Solar-powered vehicles. Paul MacCready, already famous for creating a human-powered aircraft that flew across the English Channel, designed and built Solar Challenger, which in 1981 flew from Paris to Canterbury, England, across the English Channel, flying a total of 163 miles and reaching an altitude of 11,000 feet. NASA developed solar-powered aircraft that have greatly exceeded that record.18
Space travel and solar energy. If you’re planning a trip to outer space, perhaps to the moon or to Mars, you have two sources of energy for the long term, nuclear and solar, and space vehicles make use of both. The space station relies on solar energy, and so do the cute little Mars rovers that captured public attention when they began to rove slowly over the Martian landscape doing the bidding of Earthbound planetary geologists.
Downsides
Why aren’t nations rushing even faster to install solar power facilities? And especially, why isn’t the United States—the world’s largest energy user—rushing to become a world leader in solar energy production? We can ask the same question about China and India, the two most populous nations and the two that have had the most rapid recent increase in energy use.
Costs
Today, primarily because of the cost of manufacturing photovoltaic devices, electricity from solar energy is more expensive than from most other sources, including fossil fuels. In the United States, according to the Department of Energy, electricity from solar energy costs 21¢ per kilowatt-hour for industrial production and 38¢ per kilowatt-hour for residential production,19 while the national average price to consumers is 13¢ for industrial users and 16¢ for residential users.20 Solar thermal towers and systems with parabolic reflecting mirrors have been cheaper to operate, providing electricity at about 12¢ per kilowatt-hour.21
Are the costs prohibitive? In 2002 Con Edison built New York City’s largest commercial rooftop solar energy system for $900,000, providing energy for 100 houses. Assuming an average of three people per home, the installed cost is $3,000 per person. For all 300 million U.S. residents, the installation cost would be $900 billion.
The U.S. balance of trade is in the red by about $60 billion a month, or $720 billion a year, and much of this trade imbalance is due to the cost of foreign oil. So, for the equivalent of one year’s trade imbalance, the United States could pay at least 80% of the cost of installing solar energy facilities for all domestic electrical consumption. The war in Iraq—justified, many say, in part to protect our petroleum sources—has cost an official federal allocation of more than $600 billion. And the Pentagon’s acquisition budget reached $1.6 trillion in 2007.22 In March 2008, a report by Nobel Prize-winning economist Joseph Stiglitz estimated that the true direct costs of the Iraq war will be $1.5 trillion or more, and the total costs, including the costs of health care and rehabilitation of veterans, will be more than $3 trillion.23
For the cost of the Iraq war, or perhaps just one-half or one-quarter of those costs, solar energy systems could have been installed to provide domestic electricity for all the people in America—energy forever!
As we saw earlier, the numbers become even more amazing for the dry, sunny climate of Arizona, where covering just 1% of the land with solar collectors would produce electricity for more houses than exist in the entire United States.
New solar cell technologies may lower costs. Although solar electrical devices are amazingly efficient, this technology is developing rapidly and costs could go down. Right now the best candidates for new kinds of solar collectors are thin film (a variation on the silicon cells that have been well established) and organic compounds. Crystalline silicon oxide, the material from which photovoltaic chips are presently made, is more expensive to make but more efficient than others. Amorphous silicon is used in “thin film” and is cheaper to manufacturer but less efficient. The engineering question is whether it is economically advantageous to pay more for higher efficiency of the fundamental receptor or to go with the cheaper basic unit. The latter will be the best choice only if the total cost is due largely to the cost of the primary photovoltaic cells.
This is not generally the case at present, but could change. Right now, photovoltaic cells represent about half the cost of a solar-electric installation,24 suggesting that perhaps more costly, more efficient units are a better economic approach than cheaper, less efficient photovoltaic cells. But this debate is ongoing and will be resolved only by more research and development. It is beneficial at present to have both approaches taken, as is happening now because some corporations are producing the crystalline product and others are producing thin films.
Although silicon is the basis of most of today’s photovoltaic cells, other chemical elements also produce a photoelectric effect, in particular cadmium and gallium-arsenide, toxic elements whose use should be either restricted or carefully monitored and controlled for health and safety.
Manufacturing limits
One of the major downsides, perhaps the major one, is that the manufacturing capacity to produce photovoltaics and solar thermal systems is presently inadequate to meet growing U.S. and global energy needs.25 But the good news is that the number of photovoltaic cells manufactured in the United States is growing about 40% per year. If this rate of increase continues, solar photovoltaics could provide as much as one-third of the total energy the United States will need in 2050, as I discuss in Chapter 13, “Solutions.” Whether this can happen without large-scale government investment that looks beyond the immediate market is unclear. Professor Nathan Lewis of Caltech writes: “Researching, developing, and commercializing carbon-free primary power technologies capable of 10–30 TW by the mid-21st century could require efforts, perhaps international, pursued with the urgency of the Manhattan Project or the Apollo Space Program.”
