Onshore wind has more than 70,800 units in the United States. Unfortunately, onshore wind is not strong enough, nor does it blow often enough, to meet our growing clean-energy needs. Offshore wind is stronger and more consistent, yet there are only seven offshore wind-turbine generators operating. A new process that starts with the signing of a wind-farm lease and ends with the cost-effective production of green energy can be achieved in three steps:
- Remove the extremely expensive and heavy steel used in turbine towers, floating platforms, and monopiles.
- Replace the steel with a high strength, durable, weldable, noncorrosive concrete material. This use of this new concrete material (NCM) will result in substantial cost reductions during component production and assembly all while being 100 percent carbon neutral
- Accelerate all aspects of the permitting, production, and installation to a one-year timeline by developing a leasable harbor wind seaport (HWS) infrastructure.
Permitting, production, and installation
Wind industry stakeholders need to reevaluate their processes and become open to a new permitting, production, and installation (PPI) plan for future 10-20 MW DD WTG offshore wind projects. The plan includes a 24/7 work environment as part of a new harbor wind seaport (HWS) work campus. Funding the new HWS leaseholds could easily be handled by the harbor or their investment group.
U.S. offshore wind stakeholders, working with the federal government, must follow the precedent of other countries and prioritize the acceleration of the permitting process. In Europe and China, the commercialization of wind has reduced the permit process from seven years to under one year. Cost saving can be achieved by using the U.S. Inflation Reduction Act to re-coup up to 30 percent of the capital cost as a refundable tax credit.
Removing steel will decarbonize offshore wind
This article is not about removing steel from the nacelle and hub components of the WTG, but rather removing the steel in the support structures: the tower, semi-submersible floating platform (SSFP) and fixed bottom monopile (FBM). These WTG support structure components will use a new higher strength, more durable, noncorrosive, new cement material (NCM). The NCM product is carbon neutral and results in a substantially lighter material that is well over two thirds less weight and half the cost of steel. The use of NCM will result in additional cost savings due to a reduction in labor, material, and time for constructing the support structure components out of NCM rather than steel. Structures composed of NCM will have a significantly longer life span at sea with a minimum of 100 years.
New cement material reduces weight and cost
Today, 100 percent of the concrete used in fixed bottom and floating structures is made with ordinary Portland cement (OPC). The OPC (binder) is the paste that holds the concrete together. OPC has deficiencies when used in marine environments. Sodium, sulfates, and chloride compounds in sea water directly attack the calcium components of OPC, and this chemical reaction essentially rots the concrete. OPC has a negative environmental impact due to its carbon intensive production methodology.
There are only two hydraulic cement (binder) sources in the United States designed for offshore wind structural element construction, OPC and NCM. Although OPC is the most widely produced man-made material on Earth, it has no real value in a marine environment. NCM, with its high strength and durability, makes it the new offshore wind-material solution. It is the only noncorrosive weldable cement/concrete. This material was developed around a geopolymer concrete technology in France.
Its geopolymer binder contains as little as 2 percent calcium and is instead made up of inexpensive and widely available ingredients including alumina-silicates, fly ash, blast furnace granulated ground slag, zeolites, and water glass. The basic definition and chemistry of NCM is glass. The advantages of NCM are concentrated around durability and strength; NCM contains no OPC and is a dry cementitious material activated with water, rather than chemical liquids. The extremely low permeability and high strength of NCM produces a material with a life span in sea water that will be measured in a millennium rather than decades or centuries.
NCM is low cost, low weight, high strength when produced and placed correctly (standard 9,000 psi), and results in the most durable, strongest, first weldable material available in the construction industry. The NCM chemistry is unequivocally superior, producing a binder that requires no air entrainment or placement with vibrators (it’s self-consolidating) to achieve its strength. The environmental sustainability of this product is further enhanced by the fact it is 100 percent carbon natural.
Harbor wind seaport campus
The harbor wind seaport (HWS) campus will be housed within a major city’s leasable harbor ports and defined acreage. The HWS will be large enough to support all the production infrastructures for both land and water component production and assembly. A large area of close-in, offshore water is required to accommodate both the semi-submersible floating platform (SSFP)and the final WTG assembly. The typical HWS campus will have sufficient dock length to tie a minimum of three large production vessels as well as various smaller material supply barges and work boats.
Harbor wind seaport production plant and vessel
The production plants and vessels, as part of the HWS campus, are necessary to begin addressing PPI’s requirements in a serious manner. By assessing the unbelievable scale, weight, craning requirements, transport, and production needs of today’s large-scale wind turbines, it becomes clear how important it is to lower the current cost and increase total unit delivery.
