A retired Clipper C96 wind-turbine blade was redesigned as a US transmission pole; engineers found it met ASCE and NESC loads with acceptable deflection

Old wind turbine blades usually end up in landfills. Their size makes them hard to grind up, so most plants can’t recycle them. So a team of engineers asked a simple question: what if a used blade was repurposed as something else, like a power pole? A 2021 study titled ‘A Decommissioned Wind Blade as a Second-Life Construction Material for a Transmission Pole’ in the journal Construction Materials found that a retired Clipper C96 wind blade can be reshaped into a transmission line pole. The blade passed the required loading tests dictated by US engineering codes and had plenty of room to spare.

A blade that would not degrade to trash

Wind blades are built to last. They are constructed from glass fiber encased in strong resins. This is precisely what makes them difficult to break down. Most blades can operate for about 20 to 25 years. However, most of them are retired much earlier. As wind farm technology advances, larger and more efficient blades are installed. The magnitude of the waste is considerable. The study, ‘Wind Turbine Blade Waste in 2050,’ found that global blade waste could reach 43 million tonnes cumulatively by 2050, with annual waste climbing to about 2.9 million tonnes a year by then. This figure has led to efforts by scientists to find practical second lives for old blades. The goal is to reuse them instead of sending them to landfill.

From wind farm to power line

The Construction Materials research was conducted by scientists from Georgia Institute of Technology and Georgia Southern University. They were exploring the concept referred to as BladePole. In practice, a section of a retired wind blade is set vertically and used as a standalone pole, directly carrying power lines as one structure in a series along a transmission line, the same role a traditional steel monopole would fill. The team used a Clipper C96 blade for their design. This blade had a tangent pole design capable of carrying a 230-kilovolt power line. The pole had a height of 31.7 meters or 104 feet. Steel connector plates were bolted to the spar cap, which is the strongest section of the blade's construction, and these plates held the arms that carry the power wires.

This wasn't the group's first attempt to explore the concept. Their previous paper, 'Structural Analysis of a Wind Turbine Blade Recycled into an Electrical Transmission Tower,' was a similar concept but a bit different. The previous design was for low-voltage lines, carrying 69 or 138 kilovolts. The newer study pushed the idea further and aimed for a higher-voltage line, with poles spaced farther apart.

Putting the blade through a stress test

A power pole doesn’t just need to appear strong; it must be able to survive harsh conditions. United States utility companies use very strict manuals to verify that the poles are up to standard. The researchers tested their BladePole design using two different manuals. The first is the American Society of Civil Engineers' standard for transmission structures, ASCE 74. The second one is the National Electrical Safety Code, NESC. These codes describe all worst-case scenarios that a pole should be able to withstand. Examples include high wind gusts, severe ice loading, and wind and ice in combination. Another is a snapped power line pulling hard on the pole. The team ran each scenario through structural analysis software. They checked the stress at many points along the blade's length.

The numbers that mattered

The results appeared to be reliable. The lowest safety factor across the pole was 4.19. It occurred in the area where the blade's exterior experienced the greatest wind pressure. A safety factor greater than 1.0 is an indicator that the structure is able to bear loads higher than what is expected. A safety factor greater than 4 indicates a good safety factor. Bending, or the extent to which the pole bends when stressed, was also within acceptable parameters. The largest sideways bend was about 315.5 millimeters. The largest lengthwise bend was about 495.4 millimeters. These fiber-reinforced composite structures are designed to flex considerably under load without losing structural integrity, which is why the allowable threshold is set relatively high: both figures were well below the maximum 2.538 meter threshold as per industry recommendations.

A small study with a big idea

The researchers were careful to describe their work as a preliminary study. They noted that it is still a work in progress and that further testing was required. This includes tests on the aging of the material over time. Checks are also made on complex forces such as wind-driven vibration. However, the early returns look promising. A blade bound for the landfill might instead be carrying electricity for decades. The idea also fits into a larger pattern in the construction industry. Some utilities already use fiber-reinforced polymer poles, which have a longer life than normal steel, concrete or timber poles, the study says. Old wind blades are made of similar glass-fiber material. So making them into poles isn't such a leap as it sounds. Thousands of blades will retire in the coming years. This early study offers a promising place to start.