Hydrogen Storage (Text Alternative Version)
This is the text alternative transcript for the U.S. Hydrogen Program podcast titled: Hydrogen Storage. The media files can be accessed on the DOE Hydrogen Program Media Files page.
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Welcome to The Hydrogen Report. I'm Mike Weiner.
This edition focuses on hydrogen storage. Most people don't think much about how their fuel is stored — maybe not until they run out of it. Here we'll explain some of the methods, issues, and challenges of storing hydrogen. We'll pay particular attention to how hydrogen is stored on-board a vehicle and the innovative ways it may be stored on vehicles in the future.
To be truly competitive in the market, hydrogen vehicles have to perform as well or better than what we're driving today. From a fuel storage standpoint, that means a couple of things. The first involves driving range. Today's gasoline cars can travel about 300 miles or more before having to refuel. Hydrogen cars must have comparable driving range, or better yet, go further. The second issue involves the space and weight constraints of a vehicle. Unlike fuel storage for other applications, the available area for storing fuel on board a vehicle is limited. The storage system can't compromise trunk space — we want to have room for our groceries and golf clubs — and it can't be too heavy or it will affect the car's fuel economy. Hydrogen has almost three times the energy content of gasoline by weight. But because it's a gas at room temperature and pressure, it has less energy content by volume than gasoline. So what are the options for storing hydrogen?
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Today hydrogen is stored on-board vehicles as either a compressed gas or cryogenic liquid. Let's take a closer look at what this really means...
Compressing any gas allows for more compact storage. Hydrogen used by industry today is usually stored at about 2,000 pounds per square inch, or psi, in steel cylinders or tubes on trailers. But passenger cars have to carry more hydrogen in less space, so they require compressed gas storage at higher pressures — up to 10,000 psi. Even at 10,000 psi, the compressed hydrogen gas tanks are heavier and larger than what's ultimately desired. And are there concerns about high pressure storage? Here's what Dr. Sunita Satyapal of the U.S. Department of Energy says:
"Most of the hydrogen cars to date use high pressure hydrogen tanks on board. And these tanks are built according to strict guidelines, they are equipped with safety systems, and undergo rigorous testing — they're subjected to drop tests and even fire and gunshot tests to verify their structural integrity. But they're also large, heavy, and expensive so they're not the ideal option."
Although slightly less common, liquid hydrogen is also stored in tanks on-board hydrogen vehicles. Liquid hydrogen is denser than hydrogen gas, so you can store more of it in a smaller space. But to liquefy hydrogen, it must be cooled to -423 degrees Fahrenheit, which takes energy. Another drawback is that as the tank warms, some of the hydrogen can "boil off" which can result in loss of fuel as the hydrogen changes from liquid to gas. The tanks require special insulation to help reduce hydrogen loss, but this increases the size of the tank so you have less room to store fuel.
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So what does the future hold for hydrogen storage?
"On-board hydrogen storage is often called one of the greatest challenges to the widespread use of hydrogen, and it's an area of significant research. We're looking at lighter-weight materials for tanks, and a new concept to today's cylindrical tanks that don't package well in a vehicle. The most exciting but challenging research, though, is focused on storing hydrogen in materials."
Materials-based hydrogen storage may overcome some of the challenges facing compressed gas and liquid hydrogen storage — it may be possible to store larger quantities in smaller volumes, at lower pressure and near room temperature. But how does it work?
"Hydrogen can be stored in materials in different ways. It can be stored on the surface and within the pores of solid materials in what's called adsorption — carbon-based materials or powders are a good example. Hydrogen also can be stored directly within the material itself, in what's called absorption. Metal hydrides store hydrogen this way. And there are also materials with hydrogen atoms that are strongly bound within their molecular structures that may even be liquids, which are possible candidates for hydrogen storage. Researchers around the world are in a race to develop viable materials to store hydrogen and they're conducting research to better understand how these materials might work at practical operating conditions."
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Hydrogen storage is a complex issue that has attracted some of the brightest minds around the world. The Federal government is even considering the possibility of a hydrogen storage-related research prize — similar to the Ansari X prize for space flight — to be awarded to the scientist or team of scientists achieving a significant breakthrough in this important area of energy research.
Thanks for listening. If you'd like to learn more about hydrogen — and increase your H2IQ — visit hydrogen.energy.gov. And be sure to listen for future episodes of The Hydrogen Report.