Why Tidal Power Should Play a Critical Role in Renewable Energy's Future

The following excerpt is from the book Tides: The Science and Spirit of the Ocean by Jonathan White (Trinity University Press, 2017).

In 2013 I took a two-hour train ride from London to see the Eling Tide Mill, which has straddled the mouth of the Bartley River near Southampton for 230 years. From the train station, a cabdriver shuttled me through progressively smaller villages and narrower streets until he stopped in front of an unassuming red-brick building. I stood on the street for a few minutes after the cab left, taking in the building and the estuary beyond. The tide was on its way up, slipping under fifty or more boats crowded into the anchorage. Many were still aground and listing in the mud, their masts leaning every which way. I imagined sailing ships laden with raw corn and wheat standing off the estuary during the mill’s heyday in the eighteenth and nineteenth centuries, waiting for enough water to float them in. At high slack, they would have sailed in, tied off to the mill just long enough to exchange raw goods for flour and set sail again before getting caught by the falling tide. Raw goods were also brought from inland by horse and carriage across the one-lane bridge that still connects the mill with the rest of Eling

The mill itself has three floors and a steeply pitched slate roof. It was built in 1785, but there’s evidence that the site may have supported two corn mills, one of them fueled by the tide, as early as 1086. The present building, damaged and restored several times, is now under the care of the town council, which manages a museum in the old miller’s quarters as well as the operation of the mill itself, which today produces a monthly average of 1,700 pounds of whole-meal brown and strong white flour. Some of this is baked into breads and cookies sold in the museum gift shop, and the balance is sold to local bakeries. The three-pound bags for sale at the museum boast “Canute 100% Stoneground: Milled from English bread-making grain for a fuller flavour at the only working tide mill in the United Kingdom.” On the back is a recipe for a “delicious 2 lb loaf.”

The Canute packaging is a reference to King Canute of England, Denmark, and Norway, 995–1035 ce. Legend has it that to dispel his court’s claim that he was powerful enough to “command the tides of the sea to go back,” Canute directed his throne to be carried to the seashore—ostensibly near Southampton—and sat as the tide came in, commanding the water to “advance no farther.” When the tide paid no heed, the king’s point was made: sovereign power might be great, but nothing was greater than the hand of God. (Indeed, during Canute’s day the cause of the tide was still a complete mystery.)

Today the lead miller is David Plunkett, a retired stonemason with deep-set blue eyes and ruddy cheeks. I had missed the previous tide cycle, and the next wouldn’t start until six o’clock that evening, after the building was closed. Plunkett, however, invited me to stay. He and his apprentice, Andrew Turpin, would run the mill, and I would be put to work lifting sacks of grain and refilling the grist bin.

After returning from a dinner of stew and beer at the local pub, Plunkett flicked the tide gauge with his thumb. “We’ll be ready to fire up the wheel in about fifteen minutes,” he said as he pumped grease into the main waterwheel’s brass cap and donned a white apron. Turpin grabbed a bag of raw wheat supplied by a local farm and asked me to pour two scoopfuls in the grist bin. The two of them walked through the building, methodically adjusting valves, cables, and the two four-foot-diameter grinding stones, each weighing a ton, fabricated in France of composite granite. The massive timber-framed structure, some of it cobbled together or partially eaten by insects, reminded me of an old ship. As if below decks, I had to duck under low-slung oak beams and knee braces.

“Here we go,” announced Plunkett as he turned an iron valve opening the sluice gates. Laboring at first, the wheel eventually rumbled to speed. The whole place seemed to come alive, creaking and groaning like a ship at sea. Windows shook. Iron latches and levers rattled. A spoon and pencil chattered in a jam jar. Upstairs, the grist bin’s tick tick tick confirmed that grain was being fed to the grinding stones. When I looked up from the swishing and gurgling waterwheel, a stream of golden flour was pouring from the chute.

The waterwheel ran for four and a half hours. Through the windows, I watched the tide disappear from the harbor, leaving all the boats aground. The mill’s wheelwash gushed into the estuary like a whitewater rapid. Plunkett and Turpin were constantly tinkering with valves, watching, touching, listening. A fine powder had filled the air as soon as we started producing flour, settling on everything, including our eyebrows and lashes. The place smelled like baking bread, hot grease, and low tide.

A few times an hour, Plunkett put his hand under the warm flour spilling from the chute. Spreading it on his open palm, he’d run his thumb through it, feeling for temperature and texture. “What we’re after is a balance of wheel speed and distance between the two grinding stones,” he said. “If the stones are too close, the flour gets hot and sticky. If they’re too far apart or we’re turning too slow, the flour’s coarse.”

“How do you know when all the elements are perfectly tuned?” I asked.

“There’s a vibration that feels just right,” he answered. “I can feel the humming in my skull.”

The waterwheel shut down when the rising tide reached its axle and there was too much drag for it to continue turning. I drank a celebratory beer with Plunkett and Turpin at the local pub and caught a midnight train back to London, carrying a bag of fresh Canute Stoneground, flour of the tide. The train’s soothing hum reminded me of the tide mill and Plunkett’s words: “After fifteen years, I’m still amazed,” he had said. “There are no engines, no gasoline, no coal, no electricity except for a couple of light circuits. All this is powered by the moon and tides.”

The energy sources of fire, petroleum, coal, and their by-products have been used by humans for a long time—fire for 400,000 years, petroleum for 4,000 years, and coal for at least 3,000 years.

