Greentech Media got an early look at GE’s new space frame wind turbine tower in advance of its official debut at next week’s European wind industry conference.
The space frame advances the potential of GE to deliver taller towers capable of more power production at a lower cost.
The GE Tehachapi facility’s enclosed-lattice, five-legged space frame prototype is 97 meters tall with a “brilliant” GE 1.7-megawatt, 100-meter rotor turbine on top. GE will introduce a 139-meter space frame for its 2.75-megawatt, 120-meter rotor turbine at the EWEA conference March 11.
A space frame is a three-dimensional structure built on struts locked together. These structures can accommodate very heavy weight with limited materials and supports.
Open lattice towers were used for early utility-scale wind turbines with unfortunate results. Bolts wererattled loose, leading to structural failures, and birds took up perches, leading to serious avian mortality.
In searching for a way to cut costs, GE engineers returned to the lattice. But the space frame eliminates danger to avian life by enclosing the lattice with a translucent, non-weight-bearing, UV-protected PVC-polyester fabric coating.
And it eliminates structural failure because of splined bolts, explained GE Wind Products General Manager Keith Longtin.
“The direction of the wind industry is higher hub heights,” Longtin said. “But tube towers scale poorly because increasing load and material requirements do not pay off in increased output.”
GE’s R&D goal is to scale towers up and keep costs down. The space frame’s ten-meter diameter base will allow a 120-meter tower to use 20 percent to 30 percent less steel than a traditional 100-meter tube tower because the broader base means less support is needed from the tower walls.
Another benefit of the larger tower base is that advanced power electronics and battery storage capability can be housed inside and protected from weather and vandalism.
Because the space frame narrows at its top, it can interface with any nacelle without structural alterations.
One of the two key design parameters of the space frame, Longtin said, was limiting all parts to the 40 foot size of a standard shipping container so all the pieces of a tower can be delivered by long haul trailers. That should have a significant impact on transportation logistics.
Turbine manufacturers now deliver tube towers in three 30-meter-long, 60-ton sections. It requires special vehicles, elaborate planning and permitting and, often, police escorts.
The space frame will arrive in shipping containers. On-site assembly will replace complex transport logistics. It took about 30 days to assemble the Tehachapi prototype, but Longtin believes the average assembly time can be four days.
The other key design parameter was that the fastening system be maintenance free. The space frame’s splined bolts, once inserted, are essentially like rivets. They have long been the standard, maintenance-free fasteners used in bridges, aircraft carriers, and skyscrapers. Accelerated testing by GE engineers and third party labs validated the maintenance-free durability of the GE splined bolts.
The cost savings from the space frame will be site specific, Longtin explained. Savings from reductions in materials, shipping time and costs may be offset by increased on-site labor and time.