Gregoire's CleanTech Blog

The Energy & Resources Institute (India) develops new plants for Biodiesel

Biodiesel could be an important renewable substitute for fossil fuels. And, in certain parts of the world, governments and some corporations consider the jatropha plant, common in hot climates, one of the most promising sources of biodiesel. The plant can grow in wastelands, and it yields more than four times as much fuel per hectare as soybean, and more than ten times that of corn. But the commercial-scale cultivation of jatropha, which has not previously been grown as a crop, raises several significant challenges.

This year, the Energy and Resources Institute (TERI), an Indian research group, launched a 10-year, $9.4 million project to research issues involved in taking jatropha from seed to filling station. One challenge is growing the plant in poor soil.

The first crops of jatropha, planted in what was wasteland, have now flowered, says Alok Adholeya, director of TERI's Biotechnology and Management of Bioresources division. "It proves that we can do this," he says. He and other researchers at TERI spent five years testing different mycorrhiza microorganisms, symbiotic fungi that improve the ability of many plants to grow in poor soil. Adholeya's team found that the most effective was a fungus in the glomus species (he is not currently disclosing the exact fungus), which improves jatropha yields by 15 percent.

The TERI project is working in rural Andra Pradesh, a state in southeast India, collaborating with local financial institutions to develop loan guarantees to fund seed purchases; it's also collaborating with insurers to back the farmers against potential losses. In addition, it had to educate the farmers on how to cultivate the plant.

So far, the project has signed up 5,000 farmers representing 1,000 hectares of land. The goal is to have 8,000 hectares under cultivation by March 2008, and Adholeya says that the success of the first crops has drawn interest from many more farmers. By the end of 2008, TERI plans to have a production facility producing biodiesel from jatropha. Eventually, it aims to produce 90 million liters of biodiesel annually.

Adholeya is also working on genetically modifying jatropha to improve its yields. He leads a team of 20 microbiologists, molecular biologists, and field breeders who are looking for the genes in jatropha that cause it to fruit so that they can enhance the percentage of oil in the seed. He expects that it will take 18 months to isolate the genes and begin working to enhance them. The researchers plan to use a technique called molecular-assisted breeding, in which they identify a gene of interest, select particular genotypes, and breed them. Adholeya expects that by 2012, modified jatropha plants will be in cultivation.

He says that the Indian government, taking note of a report by TERI, is considering a national initiative around developing jatropha crops as a major source of fuel. That report calls for India to plant 400,000 hectares of jatropha in 22 of India's 28 states.

India is not alone in its interest in jatropha. Indonesia's government is promoting jatropha cultivation, as are several governments in Africa. Jatropha is attractive because of several desirable properties: it can grow in poor soil and survive drought; it's a perennial with an economic life of about 35 to 40 years; and it only needs two to three years to develop into a cash crop.

Jatropha seeds, when crushed, produce large quantities of an oil that can easily be converted to biodiesel that performs at levels close to that of conventional diesel oil. In fact, a hectare of jatropha produces 1,892 liters of fuel, which is better than rapeseed and far better than soybean or corn, according to data gathered by the Global Petroleum Club, an energy networking organization funded by the private-equity firm Forrest Equity Management.

"Jatropha is a one-stage conversion [to biodiesel]," says Adholeya, explaining that converting the plant oil to an oil that can be burned as fuel requires only one stage of heating and mixing with methanol. The resulting fuel, he says, "is a very good quality diesel that can be used in any transport vehicle."

 

Source : Technology Review

US Department of Energy considers that plug-in hybrid could save the grid

Major automakers and the Department of Energy are pouring money into research on plug-in hybrid vehicles. These cars promise to cut petroleum consumption by allowing commuters to drive to work using primarily electricity--stored on board in batteries--rather than gas. Although critics have warned that the vehicles could put too much pressure on an already strained electrical grid, experts are now arguing that rather than being a strain on the grid, plug-in hybrids may actually help prevent brownouts, cut the cost of electricity, and increase the use of renewable energy.

