Competition

“Current Installation methods rely on specialist vessels such as heavy lift, drilling rigs and DP2 vessels at expensive day rates more typically used within the oil and gas industry”

Gravity Based Foundation Installation

Generally gravity based foundation solutions require large heavy lift capabilities to install the foundations to support the turbines and solid ballast to secure the foundations in position.

At utility scale the foundations are typically over 350 tons and require jackup rigs costing circa £250k per day making the installation a multi-million pound excercise typically £3.5m to £8m contract.

A jackup is required since the vertical heave forces caused waves cause huge and dangerous snatching loads when lifting heavy objects subsea.

Jack-up rig used to install the MEYGEN foundation structures and ballast blocks weighing up to 400t.

Alternatively, using large installation barges such as the OpenHydro Installer severely restricts the weather windows and seastates that installations and recovery of tidal turbines. Only very slight seastates can be used which limits the operational availability of the turbines if a shut down or problem occurs offshore. It has been shown over 6 months delays have occured in energy generation in several examples.

A case in point is the OpenHydro installer, gantry crane barge where they deployed their open centre turbine in Nova Scotia. A simple electrical failure shut it down within 2 weeks of installation but the tidal turbine couldn’t be recovered for 6 months due to weather conditions and availability of marine vessels.

OpenHydro’s Installer which is a gantry crane barge used to install 1300t OH turbines and foundation together. Note the sea state.

Tidal Turbine Installation

Utilising DP2 vessels to install and retrieve utility scale tidal turbines is also common place. Typically DP2 vessels cost circa £100,000/day and you can’t charter one for a single day. This makes the installation and retrieval of tidal turbines a multi-million pound exercise.

Typical examples of DP2 installations are show below where Aker Wayfarer was used to install a utility scale tidal turbine. This vessel is 16,600 tons and looks slightly disproportionately large for the tidal turbine. Note the very slight sea state of this marine operation.

Aker Wayfarer DP2 vessel which are typically used to install and recover utility scale tidal tubines.

The other issue with the DP2 vessel installation is the requirement of a wet mate connection with the foundation structure. These connections have a significant bearing on the overall cost of the turbine along with a yawing control system.

Monopile and Pin Pile Installation

The offshore wind community technology has converged on monopile and pin pile jacket solutions. This is mainly because the field sizes of over 100MW the massive cost of the jackup’s required to installed them are offset by number of units installed.

Monopiled solutions also require DP2 vessels to deploy the drilling rigs and the tidal turbines with a wet mate connection and yawing control system. The environmental costs is also significant given the noise of the drilling and also the grouting which introduce potential issues with habitual behaviours of marine mammals, birds and other marine fauna.

Installation vessel used to support the drilling operation at EMEC.
Subsea drill rig being installed onto the seabed.

Floating Platform Installations

Floating platforms are often considered the cheaper alternative to seabed foundations and despite this largely being the case there are other short comings which make them expensive deploy and maintain.

Floating solutions clearly need moorings to connect into and in tidal areas these are difficult and expensive to install and maintain. This often requires multiple marine operations. Any mooring needs to checked, typically on an annual basis, replacing fair wear and tear items.

The power take off and export cable is possibly the most important part of the power train since any break of this vulnerable component will result in loss of power generation and income. Putting this component in a highly dynamic and complex loading environment is very challenging. It often results in the use of slip rings for power transmission which require constant maintenance and loss in efficiency.

The other main issue with floating systems they are significantly effected by wave motions often having to be de-powered to cater for the extreme loading on the turbines, and rotating machinery.

Typical mooring solution and power export cable for floating platforms exposed to highly turbulent, dynamic loading.

Decommissioning

Decommissioning costs are a serious consideration when using this method of installation of the foundation. Recent experience from the removal of MCT’s tidal turbine in Strangfrod Lough has shown that the removal costs can rival the installation costs at a reputed £5m price tag.

Heavy lift vessel Rambiz used to install 1000t MCT tidal turbine foundation.
Seagen in maintenance condition above the water.
Decommissioning of Seabed Phase I -Turbine removal
Decommissioning Seagen Phase II – Cross beam removal
Decommissioning phase III – Cutting the pin piles
Decommissioning Phase III – Removal of quadrapile.

RSS
Follow by Email
YouTube
YouTube
LinkedIn