No matter how the nation's energy portfolio changes, an increasing share of future needs will be met by technologies now in the research or development stages. Some will require substantial improvements – or even research breakthroughs – to have a major impact on our energy budget. The following are some of the options.
Advanced Nuclear Fission
Although nuclear power plants account for 20% of U.S. electricity generation, no new reactors have come on line since 1996. Designs conceived in the 1990s (so-called Generation III+) may provide significant improvements in economics and safety. Consortia of companies are working with the Nuclear Regulatory Commission to secure federal approval for these types of nuclear power plants, and several utilities recently requested approval of a combined construction and operating license. Generation III+ plants are also under construction in Europe and Asia, with the first scheduled to come on line in 2009 in Finland.
Longer term advances could broaden the desirability and future use of nuclear energy. The U.S. Department of Energy (DOE) has engaged other governments, international and domestic industry, and the research community to develop “Generation IV” systems. The goals of these efforts are to improve the economics, safety, fuel-cycle waste management, and proliferation resistance of nuclear reactors, as well as widen their applications. DOE is pursuing the demonstration of one such design, a very-high-temperature reactor, through its Next Generation Nuclear Plant program, and the facility is scheduled to begin operations by 2021.53
Sunlight is Earth's most abundant energy source and is delivered everywhere free of charge. Yet direct use of solar energy – that is, harnessing light's energy content immediately rather than indirectly in fossil fuels or wind power – makes only a small contribution to humanity's energy supply. In theory, it could be much more. In practice, it will require considerable scientific and engineering progress in the two ways of converting the energy of sunlight into usable forms.
Photovoltaic (PV) systems exploit the photoelectric effect discovered more than a century ago. In certain materials, the energy of incoming light kicks electrons into motion, creating a current. Sheets of these materials are routinely employed to power a host of devices from orbiting satellites to pocket calculators, and many companies make roof-sized units for homes and office buildings.
At the present time, however, the best commercial PV systems produce electricity at five to six times the cost of other generation methods.54 In addition, PV is an intermittent source, meaning that it's only available when the sun is shining. Furthermore, unless PV energy is consumed immediately, it must be stored in batteries or by some other method. Adequate and cost-effective storage solutions await development. One factor favoring PV systems is that they produce maximum power close to the time of peak loads, which are driven by air-conditioning. Peak power is much more expensive than average power. With the advent of time-of-day pricing for power, which is technologically feasible, PV power would be much closer to being economical.
Sunlight can also be focused and concentrated by mirrors and the resulting energy employed to heat liquids that drive turbines to create electricity – a technique called solar thermal generation. Existing systems produce electricity at about twice the cost of fossil-fuel sources. Engineering advances will reduce the cost, but solar thermal generation is unlikely to be feasible outside regions such as the southwestern United States that receive substantial sunlight over long time periods.
Many new vehicle technologies have the goal of steering automobiles away from a dependence on fossil fuels. One vision is an all-electric vehicle (EV) that uses no gasoline or diesel fuel and does not emit any CO2. But affordable and reliable EVs will require advances in energy storage. At present, batteries that store enough electricity to give a vehicle acceptable driving range are expensive, large, and heavy. Yet technology may provide new options. For example, recent advances in nanotechnology, applied to the lithium ion battery, may permit significantly more energy to be stored in a smaller, lighter package.
A compromise – plug-in hybrid electric vehicles (PHEVs) – may secure a significant place in the market sooner. PHEVs have conventional gasoline engines as well as batteries that can supply enough energy to travel 10 to 40 miles, depending on the kind of batteries used. They run on electric power until the batteries are discharged, then switch to gasoline for additional range. As of January 2008, no PHEVs were in production. But several major motor companies – including Toyota, General Motors, and Ford – have plans to introduce PHEVs within the next few years.
EV and PHEV batteries are recharged by plugging them into an electricity source while the vehicle is parked. This provides the immediate benefit of shifting some transportation energy demand from onboard petroleum-based fuels to the electrical grid. However, CO2 emissions would not decline proportionally because about half of the electricity used to recharge the vehicle's batteries is produced at coal-based plants.
This renewable technology, already widely deployed in 36 states and producing almost 1% of America's electricity, uses the wind-induced motion of huge multiblade rotors – sweeping circles in the air 100 yards in diameter – to drive emission-free turbines.55 But like solar energy, the source is intermittent and currently lacks an economically practical way to store its energy output. In addition, the huge wind turbines (sometimes grouped into “wind farms” containing hundreds of turbines) can prompt complaints on aesthetic grounds from communities whose sight lines are altered. Current designs can also be a hazard to birds and bats. Wind energy's potential contribution is large, though, and with developments in storage technologies and an expanded and upgraded electrical grid, it could provide a substantial portion of our electricity, especially in some regions.
Advanced Coal Technologies
In the endeavor to reduce – or even eliminate – the emission of CO2 when fossil fuels are burned, coal is a prime target: It accounts for about one-third of the nation's CO2 emissions. New technologies focus on separating, capturing, and safely storing the CO2 before it is discharged from the smokestack. Several approaches are possible. One is coal gasification, a process in which coal is converted to a gas (called syngas) before it is burned, making it easier to separate the CO2 as a relatively pure gas before power is generated. Such Integrated Gasification Combined Cycle, or IGCC, plants are projected to be up to 48% efficient, a significant improvement over current coal-power plants, which are about 38% efficient.
Another option is to burn coal in oxygen instead of air (as is currently done), to reduce the amount of flue gas – essentially exhaust – that must be processed to isolate CO2. These techniques show promise but require more research and development. They also substantially increase the cost of the electricity produced.