Plug-in hybrids, like today's hybrid cars, can run on either an electric motor or an internal combustion engine. But plug-ins have much larger battery packs and can be recharged by being plugged into the wall, making it possible to rely much more on the electric motor. Although a handful of companies sell conversion kits to change conventional hybrids into plug-ins, the kits add thousands of dollars to the cost of the car (see "Plug-In Hybrids Are on the Way"). This additional cost, which is primarily from the batteries, is one of the reasons the major automakers haven't yet mass produced such vehicles, although they are now developing them. GM, for example, recently committed to making a plug-in version of a Saturn SUV (see "GM's Plug-In Hybrid").

The concern is that plug-ins are not a good way to reduce gasoline consumption, because if they become popular, and millions of car owners recharged their cars at three in the afternoon on a hot day, it would crash the grid. But plug-in hybrids could actually help stabilize the grid if owners charged their cars at times of low demand, and if the vehicles could return excess energy to the grid when it's needed--say while parked in the company lot at work during peak demand.

Since utilities have built enough power plants to provide electricity when people are operating their air conditioners at full blast, they have excess generating capacity during off-peak hours. As a result, according to an upcoming report from the Pacific Northwestern National Laboratory (PNNL), a Department of Energy lab, there is enough excess generating capacity during the night and morning to allow more than 80 percent of today's vehicles to make the average daily commute solely using this electricity. If plug-in-hybrid or all-electric-car owners charge their vehicles at these times, the power needed for about 180 million cars could be provided simply by running these plants at full capacity.

This could be a boon to utilities, because they'd be able to sell more power without the added cost of building more plants. Ideally, this will translate into lower electricity prices, says Robert Pratt, a scientist at PNNL. It might also help utilities justify the added capital costs of building cleaner coal-burning plants, because they'll be able to recover their investment faster by "selling more electricity with the same set of iron, steel, and concrete," Pratt says.

Such a system could be further optimized by using smart chargers and other electronics. This system would include a charger that runs on a timer, charging cars only during off-peak hours. Researchers at PNNL are taking this a step further with smart chargers that use the Internet to gather information about electricity demand. Utilities could then temporarily turn off chargers in thousands of homes or businesses to keep the grid from crashing after a spike in demand.

The next step would be to add smart meters that would track electricity use in real time and allow utilities to charge more for power used during times of peak demand, and less at off-peak hours. Coupled with such a system, the PNNL smart charger could ensure that the plug-in batteries are charged only when the electricity is at its cheapest, saving consumers money.

But what many experts are excited about now is a concept called "vehicle-to-grid," often abbreviated V2G. In such a system, plug-in hybrids, rather than being merely an extra burden to the grid, become a much needed way for grid managers to balance the amount of energy generated at any given time to match the amount of energy being consumed. Millions of cars, each with several kilowatt hours of storage capacity, would act as an enormous buffer, taking on charge when the system temporarily generates too much power, and giving it back when there are short peaks in demand.

In a V2G system, the batteries of millions of plug-ins would be used as a buffer to even out supply and demand and to help keep the grid stable, says Karl Lewis, chief operating officer of GridPoint, a startup based in Washington, D.C., that has developed technology that could help make such a system work. In this kind of system, each vehicle would have its own IP address so that wherever it is plugged in, the cost of the energy it uses to recharge would be billed to the owner. With the right equipment, the car could also return energy to the grid, giving the owner credit. Mock-ups of such systems have already been tested by the National Renewable Energy Laboratory (NREL), in Golden, CO, and by a company called AC Propulsion, based in San Dimas, CA.

Plug-ins could also serve as backup sources of power. In extreme cases, such as a blackout from a hurricane, the cars could keep essential systems up and running in homes and businesses. Even in this case, when the batteries could be drawn down considerably, the owner could rely on the internal combustion engine in a plug-in hybrid for transportation.

As an added benefit, "if millions of these [plug-in hybrids] were produced, it would enable some of the renewable technologies to really take off," say Terry Penney, a technology manager for advanced vehicle technologies at NREL. The challenge of using a renewable source such as wind is that wind is intermittent, varying day by day and minute by minute. A network of plug-in hybrids could smooth out these fluctuations by storing extra energy and sending it to the grid when the wind dies down. Such a network would also improve the economics of wind power by making it possible to capture more of the excess power generated on windy days, says Willett Kempton, senior policy scientist in the Center for Energy and Environmental Policy at the University of Delaware.

Such systems are many years off, as it will take time to install the needed infrastructure. Once plug-in cars are widely available, however, they could help relieve some of the pressure on the grid today.

