In modern debates about power generation—whether in Congress or the coffee shop—the dichotomy is almost always between wind and solar on the one hand and coal and gas on the other. Nuclear might come up as a third option if both sides are feeling tired of rehashing the same old arguments, but hydropower never seems to get the same level of attention.
Perhaps it’s because hydroelectric power is so dependent on location, even more than wind or solar. It’s easy to forget that almost a third of all renewable energy generated in the U.S. comes from hydropower if you don’t work in the industry or live near a major dam. But hydroelectric power has been lighting up our homes and business for a long time. It’s an industry built on traditional manufacturing methods and materials.
Unfortunately, that may be it’s biggest weakness.
Between international supply-chain issues, ongoing maintenance needs and environmental-impact mitigations, the U.S. hydropower industry is very much in need of an update. According to a recent report from Oak Ridge National Laboratory (ORNL), the time is right for advanced manufacturing and materials to bring the hydropower industry up to speed.
Challenges Facing U.S. Hydroelectric Power
The report, entitled Advanced Manufacturing and Materials for Hydropower: Challenges and Opportunities, is a joint effort of ORNL, GE Research, the Department of Energy’s Water Power Technologies Office and Kearns & West. It was informed by literature reviews, stakeholder interviews and an in-person workshop at the Oak Ridge National Laboratory Manufacturing Demonstration Facility.
One of the most pressing challenges for this industry is maintenance, brought on by the aging of the existing hydropower fleet. Repairs are happening more frequently and often involve legacy parts that are no longer being manufactured. As anyone who’s worked in manufacturing well knows, unplanned downtime is expensive, especially when the necessary replacement components aren’t easy to procure.
The report goes so far as stating that “Procurement and/or manufacturing of large metal components, which are essential to the hydropower industry, are currently impossible in the United States, and reliance on international suppliers places the fleet at risk.”
That’s a tough pill to swallow, made all the more bitter by the proportion of renewable energy accounted for by hydroelectric power. Fortunately, advanced manufacturing technologies, such as additive manufacturing, can help modernize the hydropower industry and overcome its pressing difficulties.
1. 3D-Printed Parts and Tooling
The obvious solution to unavailable replacement parts is to manufacture them yourself. However, using traditional methods means having a dedicated facility housing numerous machine tools and other production equipment. 3D printing offers a way to consolidate multiple fabrication and machining operations into a single step. The ORNL report identifies a number of potential use cases for 3D printing replacement parts for hydropower from metal—including magnetic materials—as well as polymer composites.
In one such case, a corroded log-boom anchor for the Nimbus Dam near Folsom, California was redesigned so it could be additively manufactured on a Concept Laser machine. Engineers reduced the number of aluminum parts from three to one and reduced the total mass by 50%. What’s more, the cost of the part dropped by almost 150%, from $1,800 for one to $1,570 for six.
Aside from direct fabrication of parts, metal additive manufacturing can also be used for tooling, including stamping dies for sheet metal, die-casting molds, injection molds and compression molds. In another case study, ORNL 3D printed and finished machined patterns of hydrofoils and spokes for use in a sand-casting process. The result of this pilot study was an estimated 78% cost savings compared to previous builds that used subtractive manufacturing alone.
2. Hybrid Manufacturing
The combination of additive and subtractive manufacturing—also known as hybrid manufacturing—brings both additive and subtractive processes together in a single machine. Since additively manufactured parts can require additional finishing to improve surface quality or obtain more accurate geometric tolerances, hybrid manufacturing can save considerable time by eliminating the need to transfer and reorient parts between stations.
The ORNL report also notes that alternating between additive and subtractive processes over the course of a build allows for the machining of areas of a part that are inaccessible once the printing process is complete. One promising application of this technology to hydroelectric power is manufacturing turbine runners, which normally require welding as well as long-reach machining tools.
The figure above shows how alternating between additive and subtractive processes in each step of the build streamlines production of a test part made from 1.4404 stainless steel using a combination of direct energy deposition and conventional milling. The first milling operation at step (b) eliminates the need for the cutting tool to reach all the way to the bottom of the part in step (d) after the second additive operation at step (c).
