The Hydrogen Economy, Hydrogen Sources, and the Science Behind These

The hydrogen-filled Hindenburg in 1936 or 1937. Photo from DeGolyer Library at Southern Methodist University.

THE HYDROGEN ECONOMY

The hydrogen economy is a hypothetical future in which energy can be bought, sold, stored, and transported in a currency of hydrogen, much like today’s energy is often exchanged in electricity. Because hydrogen doesn’t need to be attached to the electricity grid, it can be used in forms of transportation like buses and cars.

The end-user of the hydrogen, for example an automobile driver, doesn’t experience significant pollution beyond the formation of water from burning the hydrogen.

For more details about the hydrogen economy see here.

Hydrogen, a gas, isn’t a fuel like gasoline or coal; hydrogen is a way to store and transport energy made from other fuels, like a battery or electricity. Unlike fossil fuels, pure hydrogen isn’t stable, so forming hydrogen in the first place requires energy and produces carbon dioxide, and storing hydrogen involves special considerations because this light gas is very flammable and also quickens rust and oxidation in pipelines and storage containers.

HOW HYDROGEN IS DIFFERENT FROM FOSSIL FUELS

Allowing hydrogen (a gas) to burn in the presence of oxygen releases that stored energy in the form of heat. Hydrogen can also be reacted in a fuel cell to produce electricity. In either case, electricity or heat can then be used to power cars or any number of other devices. Gasoline, biofuels, wood, and other carbon-based fuels all produce carbon dioxide when they are burned, and rising carbon dioxide levels are widely implicated in climate change. Burning hydrogen produces energy, water and a few trace compounds, but it doesn’t produce carbon dioxide.

2 H2 (hydrogen gas) + O2 (oxygen gas) = 2 H2O (water vapor) + energy

It’s unclear what widespread emission of water vapor could do. According to recent published estimates, atmospheric water vapor is responsible for 75 percent of the greenhouse effect. However, water vapor can condense, and it’s naturally-occurring in the atmosphere. It is much easier to trap and transform to liquid than the carbon dioxide normally emitted by burning gasoline. Carbon dioxide won’t form a liquid at atmospheric temperatures and will solidify into dry ice only below -108.4 Fahrenheit, so proponents say it can be easier to trap the vapor in hydrogen-powered machines.

If the energy used to generate and purify and store and ship hydrogen doesn’t require emitting greenhouse gases or toxics, proponents argue that hydrogen is a clean alternative.

SOURCES OF HYDROGEN: THE UNFORTUNATE REALITY TODAY

Hydrogen, not carbon, is the most prevalent atom in the human body. There are two hydrogen atoms in every water molecule, and as many as hundreds of hydrogen atoms on the basic building blocks of life, from DNA to plant fibers. Nonetheless, harvesting the hydrogen atoms out of any of these structures to make hydrogen fuel isn’t easy because hydrogen likes to be bonded to carbon or oxygen; it doesn’t like to be elemental gas.

To produce pure hydrogen today, industries use primary fuel source like petroleum, natural gas, coal, or biomass. Through chemical processing, the hydrogen atoms are stripped from the fuel by way of an input of energy from electricity (more than 80 percent of which comes from fossil fuels in the United States). Furthermore, the leftover material from the stripping is carbon dioxide, the same carbon dioxide that would have been produced if the fuel was burned in an engine.

The reactions for various fuel to hydrogen conversions can be found on the U.S. Department of Energy website here.

Hydrogen can also be produced, at great energy loss, through the electrolysis of water: using electricity, water is divided into its constituents, hydrogen and oxygen. However, water electrolysis is the least carbon-neutral hydrogen production method, and it is very expensive ($3 to $6 per kilogram instead of a little more than $1 in the case of using coal for hydrogen), according to the U.S. Energy Information Administration. All hydrogen production methods result in a net energy loss.

 

 

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Thermodynamics and Thermal Energy

Thermodynamics is the study of how energy moves and changes form, usually by way of heat, as suggested by the components of its name: thermo-dynamics. Its laws and equations help to predict what could happen in various situations, based on the temperature, pressure, materials, and shape of a system.

Thermodynamics tells us how to calculate the ultimate temperature of a refrigerator or how much energy we can get out of a steam engine. Thermodynamics can also be applied to chemistry and the world on an atomic level, predicting which compounds are stable at specific temperatures and pressures. Thermodynamics explains why diamonds form naturally and spontaneously from carbon-based compounds deep inside the Earth, but they cannot form spontaneously here on the surface.

Thermodynamics relies on the idea that energy is conserved, even if it is transferred from or to a system to its surroundings through heat, changes in momentum, or other forms of energy.

 

TEMPERATURE AND HEAT

Heat and thermal energy are directly related to temperature. We can’t see individual atoms vibrating in solids, liquids, and gases, but we can feel their kinetic energies as temperature. Atoms in solids, liquids, and gases do vibrate. If they didn’t, they would be at absolute zero, a theoretical state of zero thermal energy at ­-459.67 Fahrenheit.

When there’s a difference between the temperature of the environment and a system within it, thermal energy is transferred between them as heat. Something doesn’t have heat. Instead, as an object or system gains or loses heat, it increases or decreases its thermal energy.