 

Source : Technology Review

Carbon capture and storage : North Sea is emerging as center of development

The North Sea is emerging as a center of development of carbon capture and storage technology, and it's not just because of the region's tightening regulation of greenhouse gases. The main attraction is the North Sea's rapidly-maturing offshore oil reservoirs, which offer both a place to store carbon dioxide from fossil-fueled power plants and an opportunity to use it to increase oil extraction. Oil production is slowing as many of the North Sea wells mature, and carbon dioxide pumped down the hole can loosen up and release the remaining oil.

Several oil giants, including BP, Shell and Norway's Statoil, recently announced plans to build new power plants designed to convert North Sea natural gas into hydrogen, burn the hydrogen to produce electricity, and ship the resulting carbon dioxide to offshore oil wells. BP expects to produce an extra 40 million barrels of oil as a result of its plant between 2010 when the plant starts and 2030.

Meanwhile, an Oslo-based startup, Sargas SA, has secured industrial backers to build a coal-fired power plant in Norway using a new technology called pressurized combustion that co-produces power and carbon dioxide; it plans to sell its CO2 to offshore drilling sites. Before that, Sargas hopes to begin building a smaller plant early in 2007 that could be the prototype for offshore platforms producing power and CO2 where they're needed most: out in the North Sea oil fields.

"There is a real economic driver for the use of the CO2 for enhance oil recovery," says MIT process design expert Gregory McRae, who is tracking developments in carbon capture. "Its an incredibly exciting time."

Using industrial CO₂ to enhance oil recovery could squeeze an extra 7.3 billion barrels of oil from the North Sea and simultaneously stow away 10 billion metric tons ofcarbon dioxide, according to a December 2005 study by the European Commission's Institute for Energy. The latter is the equivalent of stopping Europe's greenhouse gases releases for two and a half years.

What is holding up full development of the use of carbon dioxide for enhancing oil recovery is, ironically, a dearth of CO2. Dozens of natural gas and coal-fired power plants ringing the North Sea produce plenty, but capturing it is expensive because the CO2 in the flue gas is at very low pressure and concentration (most of the exhaust from a conventional planet is actually nitrogen gas carried through from the air used to fire the fuel). Carbon capture is estimated to add a 30 percent to 50 percent premium to the cost of producing electricity.

BP, Shell and Statoil's solution to the problem is a new plant design. Instead of just burning natural gas, the plants will use a chemical process called reforming to convert the fuel into concentrated streams of pure hydrogen and CO2. The hydrogen will be burned to produce electricity, while the CO2 would be pressurized and sent by pipeline to offshore oil platforms to be pumped into the hydrocarbon reservoirs below.

Sargas seeks instead to make the capture of carbon dioxide more efficient by cranking up the pressure. Its plants would burn gas or coal at high pressures, thus yielding a high-pressure exhaust in which the CO2 pressure is about 20 times higher than in a conventional coal plant. That pressure makes separating the CO2 from nitrogen and left-over oxygen in the exhaust far less costly.

Last week a consortium of companies in Norway including aluminum giant Alcan (a major power consumer) and Norwegian energy firm Norsk Hydro announced plans to build a 400-megawatt coal-fired power plant using Sargas' design; startup is targeted for 2011. Dale Simbeck, vice president of technology for Mountain View, CA-based energy consultancy SFA Pacific, calls it a "clever scheme" because coal is relatively cheap, while the high pressure system will help contain the cost of capturing the CO2. "What they're doing can make sense," says Simbeck.

Tor Christensen of Sargas says the company is working with a major United States-based oil and gas producer to exploit another feature of high-pressure combustion: the system's compact design. For a given power output Sargas' generators handle a volume of gas 40-50 times smaller than would a conventional plant. As a result the equipment is more compact—compact enough to put a 100-megawatt natural gas-fired plant on an offshore platform. "It's not much for an offshore platform," says Christensen of the 5,000 metric ton design. "A single crane can lift the whole thing."

McRae says the idea should be attractive for oil and gas producers. For one thing, Sargas' plants will capture CO2 on-site, eliminating the need to ship CO2 from shore. For another, they will serve the platform's power needs better than the diesel generators and relatively small gas turbines used today. "One of the big problems with offshore oil platforms is the power supply that you need to pump the oil and process the gas that comes out the ground. Sargas will allow you to get much larger power in a smaller space," says McRae.

