Figure 8.3 La Rance Tidal Power Plant, said to be the only full-scale operational tidal plant of its kind in the world. It was built in 1967 and has continued to operate without suffering major damage from corrosive saltwater.11 (Dani 7C3/Wikimedia Commons)
We can’t expect La Rance imitators to be set up and work everywhere, because only a few places have such favorable topography. Another famous one is the Bay of Fundy in Canada, whose maximum tidal range is even a bit larger, at about 49 feet. There are also good sites along the northeastern United States. Present conventional technology requires a tidal range of at least 26 feet.
One disadvantage of a tidal-power dam is that it could restrict fish traveling up and down the river. There could also be other local damage to wildlife and fish habitats.10
Great Britain is currently proposing to build the world’s largest tidal power plant in the Severn River estuary, the location of the world’s second-largest tidal range, more than 45 feet. If built, it would produce 17 billion kilowatt-hours a year.12 This is equivalent to a 2-million-kilowatt conventional power station. The British government proposes to spend $29 billion to build the facility, which means that the installation cost would be $0.07 per watt, cheaper than any other commercial form of energy. The tidal power plant is expected to run for 120 years.13,14
Environmental groups are opposing its construction, however. They say that it would threaten 70,000 acres of protected wetlands where almost 70,000 birds winter and also disrupt salmon, shad, lamprey, and sea trout migrations. They argue in addition that the project is too expensive and that there are other, much cheaper alternatives.
Proponents point out that if global warming raises the sea level as some climatologists forecast, the Severn estuary will be flooded anyway. And as for the cost, is it really so expensive?
Experimenting with ocean waves and currents
With all the energy potentially available from the ocean, a lot of imagination is going into designing machines to turn the energy in ocean currents and waves into electricity. The idea is to get away from building dams and other fixed structures, which fight the very motion that they try to use, and instead seek devices that would be immersed in the ocean and convert the motion of currents into electricity in a more forgiving way.
An Australian company has taken a bioengineering approach, using designs that occur in nature. One of their devices looks like a frond of giant kelp, the brown seaweed that forms underwater “forests.” Like the kelp, the new device has holdfasts that anchor it to the bottom of the ocean and a flexible arm that waves back and forth with the motion of the water like the kelp’s frond. This motion turns a generator that makes electricity.
Another device, shaped like a shark’s fin, rolls with the moving water and lets extremely large waves pass by (Figure 8.4). Still another, called the Pelamis, is being developed by Ocean Power Delivery in Edinburgh, Scotland. The New York Times describes it as “a snakelike wave energy machine the size of a passenger train, which generates energy by absorbing waves as they undulate on the ocean surface.”15
Figure 8.4 One of the new approaches to harnessing the ocean’s energy is this device, shaped like a fish’s fin so it can “swim” with the ocean currents and thus is less likely to be damaged. (bioSTREAM™, Biopower Systems, ©www.biopowersystems.com)16
Whether these turn out to be practical, efficient, and durable, only time will tell, but the potential energy is so great that this seems a worthwhile area to explore. In addition to the obvious benefits of not producing greenhouse gases, the devices are within the ocean, so they are not unsightly. One caveat: The extent to which they might affect ocean habitat, if installed on a large scale, remains unknown.
In addition to small start-up companies, some of the large electrical generator corporations are getting interested in this kind of ocean technology, including General Electric, the Norwegian company Norsk Hydro, and Eon Corporation of Germany.17
Thermal energy: using the ocean’s temperature differences
The engines we are most familiar with today—gasoline and diesel internal combustion engines, steam turbines, and jet engines—are heat engines: They rely on the temperature difference between a hot and cold gas or liquid in different reservoirs to produce usable mechanical and electrical energy. Usually, the cool reservoir is the same temperature as the outside air or water, whereas the hot gas or liquid is heated by burning a fuel.
The idea of an ocean heat engine is not new. This classic kind of energy device was the focus of (and the motivation for) development of the science of thermodynamics in the 19th century. Jacques Arsene d’Arsonval, a French physicist, first proposed using the heat energy of the ocean in 1881. No one tried it, however, until 50 years later, when a student of his, Georges Claude, built an experimental system at Matanzas Bay, Cuba. It worked, producing 22 kilowatts—enough to light 220 100-watt incandescent lightbulbs. Five years later he built a bigger plant housed on a cargo ship off the coast of Brazil. The Cuban and Brazilian systems worked but were destroyed by storms.18 More recently, in 1993, a system was installed by the Electric Power Research Institute at Keahole Point, Hawaii, and ran for a while as an experiment, during which it produced 50 kilowatts of electricity. These systems are still considered experimental and not ready for large-scale electrical generation.
In theory, you can produce mechanical and electrical energy using fluids of any two different temperatures, even if the temperatures differ by only a few degrees. But the closer the temperatures of the hot and cool fluids are to each other, the smaller the amount of useful energy yielded and the larger the machine must be to produce a practical amount. An automobile’s internal combustion engine can be relatively compact because the burning gasoline within the cylinder is much hotter than the outside air. The pistons of an old-fashioned train’s steam engine were also relatively small because the steam was so much hotter than the outside air.