Once CO2 has been captured, it must be sequestered, or permanently stored. Current options focus on such geological formations as oil and gas reservoirs, unmineable coal seams, and deep saline aquifers, all of which are geologically sealed and unlikely to allow injected CO2 to escape. While these technologies are very promising, it still must be proven that large quantities of CO2 can be stored effectively underground and monitored for long periods of time. The methods also must be acceptable to the public and regulatory agencies. Large-scale field trials of prototypes of coal-fueled, near-zero-emissions power plants are needed to test the viability of several of these new clean coal technologies.
For more than 150 years, scientists have known that when hydrogen and oxygen combine to form water (H2O), the chemical reaction releases electrical energy. (It's exactly the reverse of electrolysis, in which running a current through water separates H2O into its constituent elements.) Devices that use a controlled combination of the two gases to generate current are called fuel cells. This developing technology underlies the vision of a nationwide “hydrogen economy,” in which the only exhaust from fuel-cell-powered vehicles would be water vapor, and America would drastically reduce its dependence on foreign fuel supplies.
There are several significant obstacles to achieving that vision. Present fuel cells are too expensive and unreliable for the mass market. And hydrogen is very difficult to store and transport in a vehicle unless it is compressed to thousands of pounds per square inch (psi). Automotive companies are using containers in their demo vehicles that can store hydrogen at 5,000 to 10,000 psi, but a cost-effective and safe distribution system would have to be put in place before these vehicles could become widely available.
Furthermore, hydrogen (like electricity) is not a primary source of energy but rather an energy carrier. There are no natural reservoirs of pure hydrogen; it must be extracted from compounds such as natural gas or water. And the processes for separating it from these principal sources pose their own challenges. When natural gas (basically methane, a lightweight molecule made of carbon and hydrogen) is exposed to steam under high temperatures in the presence of a catalyst, it frees the hydrogen. However, the process itself also produces substantial amounts of CO2. Widespread use would require a carbon sequestration scheme. And, of course, hydrogen can be extracted from water by electrolysis. But that takes a lot of electric power. So unless the electricity is generated by nuclear or renewable sources, the environmental advantage of hydrogen is substantially negated.
The federal government, particularly the U.S. Department of Energy, is conducting significant research on fuel cells to accelerate their development and successful introduction into the marketplace. And hydrogen-fuel-cell cars are receiving considerable attention in the press. Some car manufacturers, including General Motors and Honda, are putting a very limited number of these vehicles on the road. There are hydrogen fueling stations in about 16 states, the greatest number being in California.56 Most of these, though, are small, private facilities intended to support a few experimental vehicles. It will take decades of research and development, as well as changes in the energy infrastructure, before a hydrogen economy on a broad scale can be achieved.
Alternatives to Conventional Oil
There are several “unconventional” petroleum sources, materials from which oil can be extracted – at a cost. Resources are abundant and could greatly impact the U.S. oil supply in the future. The three largest are oil shale (rock that releases petroleum-like liquids when heated in a special chemical process); tar sands (heavy, thick, black oil mixed with sand, clay, and water); and heavy crude oil (thicker and slower flowing than conventional oil).
The most extensive deposits of all three are in North and South America. A region covering parts of Colorado, Utah, and Wyoming contains oil shale totaling about three times the proven oil reserves of Saudi Arabia. About two-thirds of the world's supply of tar sands (estimated at 5 trillion barrels, though not all of it is recoverable) is found in Canada and Venezuela.57 Venezuela also has the largest known reserves of heavy crude oil, estimated at 235 billion barrels.58
However, extracting these resources is much more costly, energy intensive, and environmentally damaging than drilling for conventional oil. The processes by which we mine and refine oil shale and tar sands to produce usable oil, for example, involve significant disturbance of the land, extensive use of water (a particular concern in dry regions where oil shale is often found), and potential emissions of pollutants to the air and groundwater. In addition, more energy goes into these processes than into extracting and refining conventional oil, and more CO2 is emitted. But as conventional oil costs rise, more attention is being focused on alternative sources and on overcoming the challenges associated with their use. Canada already produces more than a million barrels per day of oil from tar sands, and some companies are interested in pursuing oil shale in the United States, probably using below-ground techniques to extract the oil without mining the shale.
Fuel derived from plant material, or biofuel, is an appealing renewable alternative to fossil fuels. It is uncertain, though, whether biofuels are ultimately viable in the absence of subsidies. In particular, the prospects for “biodiesel” fuel – a relatively heavy liquid derived from soybean, vegetable, rapeseed, or safflower oils, among others – are considered doubtful. Typically, those oils are already expensive compared to fossil-fuel sources, and there does not appear to be a way to bring the cost down.
As mentioned previously, corn-based ethanol is already offsetting a small amount of fossil-fuel use in vehicles. However, many experts believe that ethanol-based biofuels will not provide much benefit until the conversion technology is fully developed to use cellulose (as found in trees and grasses) for the raw material instead of corn or sugar cane. In fact, the Energy Independence and Security Act of 2007 stipulates that by 2022 the United States must produce 21 billion gallons of advanced biofuels, such as cellulosic ethanol.59 Research is under way in this field, which could provide a ubiquitous sustainable resource and perhaps take advantage of the existing nationwide infrastructure created for petroleum-based fuel distribution.
Even with this increased focus on biofuels, however, it is uncertain how much projected gasoline consumption can be replaced in the next few decades. Furthermore, biofuels contain carbon, and although they may burn “cleaner” than oil-derived fuels, they would not completely eliminate CO2 emissions.
Many of these technologies will likely contribute in some way to America's energy sources in the 21st century. But it is impossible to predict how much impact these and other technologies will have on our energy future.
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