At the same time, the most easily accessed coal beds will have become depleted: like cheap oil, cheap coal relies on reserves that lie relatively close to the surface, but these represent only a small percentage of the world"s total coal resources. As those are exhausted, producers will have to return to traditional underground mining. But many underground mines have been run down and allowed to flood. Moreover, most skilled miners have lost their jobs and have been routed into other occupations. Mining is difficult, dreary work, and few miners want their children to follow in their footsteps. In areas of the Western world where underground coal mining is still practiced, the average age of miners is over 40. Thus, in order to maintain or grow coal production in the future, the industry will have to find new workers as well as develop new methods of production. As this occurs, society will be deriving less net energy from the process.
In their book Beyond Oil, John Gever et. al. describe coal"s depletion profile and decreasing net energy yield as follows: Because the United States has used only a small fraction of its total coal supply, a Hubbert a.n.a.lysis is only speculative ....
Besides glossing over the environmental damage resulting from heavy coal use (acid rain, particulate pollution, carbon dioxide buildup in the atmosphere), optimistic projections have been based on total coal resources and have ignored the fact that substantially less net energy may ultimately be obtained from these supplies. The quality of mined coal is falling, from an energy profit ratio of 177 in 1954 to 98 in 1977 .... These estimates include only fuel used at the mine, however, and do not include the considerable amounts of energy used to build the machines used in the mines, to move the coal away from the mines, and to process it. When these costs are included, the shape of the energy profit ratio curve changes .... [and drops] to 20 in 1977... If it continues to drop at this rate, the energy profit ratio of coal will slide to 0.5 by 2040.7 The authors" last statement deserves some emphasis: an energy profit ratio of 0.5 means that twice as much energy would be expended in coal production as would be yielded to do useful work. Coal has a relatively low energy density to begin with, and as miners exhaust the more favorable seams and then move on, the average heat content of a pound of coal is gradually dropping. If the study by Gever and his co-authors is correct, from a net-energy standpoint coal may cease to serve as a useful energy source in only two or three decades.
A recently published Hubbert a.n.a.lysis of coal production in the US predicts that, depending on the rate of demand, production will peak between 2032 and 2060.8 It is theoretically possible to use coal as the raw material from which to make synthetic liquid fuels that could directly replace petroleum. The process has already been tested and used; after all, it kept the Germans going during World War II, and an improved version is currently employed by the Sasol Company in South Africal. But the net energy yield from coal-derived liquids is extremely low and will only decline further as the net energy from coal itself dwindles. Walter Youngquist writes: If coal were to be used in the United States as a substantial subst.i.tute for oil by liquefying it, the cost of putting in place the physical plants which would be needed to supply the United States with oil as we use it now would be enormous. And to mine the coal which would have to go into these plants would involve the largest mining operation the world has ever seen.9 It may be possible to improve the efficiency of the process of releasing coal"s stored energy. The most promising proposal in this regard comes from the Zero Emission Coal Alliance (ZECA), a program started at New Mexico"s Los Alamos National Laboratory. ZECA has designed a coal power plant that extracts hydrogen from coal and water and then uses the hydrogen to power a fuel cell (we will discuss hydrogen and fuel cells in more detail below). The ZECA plants would attempt to recycle nearly all waste products and heat. Promoters claim that ZECA plants could produce electricity with an efficiency of 70 percent, compared to an average efficiency of about 34 percent at current combustion-based coal power plants (though newer combustion technology already yields greater efficiencies, in the range of 55 percent). That would mean releasing twice the energy from the same amount of coal, as compared to the present average. ZECA"s system is not truly zero-emission (no energy production system is), but does represent a significant potential improvement over combustion-based technologies. However, ZECA"s process for the sequestration of CO2 will probably const.i.tute a significant drain on net energy yields, and designers say the necessary fuel-cell technology is still at least five years away from commercial application.
Abundant coal, used to generate electricity, will enable us to keep the lights burning for a few more years; but, taking into account its other limitations - and especially its rapidly declining net energy yield - we cannot expect it to do much more for us in the future than it is already doing.
Nuclear Power.
In a nuclear-powered electrical generating plant, uranium fuel rods are brought together under highly controlled conditions to create an atomic chain reaction that produces great heat. That heat is transferred to water, changing it to steam, which turns turbines to generate electricity.
The first commercial plant built in the US was the Shippingport, Pennsylvania, Atomic Power Station of the Department of Energy and the Duquesne Light Company. In a dramatic high-tech dedication ceremony, ground was broken in 1954 by President Dwight D. Eisenhower, who also opened the plant on May 26, 1958. Nuclear power was hailed as the nation"s route to permanent prosperity; in reality, however, the DoE"s highly touted "Atoms for Peace" program was a direct outgrowth of the nation"s nuclear weapons program and served both as a public relations exercise and as a source for fissile materials for warheads.
Many nuclear power stations were built during the 1960s and "70s; today, 103 are operational in the US. In the 1950s, promoters promised that nuclear power would be so cheap as to be essentially free; but experience proved otherwise. Today, electricity from nuclear plants is inexpensive - the industry sometimes cites costs as low as two cents per kilowatt-hour - but this is true if only direct costs are considered. If the immense expenditures for plant construction and safety, reactor decomissioning, and waste storage are taken into account, nuclear power is very expensive indeed.
During the 1970s and "80s, an antinuclear citizens" movement was successful in swaying public opinion against nuclear technology and in discouraging the further growth of the industry. The movement"s warnings about the dangers of nuclear power were underscored by serious reactor accidents at Three Mile Island in Pennsylvania and Chern.o.byl in the Soviet Union; other less-publicized accidents have plagued the industry from its inception and continue to do so. As a result of both greater-than-antic.i.p.ated expenses and public wariness, no orders for new plants have been placed in the US since the 1970s.
