Reforming always results in significant energy loss. Alcohol can be made from corn or sugar cane. Fossil fuel is used to grow corn and sugar cane. The energy available in the alcohol does not balance the fossil fuel energy expenditure. The energy balance is even less favorable after reforming. Electricity can be used to make hydrogen from water through electrolysis, an efficient process.
Electrolysis of water has been known for centuries and it is a common classroom demonstration. This picture illustrates how. It works better if you add a little salt to the water.
Fossil fuel is the source of most of the energy used to make electricity in the United States. Hydrogen produced by electrolysis may be viewed as a convoluted way to convert fossil fuel to hydrogen. Fossil fuel coal, natural gas, and oil can be converted to hydrogen directly, without making electricity first. The direct methods use less fossil fuel for the same amount of produced hydrogen.
Electricity from wind turbines, solar arrays, etc. It makes no sense to do so because the same electricity is better used to replace fossil fuel. The saved fossil fuel has three times more energy content. Recall that converting fossil fuel to electricity is very inefficient. The saved fossil fuel can be converted to hydrogen.
The net effect is more hydrogen for the same energy inputs. This point cannot be overemphasized. In the extreme case, all fossil fuel would be replaced by sustainable electrical energy. In that case, the surplus electricity could be used to make hydrogen. Even this is a bad idea for reasons that will be explained.
Hydrogen is difficult to store because has very low volumetric energy density. It is the simplest and lightest element--it's lighter than helium. Hydrogen is 3. Hydrogen contains 3. Hydrogen must be made more energy dense to be useful for transportation. There are three ways to do this. Hydrogen can be compressed, liquefied, or chemically combined.
Hydrogen compressed to atmospheres also called bars occupies 3 times more volume than gasoline for the same energy. It is necessary to reach this density if a vehicle is to carry enough hydrogen to be practical. A pressure of bars works out to 6 tons, or 12, lbs, per square inch.
It is very difficult to contain such pressures safely in a lightweight tank. Catastrophic tank failure releases as much energy as an equal weight of dynamite. A tank made of high strength steel weighs times more than the hydrogen it contains. A truck or an automobile using a steel tank would be impractical as the tank would weigh nearly as much as the vehicle.
High pressure hydrogen tanks made from carbon fiber may be a solution. Carbon fiber is a material used in aircraft and sporting goods. At the present time, carbon fiber tanks are very expensive. The goal for is 4. A typical 18 wheeled semi-truck carries two 90 gallon tanks, providing a range of miles. A typical 4 cylinder sedan has an 18 gallon tank, providing a range of miles.
The practical range would be somewhat less. Both vehicles could be converted to hydrogen operation. The space, weight and expense of steel tanks make them impractical. Any gains in energy efficiency would be offset by losses incurred in hauling the very heavy tanks.
Carbon fiber tanks of this size and performance do not exist--they are only goals. Gasoline, by contrast, requires only a small, low-tech tank. The laws of thermodynamics dictate the amount of energy it takes to compress a gas.
The physical properties of hydrogen make it the most difficult of all gasses to compress. This is the energy that gets instantly released in the event of a tank failure.
This is an estimate extrapolated from an actual multistage compressor working at bars. Since water is so abundant, a traditional method for extracting it is electrolysis , which applies an electrical current to water to catalyze a chemical reaction that liberates hydrogen from its oxygen bond.
The amount of energy required to split this chemical bond through electrolysis is an extremely energy intensive process and usually does not justify the energy available in the hydrogen that is produced. The most common method for hydrogen production is the steam reformation of hydrocarbons, which reacts natural gas with high-temperature steam to clip off the carbons from hydrogen.
Unfortunately, this process is anything but clean: 5 kilograms of carbon are emitted for every 1 kilogram of hydrogen produced. Finally, there is coal gasification whereby coal is made into a gas, impurities are removed, and hydrogen is recovered.
This process also results in significant CO 2. The problem with all of these methods is their inefficiency compared to other fuels, which makes hydrogen extraction expensive. Equally important, the advantages of clean hydrogen are offset by the carbon produced to extract it from hydrocarbons or coal. This makes no sense for an alternative energy source. Getting enough of it, by mass, in one place to be of practical use and worth the transportation effort is difficult.