Adjacent objects that exhibit different temperatures will spontaneously transfer heat to try to reach the same temperature as each other, or equilibrium. However, how much energy it takes to change the temperature of an object is based on what its made of, a property called heat capacity or thermal capacity.

Water has a higher heat capacity than steel, for example. An empty pot on the stove takes almost no time to get to 212 degrees Fahrenheit, or the boiling temperature of water. A pot with some water in it will take far much longer to reach the same temperature, because water needs to absorb more energy — per weight, per degree — to gain the same number of degrees as metal. (Even though the vaporization temperature of metal is far, far higher than the water’s).

 

THERMAL ENERGY STORAGE: A SOURCE OF POWER

Thermal energy storage exploits the difference in temperature between a system and the environment. In the late 1800s, Americans used thermal energy storage by cutting blocks of lake ice during the winter and storing them underground packed in insulating wood shavings. When the summer rolled around, they retrieved that stored ice to make food cold, exploiting the difference in temperature to force thermal energy out of the food and into the ice.

Thermal energy storage can also happen in the other direction. Electricity or other forms of energy can be used to heat various materials, which are stored in insulated containers. Later, when the energy is needed, the hot materials can heat water into steam, and that steam can push turbines, which in turn produce electricity.

Solar panels use thermal energy storage. The panels absorb the heat of sunlight and store that energy so it can be transformed into electricity with turbines. There are several kinds of solar panels, but all rely on heat for energy, unlike photovoltaic cells.

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Ocean Energy

You don’t have to talk about hurricanes and tsunamis to know that the oceans are powerful. People have dreamed about harnessing their energies for centuries, and today there are many projects worldwide experimenting with just how to plug into the oceans.

However, ocean energy projects are expensive because of the nature of their energy source. The salty seas can be corrosive, unpredictable, and destructive.

Several aspects of the ocean’s energy can be exploited to generate power;  we’re not limited to the crashing waves. The three most well-developed ideas are tidal power, wave power, and ocean thermal energy conversion.

There are many different projects in various stages of development in coastal states today. However, as yet, ocean energy isn’t a significant source of energy nationally.

Ocean energy is renewable, and it’s clean because of its lack of emissions. However, using ocean energy along coastlines can cause conflict with other coastal uses – transportation and scenic oceanfront – and ocean energy can as affect marine life and environmental conditions.

 

WAVE ENERGY

Wave energy capitalizes on the power of waves as they roll through the ocean. There are small wave systems generating small amounts of electricity today, though the development costs are high and it is difficult to design equipment that can withstand the salt water, weather and water pressures.

Systems have to be designed for average waves but must also withstand the much stronger waves that occur in seasonal storms and the extreme waves that appear only rarely. Waves shift direction, so systems are designed to move to optimize direction.

Prototype plants currently operating have capacities of fractions of a megawatt, which is the tiniest drop in the bucket compared to average-sized power plants in the hundreds of megawatts.

There are over 100 wave energy technologies in various states of planning and testing or in operation as prototypes. However only one type is operating commercially, the Pelamis Wave Power, according to the World Energy Council.

In the United States there are other projects in planning or testing in Hawaii, New Jersey, Oregon, Texas, and California.

 

TIDAL ENERGY

Using the potential energy of rising and falling ocean tides is called tidal energy.

One way of harnessing the tides is to trap the high tide behind dams.When the ocean rises to its highest tide, the dam is closed and high water is held in a reservoir by the dam. After the water recedes in low tide, the trapped water can be released through turbines like in hydroelectric plants.

Tidal energy plants of this type demand a large height difference between high and low tides, a condition that applies to only select global locations. However, research is ongoing to bypass this limitation.

The one major tidal power plant in operation is the 240 megawatt plant in La Rance, France, which has been operating since 1966, according to World Energy Council. There is also an 18 MW experimental plant in Annapolis Royal, Nova Scotia and a 0.4 megawatt plant near Murmansk, Russia.

Tidal energy can have the same drawbacks as hydroelectric power, such that dams may interfere with aquatic life.

 

THERMAL ENERGY CONVERSION

Thermal energy conversion harnesses the difference in temperature between the warm, surface waters of the ocean and the colder, deep water. The two temperatures of water are matched to a fluid that has a low boiling point, like ammonia. Using the heat of the warmer water in a heat exchanger, the ammonia is evaporated and, once in gas phase, it rotates a turbine. Then, the colder seawater cools the ammonia back to liquid in a second heat exchanger. The rotating turbine generates electricity.

Open-cycle thermal energy conversion is similar but uses low pressure vessels to boil the warm surface water, instead of employing a fluid like ammonia. Water will boil at lower than its boiling point if the pressure is less than atmosphere. The steam runs a turbine, and then the cold seawater cools the steam back into fluid water.

These projects are expensive and difficult to site, since they must have deep enough water to get a substantial enough difference in temperature, yet the site must also be close enough to shore to transmit electricity.

Thermal plants can change the temperature gradient of the ocean around them, having a potential affect on marine life.

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Petroleum, Natural Gas, and Coal

The world depends on fossil fuels for its energy, and the United States is no exception. The vast majority of U.S. energy — more than 80 percent in 2009 — comes from burning fossil fuels. (more…)

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