Nuclear power plants produced 3.6 percent of all the energy consumed in the US in 1980; by 2000, that number had climbed to 8.1 percent. This increase was due not to the building of new reactors, but to increased efficiency in the operation of existing plants. In 2000, the industry achieved a record overall average capacity factor (the percentage of potential output actually achieved on average) of nearly 86 percent, up from 58 percent 20 years earlier.
Today about 20 percent of all the electricity generated in the US comes from nuclear sources. Globally, 12 percent of the world"s electricity, and 5 percent of the total energy consumed, are nuclear-generated. Some nations derive much more of their energy from nuclear plants than does the US: France, for example, gets 77 percent of its electricity from atomic energy, Belgium 56 percent, and Sweden 49 percent. There are currently 442 reactors operating worldwide. In Western Europe, France is the only country still building nuclear plants; only in Asia is the nuclear-power industry expected to expand significantly in the foreseeable future.
Could nuclear power take up the slack as energy from petroleum production declines? Those who argue that it could claim that nuclear power is: Abundant: There is a virtually limitless supply of fuel (a.s.suming breeder reactors, which reprocess spent fuel); Clean: It is non-polluting, having no CO2 emissions; wastes are produced in small quant.i.ties and the problem of their disposal will be solved once a single permanent repository is created; Practical: Nuclear fuel has the highest energy density of any fuel known; further, nuclear power is inexpensive, the produced electricity being cheaper than energy from coal; and Safe: It is safer than many people believe, and becoming safer all the time. The likelihood of a person dying from a nuclear accident is already far lower than that of dying in an airplane crash, while new technology on the drawing boards will make nuclear power virtually 100 percent safe in the future.
However, when these claims are examined in detail, a very different picture emerges.
Abundant? The fuel supply for nuclear power is virtually limitless if we use fast-breeder reactors to produce plutonium - which is one of the most poisonous materials known and is used to make nuclear weapons. But only a few fast-breeder reactors have been constructed, and they have proved to be prohibitively expensive, largely as a result of the need for special safety systems. These reactors generate an extraordinary amount of heat in a very small s.p.a.ce and use molten metals or liquid sodium to remove the heat. Designing reactors to take these properties into account has made them costly to build and maintain. It also makes them susceptible to serious fires and long shutdowns: the French Superphoenix reactor operated for less than one year during the first ten years after it had been commissioned.
Figure 19. US energy consumption by source (Source: US Energy Information Administration) France and the UK, despite having pursued breeder programs for several decades, have no plans for constructing more such plants. j.a.pan has not restarted its Monju reactor, which was shut down after a sodium fire in December 1995. Among countries that have constructed breeders, Russia alone supports further development.
It is also possible to reprocess spent fuel into a form known as MOX (mixed oxide), which consists of a mixture of plutonium and uranium oxides. Reprocessed MOX fuel can then be used to replace conventional uranium fuel in power plants. However, only two MOX plants have been built (one in the UK, the other in France), and both have turned out to be environmental and financial nightmares.10 Uranium - the usual fuel for conventional reactors - must be mined, and it exists in finite quant.i.ties. The US currently possesses enough uranium to fuel existing nuclear reactors for the next 40 years.11 The mining process is wasteful, polluting, and dangerous: the early New Mexico uranium mines, which employed mostly Navajo workers, ruined thousands of acres of Native lands and poisoned workers and their families. The entire episode const.i.tutes a horrific and permanent blot on the industry"s record.12 Further, much of the energy needed to mine uranium currently comes from oil. As petroleum becomes more scarce and expensive, the mining process will likewise become more costly and will yield less net energy.
Clean? Vice President d.i.c.k Cheney told CNN on May 8, 2001, that nuclear power "doesn"t emit any carbon dioxide at all."13 But this is true only in the sense that the nuclear chain reaction itself doesn"t create such emissions. Mining uranium ore, refining it, and concentrating it to make it fissionable are all highly polluting processes. If the whole fuel cycle is taken into account, nuclear power produces several times as much CO2 as renewable energy sources.
The a.s.sertion that nuclear waste is only produced in small quant.i.ties is misleading. Direct wastes include roughly 1,000 metric tons of high- and low-level waste per plant per year - hardly a trivial amount, given that much of this waste will pose hazards for thousands or tens of thousands of years to come. Further-more, this figure does not include uranium mill tailings, which are also radioactive and can amount to 100,000 metric tons per nuclear power plant per year.14 Can the problem of nuclear waste be solved by the creation of a permanent repository? To a.s.sume so is to indulge in wishful thinking. After nearly five decades of the development and use of atomic energy, no country in the world has yet succeeded in building a permanent high-level nuclear waste repository. Moreover, the transporting of wastes to such a central repository would create extra dangers.15 Practical? It is true that nuclear fuel has an extraordinarily high energy density, but this is the case only for uranium that has already been separated from tailings and been processed - which itself is a far more hazardous and energy-intensive procedure than drilling for oil or mining coal.
The costs typically quoted for nuclear-generated electricity (1.8-2.2/ kWh) are operating costs only, including fuel, maintenance, and personnel. As noted earlier, such figures omit costs for research and development, plant amortization and decommissioning, and spent-fuel storage. Fully costed, nuclear power is by far our most expensive conventional energy source. Indeed, total costs are so high that, following the pa.s.sage of energy deregulation bills in several states, nuclear plants were deemed unable to compete, and so utility companies like California"s PG&E had to be bailed out by consumers for nuclear-related "stranded costs."16 Germany has decided to phase out nuclear power for both economic and environmental reasons.
