The Truth About Hydrogen
Jeff Wise
Источник:http://www.popularmechanics.com/science/energy/next-generation/4199381
Wild promises abound, but can the simplest element in the universe really power our homes, fuel our cars and reduce our contribution to global warming? PM crunches the numbers on the real hydrogen economy.
WHEN ASSESSING THE State of the Union in 2003, President Bush declared it was time to take a crucial step toward protecting our environment. He announced a $1.2 billion initiative to begin developing a national hydrogen infrastructure: a coast-to-coast network of facilities that would produce and distribute the hydrogen for powering hundreds of millions of fuel cell vehicles. Backed by a national commitment, he said, "our scientists and engineers will overcome obstacles to taking these cars from laboratory to showroom, so that the first car driven by a child born today could be powered by hydrogen, and pollution-free." With two years to go on the first, $720 million phase of the plan, PM asks that perennial question of every automotive journey: Are we almost there?
And the inevitable answer from the front seat: No. Promises of a thriving hydrogen economy — one that supports not only cars and trucks, but cellphones, computers, homes and whole neighborhoods — date back long before this presidency, and the road to fulfilling them stretches far beyond its horizon.
The Department of Energy projects the nation's consumption of fossil fuels will continue to rise — increasing 34 percent by 2030. When burned, these carbon-based fuels release millions of tons of carbon dioxide into the atmosphere, where the gas traps heat and is believed to contribute to global warming.
At first glance, hydrogen would seem an ideal substitute for these problematic fuels. Pound for pound, hydrogen contains almost three times as much energy as natural gas, and when consumed its only emission is pure, plain water. But unlike oil and gas, hydrogen is not a fuel. It is a way of storing or transporting energy. You have to make it before you can use it — generally by extracting hydrogen from fossil fuels, or by using electricity to split it from water.
And while oil and gas are easy to transport in pipelines and fuel tanks — they pack a lot of energy into a dense, stable form — hydrogen presents a host of technical and economic challenges. The lightest gas in the universe isn't easy to corral. Skeptics say that hydrogen promises to be a needlessly expensive solution for applications for which simpler, cheaper and cleaner alternatives already exist. "You have to step back and ask, 'What is the point?'" says Joseph Romm, executive director of the Center for Energy & Climate Solutions.
Though advocates promote hydrogen as a panacea for energy needs ranging from consumer electronics to home power, its real impact will likely occur on the nation's highways. After all, transportation represents two-thirds of U.S. oil consumption. "We're working on biofuels, ethanol, biodiesel and other technologies," says David Garmin, assistant secretary of energy, "but it's only hydrogen, ultimately, over the long term, that can delink light-duty transportation from petroleum entirely."
The Big Three U.S. automakers, as well as Toyota, Honda, BMW and Nissan, have all been preparing for that day. Fuel cell vehicles can now travel 300 miles on 17.6 pounds of hydrogen and achieve speeds of up to 132 mph. But without critical infrastructure, there will be no hydrogen economy. And the practical employment of hydrogen power involves major hurdles at every step — production, storage, distribution and use. Here's how those challenges stack up.
HURDLE 1: Production
The United States already uses some 10 million tons of hydrogen each year for industrial purposes, such as making fertilizer and refining petroleum. If hydrogen-powered vehicles are to become the norm, we'll need at least 10 times more. The challenge will be to produce it in an efficient and environmentally friendly way.
FOSSIL FUELS: At present, 95 percent of America's hydrogen is produced from natural gas. Through a process called steam methane reformation, high temperature and pressure break the hydrocarbon into hydrogen and carbon oxides — including carbon dioxide, which is released into the atmosphere as a greenhouse gas. Over the next 10 or 20 years, fossil fuels most likely will continue to be the main feedstock for the hydrogen economy. And there's the rub: Using dirty energy to make clean energy doesn't solve the pollution problem-it just moves it around. "As a CO2 reducer, hydrogen stinks," Romm says.
Capturing that carbon dioxide and trapping it underground would make the process more environmentally friendly. In July, General Electric and BP Amoco PLC announced plans to develop as many as 15 power plants over the next 10 years that will strip hydrogen from natural gas to generate electricity; the waste carbon dioxide will be pumped into depleted oil and gas fields. And the Department of Energy is largely funding a 10-year, $950 million project to build a coal-fed plant that will produce hydrogen to make electricity, and likewise lock away carbon dioxide to achieve what it bills as "the world's first zero-emissions fossil fuel plant."