In most places most of the time, surface ocean waters are somewhat warmer than deep ocean waters, and it was long ago realized that, at least in theory, you could operate a huge piston by pumping cold water from the depths and using it with the slightly warmer surface waters. However, one of the problems with developing a practical ocean-heat engine is that because there’s only a few degrees’ difference between deep and surface ocean waters, the engine would be huge and unwieldy, not likely to do well in storms.
The current focus is therefore much more on the technologies we discussed earlier that make use of “ocean motion.” Still, given the huge energy potential of an ocean-heat engine, attempts to develop a practical one continue. According to the Electric Power Research Institute, “As long as the temperature between the warm surface water and the cold deep water differs by about 20°C (36°F), an OTEC [Ocean Thermal Energy Conversion] system can produce a significant amount of power. The oceans are thus a vast renewable resource.” Such a system would provide about 10 billion KW, or two and a half times the amount of electricity available from present generating systems around the world.19
The bottom line
• The ocean offers huge amounts of energy from its currents, tides, and waves, but this is little developed, largely because of the problems posed by storms and the corrosive power of seawater. Progress seems possible, however, and this may be the best source of waterpower in the future.
• Tidal energy has been captured and used for several thousand years and is used today where conditions are best—a large tide and not much chance of severe storms. Considerable potential exists to expand tidal power in such specific locations.
• A proposed tidal power plant on the Severn River estuary in Great Britain would be the world’s largest, providing 5% of that nation’s electricity. It is, however, controversial among environmentalists because it could affect bird and fish habitats.
• Wave energy is obviously widespread, and rapid invention and technological development are under way. Whether the new devices will make tapping wave power practical enough to prov
ide a significant amount of the world’s energy is unknown, but it is promising enough to warrant research and development.
• The Electric Power Research Institute, a nonprofit backed by major U.S. power corporations, is sponsoring several projects to test technology for harnessing ocean energy. However, few large corporations and government agencies around the world have been set up to use ocean energy.
• Because ocean energy is still in the developmental stage, it is probably a place for venture capital and small start-up companies. But in a truly enlightened world devoted to renewable, sustainable, nonpolluting energy sources, funds now going to nuclear energy and the quest for more fossil fuels would be diverted to ocean energy technologies.
9. Biofuels
Figure 9.1 Harvest of experimental oilseed crops at Piedmont Biofuels farm, in Moncure, NC.1,2 (Photo by Debbie Roos, North Carolina Cooperative Extension)
Interest in and enthusiasm about biofuels are growing among some small farms, like the members of the Piedmont Biofuels Cooperative in North Carolina. Will biofuel agriculture be the wave of the future and prove environmentally sound and sustainable?
Key facts
• The three kinds of biofuels are crops grown to be turned into fuels; organic wastes that can be burned for energy rather than dumped as is; and firewood.
• Biofuels currently provide only about 3% of America’s energy, but two-thirds of this is from firewood and one-fifth from wastes. Agrifuels—crops grown to be made into fuels—provide only 12% of this total, or less than 1% of America’s energy.
• Before the Industrial Revolution, firewood was a primary source of energy, along with the energy of domestic animals. At the turn of the 21st century, firewood was still important, providing 5% of the world’s total energy use. In the United States, it provides heating for about 2 million homes.
• Firewood is especially important in poor, developing nations. In Rwanda, locally grown trees provide 84% of fuel for domestic cooking and heating.
• Wastes might provide as much as 8% of America’s energy. Waste cooking oil makes a cheap fuel, but you have to be careful about its cleanliness, as dirt in it can clog internal combustion engines.
• Many scientific studies indicate that crops planted and harvested today to be turned into biofuels either take more energy than they yield or else provide only a small energy benefit.
• Any large increase in cropland devoted to biofuels will tax the supplies of water for irrigation and phosphate fertilizers. The price of such fertilizers has risen rapidly in the past several years because of increasing demand to meet the world’s food needs.
• In the United States, biofuels are heavily subsidized. Direct subsidies are $1.00 a gallon for biodiesel produced as an agricultural crop directly for use as a fuel and $0.50 a gallon for biodiesel produced otherwise (such as from wastes).
Let me tell you about my father-in-law
My father-in-law, Heman Chase, a New Hampshire surveyor and country philosopher, heated his house with firewood he cut by himself for more than 30 years. He owned more than 200 acres of farm and woodland and kept about 60 acres of it as his primary woodlot. He also gathered wood from trees that blew down on his land or a neighbor’s, who asked if he would mind clearing it away. Heman burned about ten cords of wood a year in a modern furnace that provided heat through a system of hot-water radiators. It was a lot of work to cut trees down, saw them into lengths that would fit in his pickup, drive them home, unload them, cut them into smaller chunks with a power rig he built for his small tractor, split the chunks by hand, and stack them. He enjoyed the work, but it did take a lot more of his time than he realized.