If nuclear energy is not cheap, is it at least reliable? Certainly more so than it was two or three decades ago. However, it is worth noting that problems at the Diablo Canyon and San Onofre reactors contributed significantly to California"s energy crisis in 2001. Nuclear power plants are extremely complex - many things can go wrong. When technical failures occur, repair costs can be much higher than is the case with other types of generating plants.
Safe? For the general public, safety is probably the foremost concern about nuclear power. Siting nuclear plants has always been a challenge, as communities typically fear becoming the next Three Mile Island or Chern.o.byl. Earthquake zones must be ruled out, along with most urban areas (due to evacuation problems). While the statistical likelihood of any given individual dying in a nuclear accident is quite low, if a truly catastrophic accident were to occur many thousands or even millions could be sickened or die as a result. Nuclear power"s record of mishaps is long and disturbing. It is a telling fact that the industry has required special legislation (the Price-Anderson Act) to limit the liability of nuclear-power plant operators in the event of a major accident. If the technology were as safe as that in conventional generating plants, no such measure would be needed. Following the terrorist attacks of September 11, many commentators pointed out that if the airplane hijackers had targeted nuclear power plants rather than office buildings, the resulting human toll would have been vastly greater.
Extraordinary safety claims have been made for a new design of high-temperature reactor, the Pebble Bed Modular Reactor. However, this technology is strictly theoretical, never yet having been tested in practice. Even the International Atomic Energy Agency"s International Nuclear Safety Advisory Group has expressed misgivings about claims that the ceramic coating of the fuel "pebbles" can take the place of a normal reactor containment building. This coating consists mostly of graphite; and though graphite has a very high melting point, it can burn in air (graphite burned in the Chern.o.byl disaster as well as in the 1957 Windscale fire), so it is important to exclude air from the reactor. Current a.s.sertions that these untested technologies will be "100 percent safe" are probably about as believable as claims made in the 1950s that nuclear-generated electricity would be "too cheap to meter."17 These are all important concerns in a.s.sessing to what extent the deployment of nuclear power has been successful or even acceptable so far. But in deciding whether this energy source can help us through the transition away from oil and natural gas, we need to consider three other questions: Can the technology be scaled up quickly enough? What is its EROEI? And to what extent can it subst.i.tute for petroleum in the latter"s current primary uses, such as in transportation and agriculture?
Scaling up the production of electricity from nuclear power would be slow and costly. In the US, just to replace current electricity generated by oil and natural gas, we would need to increase nuclear power generation by 50 percent, requiring roughly 50 new plants of current average capacity. But this would do nothing to replace losses of energy to transportation and agriculture as petroleum becomes less available.
Since coal is currently used mostly for electricity generation, nuclear power could conceivably subst.i.tute for coal; in that case, nuclear generation would have to increase by 250 percent - requiring the construction of roughly 250 new atomic power plants.
But using atomic energy as a replacement for petroleum is much more problematic. To replace the total amount of energy used in transportation with nuclear-generated electricity would require a vast increase (on the order of 500 percent) in nuclear generation capacity. Moreover, the replacement of oil - gasoline, diesel, and kerosene - with electricity in the more than 700 million vehicles worldwide const.i.tutes a technical and economic problem of mammoth proportions. Current storage batteries are expensive, they are almost useless in very cold weather, and they need to be replaced after a few years of use. Currently, there are no batteries available that can effectively move heavy farm machinery or propel pa.s.senger-carrying aircraft across the oceans. (We will return to the problem of storing electrical energy later in this chapter, in discussions about hydrogen and fuel cells.) Finally, the EROEI for nuclear power - when plant construction and decommissioning, waste storage, uranium mining, and all other aspects of production are taken into account - is fairly low. Industrial societies have, in energy terms, been able to afford to invent and use nuclear technologies primarily because of the availability of cheap fossil fuels with which to subsidize the effort.
For all of these reasons, it would be a disastrous error to a.s.sume that nuclear power can enable us to maintain business as usual when energy shortages arise due to the depletion of fossil fuels. New nuclear plants will no doubt be proposed and built as energy shortages arise; however, the a.s.sociated costs will be too high to permit the construction of enough plants, and quickly enough, to offset the decline of cheap fossil fuels.
Wind.
As we saw in Chapters 1 and 2, the capture of energy from wind - first by sails for transportation over water, and then by mills used to grind grain or pump water - predates industrialism. Today, sleek high-tech turbines with airplane propeller-like blades turn in response to variable breezes, generating an increasing portion of the world"s electricity.
Winds arise from the uneven heating of the Earth"s atmosphere by the Sun, as well as from Earth"s surface irregularities and its axial rotation. Winds are generally strongest in mountain pa.s.ses and along coastlines. The world"s best coastal wind resources are in Denmark, the Netherlands, California, India, southern Argentina, and China; "wind farms" have been developed in all of these places.
Wind is a limited but renewable energy resource: unlike fossil fuels, winds are not permanently "drawn down" by their use. Once a wind turbine is installed, costs are incurred primarily for its maintenance; wind itself is, of course, free. Of all renewables, wind is the one that, on a global level, is being developed the fastest. Wind power is approaching 40 gigawatts in installed capacity worldwide, out of the total electrical generating capacity of 3000 gW. Germany and Spain have recently become the world leaders in installed wind generating capacity. In the US, growth in the industry slowed in the 1990s but began a resurgence in 2000; about one percent of all electricity generated in the nation now comes from wind.
Wind-turbine technology has advanced dramatically in the past few years. Only a decade ago, engineers envisioned turbines with a maximum capacity of 300 kW, and blade rotation speeds were such that many areas had to be excluded from siting consideration for environmental reasons (turbine blades sometimes kill endangered birds, which tend to migrate along coastal areas). The optimum wind speeds for the turbines produced then were 15 to 25 MPH and only about 20 percent of actual wind energy could be converted to electricity.