Petroleum was used by the Babylonians to make asphalt as early as 1894 bce. Almost four thousand years later, Londoners were distilling it into kerosene to fuel streetlamps (replacing whale oil). Natural gas, a by-product of coal mining and oil drilling, was also used for lamps.

Coal, first burned in ceremonies by the ancient Romans, was used by London blacksmiths in the twelfth century. Its smelly, dirty prop- erties were well known. When Queen Eleanor visited Nottingham in 1257, the air was so sooty she fled, fearing for her health. Forty years later, coal burning was banned because of its polluting qualities.

By the time Magellan set sail from Spain in the sixteenth century, Great Britain was facing perhaps the world’s first energy crisis. Wood, the fuel of choice for heating and cooking, was in low supply. Forests were shrinking.

Coal, dirty or not, was the ready answer. “By the mid-1600s,” writes Barbara Freese in Coal: A Human History, “Londoners did not merely welcome coal into their homes, they were desperate to have it.” Mined at nearby Newcastle and Tyne River, coal solved London’s energy cri- sis but at the expense of stifling air pollution. In 1700, addressing the insidious smoke that plagued London, essayist Timothy Nourse wrote of London, “There is not a more nasty and a more unpleasant Place.”

That was more than three hundred years ago.

The steam engine, invented in 1781 and fueled by coal, catapulted Britain  and  eventually  the  rest  of  the  world  into  the  Industrial Revolution. By the end of the nineteenth century, steamfueled mills had largely displaced wind- and tide mills. The Eling tide mill itself was converted to steam in 1890. Thirty years later, unable to compete in the flour and textile industries, Eling was producing only animal feed. Prior to the Industrial Revolution, the world’s consumption of fos- sil fuels was negligible. By the year 2000, our consumption had grown  by a factor of forty, and by 2015 it had grown by a factor of eighty. In the overall global energy budget, 50 percent comes from coal, 20 percent from oil, 15 percent from natural gas, 5 percent from nuclear fission, and 10 percent from renewable sources such as biomass (wood burning, etc.), hydropower, wind, and the sun.

Accelerated fossil fuel use is tied to the planet’s population growth, and such use is tied to lethal concentrations of pollutants that have changed the planet’s chemistry and lessened the quality of life for everything that lives on it. A growing concern about this problem was best signaled by the landmark Paris climate deal in December 2015. But the awareness has been growing for years. In an August 2013 letter to the New York Times, four former Republican administrators of the Environmental Protection Agency (epa) wrote, “There is no longer any credible scientific debate about the basic facts: our world continues to warm, with the last decade the hottest in modern records, and the deep ocean warming faster than the earth’s atmosphere. Sea level is rising. Arctic Sea ice is melting years faster than projected.” The letter calls for a reduction in carbon dioxide emissions and increased investment in clean, renewable energy. Signed by William D. Ruckelshaus, Lee M. Thomas, William K. Reilly, and Christine Todd Whitman (representing forty-three years of EPA leadership), the letter concludes: “The only uncertainty about our warming world is how bad the changes will get, and how soon. What is most clear is that there is no time to waste.”

From our Punta Arenas hotel conference room, the view of Magellan Straits is strikingly raw and elemental, offering no hint of an environmentally troubled world. How did we lose our way so quickly? What level of environmental health will we use as a baseline for recovery, if there is to be a recovery? Gareth Davies, who takes the podium next, begins as if his words were the next sentence of the New York Times letter: “I believe the world is in a hurry for us to come up with a better solution for energy,” he says, “because we’re not in a good place at the moment. The energy we use is killing the world.

“Only 10 percent of the world’s fuel supply currently comes from clean, renewable energy,” Davies explains. “And of that, only 2 percent comes from tidal energy. But these numbers are growing. In the next twenty years, I hope to see the renewable sector increase to 40 percent.” According to Davies and many of his colleagues, tide energy will probably remain a small but important part of that 40 percent. This is not because harnessing the tide is so difficult, but because in terms of raw available power, wind and solar far outstrip all the other fuels combined, renewable or not.

What tide energy does offer is predictability—more than most other renewables. The wind doesn’t always blow and the sun is sometimes hidden by clouds, but the tide always ebbs and flows.

“For tide energy to flourish,” Davies continues, “we will have to resolve many of the same issues we face with other renewables. Getting the engineering right—building devices that work—is just one of them. Launching and servicing the devices is another, and so is political support, both nationally and internationally. We need more mechanisms in place that provide financial support during this early—and expensive—development stage. Utility companies, which frequently have near-monopolies on supplying power, will have to change. Environmental concerns need to be addressed, and the communities that will live with these devices in their backyard have to be on board. For them it means jobs and cheaper, cleaner energy. But it also means making reasonable compromises for the sake of the big picture.”

From my time with Davies as well as my own research, I’ve learned to appreciate his cautious optimism. Technology is one of the obstacles for all renewable energy sources. Wind and solar technologies are far more advanced than marine technologies, still in their nascent stages. Designs similar to the Eling Tide Mill, a barrage across a tidal estuary, have been revisited several times in the past hundred years, often in response to a fossil-fuel crisis. Perhaps the earliest modern-day effort was in Passamaquoddy Bay on the border of Maine and New Brunswick, which has a twenty-six-foot tide and a network of inlets that could be blocked off by barrages to form inland “pools.” The hydraulic head of these pools could then be utilized to funnel water through electricity-generating turbines.

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