The rapid growth of the onshore wind industry is providing the world with an important source of renewable energy. To scale up and achieve the outputs needed, turbines are increasing in size, whilst a greater range of wind farm locations are being considered in order for higher yields to be gained from stronger winds.
However, these positive changes also present challenges in how the construction of wind farms can keep pace to ensure projects remain efficient and cost-effective. These challenges are interrelated – Mammoet explores what can be done to ensure wind farms are brought online as quickly and safely as possible.
What’s happening now?
Balance of plant (BoP) work is a major part of onshore wind projects; roads and other infrastructure may need to be upgraded or changed to accommodate transport movements, whilst hardstands are needed to allow the erection and operation of cranes. There is a significant cost involved in this kind of civil work, which means a middle ground must be found between facilitating smooth logistics and the expense of achieving it.
The planned lifting methodology and site logistics will have a major bearing on how this is done – the larger the footprint of the cranes selected, the greater the increase in road width and size of hardstands required. In terms of ground bearing pressure, spending less money on civil works can result in low axle capacity, which will in turn increase the time needed to relocate mobile cranes (and parts of tower cranes) and therefore mean greater costs.
Bigger moves mean bigger challenges
The sheer scale of modern WTG components presents challenges for the transport scope. Where 1.5 MW nacelles weighed around 60 t in the past, the 4 - 6 MW nacelles of today can be up to 136 t, whilst blades can measure over 80 m. This growth in size and weight means more work to get them safely and efficiently to site.
Transporting these gigantic blades, lower tower sections and nacelles on public roads increases the need for expensive route modifications and often requires permits and police escorts to be arranged. Alternative longer routes can often be found – but these may add hundreds of kilometers to journeys and impact later lifting and installation phases.
The nature of the transportation challenge is heavily dependent on other phases – for example, the date on which a specific number of components need to be on site for installation will govern what options are viable in terms of transport routes and associated permits, escorts and so on. It is therefore important to consider the interface between phases when preparing the execution plan.
Fewer lifting options
The trend towards larger turbines is of course also a major challenge for lifting operations. Whilst around 10 years ago the average turbine tower stood below 100 m hub height, today they are commonly above 160 m. Most of the commonly-used wind turbine erection cranes have a maximum hook height of 180 m, which means we are starting to operate at the upper limits of existing technology.
In turn, this demand to lift higher and heavier means that there is a smaller number of suitable cranes available globally – so at best equipment must be deployed from further afield and at worst projects are delayed until the right crane is available. Larger cranes also typically need a larger area to operate within – requiring more BoP work on the likes of hardstands and access roads.
An important related consideration here is the assembly and relocation process, as the time taken to disassemble the crane when a turbine is completed and move it to the next pad has always been crucial to the success of a project.
The work involved here is largely dictated by the type of crane being used. Truck-mounted mobile cranes such as the LG1750 require near-total boom disassembly before they can be transported from pad to pad, whereas crawler cranes could in theory relocate fully erected if site conditions allow and boom configurations are simple enough – although they are often fully dismantled between assemblies as this minimises BoP work. Tower cranes can present a more efficient option depending on project requirements but need to be almost fully dismantled between pads.
What are the current solutions?
With this range of interrelated issues at play, it is important to take a holistic view across the entire project to identify where savings – or indeed investment – may yield greater benefits further in the schedule. Here we look at some specific examples of where this approach can improve project efficiency.
Close co-operation to streamline BoP
Optimising BoP work means more efficient movements to and around site – savings that are multiplied many times over across the project. But this cannot be done effectively without taking full consideration of the crane and transport equipment that will be used. For example, there are many factors affecting the choice of the right main crane and hence civil work requirements – such as a crawler crane requiring different BoP work to a tower crane.
As civil works can have a huge effect on productivity and depend so closely on the choice of crane, close co-operation between developers, OEMs and crane providers is vital to optimise overall project costs during wind farm construction.
Specialist equipment can optimise operations
Specialist devices such as blade lifters and tower clamp trailers can be used to avoid the need for expensive route modifications or detours that are common with larger WTG components. Although this may add to equipment costs, these are typically offset by the greater potential savings in allowing a quicker route to be used with fewer modifications.
Taking a broader look at the equipment available can also help to overcome issues during the installation phase, too. For example, due to a lack of suitable equipment in Argentina, Mammoet created a pedestal solution using self-propelled modular trailers (SPMTs), which allowed wide track crawler cranes to be relocated along 6 m roads designed for smaller equipment. This was also beneficial because the narrow track crane that was originally specified needed partial dismantling between assemblies – taking 15 hours. However, with this solution, the company was able to relocate a fully assembled crane in just five hours, which meant significant extra schedule savings.