Turbines that are being developed and installed today have capacities in the range of two to three megawatts. Blade rotation is much slower (resulting in less likelihood of bird kill), and efficiencies have been improved significantly. Moreover, the newer turbines can operate in more variable winds - with speeds ranging from about 7 to 50 MPH.
The cost of wind-generated electrical power is declining quickly. The National Renewable Energy Laboratory (NREL) estimates that by 2010 average prices will be in the range of 3.5/kilowatt-hour. The Lake Benton Wind Farm in Minnesota, operational as of 2002 and using 1 mW turbines, produces wind-generated electrical power at 3.2/kWh. Another large project, on the Oregon/ Washington border, is expected to produce power at 2.5/kWh. These prices are already compet.i.tive with other generating sources; and as the EROEI of coal declines and natural gas supplies dry up, wind power will look even more inviting.
Figure 20. US energy consumption by source, showing renewables, 2003 (Source: US Energy Information Administration) New vertical-axis turbine designs being developed at Lawrence Berkeley Laboratories in cooperation with the Makeyev State Rocket Center in Mia.s.s, Russia, could make wind power more feasible in a wider range of situations. Prototypes feature vertical fibergla.s.s blades that rotate around a central mast. The company that has been formed to commercialize the design, Wind Sail, expects to market small turbines to homeowners. Previous horizontal-axis designs were noisier and had a tendency to kill birds - problems solved by the new design. Vertical-axis turbines are also potentially more efficient than similar-sized horizontal-axis turbines.18 How much energy could be derived from wind? Theoretically, a great deal. A good guide is a 1993 study by NREL that concluded that about 15 quads (quadrillion BTU) of energy could be produced in the US per year. Since the newer turbines are capable of operating in a wider range of wind conditions, that potential could conceivably now be in the range of 60 quads. Total energy usage in the US is about 100 quads.19 However, the realization of that potential will require huge investments and a strong commitment on the part of policymakers. Investment will be required not just for the turbines themselves, but also for new transmission lines: a 1991 California study estimated that only 12 percent of the "gross technical potential" for wind power in that state could be realized given the existing transmission infrastructure.
In addition, it will be necessary to solve technical problems arising from wind power"s intermittent daily, monthly, and seasonal availability. Often, peak availability of wind does not correspond with peak energy demand. This is not an insurmountable problem: energy storage systems (such as the Regenesys regenerative electrochemical fuel cell) are in development that may in the future eliminate the daily variability of electricity generation from wind.20 Also, peak wind generation that exceeds momentary demand could be used to produce hydrogen (see 167).
Over the short term, the problem of intermittency should not simply be shrugged off. Germany, which now leads the world in installed wind electrical generation capacity (14,350 Megawatts at the end of 2003), therefore also has the most experience with the practical problems a.s.sociated with wind energy. A recent report from EON, the largest grid operator in Germany, points out that it is necessary to have 80 percent of wind capacity available at all times from power stations that can produce on-demand energy (i.e., coal, nuclear, hydro, geothermal, or natural gas plants). In addition, according to the report, "if wind power forecast differs from the actual infeed, the transmission system operator must cover the difference by utilizing reserve capacity. This requires reserve capacities amounting to 50 to 60 percent of the installed wind capacity." The report"s authors also point out that wind power often requires the construction of new grid capacity to transport the electricity from remote areas, where the wind farms operate, to populated areas where the electricity is consumed.21 Though the siting of wind turbines presents a challenge, imaginative solutions are being proposed. Most of the best sites are privately owned and in use for other purposes - princ.i.p.ally, for agriculture. However, wind turbines do not take up exorbitant amounts of s.p.a.ce, and wind farms and conventional farms need not be mutually exclusive. A Minnesota farmer earning less than $30 per acre per year from livestock and $250 per acre from crops might earn $1,000 per acre from land rental for a wind farm and continue to use most of the land for cattle or corn.
At the moment, the EROEI for wind is the best for any of the renewables that has much opportunity for expansion. While Odum gives a figure of 2+, a Danish study suggests an energy payback period of only two to three months, which might translate to an EROEI of 50 or more.22 Though even the latter number may be relatively low when compared to the EROEI for oil and natural gas during the expansion phase of industrial civilization (when it occasionally surpa.s.sed 100-to-1), it probably already exceeds the EROEI for these fossil fuels as their net energy yield gradually wanes due to depletion.
Wind can deliver net energy; the challenge for industrial societies is to scale up production quickly enough to make up for the energy decline from dwindling oil and natural gas supplies. Just to produce 18 quads of wind power in the US by 2030 (never mind the 60 quads of theoretical potential) would require the installation of something like half a million state-of-the-art turbines, or roughly 20,000 per year starting now. That is five times the present world production capacity for turbines. This feat could be accomplished, but it would require a significant reallocation of economic resources. Meanwhile, most of the energy needed for that undertaking would have to come from dwindling fossil fuels.
Thus even if current policymakers had the political will to undertake such a transition, industrial societies would still face a wrenching adjustment to a lower-energy regime. This sobering a.s.sessment is underscored by the difficulty of subst.i.tuting wind-generated electricity for oil"s current uses. As we saw in the previous section on nuclear power, electricity is not well suited to the powering of our current transportation and agriculture infrastructure. The rebuilding of that infrastructure is itself a gargantuan task in both economic and energy terms, and one that is still beset by technical challenges.
Nevertheless, it is clear that, of the alternatives we have surveyed so far, wind is probably the most practicable.
Solar Power.
Since virtually all terrestrial energy sources derive ultimately from the Sun, the development of direct means of capturing usable energy from sunlight seems an obvious way to satisfy industrial societies" prodigious appet.i.tes for power. There is, after all, plenty of solar energy available: the average solar energy influx in North America is about 22 watts per square foot (200 watts per square meter), which means that the typical suburban house in the US continuously receives the equivalent of over 25 horsepower in energy from the Sun. However, there are technical obstacles to gathering that energy, converting it to useful forms, and storing it for times when the Sun is not shining.