Christensen says Sargas' goal is to deliver CO2 to oil platforms at roughly $20 per metric ton and, as a rule of thumb, each metric ton of CO2 should yield two or three extra barrels of oil. If oil prices stay high, says Christensen, "there's a tremendous amount of money to be made."

 

Source : Technology Review

Solar-powered hydrogen generation technologies

Researchers in Switzerland have demonstrated more-efficient water-splitting solar cells based on a cheap, abundant, and long-lasting material: rust. The advance could lead to a cheap and energy-efficient way to generate hydrogen for fuel-cell vehicles using solar energy.

Water-splitting solar panels would have important advantages over existing technologies in terms of hydrogen production. Right now, the primary way to make hydrogen is to separate it from natural gas, a process that generates carbon dioxide and undercuts the main motivation for moving to hydrogen fuel-cell vehicles: ending dependence on fossil fuels. The current alternative is electrolysis, which uses electricity to break water into hydrogen and oxygen, with the two gases forming at opposite electrodes. Although electrolysis is costly, it can be cleaner if the source of the electricity is wind, sun, or some other carbon-free source.

But if the source of the electricity is the sun, it would be much more efficient to use solar energy to produce hydrogen by a photochemical process inside the cell itself. By improving the efficiency of such solar panels, Michael Grätzel, chemistry professor at the Ecole Polytechnique Fédérale de Lausanne, in Switzerland, and his colleagues have taken an important step toward this goal.

The researchers have shown that by including small amounts of silicon and cobalt, they can grow nanostructured thin films of iron oxide that convert sunlight into the electrons needed to form hydrogen from water. And the iron oxide films do this more efficiently than ever before with this material.

Iron oxide has long been an appealing material for such solar panels, in part because it holds up well in contact with water. But although it can absorb sunlight, the resulting charge carriers could not easily escape the material, so they recombined, canceling each other out before they could split any water. By doping the rust with silicon, the researchers coaxed the material to form cauliflower-like structures with extremely high surface area, ensuring that a large part of the atoms in the material were in contact with the water, or very close to it. That way, holes could easily escape into the water, where they prompt the generation of oxygen gas. The silicon also improves electron conductivity in the material, which is important for generating hydrogen gas at an opposite electrode. The researchers further improved the process by adding cobalt, which acts as a catalyst for the reactions.

Grätzel's new iron-oxide films can convert an impressive and, according to the researchers, "unprecedented" 42 percent of ultraviolet photons in sunlight into electrons and holes. But the system's overall efficiency is only about 4 percent, in part because iron oxide doesn't absorb all the parts of the solar spectrum.

The main achievement of Grätzel's new research, which appears in the current issue of the Journal of the American Chemical Society, is that it examines the interactions at work in the system in great detail, says Brian Holcroft, CEO of Hydrogen Solar, a company based in Guildford, UK, that is developing ways to mass-produce panels inspired by Grätzel's materials. The findings suggest several strategies that could help the iron-oxide-based panel reach the 10 percent efficiency level that would make the technology competitive with current ways of creating hydrogen, Holcroft says. (Iron oxide could theoretically be as much as 20 percent efficient.) These include adjusting the amount and arrangement of silicon and cobalt, and improving the structure of the films.

If this level of efficiency can be met, hydrogen-generating solar energy could mitigate some of the challenges that threaten to make hydrogen fuel-cell vehicles impractical, says George Sverdrup, hydrogen technology manager at the National Renewable Energy Laboratory (NREL), in Golden, CO. For example, if consumers and businesses used these panels to make hydrogen, rather than getting hydrogen from a large facility, it would cut out the cost of shipping hydrogen, making hydrogen more affordable. Solar-to-hydrogen panels would be more efficient than small electrolysis machines, and they would ensure that the hydrogen comes from a renewable source.

But challenges remain. Researchers at Hydrogen Solar, for example, are looking for a replacement for the expensive platinum now used in one of the cell's electrodes, which will be important for keeping down costs, especially as demand increases for platinum in this and other applications, such as fuel cells. Meanwhile, Sverdrup says other researchers, including those at NREL, are working with materials that are much more efficient than iron oxide but so far have lasted only hours. If researchers can make them last longer, the materials could challenge iron oxide.