What solutions might exist in the future?
There is a general belief that the weekly turbine installation rate depends on just two things: how fast the main crane can lift?and how fast the main crane can relocate. But this is in fact an oversimplification; there are many other activities that must occur during this phase such as placing outrigger mats, installing counterweights and booming out. These activities could be optimised with the use of a small telescopic crawler which would just track about the hardstand lifting and carrying everything in its path efficiently. Although this will never drive hardstand to hardstand at the same pace as a mobile crane, it would save a significant amount of time across the project as a whole.
Smarter ideas for more efficient projects
Close collaboration between all those involved in onshore wind projects is not simply a benefit for current projects, but is also proving invaluable in finding new, more strategic solutions to the industry’s biggest future challenges. This has allowed Mammoet to develop a number of new technologies that will help the wind farm of the future to become safer, more efficient and more profitable.
More sustainable groundworks
Enviro-Mat is a product that can be added to a mixture of site soil and cement to produce either temporary or permanent pavement for roads, lay down areas, hardstands and crane pads. The resulting surface can be constructed to easily achieve the typical ground bearing pressure of 25 – 30 t/m2 (even up to 50 t/m2) – sufficient for large crawler cranes and their loads.
During past projects, Mammoet has been able to cover areas as large as 5000 m2 in a single day, so should crane requirements change at short notice, roads and hardstands can be built to compensate for this in a way that allows build work to continue quickly. Once it has been used, Enviro-Mat can be crushed and returned to the soil with no environmental impact.
Crane technology needs to keep pace with increasing hub heights, which is why the company has designed the LTC4,000 – a tower crane with a maximum hook height of 222 m and the capacity to lift 200 t at a 20 m working radius.
Importantly, the LTC4,000 operates on a comparable hardstand area to smaller, existing tower cranes. Which means that developers can install taller generations of turbines without the need for additional BoP work.
The LTC4,000 is free-standing, meaning that it can be used with any future tower type without the need for design modification. It is capable of operating in wind speeds of up to 15 m/sec; mitigating project risks by extending the length of time during which the build can occur.
Looking further to the future, we have also been approached by tower manufacturers to create tower installation solutions capable of taking on the 200 m hub height challenge. This has resulted in a range of prototype solutions based on a variety of different technologies, from concrete telescopic towers, though lattice tower sections, to the use of climbing cranes.
Research into alternative lifting systems has shown they can offer significant benefits, such as reduced working at height and more simultaneous turbine assemblies.
One such innovation is the Wind Turbine Assembly (WTA) climbing crane, which uses the turbine’s tower as its point of support – meaning the only limit on lifting height is the tower itself. It has a capacity of 150 t and climbs each turbine tower by means of supports at flange level of the tower. For maintenance projects, the Wind Turbine Maintenance (WTM) crane has a designed capacity of 40 t, although this can be scaled up or down depending on turbine type. It does not require supports at flange level, but instead uses hoists to pull itself upwards, and claws to keep the load steady.
Both cranes require no ground reinforcements and are cheaper to manufacture than conventional cranes – improving the availability of lifting technology for greenfield and maintenance projects.
Taming inhospitable locations
Over the next decade, we will see greater numbers of wind farms built in more inhospitable locations, with alternative and taller towers growing beyond the reach of all but the largest cranes. Executing these projects within developing economies will provide further challenges – and increase the importance of working together across the supply chain to find the most efficient and effective solutions.
Mammoet has successfully executed projects in very remote locations such as South Sulawesi in Indonesia, Garayalde in Argentina, and right in the middle of the Saudi and Omani deserts.
For example, in Thailand, the company worked closely alongside its customer to transport, lift and install 13 turbines, covering over 1000 km in the process. The project required careful logistical planning, given the distances involved and infrastructure between source and site.
Together we can be smarter, safer and stronger
As with any other rapidly maturing industry, onshore wind faces a number of challenges to reach its true potential – many of which concern the work required in getting components to site and installing them efficiently.
As we have seen, it is possible to overcome these challenges if developers, contractors and suppliers take a holistic view of projects and work closely together from the planning phases right through to installation and maintenance.
For more news and technical articles from the global renewable industry, read the latest issue of Energy Global magazine.
The Spring issue of Energy Global features a varied spectrum of in-depth technical articles detailing recent projects, future projections, and technological advancements in the renewables sector, from companies including GlobalData, Atlas Copco, Watlow, QED Naval, TRACTO, AB Energy, and more.
Read the article online at: https://www.energyglobal.com/wind/31032021/mammoet-explores-the-costs-associated-with-onshore-wind-energy/