Whether carbon dioxide will remain underground in large-scale operations remains to be seen. In addition, natural gas is a limited resource; the cost of hydrogen would be subject to its price fluctuations.
ELECTROLYSIS: Most of the remainder of today's hydrogen is made by electrically splitting water into its constituent parts, hydrogen and oxygen. This year, a PM Breakthrough Award went to GE's Richard Bourgeois for designing an electrolyzer that could drastically reduce the cost of that process. But because fossil fuels generate more than 70 percent of the nation's electrical power, hydrogen produced from the grid would still be a significant source of greenhouse gas. If solar, wind or other renewable resources generate the electricity, hydrogen could be produced without any carbon emissions at all.
NUCLEAR POWER: Next-generation nuclear power plants will reach temperatures high enough to produce hydrogen as well as electricity, either by adding steam and heat to the electrolysis process, or by adding heat to a series of chemical reactions that split the hydrogen from water. Though promising in the lab, this technology won't be proved until the first Generation IV plants come on line — around 2020.
HYDROGEN IS THE universe's simplest atom: a single electron orbiting a single proton. In a fuel cell, incoming hydrogen gas is separated by a catalyst at the anode into protons and electrons. The protons pass directly through a proton exchange membrane (PEM), while electrons are forced through an external circuit, causing electric current to flow. When the protons and electrons meet at the cathode, they join with oxygen to form water and heat, which are released as exhaust.
A single fuel cell produces just over 1 volt, so hundreds are stacked together for typical applications. PEM fuel cells, used in NASA's Gemini flights in the 1960s, are the design of choice for fuel cell cars, but other configurations are suited for applications ranging from laptops to power plants.
Electrolysis is the exact opposite process. Electricity from a power supply splits incoming water into protons, electrons and oxygen, which is released as a gas. Electrons reunite with protons at the cathode to produce hydrogen gas.
Other electrolysis designs being developed use solid-oxide membranes instead of PEMs, which improve efficiency but require operating temperatures of 900 to 1500 F — heat that could be supplied by nuclear reactors.
HURDLE 2: Storage
Once hydrogen reaches consumers, is there anything they can do with it except drive vehicles? Home energy generation is one other option. The question is whether hydrogen would be more practical than current methods. Hydrogen produced by steam reformation or by electrolysis loses energy when it is converted into electricity. The resulting efficiency is roughly equal to that of today's power plants — which pay a lot less for raw materials. Direct generation of electricity through wind and solar power will also be more efficient for most stationary applications. That leaves transportation as the most promising use for hydrogen.
NTERNAL COMBUSTION: The most straight-forward approach is to burn hydrogen in an adapted model of your garden-variety internal-combustion engine (ICE). Since little modification is required, these engines are relatively cheap, and 25 percent more efficient than gasoline-powered engines. BMW built its first hydrogen ICE back in the 1970s, and the concept still has legs: Ford began production of a hydrogen ICE shuttle bus last July.
FUEL CELL: First invented in 1839, a fuel cell combines hydrogen and oxygen to generate electricity without any moving parts. Several different varieties exist, but only the proton exchange membrane (PEM) fuel cell is lightweight and responsive enough to be practical for vehicle use. Though twice as efficient as ICEs, PEM fuel cells are hindered by high prices — even in mass production, they would currently cost about $36,000 each.
Once the technical hurdles are crossed, hydrogen's huge price tag may still make the technology prohibitive. A recent analysis by the Department of Energy projected that a supply network adequate for even 40 percent of the light-duty fleet could cost more than $500 billion. And that leads to a classic chicken-and-egg problem: How do you get millions of Americans to buy hydrogen-powered vehicles before there's an infrastructure in place to refuel them? And how do you get energy companies to build that infrastructure before there's a potential customer base?
"Companies are not willing to invest if they don't think there's going to be a market," says Daniel Sperling, director of the Institute of Transportation Studies at UC Davis. "The government has to be behind it. There has to be leadership."
There's reason to hope the technology will advance even without much government involvement. Hydrogen fuel cells already replace batteries in niche equipment, such as TV cameras and forklifts, and provide power at remote locations, such as at cellphone towers. They even power the police station in New York's Central Park. As these applications continue to develop, they will force advances in technology that will make hydrogen vehicles more feasible. Even then, hydrogen might make the most sense for fleet vehicles that don't require widespread infrastructure for service and refueling.
Ultimately, hydrogen may be just one part of a whole suite of energy alternatives. Any one of them will involve investing heavily in new infrastructure. Though the price tag will be steep, we can't afford oil's environmental, economic and political drawbacks any longer.