3. Additively Manufactured Concrete
You’ve probably seen images or videos of 3D-printed concrete structures: ridged, vaguely organic shapes created by large printers or robots with printer heads extruding premixed concrete on selective toolpaths. These days, gantry-based systems with print volumes as large as 100 feet by 100 feet by 18 feet are commercially available, with custom options for even larger setups.
Oak Ridge’s SkyBAAM system uses tensioned cables running through a large overhead crane with three base drives for positioning the print head. It’s capable of printing up to 2,000 pounds per hour, depending on layer curing time, and the build volume is mainly constrained by the size of the crane. Unlike its smaller counterparts, SkyBAAM isn’t yet commercially available, but it’s easy to envision how systems like it could soon be deployed to produce large industrial structures, including dams.
The ORNL report also notes the potential to utilize additively manufactured concrete for repairs as well as 3D printing molds or forms for use in more traditional concrete fabrication, with similar benefits to 3D-printed tooling, i.e., faster production times and lower costs.
Compared to metal additive manufacturing and hybrid manufacturing, additively manufactured concrete has fewer immediate applications for hydropower and other industries requiring large or difficult-to-obtain replacement parts. Nevertheless, its potential to facilitate faster structural repairs as well as entirely new builds should not be discounted.
The Future of Additive Manufacturing in Hydropower and Beyond
We reached out to the authors of the ORNL report to learn more about the trends they’re seeing in additive manufacturing (AM) and what the future holds for this technology. Mirko Musa, a water-resources engineer and lead on the report, and Jesse Heineman, a technical staff member at ORNL’s Manufacturing Demonstration Facility and co-author, gave their answers to our questions below.
Engineering.com: The report discusses using AM for metal parts, for polymer and composite parts, for tooling for sand casting, and for magnetic materials. Which of these processes is most immediately applicable in the hydropower industry and which will have the largest impact in the long term?
Musa: The Hydropower Supply Chain Deep Dive Assessment [another ORNL report] highlighted that large metal components (i.e., those weighing more than 10 tons, such as turbine runners) cannot be manufactured in the U.S. Procurement of these components relies on international steel foundries, often resulting in long lead times that cause loss of revenues during required generation shutdowns (in the case of a turbine repair/replacement). This was confirmed also during the in-person workshop that we organized at DOE’s Manufacturing Demonstration Facility at Oak Ridge National Laboratory, bringing together hydropower manufacturers, owners and operators, and AM R&D experts.
AM tooling technology (i.e., creation of molds and tools via additive manufacturing) is already being implemented in other industries and is also applicable to the hydropower industry. For example, binder-jet AM processes to produce sand-casting molds could offer a cost-effective solution for hydropower components. Implementing this technology can lead to great reductions in time and cost for manufacturing compared to traditional methods of tooling.
Hybrid manufacturing processes at larger scales are likely to have the greatest impact long term. This technology can also lead to reductions in time and cost, but more importantly it will help alleviate U.S. reliance on foreign suppliers for large castings and forgings. The technology is already quite mature, but additional effort is needed in the certification, qualification, and testing areas to mitigate the risk to hydropower owners.
Finally, resource assessments have revealed that future hydropower development will mostly target small hydropower (i.e., low-head sites with less than 30 feet of head), especially from non-powered dam retrofits. Therefore, direct additive and hybrid manufacturing may enable cost-effective solutions for new small-scale components while increasing and optimizing the design space.
Which do you believe is the greater limiting factor for the usefulness of 3D printing in hydropower manufacturing: build volume or build rate?
Heineman: Build volume is probably the greater limiting factor for now. Many components of the larger hydropower assets exceed the size of most state-of-the-art AM cells. However, the technologies are scalable in both volume and build rate to meet the demands of these larger parts. This said, manufacturing of small-scale components could be achieved now with current capabilities.
Beyond the hydropower industry, where do you see additive manufacturing making the biggest impact in the next 5-10 years?
Heineman: Similar to the answer above, hybrid manufacturing processes will have a huge impact for all industries that use castings and forgings, especially for very large parts. Examples include transportation, defense, wind energy, construction and industrial machinery, and domestic infrastructure.