Hydrogen molecules are very small and, therefore, more prone to leakage—a problem exacerbated by the fact that it must be stored at high pressure to provide sufficient energy density. Thus, the second difficulty encountered is storing hydrogen as a fuel. Today, liquid hydrogen, which is the most common form of storage, is hard and expensive to handle. Like natural gas, hydrogen in its elemental form is volatile and flammable. To make storage even more challenging, a fraction of the liquefied hydrogen boils off every day.
This is because hydrogen becomes a liquid only at the ultra-frigid temperature of minus degrees Celsius minus F at atmospheric pressure.
Also, hydrogen tends to permeate metal due to its tiny size. Storage tanks, known as cryogenic storage, have to be super-insulated and even so, eventually some of the hydrogen seeps out. The cost of cryogenic storage including the cost of the storage tank, the equipment to compress or liquefy hydrogen, and to maintain compression is high. In fact, the sheer complexity and cost of building and operating hydrogen infrastructure on the scale we take for granted with natural gas or petroleum are the biggest roadblocks to widespread adoption.
Despite these difficulties, significant progress continues to be made in hydrogen storage. Companies like Cella Energy for example, are working on advanced materials and technologies for safe, lightweight, high-performance hydrogen storage technology. Hydrogen storage is important if it is to be part of our future clean energy solutions, yet more research and infrastructure improvements are required in order for hydrogen to realise its full potential. Meanwhile, the United States Department of Energy DOE supports research and development of a range of technologies to produce hydrogen economically and in environmentally friendly ways.
Hydrogen is difficult to store due to its low volumetric energy density. It is the lightest of and simplest of all elements, being lighter than helium, and so is easily lost into the atmosphere.
Storing hydrogen as a gas also has its challenges as it typically requires the use of high pressure tanks bar or , psi. As mentioned above, another solution for hydrogen storage is through adsorption or absorption, although with these storage techniques, further steps are then required to release the hydrogen once again.
All fuels have a level of danger associated with them based on three factors; ignition source, oxidant, and the presence of the fuel itself. Using the correct engineering controls can limit the dangers of any given fuel type, including hydrogen.
In fact, hydrogen has a number of properties that make it safer than many other commonly used fuel types. It is non-toxic, for example, and because it is lighter than air, it dissipates quickly into the atmosphere when released.
This is important as it means that the fuel will dissipate into the air in the event of an accident, rather than remaining in place to potentially catch fire, as is the case with batteries or petroleum, for example. However, there are still hazards related to hydrogen that mean additional engineering controls need to be put in place to ensure its safe use. With a lower ignition energy than petrol or natural gas, hydrogen has a wide range of flammable concentrations in the air meaning that ventilation and leak detection are important for hydrogen systems.
Special flame detector are also required as hydrogen burns with a near-invisible flame. Material selection for hydrogen systems is also important as some metals become brittle when exposed to hydrogen.
Hydrogen requires staff training in how it should be safely handled, while systems should be tested for leaks and other potential problems, ensuring it is produced, stored and dispensed safely. Of course, for all of these measures, we have already seen hydrogen used in a wide variety of common applications, which shows that we can improve safety and build confidence in hydrogen as a safe, clean and renewable fuel for the future.
A hydrogen fuel cell uses the chemical energy of hydrogen to produce electricity Renewable energy comes from sources or processes that are constantly replenished. Clean energy is energy that comes from renewable, zero emission sources that do not pollute the atmosphere when used. Support for SMEs. Software Products. Go to Technical knowledge Search. Login Login. Members' Portal. Contents Use the links below to skip to the section in the guide: How does it work?
Why is it important? Why is it difficult to store? Is hydrogen storage safe? Hydrogen can be stored in three different ways: As a gas under high pressures In liquid form under cryogenic temperatures On the surface of or within solid and liquid materials Each of these storage techniques has its own requirements and challenges, as shown below: Compressed Gas Hydrogen can be compressed and stored in a gaseous form under high pressures.
Cryogenic Liquid Storage Hydrogen can be stored cryogenically in a liquid form.
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