Tuesday, July 11, 2006

Exploding the myth of the hydrogen economy
Posted by Dan Welch under Peakist , Energy , Gas
Source: The Peakist

Tim Flannery debunks the idea that hydrogen is going to provide us with the fuel of the post-oil energy regime:

“TO PEOPLE IN THE PETROCHEMICAL and motor vehicle businesses, the solution to the climate change problem lies in ascending a metaphorical staircase of fuels, which, at each step, contains an ever diminishing amount of carbon.

Yesterday, the argument goes, it was coal, today it’s oil, and tomorrow it will be natural gas, with Nirvana being reached when the global economy makes the transition to hydrogen—a fuel that contains no carbon at all.

Although the transition from oil to gas is now well under way, it’s been some time coming. For many years the oil companies regarded natural gas as a volatile waste product, to be either burned off or pumped back underground to increase oil pressure at the well head. Because of its greater hydrogen content, gas burns hotter and cleaner than oil, so it was always valuable stuff; but the technology needed to transport it safely and cheaply did not exist.

One of gas’s greatest drawbacks is its low density, which makes it bulky and prone to leaking. It takes a house-sized volume of gas to yield the same energy as a barrel of oil, so barrels—and even tankers—were never an option for its transport. Pipelines were the obvious solution, but suitable pipelines cost around a million dollars for each mile laid, which meant that until recently, investing a dollar in oil returned twice the profits of one invested in gas.

Technological advances in handling gas, high oil prices, a looming lack of oil, and the demand for a cleaner fuel to replace coal have all combined to change the economics of gas, and today it is big business. The most important technical advance involved the refrigeration of gas so that it becomes a supercooled liquid, which permits cost-effective transport, in purpose-built ships, over large distances. With an international trade in shipping developed, and with the larger corporations willing to invest the billions required for gas pipelines, gas appears to be the fuel of choice for the twenty-first century.

Although gas is a more expensive fuel than coal, it has many benefits that make it ideal for producing electricity. Gas-fired power plants cost half as much to build as coal-fired models, and they come in a variety of sizes. Instead of having one massive, distant generator of electricity, as with coal, a series of small gas-fired generators can be dotted about, saving on transmission losses. They can also be fired up and shut down quickly, which makes them ideal for complementing intermittent sources of energy generation such as wind and solar. Furthermore, combined-cycle plants, which burn gas to turn a turbine then capture the ultra-hot exhaust emissions to generate more electricity, are extremely efficient at converting fuel to power. If coupled to a heat-using industrial process (called cogeneration), they can achieve efficiencies of 80 percent. All of this has led Lord Browne, CEO of BP, to comment that “one dollar invested today in gas-fired generation capacity produces three to four times the amount of electricity [as] the same dollar invested in coal-fired generation capacity.”

Over 90 percent of new power generation in the United States today is gas-fired, and around the world it is fast becoming the favored fuel. Despite this, gas is not without its problems, including safety issues and the possibility of terrorist attacks on large plants or pipelines. And because methane is a powerful greenhouse gas, its potential to leak must be addressed: Parts of the gas infrastructure—such as the old iron pipes used for reticulating gas throughout cities—are decidedly leaky.

GAS IS THE THIRD STEP on the stairway to climate-change heaven; but even if all the coal-fired power stations on Earth were replaced with gas-fired ones, global carbon emissions would be cut by only 30 percent. So despite these savings, if we were to stall on this step of the energy staircase, we would still face massive climate change. In this scenario, a transition to hydrogen is thus imperative; but how likely is it?

In the 1970s the Australian electrochemist John Bockris coined the phrase “hydrogen economy,” and ever since, for many people, hydrogen appears to be the silver-bullet solution to the world’s global warming ills. “Boiled down to its minimalist description,” Bockris wrote, “the ‘Hydrogen Economy’ means that hydrogen would be used to transport energy from renewables (at nuclear or solar sources) over large distances; and to store it (for supply to cities) in large amounts.” As with so many silver-bullet solutions, however, there’s a lot of devil in the detail.

The power source of the hydrogen economy is the hydrogen fuel cell, which is basically a box with no moving parts that takes in hydrogen and oxygen and puts out water and electricity. While a wondrous-sounding device, it is hardly new technology: The first hydrogen fuel cell, known as a “gaseous voltaic battery,” was built by Sir William Grove in the 1830s. His cell resembled a standard lead-acid battery, in that it used sulphuric acid as an electrolyte, but instead of employing lead electrodes it used platinum, which hastens the reaction of hydrogen and oxygen that generates the electricity. The use of such an expensive catalyst was a drawback in developing the technology, but today there are several kinds of fuel cells that use other materials. Whatever their composition, from an economic perspective, hydrogen fuel cells can be divided into two types: stationary cells used to produce electricity, and those used in transport.

The most promising cells for the stationary production of electricity are known as molten carbonate fuel cells, which use molten potassium carbonate instead of sulphuric acid, and nickel in place of platinum. They operate at a temperature of around 1202°F, and although highly efficient (possessing an electric efficiency of around 50 percent), they take a long time to reach working temperature. They are also very large—a 250-kilowatt model is the size of a railway carriage—making them unsuitable for use in motor vehicles.

Several demonstration projects based on this technology already exist, and a commercial stationary hydrogen cell (using an earlier technology) has been in operation in the United States since 1999. It is predicted that a decrease in cost resulting from economies of scale will soon lead to more widespread use of the cells. Although this represents a tremendous technological advance, it does nothing immediate to abate CO2 emissions, for the hydrogen used today comes from reforming natural gas. Because some of the energy in the gas is used in this process, and all of the CO2 it produces is released into the atmosphere, from a climate perspective the world would be better off burning the gas directly to create electricity.