Solar energy is most easily harvested and used in the form of heat. For millennia, people have oriented their homes to take advantage of the Sun"s warming rays; today, the design of houses to maximize pa.s.sive solar heating is still one of the most effective ways to increase energy efficiency. Simple rooftop collectors for home hot water or swimming pool heating also take advantage of free solar heat.
The ancient Greeks and Chinese used gla.s.s and mirrors to focus the Sun"s rays in order to start fires. Modern solar-thermal electrical generation technologies use the same principle to produce electrical power by heating water or other fluids to temperatures high enough to turn an electrical generator. Several distinct types of solar-thermal generating systems have been developed (including dish concentrators driving Stirling engine generators; trough concentrators heating a liquid-to-gas system driving a turbine generator; solar towers using large reflector arrays to heat molten salts which, through a heat exchanger, drive steam turbines; and plastic film collectors that work much like trough concentrators, but are much cheaper to build). Relatively few such systems of any type are in use, but ambitious plans are on the drawing boards, including some that integrate solar-thermal systems into the roofs of commercial and industrial buildings.
The photovoltaic effect, in which an electrical current is directly generated by sunlight falling upon the boundary between certain dissimilar substances, was discovered in 1839 by a nineteen-year-old French experimental physicist named Edmund Becquerel. Albert Einstein won the n.o.bel Prize in 1923 for explaining the effect. The first silicon solar-electric cells were made in the 1950s by researchers at Bell Laboratories, who achieved an initial conversion efficiency of only 4.5 percent. The development of photovoltaic (PV) technologies soon received a significant boost from research undertaken by the US s.p.a.ce program, which used solar cells to power satellites. By 1960, efficiencies had been boosted to nearly 15 percent. In the 1970s, alternative energy enthusiasts began to envision a solar future in which photovoltaics would play a significant role in powering a post-petroleum energy regime.
Today there is roughly 1 gW of PV generating capacity installed worldwide (versus roughly 3000 gW of capacity in conventional power plants). Power-conversion efficiencies are now as high as 30 percent, and the cost of solar cells - initially astronomical - has fallen a hundred-fold. A typical small system now costs as little as $6 per watt of production capacity, whereas on large-scale projects costs as low as $3 are possible; at the latter price, with financing of the system at 5 percent interest over 30 years, the price of produced PV electricity amounts to roughly 11/kWh - though few installations actually achieve such a low cost. Photovoltaic electricity is still expensive.
PV technologies have the advantage of being able to provide electricity wherever there is sufficient sunlight, so they are ideal for powering remote homes or villages that are difficult to connect to a power grid. With a PV system, homeowners can become independent of electrical utility companies altogether. The disadvantage of such "stand-alone" systems is that a means must be provided to store electrical power for use when the Sun isn"t shining - at night or on cloudy days. The typical solution is a bank of batteries, which require maintenance and add substantially to the system"s cost. A complete system normally includes a collector array, a controller, an inverter (to change the generated current from DC to AC), and a battery bank, which altogether may represent an investment of more than $20,000 for even an energy-conserving home. In many states, businesses and homeowners can tie their PV panels directly to a power grid; by doing so, they avoid both electric bills and the need for batteries (though an inverter is still required). In this case, the system owner becomes an independent commercial electricity generator, selling power to the local utility company. Such grid-tied systems are typically much less expensive than stand-alone systems.
Two technical improvements in PV technology that are now in the developmental stage - thin-film panels and PV dye coatings - seem especially promising for reducing the cost of photovoltaic electricity. To date, the biggest obstacle to further implementation of the technology has been that production costs are high. The fabrication of even the simplest semiconductor cell is a complex process that has to take place under exactly controlled conditions, such as a high vacuum and temperatures between 750 and 2550 degrees Fahrenheit (400 and 1400 degrees Celsius). These new technical improvements promise to lower production costs dramatically.
Researchers are now experimenting with the use of hybrid materials that are inexpensive and allow for the use of flexible substrates, such as plastics. Manufacturers of such thin-film PV collectors claim a possible production cost of electricity of 7/kWh. There are three forms of thin-film PV technology in commercial production: amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium diselenide (CuInSe2, or CIS). There are two more on the way: spheral and CIGS (copper indium gallium diselenide).23 Already, amorphous silicon accounts for more than 15 percent of the worldwide PV production. Amorphous silicon technology holds great promise in building-integrated systems, replacing tinted gla.s.s with semi-transparent modules; however, the efficiency is low: while some experimental a-Si modules have exceeded 10 percent efficiency, commercial modules operate in the 5 to 7 percent range. Cadmium Telluride laboratory devices have approached 16 percent efficiency, though production modules have achieved only about 7 percent. Copper Indium has reached a research efficiency of 17.7 percent, with a prototype power module reaching 10.2 percent, but production problems have so far prevented any commercial development.
Figure 21. Shipments of PV cells and modules, 1993 - 2002 (Source: International Energy Agency) Meanwhile, scientists at Switzerland"s ecole Polytechnique de Lausanne have developed a fundamentally different solar pholtovoltaic cell that may eventually result in the cheapest PV devices of all. The production process uses common materials and low temperatures: a photosensitive dye, whose properties enable it to perform what the technology"s promoters call "artificial photosynthesis," is simply silkscreened onto a substrate, such as gla.s.s. The resulting cells, known as t.i.tania Dye Sensitised Cells (t.i.tania DSC), can be a.s.sembled into colored opaque or translucent modules that could potentially be incorporated into the walls of buildings or the sunroofs of cars. t.i.tania DS cells demonstrate performance in low light and at high temperatures that far surpa.s.ses that of silicon cells. t.i.tania cells are currently only 10 percent efficient in energy conversion.24 In this case, lower efficiency (relative to silicon-crystal cells) may not be much of a problem because of the potential for enormous cost savings: it may not matter much if a solar cell is inefficient if it can be put where otherwise only tarpaper, a sheet of plywood, or gla.s.s would go.