Source : Technology Review

MIT makes new strain of yeast to make more ethanol and faster

Researchers at MIT have created a new strain of yeast that tolerates high levels of ethanol and ferments sugars more efficiently, making more ethanol and doing it faster.

The advance could lead to smaller, cheaper ethanol manufacturing plants, as well as reduce the notoriously high amounts of energy needed to make ethanol.

The result, described in the current issue of Science, is also an important advance in the wider effort to make organisms that can convert cheap biomass, such as corn leaves and stalks, agricultural waste, and fast-growing plants including willow and switchgrass, into ethanol. Ethanol from such sources is widely agreed to be the key to making this biofuel economically competitive with fossil fuels.

Researchers hope to engineer a single organism that will both break down the cellulose in these sources into sugars and ferment them to produce ethanol. The work by MIT chemical-engineering professor Gregory Stephanopoulos and his colleagues focuses on the second part of this process: fermenting sugars to make ethanol. The yeast strain they made can tolerate ethanol concentrations as high as 18 percent--almost double the concentration that regular yeast can handle without quickly dying. In addition, the new strain makes about 20 percent more ethanol by processing more of the glucose, and it speeds up fermentation by 70 percent.

Higher ethanol tolerance could lead to smaller, cheaper equipment for ethanol plants. Michael Ladisch, director of the laboratory of renewable-resources engineering at Purdue University, says ethanol fermentation is primarily carried out in tanks that have to be emptied and cleaned between batches. "The same volume of tank will make double the amount of ethanol in the same time period for a 10 percent final solution than for 5 percent, or the same amount of ethanol if the tank volume is halved," he says. "If the fermentation proceeds 10 percent faster for the same final concentration, the reduction in tank volume would be 10 percent." The higher concentrations also reduce the amount of water that must be removed in a final distillation step, thereby saving energy.

Improving yeast-ethanol tolerance is difficult because it is a complicated trait involving many genes. To tailor the expression of many genes at once, Stephanopoulos uses a process to induce random mutations in the genes for master regulator proteins. Each of these proteins controls the expression of multiple genes, so by altering them, Stephanopoulos sets off a cascade of changes in gene expression widespread enough to alter a trait like ethanol tolerance. The researchers randomly changed these proteins in a large yeast population, which led to some with an increased tolerance for ethanol.

So far the researchers have only modified a laboratory strain of the yeast, not the type now used in ethanol plants. "The next step is to show that this technology works with industry strains," Stephanopoulos says.

If their approach can modify industrial yeast, it would drive down the cost of ethanol, Ladisch says. And eventually this research could have a wider impact, he says, because the mechanism that the researchers used to make the ethanol-tolerant yeast could be used as a blueprint to develop other wanted traits in microbes. "They now have a handle into fundamental metabolic pathways in how the yeast might be modified," he says.

Stephanopoulos believes that cellulosic-ethanol yields could be improved by tailoring certain traits in microbes using his technique. It might be possible to make microbes that are tolerant of compounds other than ethanol that are created in the fermentation process and toxic to the microbes. He also hopes to produce strains that eat sugars with five carbon atoms, such as xylose, that are produced when cellulose is broken down. The microbes used in today's processes only ferment sugars like glucose that have six carbon atoms.

Much work remains to be done to develop a single organism that can first break down cellulose into sugars before fermenting these sugars. Breaking down cellulose is a key constraint to the viability of making ethanol from biomass, says Lee Lynd, professor of engineering at Dartmouth College. "The research and development-driven advances with the greatest impact on producing cellulosic ethanol at low cost and high efficiency have to do with converting biomass into sugars," he says.

 

Source : Technology Review

Texas Tech and GE team up to use wind turbines to power water-desalination plant

Researchers at Texas Tech are teaming up with General Electric (GE) to try to optimize what is in theory an ideal marriage: using wind turbines to power water-desalination plants. That way, many water-deprived areas could ultimately obtain clean drinking water in a sustainable way. And wind-turbine farms could gain a place to use excess electricity on high-wind days.

It may sound straightforward, but it's a tricky task: the water-desalination process envisioned for the project--known as reverse osmosis--operates best at stable, continuous rates. And that's difficult to achieve when the electricity source is variable. The technology goal is a control unit that can keep the desalination plant running as stably as possible, store some power at certain times, sell some to the grid at peak times, and also pump water to and from the system as necessary.

