Is hydropower the ideal "green" industry? Not quite.
Critics point to changes in habitat and stream flow when attacking hydropower. Another concern - and a big concern, at that - is fish mortality. Anecdotal observations compared hydropower facilities to blenders, suggesting their outflow was little more than fish puree.
Thirty years ago, Voith Siemens Hydro Power Generation partnered with others in the industry to solve the problem of fish mortality. The first step was to lay to rest the anecdotes and replace them with facts. By 1990, a more precise method of measuring fish mortality was in place. At 94 percent, peak survival rates were found to be much higher than expected. Rates for fish passing directly through large turbines were within three percentage points of those going through a bypass system, and within five points of those navigating a spillway.
Still, there was room for improvement.
Further studies concluded there are two primary areas of concern, and that each is related to different parts of the country.
Along the coasts and especially in the Pacific Northwest, the problem is physical harm done to fish as they pass through turbines. Injuries result from:
-- Turbulence from turbine design or plant operating strategies;
-- Turbulence and the trapping and cutting of fish in gaps near the turbine hub;
-- Fish being struck by the turbine blades or being thrown against other turbine structures;
-- Cavitation in turbine water passages;
-- Abrasion caused by contact with rough surfaces.
In addition, fish experience dizziness caused by turbulence or impact. When they exit the turbine like grandparents coming off the Tilt-a-Whirl, they're easy pickings for predators, such as birds and other fish.
The reason this is primarily a coastal problem is that the coasts are where anadromous fish live. Anadromous fish spend most of their lives in saltwater, but migrate to fresh water to spawn. Some fish make the trip once and then die; others make annual pilgrimages to their spawning grounds. While the fish can get upstream without going through the turbines, species that make multiple trips and the babies of all anadromous species pass through turbines on their way to saltwater. East Coast anadromous species include striped bass, Atlantic salmon, and short nose sturgeon. West Coast species include five types of salmon, steelhead, and white sturgeon.
Some of the solutions were relatively simple engineering changes. Gaps in the turbine itself shrank to mere millimeters, much too small to trap fish. Rough surfaces were smoothed. The basic design was altered to provide high efficiency over a wider operating range with reduced potential for cavitation.
Some of the solutions depended on higher technology. Sophisticated control systems, acting on information provided by sensitive (yet rugged) measurement transducers, control turbine performance. The operating mode that is safest for fish is not the mode that yields the highest efficiency. The turbines are run in their most efficient mode until the transducers sense the presence of fish. When fish are detected, the control system automatically changes the operating parameters to a "fish-friendly" mode.
As stunning as that control technology is, better technology is near. Advanced computational methods for estimating the trajectory of fish through a complex flow field will help design new turbines with even lower fish mortality rates.
One benefit of these improvements is a lowering of dissolved gas that results from spilling. Gas saturation in spillwater is so high that fish can experience what human divers refer to as "the bends," where excess gas is trapped in the bloodstream.
Quite the opposite condition is the hallmark of the second area of concern. In some parts of the country, notably the Southeast, water used to power turbines has too little gas in it. Fish literally suffocate in the oxygen-depleted water downstream of hydropower plants in these areas.
This phenomenon occurs because the deep, steep-walled reservoirs that feed turbines get thermally stratified in summer. Hot water stays on top, and cold, oxygen-poor water stays on the bottom. It is this bottom water that drives the turbines. It is this bottom water that then fills the stream below the hydro dam.
In the 1950s, Voith Siemens Hydro conducted research in Europe to develop turbines that would increase dissolved oxygen (DO) levels in water passing through turbines. In the 1980s, Voith Siemens Hydro teamed with the Tennessee Valley Authority to improve DO concentrations by designing auto-venting turbines (AVTs).
Bioenergetics modeling of trout growth and fisheries studies suggested that a DO concentration of 6 mg/L would result in a 270 percent increase in annual growth over a base case where no environmental improvements were made. Voith Siemens Hydro achieved this at TVA's Norris Dam with a turbine design that provided 5.5 mg/L accompanied by re-regulating weirs downstream from the powerhouse. Air entrainment in the flow over these weirs contributed the additional 0.5 mg/L necessary for an optimal growing environment.
One of the challenges in designing these oxygenating turbines was to preserve efficiency. Water is the source of power for a hydro station. Water is not compressible. Air is. Compression of air results in a loss of power. More air, more power loss. What's good for fish is bad for efficiency.
It's remarkable, then, that at peak efficiency the new turbines at TVA's Norris Dam are 3.7 percent better than the original turbines. In fact, efficiency losses due to aeration range from zero to four percent. The average loss for the July through November period when aeration is employed is less than two percent.
Voith Siemens Hydro has developed these sophisticated solutions because customers needed them. Hydropower plants must be licensed, and those licenses typically last for 50 years. Many licenses have come up for renewal recently, and many more will need to be renewed over the next five to ten years.
"Re-licensing is a major headache for utilities," said Richard "Dick" Fisher, Jr., P.E., senior vice president and chief technology officer for Voith Siemens. "It's a ten-year process costing tens of millions or even hundreds of millions of dollars."
Fisher says one of the major stumbling blocks on the road to re-licensing is a facility's environmental impact. In addition to the government's environmental standards, hydropower plants are also held accountable by non-government organizations, such as Trout Unlimited. If these NGOs feel the plant's environmental record is questionable, they may try to block its license renewal. NGOs often use lawsuits in their attempts to stymie renewal.
"By analyzing the causes of fish mortality and designing turbines to address those causes, we're helping our customers minimize the environmental impact of their hydropower stations," said Fisher. "In some cases, fish are more likely to survive their journey if they go through one of our turbines than if they navigate an adjacent spillway.
"We're providing the technology and the facts our customers need to answer the challenges posed by their critics."
With these improvements, is hydropower now the ideal "green" industry? Arguments could be made either way, but of this there's no doubt: hydropower is closer to being ideal thanks to the innovative work of Voith Siemens Hydro Power Generation.