Nanosolar, a startup company in Palo Alto, California, is planning to commercialize this new technology, with its first product slated to hit the market in 2006. The production process will involve spraying a combination of alcohol, surfactants (substances like those used in detergents), and t.i.tanium compounds on a metal foil. A Technology Review article describes what happens next: "As the alcohol evaporates, the surfactant molecules bunch together into elongated tubes, erecting a molecular scaffold around which the t.i.tanium compounds gather and fuse. In just 30 seconds, a block of t.i.tanium oxide bored through with holes just a few nanometers wide rises from the foil. Fill the holes with a conductive polymer, add electrodes, cover the whole block with a transparent plastic, and you have a highly efficient solar cell."25 Nanosolar hopes to reduce the cost of solar electricity by up to two thirds, making it compet.i.tive with commercial grid electricity rates. Eventually, it may be possible to paint a photovoltaic material directly onto buildings, cars, and other objects.
Still another new solar photovoltaic technology, this one involving organic materials, was recently announced by researchers at the Georgia Inst.i.tute of Technology.26 Using a crystalline organic film, pentacene, together with C60, a form of carbon more popularly known as "buckyb.a.l.l.s," the research group was able to convert sunlight into electricity with 2.7 percent efficiency, and they hope to reach 5 percent efficiency in the near future. Though the efficiency of the material is likely to remain low, its flexibility and minimal weight would allow it to be used on nearly any surface, including tents and clothing. The developers estimate that commercial residential applications are five years away, though versions to power small devices could be marketed within two years.
Net-energy calculations for current photovoltaic technologies are a matter of some controversy. Clearly, conventional silicon-crystal cells have so far had a relatively low return for the energy invested in their manufacture, even though promoters of the technology staunchly claim a favorable figure (typically, they exclude from their a.n.a.lyses the energy expended in transportation as well as that embodied in production facilities). In this instance at least, net-energy payback appears to be highly sensitive to the volume of production: PV modules are still manufactured on a very small scale; if demand were to surge, the energy returned on investment would likely rise very noticeably. It is likely that, even if the most pessimistic a.s.sessments of silicon-crystal cells - which suggest a current net return of less than 1:1 - are correct, the newer thin-film and DSC technologies may be able to achieve a substantially more favorable EROEI (the more optimistic a.s.sessments of silicon-crystal cells suggest a current net return of roughly 10).27 At some point the net energy available from PV electricity will overtake the EROEI that can be derived from petroleum, as the latter is depleted.
However, solar photovoltaic and thermal-electric technologies present us once again with the problem we noted concerning nuclear power and wind: electricity cannot easily be made to power our current transportation and agriculture infrastructure. What is needed is some efficient medium for storing electrical energy that also renders that energy transportable and capable of efficiently moving large vehicles.
Many people believe that the solution lies in the simplest and most abundant element in the universe.
Hydrogen.
Hydrogen is the lightest element, and it combines readily with oxygen; when it does so, it burns hot; and its combustion product is water - no greenhouse gases, no particulate matter or other pollutants. For these and other reasons, hydrogen would seem to be an attractive alternative to fossil fuels.
However, there are no exploitable underground reservoirs of hydrogen. Usable hydrogen has to be manufactured from hydrocarbon sources, such as natural gas or coal (a gallon of gasoline actually contains more hydrogen than does a gallon of liquid hydrogen), or extracted from water through electrolysis. Hydrogen production from algae and from sewage wastes has been demonstrated in the laboratory, but it is unclear whether these processes can ever be scaled up for commercial application. The crux, however, is this: The process of hydrogen production always uses more energy than the resulting hydrogen will yield. Hydrogen is thus not an energy source, but an energy carrier.
Still, many people foresee a prominent role for hydrogen as a means to enable renewable wind- and photovoltaic-generated electricity to be stored and transported. Proposals for a "hydrogen economy" have been circulating for decades (a 1976 study by the Stanford Research Inst.i.tute was ent.i.tled The Hydrogen Economy: A Preliminary Technology a.s.sessment), and in recent years a chorus of proponents has proclaimed the desirability and inevitability of a full transition from fossil fuels to an energy regime based on renewables and hydrogen. "Hydrogen-powered fuel cells promise to solve just about every energy problem on the horizon," writes David Stipp in an article called "The Coming Hydrogen Economy."28 At the Hyforum held in Munich, Germany, in September 2000, T. Nejat Vezirogllu, President of the International a.s.sociation for Hydrogen Energy, proclaimed, "It is expected that the petroleum and natural gas production fueling this economic boom will peak around the years 2010 to 2020 and then start to decline. Hydrogen is the logical next stage, because it is renewable, clean, and very efficient."29 Much of the optimism surrounding the hydrogen-economy vision - whose boosters occasionally exhibit a techno-utopianism of almost messianic intensity - derives from recent developmental work on fuel cells, which chemically produce electrical energy from hydrogen without burning it. Fuel cells have more in common with batteries than with combustion engines.
