The MonoBase Wind concept from ORCA Offshore promises to solve the problems associated with installing a large offshore gravity base. Managing director Herm Bussemaker explains how this novel turbine installation system can benefit the offshore wind sector.
Herm Bussemaker: MonoBase Wind is a foundation concept for wind turbines - a special design for deeper-water and larger turbines. It basically solves the problem of transporting and installing the foundation. The main idea is to transport and install the foundation and the wind turbine as one complete unit in one offshore operation.
Assembly takes place inshore - which involves installing and building the wind turbine, and attaching the turbine blades under controlled conditions - and when that's all finished, you can go out and install it. This saves you the cost and hassle of hiring expensive offshore construction vessels, and also eliminates the risk of delays as a result of bad weather.
The idea came from an offshore operation that I was involved in as assistant superintendent, during which we lowered large foundation legs using a strand jack-based lift system. The jacking went smoothly, but building up and removing the lift system took a lot of time and money. So when I went home, I tried to develop ideas on how to lower a foundation to the bottom without using strand jacks, in a way that was suitable for wind turbines.
The obvious answer is to just ballast it down and set it on the bottom. When lowering a single leg foundation, however, it can lose stability and capsize; you need to have temporary supports in place to keep it stable. I decided to split the foundation into two concentric sections, which appeared to solve the stability problem during lowering.
It's a concept that can accommodate large water depths and big wind turbines. This will obviously bring the cost down per installed megawatt.
Another important feature of the concept is its reduction in project cost exposure related to weather delays and fluctuating vessel rates.
The gravity base solution is a standardised solution with well-known challenges. It is a technology that currently seems expensive compared with other solutions, but you must remember that many other solutions are already mature, so their costs have gone down as their designs and logistics were optimised. I think gravity base solutions are promising and can be cost-effective when they are scaled up for use with larger wind turbines and water depths.
This is quite an exceptional project because the client specifically asked for gravity base solutions. They also specified that it should be a single-offshore-operations solution, which means that the wind turbines should be assembled onshore and installed as one combined unit. There are a few other solutions available at the moment that can do that, but I think that if you examine the technology and costs involved, MonoBase is the most effective solution.
I don't think gravity base technology will completely replace all other solutions, but I think that in locations with difficult conditions, gravity bases could claim quite a large share of the market - say, 5-10%.
We're currently at the conceptual design phase. We have engineered the concept at such levels that we are confident in its technical aspects, and are now reviewing what kinds of cost savings we can achieve. We are planning to perform model tests and further engineering in order to explore the concept in more detail. This is an exciting time for us.