IN DEPTH: GE's space-frame tower
High in the Tehachapi Mountains north of Los Angeles, GE has unveiled its space-frame turbine tower, a steel and architectural fabric concept seen as a breakthrough in the campaign to cut the capital cost of wind power.
The design, launched at EWEA 2014 in Barcelona in a 139-metre version topped with a 2.75-120 GE turbine, is build around an “Eiffel-tower-like” lattice structure clad with high-tensile polyester panels.
The technology could carve “a large slice” out of the price of a conventional tubular tower by streamlining fabrication and transportation, while opening up the possibility of ultra-tall 150-metre turbines.
“When we started doing this project, I and a lot of other people had reservations about how it would look. Seeing it up, everyone is converted,” Keith Longtin, GE’s wind product-line general manager, tells Recharge.
“It is a leap forward for the industry. It... shows clearly there is great potential for cost-effective scale-up of wind turbines with much taller towers.
“The industry is moving toward taller towers, that’s no secret. And when you get up into the 130-150-metre-plus technologies, the material cost savings go from being 20-30% lower [for a 100-120-metre tower] to closer to 40%.”
GE expects the tower to be a “perfect fit” for the emerging markets of lower-wind and heavily forested sites in Scandinavia and the rest of Northern Europe. “The next round of permits going out in these regions, they are looking for 140 metres,” notes Longtin. “And our design can be extended in 12-metre sections, so we can go still higher, as required. The physics aren’t limiting.”
The 97-metre-tall prototype was assembled with a 1.7MW 1.7-100 turbine at Tehachapi, where a three-month testing programme begins this week.
The prototype took a month to install, but GE expects to whittle that down to “around four days, like a conventional tower”.
“Overall time of construction will be the same, material usage much less,” Longtin adds. “Once the panel material was decided on, that drove us toward the five-legged design and overall architecture. The beauty of it is that you are not constrained by diameter.”
Conventional steel tower sections must be less than 4.3 metres wide to be manoeuvrable under bridges and along most roads. The space-frame tower, designed with a maintenance-free bolting system, can been packed up in a dozen freight containers and trucked “pretty much anywhere in the world you want it”, says Longtin.
“Shipping a 150-tonne steel tower section to some of the more remote locations where there is little or no road infrastructure is a real challenge. With the new tower, everything changes,” he says.
Project leader Kathy Verna adds: “When you are transporting huge tubular tower sections, you are talking fleet permits, weather delays, restrictions on travelling through certain areas at certain times. With the space-frame tower, all the parts [supplied by a ‘Midwest manufacturer’] were onsite in California two days after our phone call.”
One of the hidden benefits of the five-legged design, notes Longtin, is its stability in seismically active zones. “In earthquake-prone areas you are going to have a big advantage over tubular towers — our tower will be much more stable.”
The modular design also means the component parts can be built on assembly lines, speeding up fabrication and honing quality control.
“This project has required an entirely different business model — from how engineering interacts with project development and sourcing and supply chains,” concludes Verna.