Within several years, the Texas Tech researchers hope to erect a 1.5 megawatt turbine that will power a desalination plant capable of supplying water to the town of Seminole, TX, which has about 10,000 residents. A 1.5 megawatt wind turbine, generating full power and supplying electricity to a reverse-osmosis unit, could generate about 1,500 cubic meters of clean water per hour from brackish supplies. (Ocean water is saltier and would yield less fresh water.) GE hopes the project--one in a handful of similar R&D initiatives around the world--will yield a commercial product capable of meeting the demands of municipal water suppliers.

The project will get started in early 2007 with a scaled-down test model at Texas Tech that uses a very small, five kilowatt wind turbine.

Supplies of fresh water around Lubbock, a windy but dry area in west Texas, are running out fast. The vast Ogallala aquifer--which sits under eight Great Plains states--is being exhausted by farms, businesses, and homes far faster than it can be naturally replenished. "We are now looking at a potentially serious water problem in west Texas," says Andy Swift, director of the wind-science engineering center at Texas Tech. "That aquifer is simply being drained faster than it recharges. It could be bled dry within 50 years." Beneath the Ogallala aquifer, there is a brackish aquifer at depths of 1,000 to 2,000 feet that these states may have to tap.

In a reverse-osmosis system, brackish or salt water is pumped against one side of a special membrane. Fresh water passes slowly through the membrane, with the brinier water staying behind. A lot of electricity is required to pump the brackish or salt water into the system, maintain water pressure against the membranes, and, finally, pump the resulting fresh water to water towers to meet demand.

The key goal is keeping costs reasonable. "We do know you can bring [wind power and desalination] together, but can you bring down the cost of the system?" asks Minesh Shah, the project leader at GE Global Research, in Niskayuna, NY. "To be able to bring down capital, energy, and life-cycle costs, we need to be smarter in how we operate. It's all about the energy-management system for these two integrated products. We look at it as energy sustainability and water sustainability."

Any excess wind power could be sold to the power grid during peak times, when--in some regions--electricity fetches higher prices. "You would be making a real-time decision as to how the output of the wind turbine is going to be used: to deliver electricity to the grid, or to run the reverse-osmosis unit," says Swift.

Source : Technology Review

GM announces a new plug-in hybrid vehicle

Last week General Motors (GM) gave a boost to plug-in hybrid vehicles. It announced a new gas-saving technology that could transform transportation and make renewable sources of electricity, such as wind and sun, more feasible.

At the Greater Los Angeles Auto Show, the automaker committed to manufacturing versions of its hybrid Saturn Vue SUV with a much larger battery pack that can be charged via an ordinary household socket. The increased size of the battery pack makes it possible to rely more on electric drive than current hybrid vehicles do, thereby saving much more gasoline. The actual rollout date will depend on the development of suitable battery technology, according to GM chairman and CEO Rick Wagoner.

With the announcement, GM joined other major automakers that are developing plug-in hybrid technology, including Ford, Daimler Chrysler, and Toyota. "We hope to have some products in the near future, but we're not prepared to say yet when that will be," says Bruce Brownlee, the senior executive administrator at Toyota Technical Center, in Gardena, CA. "The potential [of plug-in hybrids] is terrific." (None of these car companies have yet committed to widespread production of such a vehicle.)

The announcement marks a change in strategy for GM, which has previously focused on addressing environmental issues and high fuel prices by modifying existing vehicles to run on ethanol and by developing hydrogen fuel-cell vehicles. Although GM still plans to continue its fuel-cell program, the decision to produce plug-in hybrids represents a move toward a more evolutionary transition from internal combustion vehicles. "It's nice to see General Motors not just putting all their bets on hydrogen," says Jason Mark, vehicles director for the Union of Concerned Scientists, based in Cambridge, MA.

