Low water levels in the Great Lakes pose potential operating and efficiency problems for Midwest power plants.
It's one of several ways power plants are increasingly vulnerable to climate change and extreme weather, an issue recently highlighted in a Department of Energy report.
Several plants in the Midwest have already had to take action in response to water-related conditions. Others must monitor conditions carefully to avoid being left high and dry.
Michigan’s Cloverland Electric Cooperative knew it had a problem last year. Output at its hydroelectric plant at Sault Sainte Marie kept dropping dramatically before bouncing back up.
“We experienced about a 60-80 percent drop in the plant’s output,” says Phil Schmitigal, Cloverland’s Director of Generation.
The problem wasn’t inside the 36-megawatt plant, but outside in the St. Mary’s River, which connects Lake Superior with the lower Great Lakes. Cloverland’s plant draws river water in from a 2-1/4 mile long canal that runs from near Ashmun Bay on the west to downstream of the Sabin Lock on the east.
Lower levels in Lake Superior reduced the canal’s water allocation from the International Joint Commission. The lower lake levels also reduced the river’s level at Cloverland’s discharge area. Low water levels there were letting air into the system. As a result, the plant’s underwater turbines couldn’t run properly.
“If air enters the draft tubes, it reduces the head pressure, which reduces the power output,” explains Schmitigal.
A temporary fix for Cloverland’s operating problem cost $300,000. In October and November, workers lowered 2,000-pound concrete bricks into the water under three dozen of the plant’s arches. Divers fit the blocks together like Legos to make a series of temporary weirs, or dams. The project raised water levels for discharge pits on the plant’s west side, where the highest-output turbines run.
“The weirs kept our plant operational, especially this winter, when Lakes Michigan-Huron set record low levels,” says Schmitigal. “If the lake levels dropped another 6 inches or so, we would have needed to install a more substantial weir.”
Cloverland’s water woes are part of a bigger problem.
“Water levels on Lake Superior, Michigan and Huron are and have been for the past 15 years below their long-term average,” says hydrologist Drew Gronewold at the National Oceanic and Atmospheric Administration.
Indeed, data from NOAA’s Great Lakes Environmental Research Laboratory show that Lakes Michigan and Huron hit a record low this past winter. Lake Erie and Lake Ontario have been “hovering” around their long-term average, says Gronewold.
Hydropower plants like Cloverland’s obviously depend on the water sources feeding into them. Thus, it’s not surprising that lower water levels could cause problems.
Previously, such problems have been rare. The last time Cloverland had a similar problem was in 1923. At that time, it extended the plant’s draft tubes down an extra foot.
Because of climate change, however, many power plants are now vulnerable, and hydropower plants aren’t the only ones facing trouble.
More water worries
Midwest generating plants that use nuclear energy, coal, or gas boil water to make steam that runs generators. Then they use more water to condense the steam for reuse.
Facilities along the Great Lakes typically use pumps to draw cooling water from the lakes into the plant.
“Those pumps will require a certain amount of suction head that’s above the water level of the pipe,” notes Kent Zammit, Senior Program Manager for water and environmental matters at the Electric Power Research Institute. In extreme cases, a drop in water levels could let vapor form and cause the water pump’s impeller to shake violently.
“You usually have quite a bit of leeway before you start running into this problem,” says Zammit. Power plant designs generally anticipate a variety of high and low-water level conditions over several decades.
Temperature is a bigger problem.
“As you lower water levels, you tend to see increased temperatures,” says Zammit. As a result, power plants draw in warmer water.
“Lake temperature does have a significant impact on our efficiency,” notes spokesperson Bill Schalk at Indiana Michigan Power’s Cook Nuclear Plant. There would have to be “a drastic change” before the plant couldn’t operate or faced safety problems.
Nonetheless, he adds, lower efficiency reduces the facility’s output. That, in turn, raises the cost per megawatt, though Schalk said the company doesn’t release specifics.
Drawing in warmer water for cooling can also raise the discharge temperature for both nuclear and fossil fuel plants, notes Zammit. Consequently, plants can have problems complying with permits from state environmental agencies. Permits generally have seasonal temperature limits to protect fish and other organisms living near water discharge points.
Schalk says Cook Nuclear Plant currently has “enough margin” to comply with its permit. Nonetheless, all power plants that discharge cooling water need to monitor its temperature.
If problems do arise, one option would be to ask the state environmental agency for a variance—a temporary exception to the permit terms. In July 2012, four coal-fired plants and four nuclear plants sought and obtained permission from the Illinois Environmental Protection Agency to discharge hotter water than their permits allowed.
Another possible solution, says Zammit, would be temporary towers to provide additional cooling before water goes back into the lake. Discharge water would be cooler, but additional evaporation would occur. The net result would be less water returning to the lake.
Ignoring the situation entirely could make power plants liable for penalties of up to $37,500 per day under the Clean Water Act.
Forecast for the future
With one-fifth of the world’s surface fresh water, the Great Lakes won’t dry up anytime soon. Nonetheless, lake levels are lower because rainfall and other inputs lag behind evaporation and other outputs.
Climate change explains much of the problem.
“Up until the past 15-20 years or so, Great Lakes water levels have largely followed changes in precipitation,” notes Gronewold. “In the late 1990s, there was a remarkable shift in evaporation rates over the lakes.”
Increased evaporation is “coupled largely” with changes in surface temperature and ice cover, says Gronewold.
Warmer water evaporates faster. Less ice cover and shallower depths also allow water to heat up faster and evaporate.
Indeed, the Midwest isn’t the only area where power plants face problems as a result of climate change. Last week the Department of Energy issued a 46-page report, plus appendices, detailing energy sector vulnerabilities to climate change.
“Climatic conditions are already affecting energy production and delivery in the United States,” says the report. Risks of problems “are expected to increase.”
Current adaptation efforts may not be enough for the “aging and already stressed U.S. energy system,” adds the Department of Energy report.
The report encourages increased investment in “innovative energy technologies.” It also calls for improved efficiency and reduced water intensity for thermoelectric power generation.
Power plants indeed use lots of water. Every minute, United States thermoelectric plants draw in about three times as much water as that flowing over Niagara Falls, reports the Union of Concerned Scientists. On an annual basis, they use roughly four times as much as all homes in the U.S.
The Union of Concerned Scientists is a member of RE-AMP, which also publishes Midwest Energy News.
Of course, the energy sector isn’t the only one affected by current low lake levels in the upper Great Lakes. Other concerns include loss of wetlands, shifting nearshore habitats, and opportunities for invasive species.
Meanwhile, Cloverland has handled its emergency—for the time being.
“For now, we are leaving the weirs in place,” says Schmitigal. “Before removing them, we’d need to see the lake levels return to their long-term average.”
“Hydro power is clean, renewable energy,” adds Schmitigal. And, for the cooperative’s members, “It’s our least expensive source of power.”
Kathiann M. Kowalski is a freelance journalist based in Ohio who writes often on science and policy issues.