[Editor's note: Kiril Lozanov, CEO of Capital City Renewables, is the husband of author Sarah Lozanova. Capital City Renewables installed the aluminum lattice meteorological tower that is the subject of this article.]
In recent years, wind turbine technology has advanced considerably, with many onshore industrial-scale wind turbines in the U.S. now standing at 100 meters and capable of powering more than 1,000 households.
Although turbines have advanced greatly, the wind assessment technologies used to determine if a site has suitable wind resources and is economically viable have not kept pace. A recent development, however, is boosting wind data quality, while also reducing the environmental impact and cost of wind data collection.
Capital City Renewables recently installed a 100-meter aluminum lattice meteorological tower in Colorado, the second tower of its kind in North America. It is unique in that it is made of aluminum, instead of steel, and mounted on a steel plate, rather than a cement pad. It can also be climbed and easily moved by tilting it down. This tower lets wind developers assess wind resources at various heights, including at the hub and the turbine off the ground, not including the blades.
The tower was specifically designed to meet the needs of the wind energy industry, a relatively new industry that is struggling to assess wind resources at increasing heights. The majority of the hub-height towers currently in use by wind energy developers were designed for the communications industry. Although they are proven reliable, the needs of the two industries are different. This results in wasteful practices that are both expensive and resource intensive.
"Communication towers are designed to remain in a given location for decades and the weight of 100-meter steel lattice towers requires them to be mounted on cement," says Kiril Lozanov, CEO of CCR. "These towers are really cumbersome to install and wind developers usually scrap them after just one use, instead of moving them to a new project. This is a wasteful practice that doesn't allow developers to make good use of their assets. The wind energy industry generally uses meteorological towers for one to three years per project during the pre-construction phase, so our structures do not need to be permanent."
A 100-meter steel tower with equipment costs between $160,000 and $200,000 to install, maintain and remove, according to Lozanov. In contrast, an aluminum lattice tower costs between $120,000 and $130,000, and much of the tower can more easily be reused. He estimates it can be utilized and moved to a new location up to 10 times, although it hasn't been achieved yet because it is a new product.
It is also less complicated to install a tower on a steel plate than cement pad. "It's easier to approach a landowner to receive permission to mount a tower on a steel plate," says Lewis Gunn, director of operations for Baseline Renewables. "A lot of farmers don't want concrete going into their land and some of it usually gets left behind once the tower is removed. Typically the cement is removed only to the depth specified in the lease."
Next page: Lower costs, greater flexibility
The other towers in widespread use by the wind industry are tubular towers mounted on steel plates. Designed specifically for the wind industry, these towers can reach heights of up to 80 meters but cannot be climbed and must be lowered to repair or replace equipment. A 60-meter tower costs between $30,000 and $35,000 to install, maintain and remove, according to Lozanov.
"Climbable lattice towers will likely become more common due to the simple fact that it requires fewer resources to service the towers and accompanying sensors," says Amy Sue Karshbaum, crew leader for CCR. "As a result, it will be less expensive to achieve a higher standard of data quality for the client."
Greater flexibility in wind assessment tools give developers more options, says Katy Briggs, senior engineer at DNV Kema. There are many factors at play which could jeopardize wind projects, including market changes or permitting. Mobile towers, however, can help developers recoup some of their investment because they can move the equipment to another site if a project falls through, Briggs says.
Remote sensing technology is another tool for wind energy assessment. LIDAR uses light waves while SODAR uses sound waves to assess wind speeds up to 200 meters. It is a less reliable technology that is not always well-received by banks when obtaining financing for wind farms. Remote sensing equipment is currently used in conjunction with meteorological towers.
"The value of remote sensing is that you can often get a measurement [of wind speeds] above hub height," Briggs says. "Knowing what is going on across the full turbine rotor helps you better estimate [energy] production. Sometimes the wind doesn't increase as much as you would think up the top of the rotor and you wouldn't know that if you didn't measure the wind across the top of the rotor. Remote sensing can provide that data."
As the wind energy industry continues to advance, accurately assessing hub-height wind speeds is a perennial challenge for developers. Lack of reliable hub-height wind data often results in lower financing levels for a given project, but developers are cautious about investing large amounts of money into a project that might not be built. The new hub-height aluminum lattice towers may help the wind energy industry reach new heights by lowering development costs, while boosting data quality.
"Certainly the trend is going upwards," says Gunn of Baseline Renewables. "Typically, the higher up you go, the stronger the wind."
Image of aluminum tower by Kiril Lozanov.