How are innovative materials disrupting the hydropower sector?

The hydropower sector is currently experiencing several technological developments to improve its sustainability and also its flexibility to support the development of other renewables. Within this context, novel materials can play an important role, due to benefits like the decrease of manufacturing labor costs, pollution, waste, and weight, while improving performance and durability. In this article, we discuss innovative materials for hydropower applications, focusing on turbines, dams and penstocks, and bearings as well as applications in the ocean context.

Novel materials for turbines:

The turbine is the core hydropower component for converting water energy into mechanical energy. Superhydrophobic-coated materials can improve turbine efficiency by 4% by reducing friction. 

The development of fiber-reinforced composite materials is also riding the wave (particularly carbon fiber composites), and they are already widespread in the marine and wind energy sectors. Lightweight materials, including polymers such as high-density polyethylene, are under development for turbines. These materials ensure higher efficiency, lower weight, and higher resistance in severe environments. 

However, degradation owing to the coupling between the carbon fiber composites and metals may pose a problem in a wet environment. For example, a feasibility study on 2 MW Francis turbines revealed that the weight of a composite turbine is 50% to 70% less than a steel turbine. Meanwhile, modified steels are also under development to reduce turbine weight: for example, the use of carbon steel allowed the construction of  a lighter water wheel with respect to a Corten steel wheel, reducing the  weight from 0.98 tons to 0.7 tons.

Novel materials for dams and waterways:

The choice of the material for a dam depends on the characteristics of the site and on the dam type. Novel materials have been introduced both for embankment dams (e.g., cemented rockfill and cemented soil) and for concrete dams (e.g., carbon fiber and glass fiber materials). They increase the lifespan of the structure, reduce deformation, and simplify the installation process. 

The cemented rockfill material has a higher modulus than the rockfill material, improving the mechanical resistance. Cemented rockfill or soil dams are advantageous over rockfill embankment dams because of the higher resistance to material erosion. 

The covering of the dam surface with bituminous conglomerate is another trend that is being developed to simplify waterproofing. 

Some coating materials for waterways and penstocks have also been introduced that result in positive effects on the reduction of head losses, thus increasing the power output: 

• Polymer-modified cement-based mortar for a 12-km-long horseshoe section tunnel with an average diameter of 9.45 m, reducing the head loss by 20% at a cost of USD $30·m−2. Although it is not possible to quantify the economic benefits due to the lack of data, this intervention has led to an increase of energy production by 20%, with a reasonable increase in annual income of 20%.
• A latex-based primer and topcoat and an epoxy primer with added solids applied after cleaning, generating a power increase of 11%
• Superhydrophobic materials with a related drag reduction of up to 30% and superhydrophilic surface (drag reduction by water–water interface) with drag reduction of up to 5%. These measures are of particular interest in refurbishment projects.

Novel materials for bearings:

Bearings are the components of the turbine units that have to support rotating components, while minimizing friction and  keeping the shaft of the components aligned.

Novel materials have been introduced to replace commonly used materials such as vesconite and CIP. For example, US Synthetic is developing a novel polycrystalline diamond (PCD) bearing shaft for the RivGen Power System in a hydrokinetic context to deliver electricity to the remote community grids. Also polytetrafluoroethylene (PTFE) has been introduced to improve performance and reduce oil need, significantly reducing wear. 

Lubrication made with water and vegetable oil is a main developing strategy for reducing oil-related pollution, although it is currently more expensive.

Novel materials for ocean environment:

Advanced composite materials, such as glass- and carbon-fiber-reinforced polymers, can reduce costs and increase durability in ocean conditions. The durability of alternative composites based on basalt and natural fiber reinforcement is also being examined to develop materials with lower environmental impact. Although their mechanical properties are not as good as those of carbon fibers, the use of these materials may be justified by life cycle analysis. 

Sabella tidal turbine dockside in Brest (France), before installation
Source: Courtesy of Erwann Nicolas

Alternative biodegradable polymer matrix materials have also received attention, as indicated by these case studies:

• The 300 kW SeaFlow tidal prototype, with composite blades equipped with strain gauges. The construction involved a central 65-mm-thick carbon composite spar covered by stiffened glass/epoxy fairings. 
• Tidal power station in Norway (near Hammerfest), with 1-m-long blades made of glass fiber composite.
• The Sabella 500 kW turbine near Ushant Island, with six carbon/epoxy blades made of a central prepreg composite spar with infused composite facings. A glass-reinforced composite was used as the generator cover.
• The CRIMSON project, valued at 3.9 million EUR (made by ORPC), was made with foils made entirely of recycled carbon fiber, reducing capital and operating expenditures by 33% and 66%, respectively.

Conclusions:

Hydropower is a sector where the development of novel technologies is underway to improve its sustainability and flexibility. Novel materials, despite their current high cost with respect to traditional materials, will play a central role in improving efficiency, resistance, and reliability, extending lifespan, and making the fabrication, installation, and transport processes easier. 

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