Energy storage
A downside that is always pointed out is how to store the energy from sunlight. (This is true of wind energy as well.) The problem is perhaps most spectacularly illustrated by attempts to make solar-powered airplanes.
After Paul MacCready’s successful design of the Solar Challenger, the solar-powered airplane that crossed the English Channel in the 1980s, NASA experimented with a remote-controlled solar-powered light aircraft called the Pathfinder. The best of these, Pathfinder Plus, flew to an altitude of 80,201 feet on August 6, 1998 (Figure 7.7). However impressive this was, the Pathfinder Plus had a limitation: It could carry only enough batteries for a few hours of flight after dark. As a kind of diurnal creature that had to land not too long after dark, it was not really a practical airplane.
Figure 7.7 NASA’s Pathfinder Plus solar-powered airplane.26 (Nick Galante/NASA Dryden Historical Aircraft Photo Collection)
There’s been a lot of headshaking about the problem of storing the energy from sunlight and wind, as if this problem were unique to these two energy sources. But energy storage is also a problem for nuclear power plants, because they are most efficient when they run at the maximum electrical output all the time. In some cases, nuclear power plants have been linked to reservoirs, pumping water up into the reservoir at night when the demand for electricity was low, and generating electricity during peak demand from both nuclear reactions and waterpower. During a drought or a rainy season, hydroelectric dams and reservoirs, too, have a storage problem.
We talk about solutions to energy storage in Chapter 10. In brief, the problem can be partially overcome by (1) connecting solar generators to the grid, (2) using solar energy to heat water, and (3) using the electricity to make gaseous and liquid fuels (starting with hydrogen taken from water). Of course, (4) storing electricity in batteries is always an option, but as NASA’s Pathfinder Plus demonstrated, this has its limitations. We can also use the energy to do tasks for us whose timing is not very important, such as pumping water up into water towers for distribution later and desalinating water (processes that can be done whenever the energy is available).
Other means of storage have been proposed, and some tested. One of them is to store the energy mechanically in
a flywheel and use that energy as needed by having the spinning wheel connected to an electric generator or directly to the wheels of a land vehicle.
Storage is not a simple problem with a single simple solution, but it is solvable, as I explain later.
Environmental effects: landscape beauty and competition for space
It would be naive to think that any source of energy had absolutely no undesirable effects, especially environmental effects. As Barry Commoner told us a long time ago, there is no such thing as a free lunch in nature. So probably some environmental problems will arise even from the use of solar energy. One that comes to mind is landscape beauty. Although solar collectors usually lie horizontally and thus have much less effect on scenery than do wind turbines, it will not be surprising if in some locations many acres covered by the black surfaces of photovoltaics are considered a blight on the landscape. As with wind power, solar facilities should be situated with the help of professional landscape architects and planners and experts in ecology to minimize potentially negative effects.
Solar parks will in some cases be seen as competing with other uses for land, but one advantage of some solar park designs is that the land can be open to multiple uses. For example, many solar installations are on rooftops. The most likely environmental negative of solar energy is with the mining, manufacturing, and recycling of materials, especially once solar becomes one of the world’s major energy sources. Right now, recycling of batteries is not done efficiently. And while silicon forms some of the most common earth materials and is thus readily available, its mining creates fine dust that can be a local health and environmental problem and cause regional, even global, pollution if emitted high into the atmosphere. Surface mining for the large-scale manufacture of photovoltaic cells will damage landscapes and ecosystems in ways similar to surface mining, except that there will be less likelihood of acid drainage.
The bottom line
• The sun offers the greatest amount of energy, and could by itself, using a small percentage of Earth’s surface area, provide the equivalent of all the energy used in the world by people.
• Solar energy has great potential and is benefiting from rapid increases in research and development, which will lower its costs.
• European nations are taking the lead in the installation of large solar facilities, with Germany and Spain outstanding users of this energy source.
• Solar energy is providing electricity and heat for cooking in many developing nations where a large-scale electrical grid does not exist and may never be practical.
• For many of the world’s people, solar energy offers the only way to participate in modern, high-technology activities.
• Solar energy is bound to be a major player in the supply of energy in the future.
8. Ocean power
Key facts
• Energy in ocean currents, tides, and waves could provide twice the world’s current energy use.
• Wave energy alone, using current technology, could provide 15% of the world’s electricity.
• If the United States could harness 40% of the nearshore wave energy, it would capture as much energy as is generated by all freshwater hydropower now available in the U.S.
