Coincidentally, on the day that the world’s population hit 7 billion, three experts at a session of the Industrial Physics Forum spoke about the growing challenge of supply and demand in the electric economy. The forum, organized by the industrial outreach arm of the American Institute of Physics and titled “Energy: Transition to a Sustainable Future,” was featured at the annual meeting of AVS: Science and Technology of Materials, Interfaces, and Processing held last week in Nashville, Tennessee.
The electricity infrastructure is expanding everywhere. Most societies embrace the notion that the capacity of the electrical grid needs to keep pace. Although using renewable energy sources, such as solar and wind, is the ideal, most countries seem unable to wean themselves from their addiction to coal. In the US, and increasingly in China, coal-fired plants dominate the power generation sector. Coal is abundant, cheap, and relatively high in energy content. But like oil, it will eventually be depleted. So what can we use to supplement and eventually replace it?
Nuclear: Safe by comparison?
Nuclear energy should be considered at least as a stopgap solution, said Harold McFarlane, interim associate director at Idaho National Laboratory (INL) and one of the session’s speakers. McFarlane touted some of the benefits of nuclear energy: It does not involve burning fossil fuels or releasing greenhouse gases; its primary fuel source, uranium, is relatively abundant; and it is not an intermittent power source, like solar and wind.
But he also acknowledged the persistent hurdles that nuclear power faces. For one, it is capital intensive—nuclear plants take years and millions of dollars to build, and there are additional costs to secure them and prevent proliferation of the fuel and technology to rogue groups. Another hurdle is where to store the waste. Although nuclear waste can be stored safely, no one wants it stored near them. And most notably, nuclear accidents can occur, and when they do, the nuclear fallout can prove fatal.
The case can be made that nuclear energy is analogous to commercial air travel: Flying is safer than driving—but when accidents happen, they’re usually catastrophic. McFarlane pointed out that in the past four decades, more than 7000 people died as the result of accidents directly related to the production of electricity with oil, coal, and natural gas—and that figure does not include toxicity-related deaths caused by fossil-fuel emissions. In the same period, the number of fatalities resulting from nuclear-plant accidents was zero. And despite all the problems suffered at the Fukushima Daiichi nuclear plant in Japan, which was damaged in March by a magnitude-9.0 earthquake and 40-meter-high tsunami waves, no one died. (See the story in the May 2011 issue of Physics Today that discusses the fate of nuclear plants in the aftermath of Fukushima and the one in the November 2011 issue about Japan’s efforts to resume their scientific pursuits.)
Even as some nations, including Germany, are looking to phase out nuclear power, 65 new plants are being constructed worldwide, nearly half of them in China. McFarlane discussed R&D conducted at INL and elsewhere. Projects include designing safer, “proliferation-proof” reactors, and new designs that are cooled by gas or high-thermal-conductivity fluids such as molten salts; they would replace the current reactors, which consume large batches of water to cool the reactor rods (see the story about modular reactors in Physics Today, August 2010). In the current economy, nuclear energy faces yet another challenge—the increasing supply and decreasing cost of natural gas.
Bearing a heavy load
Speaking after McFarlane was MIT electrical engineering professor John Kassakian, who addressed the present challenge of the US electrical economy: How do we upgrade an aging grid, which is susceptible to cyber attacks and must bear an increasing load from electric vehicles and renewable-energy sources? Kassakian talked about efforts to make the grid smarter—digitally redundant so as to dissipate cyber attacks, retrofitted to handle the greater loads, and able to instantly adjust power distribution, even to electronic systems in an individual’s home.
The smart-grid concept is gaining traction for many reasons—for its reliability, security, and environmental friendliness, among other things, said Kassakian. But although smart meters could help reduce the electricity bill at an individual’s home, the smart grid presents no initial savings to the US economy overall. For one, considerable capital will be required to do the following:
• Upgrade the grid with advanced computer networks.
• Replace existing transmission lines with more compact and efficient ones, such as high-temperature superconducting cables (see the story in Physics Today, January 2008).
• Integrate large-scale energy storage systems.
• Transport wind energy from the midwestern US to the East and West Coasts, where it is most needed.
• Install smart meters in homes and commercial buildings (see the story in Physics Today, April 2009, about investments to the smart grid).
Public acceptance still remains an unknown, said Kassakian. Several US cities have tried to roll out “demand response” smart meters only to be rebuffed by the local citizens, who cite intrusion and privacy concerns.
And then there’s the issue of who’s in charge of what, said Kassakian, a former director of ISO New England, which operates that region’s power generation and transmission system (see the photo of the ISO New England control room at the top of the article). A common misconception is that the US grid network is a single entity. In fact, there are three separate grids: one west of the Rockies, another east of the Rockies, and a third in Texas. (See the story in Physics Today, April 2010, about a project under way to connect the three grids using high-temperature superconducting cables.) Within specific regions of the west and the east grids, several companies control the transmission and distribution of power. Then each state sets its own electricity prices and controls where power lines can be sited. And finally, the Federal Energy Regulatory Commission retains authority on issues related to the interstate transfer of electricity.
Backing up the grid
Finally, materials scientist Zhenguo “Gary” Yang at Pacific Northwest National Laboratory in Richland, Washington, spoke on the technical challenges of large-scale electrical energy storage. Energy can be stored many ways: in supercapacitors, by compressed-air or hydraulic pumps, or with flywheels. But the highest thermodynamic efficiency is achieved with electrochemical storage in batteries, said Yang. Actual efficiencies vary, however, depending on the battery’s specific chemistry and the corresponding engineering of the system.
Yang presented a suite of evolving technologies, including the increasingly popular lithium-ion batteries, and the emerging sodium-sulfur and vanadium redox battery technologies. Lithium-ion batteries are relatively light, and they are environmentally safe since the lithium exists in aqueous form, but the energy density is relatively low and the drop in capacity over time is relatively high. Sodium-sulfur batteries pack high energy densities, but the materials are corrosive, and because sodium spontaneously explodes in contact with water, the system must be sealed off from moisture.
Yang has conducted research on the vanadium redox battery—the flow diagram shows the simultaneous oxidation and reduction of vanadium (V)—which has a relatively high storage capacity and can be rapidly charged and discharged, but its energy density is relatively low. One emerging technology that Yang highlighted is the lithium-air battery, which is light and has a relatively high energy density but has poor charge–discharge properties. With the exception of metal-air batteries, which Yang said are still “a scientific curiosity,” most grid-scale battery storage technologies have been around since the 1970s. Now that the demand for them is here, Yang is optimistic that they will take off.
Jermey N. A. Matthews
