A prototype in-river hydropower system is currently in operation at Igiugig in southwest Alaska. It’s part of a recent surge of research that has pushed in-river hydro power closer to becoming a reality for rural communities seeking an alternative to diesel-based electricity.Download AudioGiven that most rural communities in western and interior Alaska are situated on rivers, hydropower seems like an obvious renewable energy source.Putting up dams on big rivers like the Yukon is unlikely to happen for environmental and economic reasons, but in-river hydropower is a possibility. An in-river power system is like a wind mill, but in the water, using the kinetic energy of flowing waters to move blades, which spin a turbine and create electricity.Alaska Village Electric Cooperative President and CEO Meera Kohler is keeping an eye on developments with in-river hydro technology, and says it has some promise for her member communities scattered across rural Alaska. But there’s a catch:“Obviously, moving water has a lot of energy associated with it, and trying to harness that is the goal. But being able to harness it with destroying the machine that is harnessing it every couple of weeks – that’s the challenge.”The destruction that Kohler is referring to would come from one of in-river hydro’s biggest challenges to date: driftwood and debris. Tests of small in-river turbines at Ruby on the middle Yukon River and Eagle on the upper Yukon were constantly plagued by driftwood.Unlike the design tested at Ruby and Eagle, which was suspended just under the surface of the water by a small pontoon platform, the prototype in use at Iguigig right now sits on the river bottom. It’s much wider than it is tall and looks like an old fashioned push lawn mower rather than a typical wind mill or table fan shape.The prototype is called the RivGen, and it was designed by Ocean Renewable Power Company, which is based in Maine but has an office and several projects underway in Alaska. Monty Worthington is ORPC’s Director of Project Development. Having a hydropower system sitting on the bottom of a river, Worthington says, has several advantages. It works quietly and out of sight, but….“More importantly it gets us down below the floating debris in a river. That can be wood, that can be ice in some cases. Anything that is floating on the surface of the river we are no longer in the way of, and it also includes impeding navigation in certain areas, so we can be down a depth where boats are able to pass freely over the device.”If placed in a river like the Yukon, the RivGen or any in-river hydropower system would still have to contend with heavy amounts of silt, grinding into and ruining moving parts. Worthington says that ORPC has been testing various styles of bearings and seals for 6 years through a partnership with UAA, and have found some promising solutions. But even materials containing diamonds are proving to be susceptible to silt damage over time, so bearings will need to be replaced as part of routine maintenance.The RivGen test site on the Kvichak River at Igiugig is clear and mostly free of debris – not an ideal place to test the turbine’s ability to deal with driftwood and silt. But the clear water does give researchers a better chance to watch how the blades impact fish, another important environmental consideration that hydropower designers must deal with.At a test site on the Tanana River at Nenana, researchers from the University of Alaska Fairbanks’ Alaska Center for Energy and Power are putting some different in-river hydro designs through their paces in more challenging environment, including lots of driftwood and silt.The most recent design to be tested comes from Oceana Energy Company. It’s suspended just under the surface from a barge, and looks like a ring with shark fins embedded around it. According to Alaska Hydrokinetic Research Center Program Director Jeremy Kaspar, the Oceana system worked without a problem for a month last fall and a month earlier this summer. The Oceana unit was protected by a UAF-designed debris diverter placed just upstream, which Kaspar says was highly effective.Photo: Alaska Center for Energy and Power.“The debris diverter is kind of a V, and we can adjust the angle. At the tip of the V, there is a cyclinder that rotates, and when the debris hits that cylinder the debris starts to rotate it and the debris slides off the sides.”The UAF team also changed the anchoring system to rely on a single line instead of many, reducing the amount of driftwood getting caught by the lines.Future research is going to look at the potential problems caused by subsurface debris, like water-logged trees and root balls that bounce along the bottom of a river. When silty water does not allow for video cameras to get a look at what’s going on, Kaspar says the researchers will use sonar.“The other thing that we are going to be doing in conjunction with the sonar is having a mechanical means of detecting debris – basically we’re gonna put down a grate near the bottom and see if we can get some simultaneous impact measurements along with the sonar. So then we will know what the sonar is seeing and what the impact forces are.”As more of the engineering hurdles are crossed, Kaspar predicts that in another five years in-river hydropower systems will be ready for widespread use across Alaska.“I am hoping that we start convincing the Department of Energy that they really need to fund these pilot projects in places like Alaska. I think what we will probably see in the next few years is a few communities – Igiugig is almost there – adapting these technologies, with partnerships between the developer and the community.”Regardless of the technical advances with in-river hydropower systems, no one thinks they can survive spring breakup, so they are all being designed to be removed from the water in the fall or winter before the ice goes out.