run the substation until it is connected to the grid. This avoids having to rely on costly embedded generators while the substation is being completed. Running them for operational purposes will result in costly voiding of warranties and additional cost such as heavy fuel consumption. Long term rental solutions can be customized to the platform requirements. As noted before, two generators can be on load demand and monitored by a remote monitoring system.
Heating and drying for the stores are also needed to protect important electrical equipment, along with the nacelles and blades. This can be done using heaters, dehumidifiers, or electrical (dehumidification) systems – that are also used on vessels. Also, companies with trenching machines, cranes, or ROVs may want additional power both onshore for testing and commissioning and offshore on vessels for operations.
For the offshore construction phase, 20 kVA generators are provided and placed on the man-access platform (MAP) and are charged using a wind turbine. Such units power the various electrical equipment used during the initial construction phase. These 20 kVA units weigh less than a ton, so they can be lifted off by a davit crane, further reducing developer costs by not needing a large vessel in service.
Vessels activated for offshore projects can also use temporary generators for supplementary supply. This includes a range of vessels from crew transfer boats through to cable laying and jack-up vessels. Eventually, this can potentially involve multi-megawatt applications.
Offshore, generators are used to commission or condition the turbines. This often includes the use of generators on the MAP that power the essential equipment, followed by a greater amount of power to pitch the blades and yaw the turbines.
Failure to provide this motion could result in damage to the turbine. Novel offshore solutions have been created for this requirement – resulting in generators that are lightweight, durable, and can synch together to minimize the load. LV and HV back-feeding solutions can be provided for the offshore substation (OSS), minimizing cost for the developer. Cooling can also be provided for HVDC convertor station transformers.
The electric grid has to adjust supply in response to the fluctuating characteristics of wind power and demand. These fluctuations will continue as the wind energy industry expands. For example, Texas, a world leader in fossil fuels, has to deal with the complexities of integrating the state’s utility grid with fluctuating power supplied by wind driven generators. On this scale, integration of large-scale wind power into the grid’s power systems present new challenges with the increase in the number of incoming induction generators to the grid, causing power quality problems mainly in current harmonics, reactive power, and power factor.
These problems could be more severe with “challenged” grids. For example, it is undesirable to have simultaneous switching of induction generators that leads to excessive infusion of reactive power from the grid. Power is also provided for construction equipment and other specialized requirements, such as generators during ground assembly.
Certain variability and induction problems with wind-farm projects over the past 20 years continue to make connecting to the utility grid challenging. This is where temporary power suppliers have played a pivotal role in wind farm commissioning. The average size of wind driven generators has increased from 0.5 MW in the mid-1990s to up to 8 MW in the latest offshore models. Commissioning these systems into service is being expedited with mini-grid solutions, providing the capability to manage power from the turbines, along with an associated array of scalable generators and transformers.
Above all, the generators and load banks supplied to the industry allows commissioning turbines prior to connection to the power grid, saving time and directly benefitting return on investment (ROI) by letting the developer begin production as soon as the project completes the wind farm’s substation. Saving time is important considering that tax incentives and credits are available once the wind energy system has been commissioned and fully operational.
Operations and maintenance phase
In the post-commissioning phase, low-voltage power can also be supplied at the base of each turbine to power ancillary equipment, such as lighting and the hydraulic pumps to turn the rotor (to prevent bearing lock up). Alternatively, a central high voltage package can power the integrated system from one point of connection, keeping transformers and switchgear running, in addition to the turbines.
Maintenance typically uses temporary power from standard generators, while transformers are also made available for the higher voltages, such as 690V (the industry standard for many years). In fact, transformers have been supplied for multiple uses. To connect the circuits in the field, 480 V/34.5 transformers in the 2,500 to 5,000 kVa range are provided. To keep the system operational, power has been supplied to the field when the main transformer has failed or the utility has to take the distribution system out of service.
Similar to the experience with onshore wind farms, it’s important to see offshore facilities as power plants and not wind farms. The emergence of the offshore wind-power industry makes necessary contingency plans that enable fast response to problems.
Similar to conventional (gas fired) base load power plants, important factors for maintaining plant use and run length include the availability of a service infrastructure staffed by engineers who are local and offshore qualified by organizations such as GWO Certified Basic Maintenance & Training Standards: www.GlobalWindSafety.org, and preferably by a temporary power-supply company that can provide a “full 360 degrees” of capabilities, such as remote monitoring of the system generated power. Additional and unique capabilities of the wind power industry should include supplying heat for turbine blade remediation work.
One of the many capabilities proven to benefit wind farm power plants that have been in service for several years is the installation of embedded generators for turbines and substations. With unique designs and rental models available, they can significantly reduce the lifetime cost of an outage. The capabilities of such generators continue to expand as the industry transitions into offshore projects in North American and elsewhere, requiring a turnkey package, such as auxiliary vessels and refueling capabilities for offshore projects, which is why the multiple “layers” of expertise needed in the wind energy business are already available.
Filed Under: Construction, Offshore wind