Conventional wind turbine blades are usually located upwind
of the tower, which causes the wind to push the blades back
toward the tower in operation. Therefore, the downwind
architecture of the exascale blades will prevent them from
accidentally striking the tower.
Loth believes that the ability to fold the blades together will
eliminate cantilever loads ten-fold, and will allow his team to use
much lighter blades built in segments, which would reduce the
cost of the turbine substantially.
Applying Lessons Learned
Back in 2009, Sandia started working on a design for a
13-MW system that uses 100-meter blades on which the
initial segmented rotor designs are based. The project helped
demonstrate that load alignment can dramatically reduce peak
stresses and fatigue on the rotor blades.
In contrast, conventional upwind blades need to be stiff to
avoid fatigue and eradicate the risk of tower strikes in strong
winds. Thus, they are expensive to manufacture, deploy, and
maintain beyond 10-MW to 15-MW. For the 50-MW turbine,
Griffith proposes placing a trunnion hinge at the base of the
blades, which can be controlled to fold up when winds exceed a
high speed value, such as 100 mph.
Extreme scale turbine blades cannot rely on stiff blades due
to the increased mass and gravity loads, which are also directly
related to cost. The new blade design could be manufactured
in simpler, more cost-effective segments, thus avoiding the
massive equipment needed to transport and assemble the blades
constructed as a whole entity.
“We did a couple of material studies in our 100-meter blade
project. We started with fiberglass, which is typical, because
they’re much less expensive than carbon fiber,” explains Griffith.
“However, carbon fiber comes with a much higher cost, but the
stiffness is much higher and its weight is much lower.”
The researchers hope to use a fiberglass material for the bulk
of the design, while adding the more expensive carbon fiber
selectively where needed. Other alternative materials will be
investigated over the course of their research.
A 20-Year Timeline
Many steps remain before designers and engineers can
scale up to a 50-MW turbine. For the first year of the project,
Griffith explains that the role of national laboratories is to try to
get out in front of issues that the industry might face.
“Typically, we look for pathways to make technology work
and to drive down costs, and we help the industry to adopt
that technology,” he says. “We’re hoping to do that through this
project as well – through the blade design work we’re doing;
through the controls work and development; and also through the
technology demonstration we plan.”
The next three years will determine the scope and feasibility of
the project. If achievable, the extreme-scale wind turbines could
revolutionize clean energy production in the United States and
around the world.
This image shows the sizes of various wind turbines, including the project sub-scale
demonstrator (SUMR-D) to be tested in 2018 and the two extreme-scale designs
(SUMR13 and SUMR50). Image courtesy of the University of Virginia.
Todd Griffith displays a cross-section of a 50-meter
blade. Image courtesy of Randy Montoya, Sandia Labs.
The extreme-scale SUMR design
features segmented blades that stow
and align with the wind direction at
dangerous wind speeds. Illustration
courtesy of Trevor Johnston.