Hydropower projects frequently face resistance from environmental groups for a variety of reasons. One of the more common objections to hydro is the high turbine-induced mortality of fish.
However, Natel Energy, an Alameda, California–based hydro turbine developer and independent power producer, has shown that improving hydro turbine designs could be the ultimate answer to the problem. It has developed the Restoration Hydro Turbine (RHT), a compact hydroelectric turbine that couples high performance with safe through-turbine fish passage.
“Our thesis was that if we can make it safe for fish to move through hydropower facilities in a straightforward and easy way, then we can support reimagining hydropower overall, in a bit more of a distributed approach, but one where these projects actually also help to maintain passage and river connectivity,” Gia Schneider, co-founder and CEO of Natel Energy, said as a guest on The POWER Podcast. “Core to making that vision possible is a fish-safe turbine.”
The RHT is optimized for low head (from 2 meters to 20 meters) and doesn’t require fine fish screens. The design’s thick, slanted blades transport fish away from the leading edge into wide inter-blade regions and downstream to the outlet. The progressive slant of the blades from hub to tip also minimizes the likelihood of severe strike and eliminates the risk of entrapment between moving and stationary parts.
Schneider understands the challenges presented by multiple projects in a watershed or river. “If you’re in a watershed where you, say, have 10 projects down a river, then that means you need to be greater than 99% safe through each individual passage—each individual turbine—in order to achieve [an acceptable] population survival dynamic,” Schneider said. “And so, core for us is we want to achieve greater than 99% safe passage. We’ve kind of set that as an overall target. [It] doesn’t need to be quite that strict if you have fewer projects on a river, but it’s a good rule-of-thumb metric to aim for. And, then, we also want to be highly efficient, so up to 94% efficient from a power generation perspective.”
The results achieved during intense testing have been phenomenal. In a recently released, peer-reviewed paper, the findings from an eel passage study were documented. “We’ve been able to actually show 100% passage of eel through our turbines, and with some pretty extreme conditions,” Schneider said. “We’re talking eel that are basically as long as the diameter of the turbine that they are going through—so fairly large eel relative to the size of the turbine—and where that turbine is spinning at 600, 700 rpm.”
Schneider said it’s really important to get that kind of data, because it helps substantiate the design with real results, showing it’s truly possible to design for high fish passage and high energy production at the same time. Natel has conducted several other studies, some with the Pacific Northwest National Laboratory (PNNL), with similarly impressive results.
Earlier this year, a Natel/PNNL test of 186 large rainbow trout—measuring up to 500 millimeters (19.7 inches) in length—found no meaningful difference between the fish passed through Natel’s 1.9-meter-diameter (roughly 6 feet) turbine and a control group, indicating that the RHT allows safe passage of some of the largest fish ever successfully passed through a compact hydro turbine. Earlier tests of smaller rainbow trout passed through Natel’s turbine demonstrated 100% survival.