To envision how these large-scale turbines fit within this plan for high productivity and deployment, it’s best to envision them as multiple segmented assemblies coming together much like the new assemblies in the automotive, aircraft, and ship building industry. The plan will need immediate long-term sourcing for parts and delivery of turbines, cranes, high-capacity rail power dollies, slip-form systems, and custom formwork. Building the components and assembling them into segment sub-assemblies, then into fully deployable turbines rely on the infrastructure and design of the HSW campus. It can be accomplished as follows:
- The top-weight segment, consisting of nacelle, hub, and blades (with blade placement attachment jig), will be outsourced and shipped to the designated water area within the HWS campus. It will be housed in a partial roll back building due to the weight and lift requirements of the nacelle for final placement.
- The new tower segments, consisting of three components: base, middle, and top zone, will be produced with the new cement material (NCM) at the HWS production plants.
- The largest number of in-service floating platform foundations throughout the world are now semi-submersible floating platforms (SSFP). Their new down-up slip-formed column, hull and ballast components can all be produced with the new NCM.
- The fixed bottom monopile (FBM) will be down-up slip-formed with NCM at the HWS, in the deep-water portion of the campus, off an ocean-going deck barge (OGDB) production vessel with a 100-yard batch plant and pedestal pump. Using its own on-board propulsion units to move it within the wind-park waters, the OGDB will serve both the FBM and SSFP production.
- New down slip-formed suction anchors made of NCM will be produced at HWS off the OGDB for later placement in the wind farm.
The semi-submersible floating platforms (SSFP) will be assembled in the outer harbor water of the HWS campus. The SSFP’s slip-formed components will be built, assembled, and installed in the HWS 70 feet to the sea floor water. A 15MW-DD foundation size for the SSFP, in-plan view, will require a minimum of a one-acre triangle at approximately 300 feet per side assembled in 70 feet of sea-floor water. To achieve this large size platform, assembly will require a workable sea state within the campus waters. To assure a high percentage of these optimum sea states, a floating breakwater will be required.
All the wind-turbine generator’s sea floor platform cabling, with its many attachments and components, will be sourced and built with NCM and assembled at HWS multi-acre final deployment plant.
Additional buildings on the HWS campus will be required, such as a medical facility, warehouse for food and supplies for the entire campus, plus a maintenance building for slip-form systems and other key equipment.
Offshore wind’s first noncorrosive concrete tower
There has never been a concrete tower supporting the “top-weight” (nacelle, hub, and blades) of an offshore WTG. Top-weight designers have always insisted on designing the tower in steel and contracting out its construction.
The offshore wind industry is finally committed to focusing on a standalone concrete standardization for larger, taller, stronger towers for 20 MW DD WTG and beyond. Now, with NCM and new efficient production methods and weldable non-corrosive attachments of tower internals designed in high strength structural fiber glass components, the new concrete tower’s design will reduce a large amount of weight, achieve higher strength, while producing a minimum 100-year life cycle. (The life cycle in steel is about 20 years.)
These new tower designs should now be handled by the developer’s naval architect. They will have good input from the top-weight wind stakeholder’s representatives, NCM supplier, conical slip-form design firms, PT designers and their suppliers, and tower internals designers and their manufacturers.
Tower slip-form segment production
A GC’s onsite construction slip-form is entirely different than an in-plant high production slip-form, continually producing towers 24 hours a day until completion of a specific contract.
This will be the largest land-based infrastructure due to the zone segment sizes of the towers. The production requirements will always have both a vertical and a horizontal component dictated by the different types of production demands and skills.
Tower zone sections and other production entity requirements demand all three tower-zone sections (base zone, middle zone, upper zone) be slipped at the same time. This will require a sizable high-capacity raft type pad for each turbine size with both FF and FL requirements. A minimum of two pads are required to produce one full tower size. This will ensure continuous production of the vertical component as follows:
- Conical slip-form systems (CSS) is the control that reduces wall thickness and tapering of the tower slip all at the same time. The start pad will receive three CSSs: one for the middle zone tower slip, the second for the base zone tower slip, and the third for the upper zone tower slip. All will be positioned side-by-side to produce one tower. Each tower hold-down will use a two-inch bolt, in double shear, held to the start pad by a half inch plate with a bent 90 with a two-inch tie down hole on either side of 18 one-foot-thick attachment units. These units also support the internals.
- The key to the vertical slip-form component is the environment of the long box, a year-round high production slip-form enclosure. It is designed to be a work environment to fall between a class-one and class-two office enclosure. The enclosure is designed and built as five inter-locking modules
- To start the vertical component of the slip-form, an 80-yard batch plant with an output temperature control system, tied to a pedestal delivery pump, will feed three placement hoppers above the slips. These hoppers have tremie hoses with solenoid valves, attached with Victaulic couplings to the feed hoppers for easy removal and cleaning.