Hydrogen is not the only substance that can be used to power fuel cells. The Regenesys fuel cell uses two electrolyte salt solutions; it will be useful alongside conventional and renewable commercial power plants to store output and release it when needed. In addition, zinc-air fuel cells are in development which, if the promotional literature is to be believed, are much cheaper to make than hydrogen fuel cells, use a solid fuel that has twice the energy density of hydrogen, and have an electricity-to-electricity efficiency in the range of 40 to 60 percent.30 Zinc "fuel" will come in the form of small pellets. The chemical reaction in zinc fuel cells produces zinc oxide, a non-toxic white powder. When all or part of the zinc has been transformed into zinc oxide, the user refuels the cell by removing the zinc oxide and adding fresh zinc pellets and electrolyte. The zinc oxide is then reprocessed into new zinc pellets and oxygen in a separate, stand-alone recycling unit, using electrolysis. Thus, the process is a closed cycle that can theoretically be continued indefinitely. Each cycle consumes energy; but we must remember that the real purpose of the fuel cell is not to produce net energy, but rather to make stored energy available for convenient use.
Nonrenewable and Renewable Energy Sources.
Nonrenewable Renewable.
Oil Hydroelectric.
Natural Gas Wind.
Coal Solar Power.
Nuclear Power Bioma.s.s, including biodiesel and ethanol.
Geothermal Power (geysers) Tides.
Waves.
Geothermal (ground-water heat pumps).
Net Energy Compared.
Below are the summarized results of two comprehensive comparative studies of net energy (EROEI), one by Cleveland, Costanza, Hall, and Kaufmann (1984), the other by Odum (1996). Cleveland and Kaufmann have criticized Odum"s methodology (see www.oila.n.a.lytics.com), but have not published an updated study of their own. Time is relevant to EROEI studies because the net-energy yield for a given energy source may change with the introduction of technological refinements or the depletion of a resource base.
But back to hydrogen. At present, on a global scale, about 40 million tons of hydrogen are produced commercially per year. This represents slightly more than one percent of the world"s energy budget. Most of this commercially produced hydrogen is now made from natural gas.
There are reasons to be hopeful about hydrogen"s potential. The electric drive train of a fuel cell-driven car would be much lighter than a conventional gasoline or diesel drive train. Emissions from burning hydrogen in fuel cells consist only of water and heat; thus many pollution problems - including the production of greenhouse gases - could be reduced dramatically by the widespread use of hydrogen. Even if the source of hydrogen is coal or natural gas, fewer emissions are produced in the coal or gas reformation process (the production of hydrogen) than in the direct burning of these fossil fuels for energy.
Several major car manufacturing companies are currently working on new models that will run on hydrogen fuel cells. The experimental Daimler-Benz NECAR 3 (New Electric Car, version 3), for example, generates hydrogen onboard from methanol - thus dispensing with the problematic extra weight of batteries and hydrogen tanks. Another solution to the weight problem is to redesign the entire automobile for maximum weight reduction and aerodynamics; this is the approach taken by the "Hypercar," a project of Hypercar Inc.31 Hydrogen production is also being proposed as a means to store electrical energy from solar panels or wind turbines in homes or commercial buildings, replacing bulky and inefficient batteries. Hydrogen-powered fuel cells could thus enable a transition to decentralized energy production, reducing costs for the construction and maintenance of centralized generating plants and transmission lines.
Amory Lovins of the Rocky Mountain Inst.i.tute has published "A Strategy for the Hydrogen Transition," ill.u.s.trating how "the careful coordination of fuel-cell commercialization in stationary and transportation applications, the use of small-scale, distributed fueling appliances, and Hypercars combine to offer leapfrog opportunities for climate protection and the transition to hydrogen."32 Implicit in the plan is a reliance on natural gas as the primary source for hydrogen for at least two decades, until renewable energy souces can be scaled up.
That"s the good news about hydrogen. Unfortunately, there is bad news as well.
A hydrogen energy infrastructure would be quite different from our present energy infrastructure, and so the transition would require time and the investment of large amounts of money and energy. That transition would be aided tremendously if we were to switch present government subsidies from nuclear power, oil, and coal to renewables, fuel cells, and hydrogen. But, given the political influence of car and oil companies and the general corruption and inertia of the political process, the likelihood of such a subsidy transfer is slim for the moment. Yet if we simply wait for price signals from the market to trigger the transition, it will come far too late.
An even greater problem is the current and continuing reliance on natural gas for hydrogen production. Hydrogen proponents a.s.sume the continued, abundant availability of natural gas as a "transition fuel." Without some transitional hydrocarbon source, there is simply no way to get to a hydrogen economy: there is not enough net energy available from renewable sources to "bootstrap" the process while supporting other essential economic activity. As we have seen, prospects for maintaining - much less increasing - the natural gas supply in North America appear disturbingly uncertain. Within only a few years, decision makers will be confronting the problem of prioritizing dwindling natural gas supplies - should they fund the transition to a hydrogen economy or heat people"s homes during the winter? Faced with a crisis, they would find it difficult to justify diverting natural gas supplies away from immediate survival needs.
In terms of energy efficiency (setting aside for the moment the problem of emissions and the need for energy storage), we would be better off burning natural gas or using PV or wind electricity directly, rather than going through the extra step of making hydrogen. The Second Law of Thermodynamics insures that hydrogen will be a net-energy loser every time since some usable energy is lost whenever it is transformed (e.g., from sunlight to photovoltaic electricity, from electricity to hydrogen, or from hydrogen back to electricity).
Given the already low net energy from renewables as well as the net energy losses from both the conversion of electricity to hydrogen and the subsequent conversion of hydrogen back to electricity, it is difficult to avoid the conclusion that the "hydrogen economy" touted by well-meaning visionaries will by necessity be a much lower-energy economy than we are accustomed to.
The future may well hold hydrogen fuel cell-powered cars - but not in numbers approaching the current global fleet of 775 million vehicles. In the low-energy social environment toward which we are inevitably headed, it will be possible for only a tiny wealthy minority to navigate over disintegrating streets and highways in sophisticated, highly efficient Hypercars. For the rest of us, a good pair of shoes and a st.u.r.dy bicycle will be the best affordable transport tools.
