Offshore Wind
Delivered Faster, Cheaper & Greener
The Gravity Tripod™ is a unique and globally patented offshore wind sub-structure
Financial
The Gravity Tripod™ is 11.7% lower Levelised Cost of Energy
Environmental
The Gravity Tripod™ has lower environmental impact and can accelerate reduction of the world's carbon emissions today
The Gravity Tripod
“A new asset class in offshore wind”
“Innovative… There are many good aspects of the design that assist in methods of assembly and supply chain options”
The Gravity Tripod
The Gravity Tripod™, globally patented, is an offshore subsea foundation structure designed to deliver up to 11.7% project cost reduction, to reduce project delivery times by up to 1/3 and create almost zero environmental impact.
The Gravity Tripod™ is a component base structure that benefits from the best aspects of other foundation concepts. It is a hydro-dynamic transparent structure which doesn’t require piling, is manufactured from low-cost tubular sections in a rapid assembly process and is installed with minimal seabed intervention.
The Gravity Tripod™ has two distinctive components that act together to ensure the structure has an extremely long design life (up to 100+ years) and is insensitive to turbine loads with a capacity of up to 25MWs. In addition, the structure has a low bearing pressure on the seabed and so is capable of accommodation a huge range of sediment types, with less seabed preparation required than other gravity-based designs.
75
Designed for 20m to 75m water depths
12%
11.7% reduction in LCoE
100
Designed to last 100+ years
Key Benefits
11.7% reduction in LCoE
Lower capex & opex, and greatly reduced installation time
Reduced embedded carbon
1,200 tonnes of CO2 saved per structure compared with a Jacket
Noiseless construction
Zero piling creates near noiseless installation
Reduced project construction risk
No requirement for piling
Usable in up to 75m water depth
Scalable to greater depths
Our Partners
Environmental Impact
subsea piling noise has a massive negative impact on marine mammals, fish and invertebrates
“Offshore wind is a huge tool to help the world de-carbonise, however it shouldn’t do further damage to achieve this aim”
Environmental Impact
The Gravity Tripod™ has been designed with minimising environmental impact and generating a biodiversity net gain at its heart. From initial design, materials used, installation, design life and decommissioning the Gravity Tripod™ has the ability to have a net-zero impact.
Prior to installation the Gravity Tripod™ requires no harmful seabed dredging, ensuring no existing habit destruction. The lack of requirement for piling ensures that marine life in all its forms has no negative impact due the tripod installation, mammals and fish are routinely deafened by piling leading to an inability to feed and thrive.
No piling, no dredging, no habitat destruction is reinforced by the use of lower embedded carbon concrete over traditional steel, environmental concrete also fosters marine habitat creation in and around the tripod. With a 100 year design life and a constant re-powering ability, the Gravity Tripod™ greatly increases lifespan and delivers significant environmental gain.
Key environmental benefits include
- Elimination of Construction Noise
- Biodiversity Net Gain
- Lower Embedded Carbon
Elimination of Construction Noise
The Gravity Tripod™ eliminates subsea construction noise. While competitor designs require extensive, risky, and time consuming piling operations, at high energies, the Gravity Tripod simply sits on the seabed; it does not even require the surface sediments to be dredged or the seabed to be reinforced with rock.
Biodiversity Net Gain
Designed with the environment in mind, the Gravity Tripod™ not only doesn’t destroy the habitat through noisy installation operations, or seabed dredging/rock dumping/preparation, it actually creates additional habitat for benthic flora and fauna. Its open base design allows the existing sediment profile to be reinstalled within the base so that it can be repopulated, at the same time additional niches can be sculpted into the base to create habitat for desired species. Similarly the transition piece can create habitat for a range of seabirds with suitable habitat for cliff edge nesting, ground nesting and burrowing species.
Lower Embedded Carbon
The Gravity Tripod™, as a concrete structure, has a significantly lower carbon content than competitor designs. Using conventional Ordinary Portland Cemenet the assessed carbon content of the Gravity Tripod is less than 50% of a Jacket, while with the introduciton of Alkali Activated Cements we aim to reduce that to less than 15%.
Business Case
11.7% Lower LCoE
“The novel substructure is made from concrete and has several advantages over conventional foundations”
Business Case
In 2020 OWLC engaged globally recognised renewable energy consultants BVG Associates to deliver an independent cost analysis of the Gravity Tripod™.
In order to create their report BVG assessed the costs and LCOE for the project using the Gravity Tripod and compared this to a project using a conventional foundation, in both cases it was assumed to be a 504MW farm. The cost and energy elements that were used to estimate the LCOE were development, turbine, foundation, array electrical, installation, transmission, OMS, energy production, construction timing and decommissioning.
The Gravity Tripod key areas of cost advantage were found to be
- Speed of Construction
- Installation Cost
- Structure Cost
- 100 Year Design Life
Speed of Construction
The Gravity Tripod™ builds offshore wind farms faster. The simple 2 lift installation process (in weather conditions other designs are not able to install in) significantly reduces cost reduction by bringing forward revenue and reducing debt finance payments..
Installation cost
The Gravity Tripod™ was found to be 51% cheaper than a Jacket substructure and 36% cheaper than a Monopile to install – due to its embedded design that allows installation of a complete turbine in one day.
