Blow the wind southerly: load cells and wind turbines
Wind turbines are a common site now in the UK, whether spread over high hillsides or spinning gently on the horizon out to sea. Despite the initial scepticism, wind power now provides a very significant proportion of power to the National Grid. In December 2019, the winds of Storm Atiyah resulted in a record-breaking day when wind turbines contributed over 44% of the total British power needs for that day. That compared with nuclear power (20.5%) and gas (12.8%) on the same day.
Load cells and turbine testing
Load cells play an important role in almost every stage of a wind turbine’s life cycle, including initial testing, development and monitoring to ensuring their stability in real-life conditions. Load cells can also be used to test aspects of the wind turbine tower including:
- Mounting platform loads
- Turbine blades structural monitoring
- Tower and blades tensile strength
- Compression and bending stresses
The Maine attraction: load cells and floating wind turbines
Most offshore wind turbines rest on some sort of structure on the sea bed. However, as explained in an article for the Maine News, the Gulf of Maine is too deep for this seabed method to be viable. Instead, a team led by Habib Dagher, executive director of the University of Maine’s Advanced Structures and Composites Center, created floating concrete hulls that enabled wind turbines to float rather than be tethered to the seabed rather than placed on it.
“The mooring system for the offshore floating wind turbines were tested at the W2 wind-wave basin at the center’s ocean engineering lab. The forces recorded by load cells on the one-eighth scale prototype deployed off Castine were very close to what were predicted by the models in the lab.”
The test results suggested that it would take a 500-year storm and 70-foot waves to move a tethered floating wind turbine tower just seven degrees off vertical.
Keeping wind turbines stable
Stability is key to optimum performance for a wind turbine. Most land-based turbines will sit on large concrete foundations, or hard natural rock, and their base secured into place by massive bolts. An article on a rock anchored wind turbine foundation, shows just how many bolts are required, and it’s easy to see from the photos how the four load cells have been installed to measure the effectiveness of the lock off bolts.
How much does a wind turbine weigh?
The weight of any large structure is important for its initial installation when this involves craning or lifting into place. Once in place, any change in weight overall or weight distribution could indicate stability issues, and will also affect the efficiency of the turbine itself.
This is especially true of the turbine’s rotor blades. If they are not identical in weight, the whole blade assembly will be unbalanced and potentially loosen other parts as well as being less efficient. By attaching load cells to the rotor blade root, and tips, each blade can be precisely weighed. It’s a long job which can take up to two hours, so load cells with a low creep are required.
However, blades can become unbalanced over time as wind-born particle of dirt or salt can attach to the blades, unbalancing them and reducing the turbine output by as much as 15%. It is a major concern as the dirt and salt can also erode the blade, so it’s important that every blade is properly monitored.
Retiring turbine blades in the US
Turbine blades are usually renewed every 25 years. So those installed in the early days of commercial wind farms in the 1990s are now reaching the end of their working life. Unfortunately, the fibreglass blades cannot easily be recycled and are literally piling up at a ‘turbine graveyard’ in Wyoming, USA. In time, they will be cut up and buried. It’s not very eco-friendly, but there are few other recycling options.
One is pyrolysis, which involves heating chopped up blades to break up the composite fibres, making them available for reuse in glues, paint and concrete. The process can also produce synthetic gas to power engines, and a form of charcoal which can be used as a fertiliser. The downside is that pyrolysis itself requires large amounts of energy. Needless to say the environmentally conscious Dutch found another great solution – turning decommissioned turbine blades into a children’s playground.
More modern blades are made from carbon fibre and are growing in size too; the new generation GE Haliade-X wind turbine has blades 107metres long. This offshore wind turbine yields 45% more energy than previous generations, at 12MW.
Load cells for all your testing requirements
Need load cells to test and monitor your latest project or prototype? Call us. We manufacture and design our own exceptional quality load cells here in the UK. So whatever type of load cell you need, whatever size, call us first. Or browse our online shop for quick delivery and cost-effective prices.
