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Advances in Hub-Height Met Towers Boost Assessment and Power Performance Verification Campaigns

The wind energy industry has traditionally relied on hub-height towers designed for the communications industry. Built-up lattice towers required climbers to install equipment precisely at 60, 80 or even 100 meters in the air. In recent years, the wind measurement landscape has changed rapidly and the result is more accurate wind energy resource and power performance verification campaigns to reduce the financial risk associated with wind farms and boost accuracy in determining energy output from wind farms.

There are now a few tilt-up lattice hub-height met towers on the market to choose from by different manufacturers for different environments. Capital City Renewables (CCR) recently announced that it has become the exclusive dealer and installer in North America for SME Wind, a European manufacturer of a line of lattice and tubular met towers ranging from 30 to 125 meters for the wind energy industry that includes a steel lattice hub-height tilt-up tower. CCR also installs a 100-meter tilt-up aluminum tower that is mounted on a steel plate instead of a cement base, enabling the tower to more easily be installed and reused in a new location.

Because hub height data is so beneficial for wind resource assessment at utility-scale wind farms and power performance verification, these technology improvements help the industry to advance. These tilt-up lattice towers allow instruments to be installed safely on the ground, for high quality data collection and third party verification.

“We can install the sensors, document the installation and all the measurements, and even have other consultants certify the work- all on the ground,” says Dimtcho Linkov, president of SME Wind. “Once the tower goes up, it is fully equipped and working.”

Built-up lattice towers that require instruments to be installed once the tower is erected currently dominate the hub-height met tower market. Installing the anemometers and wind vanes accurately is vital for accurate data to determine the wind resource of a potential wind farm, yet this is a very difficult feat.

Data quality is of paramount importance in the wind industry to determine the financial viability of a potential wind farm or power performance shortfalls. “As the wind energy industry matures, there is greater demand for high quality data,” explains Kiril Lozanov, CEO of CCR. “We are thrilled to work with SME Wind towers, because we can capture very accurate hub height data for our clients with these products, for a very reasonable price. Tilt-up towers are faster and safer to install and remove and save money by cooperating with wind farm construction schedules.”

Lozanov estimates the towers are 20 to 30 percent cheaper than a comparable built-up steel lattice tower. In addition, built-up towers are routinely disposed of after just one use because it is difficult and expensive to dissemble them. SME Consult towers however can be safely decommissioned and put to use at another location because properly lowering a tower doesn’t impact its structural integrity. In such cases, Lozanov estimates that cost savings can reach 40 percent over comparable built-up steel lattice towers.

Tilt-up lattice towers can be easily tilted down and reused in a new location or dismantled and stored for later use. The tilt-up hub height aluminum tower is mounted on a steel plate, allowing for minimal disruption to the landscape and greater ease in reuse.

Because these lattice towers can be climbed, instruments can be replaced without tilting the tower down, greatly reducing maintenance costs and disruption to other instruments. “We often find that one or a few sensors need to be adjusted or replace in the course of a project campaign,” says Scott George, senior engineer for DNV KEMA, in his experience with built-up lattice towers. “Being able to maintain the exact orientation of all the instruments is very helpful when we have to replace an instrument.”

Although hub height met towers are valuable for very accurate wind resource campaigns and power performance verification, the upfront cost is significant. “In the perfect world, all developers would utilize met towers of hub height or higher [for wind resource assessment],” says Jason Lowenstein, Director of Wind Resource and GIS for OwnEnergy. “Such towers, however, take longer to install and are much more expensive than the 60 meter towers; they require a permit from the Federal Aviation Administration (FAA) along with FAA approved lighting. There is always a balancing act between saving money, and minimizing uncertainty pertaining to a pre-construction wind resource assessment campaign.”

Although some wind resource assessment campaigns can get by with a 60-meter tower, hub-height towers (sometimes in combination with remote sensing equipment) are the standard for power performance verification campaigns, which are important for reducing financial risk to the project owner.

“Early on in the development process, the turbine manufacturer supplies a power curve to a developer, which quantifies how much power the turbine will produce at various wind speeds,” says Lowenstein. “When the wind farm goes into operation, we expect [turbine] output to match the pre-construction estimates. If this is not the case, we want to understand why the wind farm is over or under-performing. Power performance testing is the tool that can be used to help understand if the turbine is performing per the power curve provided by the manufacturer.”

Today developers have a much larger assortment of hub height met towers to choose from. Tilt-up tubular towers designed for the wind energy industry, can be reused, and the instruments can be installed on the ground, but the tower cannot be climbed to make repairs and the tower itself can distort data collection. Built-up steel lattice towers are climbable and are strong, but are expensive to install and reuse and instruments cannot be installed on the ground.  Lattice hub-height tilt-up towers that are now on the market combine the positive characteristics of the tilt-up tubular tower and built-up steel lattice tower.

Ultimately, they are reducing financial risk and helping the wind industry to advance. “I think performance verification campaigns have been a driving factor in identifying things that the wind industry needs to learn,” says George.

Lead image: 82 meter lattice met mast, via SME Wind

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