• The oldest use of ocean energy is from the tides. During their occupation of Great Britain, the Ancient Romans built a dam that captured tidal water and let it flow out through a waterwheel. In Medieval England, use of tidal power was not uncommon.
• The most successful modern tidal power plant is off the coast of Brittany, France, producing 10 million watts of electricity a year.
• Currently proposed is the world’s largest tidal power plant, in Great Britain’s Severn River estuary. It would have a generating capacity of 2 billion watts.
The wave of the future?
In March 2008, the Suntory Mermaid II, a new kind of boat, left Honolulu with a plan to travel more than 3,700 nautical miles (Figure 8.1). The trip had been done before, of course, but this boat’s propulsion system was new—the Suntory Mermaid II has two horizontal fins that move up and down with the waves and generate the power to push the boat forward. Solar energy provides electricity. Dr. Yutaka Terao of the Department of Naval Architecture and Ocean Engineering at the Tokai University School of Marine Science and Technology invented the system that powers the boat.1, 2
Figure 8.1 The Suntory Mermaid II—how to ride waves. (Illustration by Kevin Hand, www.kevinhand.com)
Will this be the wave of the future, or just another futile attempt to harness the vast energy of ocean waves and currents and make it an important, practical alternative source of energy for us?
In Chapter 4, “Water Power,” we talked only about power generated by freshwater—rivers, streams, hydroelectric dams. We are giving the biggie—the world’s saltwater—a chapter all its own, not just because oceans are bigger but also because harnessing their energy is a whole different ballgame. The oceans are a vast renewable resource that, constantly in motion, could be a huge source of energy. The problem is that except in a few cases, their storms, currents, waves, and tides have been too powerful for our energy-converting machines.
Think of the ocean as a giant solar-energy collector, covering 70% of the Earth’s surface. As the National Energy Research Laboratory explains it: “In an average day, 60 million square kilometers (23 million square miles) of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil. If less than one-tenth of one percent of this stored solar energy could be converted into electric power, it would supply more than 20 times the total amount of electricity consumed in the United States on any given day.”3
The ocean holds two kinds of energy: one from its moving currents, waves, and tides, which we might informally call mechanical energy, and the other from the temperature difference between surface water and deep water, which we might informally call thermal energy. The World Energy Council writes that the ocean could provide the equivalent of “twice the world’s electricity production,”4 and that wave energy alone, with current technologies, could provide 15% of the world’s electric energy.
These are rough estimates, to some extent limited to the efficiencies of existing technologies. It’s hard to forecast improvements in efficiency and advances in the kinds of environments where ocean energy could be tapped, and therefore it is difficult to figure out how this energy could be captured and turned into electricity. Engineers generally try to take limitations into account. For example, another estimate assumes that only 20% of America’s offshore wave energy would be harnessed, and that would be at 50% efficiency (meaning that half of the energy in the waves would end up as usable electricity). Even given these limitations, wave energy could still provide an amount of energy equal to all U.S. hydropower in 2003.
In other words, there’s a hell of a lot of energy out there (Figure 8.2). The big trick is figuring out a way to turn that energy into reliable electricity with technologies that won’t be quickly destroyed by ocean storms and the powerful eroding ability of seawater. There are a few successes, but big advances still lie in the future. 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.
Figure 8.2 Some regions believed to have great ocean energy potential. (Electric Power Research Institute)
Ocean motion
It is helpful to think of the mechanical energy in the ocean’s moving waters as being of two kinds: tidal power along the shore and in river estuaries; and the power of offshore waves and currents.
Tidal power
Given the difficulty of capturing ocean energy, it’s surprising that the use of tidal power traces back at least to the Roman occupation of Britain. Archaeological excavations show that dams were built then to store water from high tides, and this water was released to run mills that ground grain.5 In the Middle Ages, tidal power remained in use. The famous Doomsday Book of AD 1086
mentions tidal mills—more or less conventional water mills built to run off the tide as it flowed in and out.6, 7 The Eling Mill in England, still in operation, is believed to date back to those times.
La Rance: proving that the tides can give us electricity for decades
One of the most successful modern tidal power plants is La Rance, along the coast of Brittany, France, which for years was the only full-scale tidal power station in the world. It was built in 1967 and produces 10 MW—enough to provide electricity for 300,000 homes, or for 4% of the population of Brittany—from 24 turbines, which produce 0.5 billion kilowatt-hours of power a year (Figure 8.3).8 Wisely, this facility was built along a part of the Brittany coast that has one of the greatest tidal ranges in the world, about 40 feet between high and low tides. This maximizes the energy that can be obtained. Also impressive is that this power plant has never suffered serious damage or mechanical breakdown and, in contrast to many major energy sources that are eyesores, has become a tourist attraction.9
Powering the Future: A Scientist's Guide to Energy Independence Page 18