Structure Cost
The Gravity Tripod™ has been found to be 33% cheaper than a Jacket substructure for serial production. The mass manufacturing techniques used to produce the pre-cast concrete components facilitate a production line process that is an order of magnitude faster than the most efficient competitor.
100 year design life
Unlike most substructures that have a 25 year design life, the Gravity Tripod™ has a 100 year design, making re-powering practical and easy to achieve. The Gravity Tripod™ is also designed for turbines up to and beyond 25 MW.
Manufacturing
Production rate of 4 per day
“The component based design not only allows for extremely high production rates, but also distributed manufacturing and local jobs”
Manufacturing
In 2022 OWLC, together with our engineering partner Arup and construction partner Fuchs-Europoles, conducted manufacturing and assembly testing of the Gravity Tripod™.
The project went from a blank piece of paper, through a design, manfuacturing design, homologation, creation of the formwork, casting of the components, and assembly of the structure in an incredibly short period of only 3 months. The assembly testing demonstrated an unparalelled produciton rate for the structure, in less than 4 hours (over two days) the structure went from pre-cast components to fully assembled. On the first day the base components were assembled, pre-tensioned, and the seams were grouted, in only 3 hours. On the second day the structure was post-tensioned to the full working load, and the columns installed in only 45 minutes! Our construction modelling shows that the overall structure is expected to be able to be assembled in 3 days. With a medium sized port being able to work on 12 structures at any one time we expect to have a production rate of 4 structures per day (a rate that corresponds to our expected installation rate.)
THE GRAVITY TRIPOD’S MANUFACTURING ADVANTAGES ARE
- Use of Concrete
- Component Based Design
- Mass Manufacturing
- Speed of Assembly
USE OF CONCRETE
The Gravity Tripod uses concrete as opposed to steel. Not only does this mean the structure has a lower embedded carbon content than competitors, but also as a low cost material with less commodity price fluctuation benefits projects through mitigating their supply risk and hedging position.
In addition, as a concrete structure there is an extensive supply chain already in place. As an example the UK consumes 90m tonnes of concrete a year, just 3% of that is enough to supply all of Europe’s offshore wind substructure needs with the Gravity Tripod™.
COMPONENT BASED DESIGN
As the Gravity Tripod™ is manufactured from pre-cast concrete components, it is ideally suited to developing local supply chains. Manufacturing of components can be dsitributed across multiple sites creating employment in deprived areas and allowing smaller ports to feed the fast growing offshore wind industry. Meanwhile, the ready availability of concrete as a material, as well as the skills and loabour required to work it, means there are no restrictions to the Gravity Tripod™ creating local jobs.
MASS MANUFACTURING
The Gravity Tripod™ is designed for mass manufacture. The key components, the concrete columns, are made with a spin-casting technique that is fast and efficient. With a spinnning machine able to make 1 column per day per mold scaling of manufacturing is easy, and cost effective.
SPEED OF ASSEMBLY
Not only does the Gravity Tripod™ be manufactured locally, it can also be assembled close to the project where it is to be installed. The post-tensioned design means that the structure is simple to assemble, with even medium sized ports having space to work on 12 structures at any one time a produciton rate of 4 per day is expected, mirroring the installation rate.
Installation
Fast, Low Risk, low Cost Installation
“An order of magnitude faster to install, with less weather downtime and no seabed risks”
Installation
The Gravity Tripod™ originated from work to reduce construction time, cost, and risk. Employing offshore oil and gas techniques of “construct onshore, install offshore” the Gravity Tripod™ significantly reduces construction times, bringing forward revenue, and reducing debt costs, benefiting all.
With a modelled installation rate, backed up by evidence from other gravity base installation campaigns, of 4 structures per day the Gravity Tripod™ is an order of magnitude faster to install. At the same time the high capacity vessels employed in the installation campaign have little weather sensitivity, are utilised efficiently with the barge fed strategy, while the lack of piling avoids sub-seabed risk.
THE GRAVITY TRIPOD’S INSTALLATION ADVANTAGES ARE
- Faster to Install
- Cheaper to Install
- Less Weather Risk
- No Seabed Risk
FASTER TO INSTALL
With an installation rate of 4 per day (matching the assembly rate) the Gravity Tripod™ is an order of mangitude faster to construct that other substructure designs. The speed of the construction campaign allows developers to commission their projects more than a year earlier saving an example 1GW project over €300m in debt finance costs.
CHEAPER TO INSTALL
The extremely fast installation rate, and high utilisation of the installation vessel with the barge fed strategy supplying structures to the field, means the installation cost per structure is very low. BVG assessed the installation to be 51% cheaper than for competitor designs.
LESS WEATHER RISK
The stability and weather working capability of the high capacity lift vessels, together with the short duration of the installation process, means that the weater risk and weather downtime are both low. Weather window utilisation can be optimised with the barge fed strategy to make the most of breaks in the weather, as such installation both during the early and late parts of the construction season is feasible.
NO SEABED RISK
Placing the Gravity Tripod™ directly onto the seabed, without the need for dredging or rock reinforcement, means that all sub-seabed risk is avoided. The lack of piling completely transforms contractual clauses such as unforseable seabed conditions and the danger of problems in substructure installation campaigns cascading down through the project programme and destroying the business case.