Plug-in hybrids, which use both an electric motor and a gasoline-powered internal combustion engine, have been hailed as a bridge technology that could make it possible to cut gasoline consumption in the short term; meanwhile, researchers will continue to work out the problems with all-electric vehicles, such as the high costs that make long-range battery-powered vehicles unaffordable. The most commonly described version of this technology would allow drivers to commute about 20 miles without using gasoline at all. But in reality, plug-in hybrids will likely use a blended strategy, relying on the gasoline engine to boost power for acceleration or for climbing hills even during the first 20 miles. This blended strategy would still mean that a typical commute would use almost no gasoline. "Having an internal combustion engine for passing or hill climbing is probably a prudent thing to do," says Thomas Keim, a principal research engineer at MIT. "But if you're traveling around town or just cruising on the highway, you can do both of those things from the battery."

Plug-in hybrids have an advantage over all-electric vehicles in that the battery would be the primary source of power only for relatively short distances, allowing for a much smaller and less expensive battery pack. Since short trips represent the majority of driving in the Unites States, the result would be a dramatic decrease in gasoline use. Electricity use would go up, but the price of powering a vehicle with electricity from the grid during off-peak hours would be the equivalent of gas for about 90 cents per gallon, says Terry Penney, a technology manager for advanced vehicle technologies at the National Renewable Energy Laboratory, in Golden, CO.

For longer trips, the vehicle would switch to a standard hybrid mode once the battery has been depleted to a certain point, saving fuel the same way today's hybrids do. This includes using energy recaptured from braking, turning off the engine when the vehicle stops, and allowing the gasoline engine to run at a more constant and efficient speed. Incorporating existing technologies--such as six-speed rather than four-speed automatic transmissions, and turning off fuel to pistons that aren't needed--could further improve fuel efficiency. Indeed, Mark says these technologies alone, even without hybrid technology, could improve average fuel economy by 10 miles per gallon--enough to replace all the oil we import from the Middle East. Using ethanol rather than gasoline could further decrease gasoline consumption.

These fuel savings would only be the beginning, many experts say. As battery technology improves, and if plug-in hybrids are successful, the high-volume production of batteries could lower their price. This would make it affordable to increase battery-pack size in successive generations and rely even less on gasoline. Eventually, the internal combustion engine could be made smaller and be used exclusively to recharge the batteries on long trips in a configuration called a "series" hybrid. "As time goes on, we may look at even more electrification of the vehicle, including solutions that use fuel cells," says Peter Savagian, director of hybrid power-train systems at GM. At some point, the internal combustion engine could be replaced entirely by large electric motors and battery packs, or by hydrogen fuel cells.

But plug-in hybrids still face challenges. Their environmental benefits will depend on the source of electricity used to charge the batteries. In areas powered primarily by coal, a plug-in might not be better for the environment than a good hybrid, says Nicholas Twork, a spokesman for Ford. Penney says that plug-ins will typically be better, however, since other areas in the United States rely on cleaner sources of electricity.

What's more, Penney says, "if millions of these things were produced 20 years from now, it would really enable renewable energies like wind to take off." Wind power requires ways of storing energy generated when demand for electricity is low, he says. The cost of the storage makes it hard for wind to compete with other sources of electricity. Millions of plug-in vehicles charging at night would essentially provide free storage.

But right now the biggest challenge to plug-in hybrids is the battery technology. First, batteries are expensive. Several companies sell kits for converting existing hybrids to plug-ins with larger battery packs, and these can add $10,000 to the price of a car (see "Plug-In Hybrids Are on the Way"). The plug-in hybrid application will also be much more demanding on batteries than ordinary hybrids are. In a car such as the Toyota Prius, the battery stays at about a 50 percent state of charge, and this varies only a few percent as it absorbs power from regenerative breaking and delivers it in short bursts to augment the gas engine. With plug-ins, batteries will be charged up to at least 95 percent and then deeply discharged during the first 20 miles of driving before settling into an ordinary hybrid mode. Such deep discharging typically decreases battery life. Automakers want batteries that can last 10 years or so even under these conditions so that consumers won't need to buy new battery packs a few years into owning a vehicle.

Automakers' newfound interest in plug-in hybrids is due in part to promising new battery technologies that could be less expensive and have longer lifetimes, and in part to their being safer than the lithium-ion batteries used in laptops today (see "Safer Lithium-Ion Batteries"). "We're encouraged by the improvements in the technology represented by hybrid batteries today," Savagian says. "And we're encouraged that there are many companies pursuing different formulas for them. But we want to give them cause to continue to press forward."

Source : Technology Review