Researchers at the Energy Department's Pacific Northwest National Laboratories say that hydroelectric turbine blades that are made of lightweight composites may be able to generate as much as 20% more energy than turbines with traditional stainless steel blades at the same flow rate.

In a paper published in Renewable Energy, the researchers shared their analyses of lightweight composite turbine blades versus the stainless-steel blades used in most low head reservoirs.

A performance test loop used in the research at the national laboratory. Source: PNNLThe greater energy production comes at a cost, however. Composite blades require higher hydraulic heads due to their higher degree of blade bending.

Streams, creeks and canals are abundant worldwide and could potentially become key resources for electrification of rural areas while posing much smaller environmental and ecological impacts. However, the current design of stainless steel turbines used in smaller-scale hydropower systems can be heavy and costly, the researchers said, outweighing the benefits (energy capacity) of deploying them at those sites.

Materials testing

Materials scientists at the lab compared 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 operating conditions. They also compared the induced stress as well as the amount of blade bending that was caused. The bending was an important factor because the flex of the material can cause inefficiency in power generation, the researchers said.

After determining the best of the three composite materials, the team built a lab-scale turbine and installed it in a performance test loop at the lab'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. Both displayed similar peak turbine efficiencies, demonstrating — according to the researchers — the viability of the composite material in replacing stainless steel.

The finding may offer the hydropower industry a lighter-weight material option. At the same time, however, the researchers said that the composite turbine might require a deeper water reservoir on the dam's upstream side.