- With an accelerated low voltage cure rate of two inches an hour, and a little under three 24-hour work days, the crew will have topped out all three zones of the tower. Their next operation will be to extract the jack rods and fill the holes with NCM grout, allowing structural continuity. This can be accomplished in one 24-hour work day.
- The two-inch cure rate, that doubled the rate of the slip, is only possible with Teflon coated form plates while using NCM, which allows low voltage to heat the mix and accelerates the cure.
- The perfect slip-form is one that never stops until completed. If it does stop, restart time is critical. This is when NCM becomes invaluable because, if it has been less than 28 days, it will bond with full structural continuity to a fully cured slip-form in production both on a chemical and mechanical basis.
- Assuring a 100 percent non-corrosive tower is key. The inherent corrosion inhibition is unavoidable with NCM chemistry. The glassy rheology of NCM forces it to attach chemically to steel. This non-corrosive protection allows the designers to choose a higher strength bar and reduce the cover because of NCM’s strength and durability.
Tower vertical component attachments system
This is an integrated slip-formed vertical attachment to the inside tower’s face. The component is one-foot square in plain view, its center line to the center of the tower with the unit attached to the inside face of the tower with a four-inch continuous fillet on either side. This one-foot square section travels down the entire length of the three-zone assembled tower like a concrete square “ribbon.” There are eight of these ribbon attachment units equally spaced around a 10-MW tower, 12 units on a 15MW, and 16 on a 20MW.
Tower horizontal production facility
This land-based production facility will be one of the largest structures on the HWS campus. Its foundation will be 200 feet wide by 250 feet deep. Its front elevation will support four large 60-foot clear height bifold doors. The building will be designed to complete the non-corrosive component installation of the towers internals such as platforms, safety fall and arrest systems, ladder systems, fences, elevator, power cable tray, lighting, and small portable heat pump connection and zones section end flanges tools.
The first three bays of the four-bay plant’s floor will each have high capacity, 200-foot-wide gauge, 90-pound railroad rail support for the horizontal turbine tower section bogies, all built with the rail head face flush to the slab face. Each bay will receive one of the three turbine tower zones. Each tower will be supported by two six-foot-long deep saddles attached to a boister.
This tower horizontal component is set up to balance the labor and time factors to match its vertical counter component.
Fixed bottom monopile foundation unit
A traditional fixed bottom monopile (FBM) is a large pipe-shaped item produced by rolling an extra thick steel plate into cans, which are then slid and welded together into a longer monopile. It is the preferred option for supporting turbines in shallow water. Because wind turbines are getting larger, the monopile that supports them needs to be heavier, larger, and longer. To meet today’s requirements, the diameters of these FBMs are ranging from 10 to 42 feet, lengths from 65 to 390 feet, and weights from 1,000 to 3,900 tons.
FBM, as a foundation, is basically a high-rise structure required by design to be a large non-overturning ability with sufficient stiffness. To continue to make FBMs out of steel will be expensive and inefficient and will require a larger plant with higher floor loading and larger overhead cranes to lift the FBMs onto heavier load dollies to move it out of the plant. Continuing to make FBMs out of steel is incredibly expensive, inefficient, and environmentally irresponsible.
A new fixed bottom monopile
A very large part of the cost (more than half) can be recovered by constructing the FBM with the new cement material (NCM). The non-corrosive properties of NCM eliminate the need for cathodic protection. In addition to cost savings, the atmosphere will be saved by removing two tons of carbon for every one-ton of steel not used in producing the FBM. The FBM will be slip-formed, using a new production method called down-up slip floater/driver. The use of NCM allows the slip-form to stop and restart without a cold shot, allowing a diaphragm with a centered gate valve to be installed and the slip formwork to be set down and restarted. This diaphragm serves two purposes: to form an upright ballast chamber in the top of the FMP and to add more water weight, via the gate valve, to the chamber and vibratory hammer weight, allowing a quieter hammer.
The NCM will bond to a fully cured component, both on a chemical and mechanical basis, with full structural continuity.
The FBM storage, transport, and installation vessel
The ocean-going deck barge (OGDB) Jones act vessel, will be 480-feet long, 165-feet beam, with a 45-foot deep hull and a shallow bow. It will be a self-propelled with four Azimuth thruster units for propulsion and steerage, which will also play a role in the vessel’s dynamic positioning system. The OGDB will have a three-story bridge forward for housing two full 24/7 crew quarters on the first and second level — one for the Jones act crew, the other for the marine installation crew. The bridge on the third level will cantilever out, fully enclosed, to the vessel’s gunwales.
All of the FMPs, still floating vertically with their own air ballast, will be lifted vertically by the crane’s installation vessel to one of the many FMP vertical gripper structures and top of pile holder lock, positioned outside the gunwales, on either side of the vessel. In a shallow installation project, the OGDB can store up to 18 FBMs. The FBMs could and sometimes will extend below the OGDB hull bottom.
