Making the Blade Grade: Team Evaluates Steel against Composites for Turbines
Computation, lab-scale turbine reveals composite blades may generate more power but require higher hydraulic heads
Roughly 160 of the world's 200 countries use hydropower technology, and it represents at least 50 percent of the total electricity supply in more than 35 countries. Large-scale hydro systems—lauded for their low maintenance costs and lifespan of more than 100 years—are workhorses in the power supply chain but require water reservoirs. Smaller scale systems such as streams, creeks, and canals, however, are abundant worldwide and could potentially become key resources for electrification of rural areas while posing much smaller environmental and ecological impacts. That said, the current design of stainless steel turbines used in smaller-scale hydropower systems are heavy and costly, outweighing the benefits (energy capacity) of deploying them at those sites.
In a paper published in Renewable Energy, PNNL researchers shared their analyses of lightweight composite turbine blades versus the stainless-steel blades used today in most low head reservoirs. The paper’s findings show the turbine with the composite blades generates about 20 percent more power than turbines with traditional stainless steel blades at the same flow rate. But there’s a tradeoff: the composite blades require higher hydraulic heads due to their slightly higher degree of blade bending.
Expertise in Hydropower Materials
In this analysis, PNNL materials scientist Huidong Li led the research effort to compare three composite materials against stainless steel to determine if a new material could be used in small site turbines, equalizing the cost-benefit ratio.
Using a computational model, the team analyzed the pressure distribution of each material under simulated operation conditions and compared the induced stress as well as the amount of blade bending that was caused.
“The bending is really important because the flex of the material can cause inefficiency in power generation,” said Li.
After determining the best of the three composite materials, they built a lab-scale turbine and installed it in a performance test loop at PNNL’s Aquatic Research Laboratory. Testing revealed that the lightweight composite blades (injection molded from fiber-reinforced polymer) generated more power than the stainless steel blades. But both displayed similar peak turbine efficiencies, thus demonstrating the viability of the composite material in replacing stainless steel from the perspective of power-generation performance.
“It was good news because it gives the industry a lighter-weight material option,” explained Li. “It’s important to note, though, that the composite turbine might require a slightly deeper reservoir of water on the upstream side of a dam.”
Li and his team intend to conduct follow-on studies to examine the longevity of the composite blades. This research is internally funded at PNNL.