But let’s consider hydrogen as a transport fuel. A number of motor vehicle manufacturers, including Ford and BMW, are planning to introduce hydrogen-fueled, internal combustion engine cars to the marketplace; and the Bush administration plans to invest $1.7 billion to build the hydrogen-powered FreedomCAR. Even so, the use of hydrogen as a transport fuel is at a far more rudimentary stage of development than the technology using stationary cells.

The fuel cell type best suited for transport purposes is known as a proton-exchange membrane fuel cell. It is much smaller than the molten carbonate cell and operates at around 150°F, thus being ready for action soon after turning the ignition. These cells, however, require very pure hydrogen. In current prototypes this is supplied from a built-in “reformer” that converts natural gas or gasoline to hydrogen, which again means that, from a climate perspective, we would be better off burning these fuels directly to drive the engine. The best energy efficiency obtained by proton-exchange membrane fuel cells is 35 to 40 percent—about the same as a standard internal combustion engine.

Vehicle manufacturers hope to do away with the on-board reformer required by the prototypes and envisage fueling the vehicles from hydrogen “pumps” at fuel stations. There are several ways that this could be done. The one most closely resembling the current system of fueling vehicles involves producing the hydrogen at a remote central point and distributing it to fueling stations; and it’s here that the difficulties involved in moving such low-density fuel become evident.

The ideal way to transport it is in tanker-trucks carrying liquefied hydrogen, but, because liquefaction occurs at -423°F, refrigerating the gas sufficiently to achieve this is an economic nightmare. Using hydrogen energy to liquefy a gallon of hydrogen consumes 40 percent of the value of the fuel. Using the U.S. power grid to do so takes 12-15 kilowatt hours of electricity, and this would release almost twenty-two pounds of CO2 into the atmosphere. Around a gallon of gasoline holds the equivalent energy of one kilogram of hydrogen. Burning it releases around the same amount of CO2 as using the grid to liquefy the hydrogen, so the climate change consequences of using liquefied hydrogen are as bad as driving a standard car.

One solution may be to pressurize the hydrogen only partially, which reduces the fuel value consumed to 15 percent, and the canisters used for transport can be less specialized. But even using improved, high-pressure canisters, a 40-ton truck could deliver only 100 gallons of compressed hydrogen, meaning that it would take fifteen such trucks to deliver the same fuel energy value as is now delivered by a 26-ton gasoline tanker. And if these 40-ton trucks carried the hydrogen 300 miles, the energy cost of the transport would consume around 40 percent of the fuel carried.

Further problems arise when you store the fuel in your car. A special fuel tank carrying hydrogen at 5,000 psi (near the current upper limit for pressurized vessels) would need to be constructed and be ten times the size of a gas tank. Even with the best tanks, around 4 percent of fuel is likely to be lost to boil-off every day. A good example of the rate of evaporative loss of hydrogen occurs whenever NASA fuels the space shuttle. Its main tank takes 26,500 gallons of hydrogen, but an extra 12,000 gallons must be delivered at each refueling just to account for the evaporation rate.

Pipelines are another option for transporting hydrogen, but as with gas, they are expensive—they must be large and built from materials resistant to hydrogen (it makes steel, for example, very brittle). They must also be of high integrity, because hydrogen leaks so easily. Even if the preexisting gas pipeline network could be reconfigured to transport hydrogen, the cost of providing a network running from central producing units to the world’s fueling stations would be astronomical.

Perhaps hydrogen could be produced from natural gas at the gas station. This would do away with the difficulties of transporting it, but this process would produce 50 percent more CO2 than using the gas to fuel the vehicle in the first place. Hydrogen could also theoretically be generated at home using power from the electricity grid, but the price of electricity for domestic use, and the high cost of hydrogen generation and purification units, would make it prohibitively expensive. Furthermore, the electricity in the grid in places such as the United States is largely derived from burning fossil fuels, so home generation of hydrogen under current circumstances would result in a massive increase in CO2 emissions.

And there is another danger with home-brewing hydrogen. The gas is odorless, leak prone, and highly combustible, and it burns with an invisible flame. Firemen are trained to use straw brooms to detect a hydrogen fire; when the straw bursts into flames, you have found your conflagration.

Let’s imagine for a moment, however, that all of the delivery problems relating to hydrogen are overcome, and you find yourself at the wheel of your new hydrogen-powered four-wheel-drive. Your fuel tank is large and spherical, because at room temperature hydrogen takes up around three thousand times as much space as gasoline. Now consider that a call on your mobile phone, the static electricity generated by sliding over a car seat, or even an electrical storm a mile away all carry a sufficient charge to ignite your hydrogen fuel. When viewed in this light, the thought of a hydrogen car accident hardly bears thinking about. Even garaging your new vehicle means trouble. Current codes for hydrogen storage in the United States are onerous, requiring—among other things—expensive ventilation and explosion-proof equipment. This means that unless codes are relaxed, a plethora of infrastructure from garages to road tunnels will require modification.

Even if hydrogen is made safe to use, we are still left with a colossal CO2 pollution issue, which was exactly the opposite of what we set out to do. The only way that the hydrogen economy can help combat climate change is if the electricity grid is powered entirely from carbon-free sources. And this means acceptance of and investment in a series of technologies ranging from solar to nuclear. Strangely, neither the U.S. government nor the vehicle manufacturers have shown much interest in laying the groundwork for this essential prerequisite for transition to the hydrogen economy.