Semi-submersible floating platform production
Compared to a spar buoy, a semi-submersible floating platform (SSFP) has an increased water plane area, which provides more hydrodynamic stability and more structural stiffness to resist wave loads. There are at least five designs of SSFPs being used globally. HWS marine engineering division is two-fold: First, it removes all the steel from their designs and uses NCM lightweight, non-corrosive, weldable concrete, material at one third the weight and cost. The NCM mix design, used in the slip-form, unlike OPC, will allow low voltage to pass into the mix, accelerating the cure rate during the slip. This will allow the slip to achieve a minimum of two feet an hour rather than the traditional six to eight inches with OPC.
The SSFP components such as columns, pontoons, hull, etc., are not the problem; it is the size and weight of the platform. The platform that will support a 15 MW/DD turbine will most likely have three to six columns depending on the design and weight. The column arrangement, by design, will always be within a triangle with a buoyancy column at each of its three or six points supporting the pontoons and hull components. This 15 MW/DD triangle floating platform will be approximately 300 feet on each side, with an area of 37,173 square feet (85 percent of an acre). It will weigh approximately 2,900 tons (1,200 tons if made from NCM).
Methods to place SSFP in water are extremely large and expensive and would not fit into an HWS campus. If the HWS’ developer had plans to use an existing steel SSP design and use NCM, benefits would be substantial.
FBM and SSFP component production vessel
This vessel will support a low weight 600-ton, all-electric pedestal crane with a built-in heave compensation system for safe and accurate placement of components. This crane will be placed center deck, aft of the bridge. Aft of the crane will be a 100-yard batch plant with heater, batch testing, and sample storage lab house. The batch plant will serve three pedestal mounted placement booms.
The structural box shaped slip-form support stations of different sizes are hinged to both the port and starboard gunwale and are hinged back on deck when not in use. Most of the materials will be received on the OGDB starboard side. Most are scheduled for a two-day period every two weeks, freeing up the slip-form stations.
In a traditional slip-forming, the product being formed is moving up. Down slip-forming can be achieved by designing an end cap, or structural end plate hull structure, to support the slip weight, jacks, and load, plus a two-deck load of slip-form work assembly’s jack rods and other downward pressure components. Once it is in place, its slip will be restarted to its design depth, with no cold shot due to the NCM material.
The construction will be at deck step-off height
As the down slip-form continues to its design depth, the construction concrete work deck will always be at an elevation to allow a normal crewman to step down to the construction vessel’s work deck. This is achieved by a logarithm that controls a measured water ballast placement in the hull, while, at the same time, measuring concrete placement, rebar, and crew weight. The slip product component is always floating free in the aft well in a zero-sea state.
Semisubmersible floating platform assembly
Most of the assembly of the floating components of the SSFP will be steered into position in the platform by their three existing cranes. Since all SSFP hulls are below the ocean surface and wave action, it is easier to do the welding there, including towers and ballast tanks. The assured way of doing NCM welding is to stick to vertical and horizontal cavity welding. With slip-forming, it is easy to slip additional projected round and flat services to form cavities. These cavities, when filled with NCM, designed for structural element construction, will bond to a fully cured component both on a chemical and mechanical basis.
Prior to filling, all the components have a retrievable tie system to lock them in place. NCM can be placed in a cavity at a high depth without a tremie or a vibrator since it is self-consolidating and will not separate. When placed, the design mix for the NCM will push out the sea water. Productivity will be one platform every five 24-hour work days.
Wind turbine generator final assembly and tow out to wind park
Tower turbine hub and blade placement on the large semi-submersible floating platform (SSFP) will be achieved by a crane-type six-round-leg jack-up vessel.
The now fully assembled 15MW/DD wind turbine generators will be towed out of HWS water at a comfortable and safe rate of speed due to the shallow depth of the SSFP hull and placed at the wind farm by a HWS subcontractor. The estimated build-out and placement of each WTG in the wind energy farm is five 24-hour work days.
A huge reduction in decommissioning cost
Although the nacelle and blades will still need to be replaced every 25 years, the new generation of green materials outlined here can produce offshore WTG towers and foundation structures with a minimum lifespan of 100 years. These new structures can support four generations of wind turbines and significantly reduce decommissioning costs. The process for changing out the turbine nacelle and blade could be as little as two days per turbine.
Environmental sustainability results on fiscal responsibility
Reducing the environmental impact associated with offshore wind systems should be our paramount goal, but money is often a limiting factor.
Not only do the materials and processes discussed here significantly decrease the carbon footprint of an offshore wind farm, but an outside cost option found there would be a 32-percent reduction in the cost of materials and a 28 percent reduction in the cost of labor for construction and development.
The 100-year lifespan of the support structures will eliminate the multimillion-dollar cost.