I recently toured the Schatz Energy Research Center (SERC) at Arcata, California, one of the nation"s foremost research centers for hydrogen, fuel cells, and renewable energy. The mission of the center is to promote the use of clean and renewable energy. The Schatz lab, housed in a small, converted 1920s hospital building, specializes in generating hydrogen fuel from solar photovoltaics. The lab designed and built a 9kW fuel cell powered car based on a small European electric vehicle - the first street-ready fuel-cell car in the US. SERC has also made a fuel cell that powers a microwave relay station providing telephone service for the Yurok Tribe of Northern California.
Peter Lehman, the SERC Director, showed me several bench-top, state-of-the-art fuel cells - each handmade and expensive to build. Lehman said that for most small-scale applications (including homes and personal automobiles), batteries are still a more efficient storage medium for energy than hydrogen. In most cases, according to Lehman, it just doesn"t make sense to take high-quality energy in the form of electricity, turn it into hydrogen, and then turn it back into electricity, since there are losses at each stage along the way - if there are ways of using the electricity directly. However, in larger-scale generation situations - say, a wind farm - at times when there is no immediate use for the electricity being generated, hydrogen production could provide a way to store energy while also producing a transportation fuel for fuel cell vehicles such as trucks or buses. But in commuting situations, when mileage requirements are low, Lehman feels that battery electric vehicles are more efficient and the right choice for private cars. In the foreseeable future, gasoline or diesel hybrid cars also make more sense than do fuel cell vehicles.
The two biggest problems with fuel cells currently, according to Lehman, are that they don"t last long enough, and they"re expensive. Schatz"s cells are now able to perform for about 2,000 hours (that"s three months of continuous operation). The upside is that fuel cells can be remanufactured, so that a user could rotate two cells, with one on the job while the other is being refurbished. But this would, of course, increase the already daunting cost. The Schatz lab is working to overcome both these limitations, but Lehman admits that there is a long way to go, and advances appear to be incremental and slow. There is currently no off-the-shelf, production-model fuel cell available anywhere that could reliably power a home.
Lehman noted that the fuel-cell industry is growing quickly, but that it is rife with secrecy and inflated claims.
Like wind and photovoltaics, hydrogen fuel cells offer certain important advantages over current energy technologies and will no doubt be central features of the post-petroleum infrastructure. We should be dramatically increasing our investments in these alternatives now, while there is still cheap energy to be had. But even a.s.suming a full-scale effort toward a transition to renewables and hydrogen, industrial societies will suffer wrenching changes as a result of the inevitable drastic reduction in available net energy.
Hydroelectricity.
While medieval water mills were used to grind grain, modern hydroelectric turbines transform the gravitational potential of rivers and streams into conveniently usable electric power. Electricity generated from water flowing downhill currently const.i.tutes the world"s largest renewable energy source.
Throughout the 20th century, hydroelectric dams were built on most major rivers throughout the world - from the Colorado River in the US to the Nile in Egypt. Currently, about 9 percent of electricity in the US is generated by hydro power, a little less than half that generated by nuclear power plants. However, this represents over three times the electricity generated by all other renewable sources combined. In the world as a whole, hydro power accounts for 19 percent of electricity generation.
One of the advantages of generating electricity via hydro dams is that it is relatively easy to store energy during times of low demand. Water empounded behind dams represents stored energy; in addition, surplus electrical power can be used to pump water uphill so that it can be released to flow back through the generating turbines during times of peak demand.
Hydroelectric generation has an attractive EROEI: Odum gives hydro power a net figure of 10, while Cleveland et al. a.s.sign it 11. Hydro power is thus one of the better current producers of net energy.
Unfortunately, hydroelectric dams typically pose a range of environmental problems: they often ruin streams, cause waterfalls to dry up, and interfere with marine habitat. Dammed rivers are diverted from their geologic and biological work, such as the support of migratory fisheries. Most environmentalists would prefer to remove existing dams rather than see more of them built. Moreover, many existing hydro plants are jeopardized by siltation and foreseeable changes in rainfall patterns resulting from global climate change.
In any case, in the US the building of more large hydroelectric dams is not much of an option. Hydro resources are largely developed; there is little room to increase them. Not one large dam has been approved in the past decade.
The situation is different in Canada, which has immense potential hydroelectric resources. With hydroelectricity as with natural gas, Canada is becoming a major energy source for the US.
Most new hydro developments are being planned not for already-industrialized countries, but for the less-consuming countries of the world. But hydroelectric dams tend to be capital-intensive projects that require huge loans, trapping poor countries in a vicious cycle of debt.
Microhydro - the production of electricity on a small, localized scale from relatively small rivers or streams - offers the advantages of rural electrification with few of the drawbacks of major dam projects. Countless communities in the less-consuming countries may be able to take advantage of this technology, which requires smaller investments and enables local control of resources. Successful microhydro projects are already operating in Sri Lanka, Zimbabwe, the Netherlands, and many other countries.33 The main drawbacks of such projects are their inability to supply large urban areas with power as well as their reliance on an endangered resource: fresh water.
In sum, hydro power is already a significant energy resource and will continue to be so throughout the coming century. But in many regions of the world - and especially in the US - it is already thoroughly exploited.
Geothermal Power.
Humans have enjoyed natural hot springs for millennia, and technologies have more recently been developed for using geothermal waters for home and commercial heating - as is commonly done, for example, in Klamath Falls, Oregon. Underground steam was first used to generate electricity near Rome, Italy, in 1904. The first commercial geothermal electric power plant was built in 1958 in New Zealand; and in 1960, a field of 28 geothermal power plants was completed in the region of Geyserville in northern California.