When he got into his seventies and wasn’t well enough to do this anymore, he had a propane gas tank put in his backyard and a gas furnace installed next to the wood furnace. After a year he told me, laughing, that it was costing him so little to heat the house with gas that he probably should have saved himself a lot of time and effort years earlier. His ten cords of wood contained about the same amount of energy as 1,300 gallons of gasoline or 1,180 gallons of diesel fuel.3 At early-1970s prices,4 Heman might have paid about $600 for fossil fuel to heat his house—pretty cheap compared with what his time was worth as a professional surveyor and how much time he spent on his firewood. I don’t think he would have made that choice, but it tells us something about what is required if you want to go the biofuels route.
Heman built his house with his own hands in the 1930s. Most of us think nobody back then gave much thought to the environment, but he and his New England friends were conscious of their surroundings and tried to care for them. Even so, Heman’s 60-acre woodlot looked quite different from his other woods. The species were different, because he cut out the trees that made the best firewood—sugar maple and oak—and left what he considered trash trees, like poplar. The woodlot was more open, and the soil looked more compressed and used.
Use of wood and dung as fuel today
My father-in-law had a choice—many people today don’t. Before the 20th century, wood was a major fuel in the United States. Many people in the world still use it. Around the turn of the 21st century, 5% of the world’s total energy use was supplied by about 1.5 billion tons of fuelwood.5 People who live in developing nations continue to depend on firewood and animal dung as their primary fuels for heating and cooking. In Rwanda, for example, locally grown trees provide 84% of domestic cooking and heating fuel. At this point, consumption outstrips the supply, so Rwandans are facing a firewood shortage.6
As arduous as Heman Chase’s use of firewood in New Hampshire might seem, still harder is the collection of firewood for cooking among the Maasai in Kenya. The grueling task falls to women and girls, who must walk long distances to collect wood and then carry their heavy loads of wood home on foot. On average, by the time a Maasai girl reaches the age of 16 she has carried 16 tons of wood home, on each trip carrying half to two-thirds of her own weight.
Perhaps more than any other story in this chapter, the toil of the Maasai and other African women to collect firewood by hand points out how important energy is for human life, and how difficult it can be to obtain the material goods necessary for life without modern machines and superabundant energy.7
Since the beginning of the 20th century, the use of wood for home heating has gone in and out of fashion several times in the United States. With easy access to inexpensive fossil fuels, a general transition away from firewood took place, especially in cities, by the mid-20th century, although it continued to be used widely in rural areas. Then in the 1960s, the era when hippies and flower children and many others began a back-to-the-land migration, woodstoves became popular again. So popular that small valleys in Vermont, New Hampshire, Colorado, and California suffered air pollution on days of temperature inversions, when the wood smoke from all those homes couldn’t get out over the mountains. As a result, the Environmental Protection Agency established regulations for clean-burning woodstoves, and firewood went out of fashion. As recently as 1993, some 3.1 million homes were heated with wood; but by 2001 the number had fallen to only 2 million.
Recently, with the price of petroleum skyrocketing, woodstoves became popular again. By midwinter of 2008, New Englanders were heading back to stores to buy woodstoves. In an article in the New York Times, Roy L’Esperance, the owner of the Chimney Sweep in Shelburne, Vermont, said he has seen sales of woodstoves increase 20%. “There’s a lot of people buying big stoves, planning on tackling oil head-on,” he explained.8
Right now there are an estimated 40 to 45 million wood-burning appliances in the U.S., 15 million of them woodstoves. Only one-quarter of these were built after the EPA set up air-pollution standards for woodstoves.9 These contribute 430,000 tons—about 6%—of the total particulate-matter pollution in the U.S.10
Interest in biofuels has been growing
Biofuel (also called biomass power) became popular with environmental groups and agricultural industrial corporations, and the darli
ng of Washington politicians, in the 2000s, promoted by agricultural subsidies. Scientific American liked it—a 2006 special issue featuring “Energy’s Future Beyond Carbon” listed “15 ways to make a wedge” in carbon production. Number 13 was “drive 2 billion cars on ethanol, using one sixth of the world cropland.”11 As recently as May 5, 2007, an editorial in the New York Times supported corn-based ethanol.12 Signaling this popularity, on February 24, 2008, Virgin Atlantic Airline flew a Boeing 747 from London to Amsterdam using 20% biofuel and 80% conventional jet fuel, the first test of biofuel by a commercial jet.13 In the fall of 2008, Air New Zealand did a test flight with the same model airplane, fueling one engine with a 50-50 mixture of conventional fuel and biofuel. And at the time of this writing, the U.S. Air Force is planning in the spring of 2010 to fly an F/A–28 Super Hornet with a variety of biofuels.
Powering the Future: A Scientist's Guide to Energy Independence Page 19