Renewable Energy 7 – Hydrogen fuel and fuel cells.

Often touted as a renewable fuel option, but it is not a direct renewable fuel but a secondary fuel option.  This means that it requires energy to break the bonds of another chemical become useful as a fuel.  The great thing about hydrogen is that burning it as a fuel is almost pollution free – the main waste being oxidized hydrogen – water!  With only minor modification, a standard engine can burn injected hydrogen fuel.  If used in a fuel cell it is completely pollution free, except as I have said several times already within this blog, for the construction of the fuel cell. 

Hydrogen Fuel – While hydrogen is one of the most abundant atoms in the universe, its down side is that it is almost always attached to other atoms e.g. Water (H2O) and methane (CH4) being the two most common sources used.  Deriving hydrogen from methane does little to alleviate the pollution problems associated with fossil fuels, but deriving hydrogen from water can be a renewable source.  Think about it for a second.  You pass a small electrical charge (electrolysis) into pure water and you get hydrogen gas and oxygen, and when you burn the hydrogen (oxidize it) you get water back again with the added bonus of the energy of the oxidation.  Essentially the whole process is non-polluting, depending of course where the energy for electrolysis is derived. The kicker here is that obtaining hydrogen takes energy so at best it is a zero-sum gain.  What makes it valuable though is the fact that hydrogen is a storable energy form that can be used in several ways to produce electricity or to power transportation.  When renewable energy generation sources are used (e.g. wind, solar) and demand is down, the extra energy generated can be used in electrolysis to form hydrogen stores.  (Scroll down for more about storage options)       

Hydrogen Fuel Cell – in its simplest form, a fuel cell is where the hydrogen atom is stripped of its two electrons (anode) and the hydrogen ion allowed to pass through a proton exchange membrane (only conducts positively charged ions).  The two electrons then must flow through a wire to the other side of the membrane to rejoin the hydrogen ion at the cathode, which then oxidizes to form water as the waste.  (Electricity as we use it is simply the movement of electrons in a wire).    

Hydrogen Flammability and storage – When talking about storing hydrogen fuel, skeptics always point to the 1937 disaster of the Hindenburg dirigible.  It is true that hydrogen is a highly reactive gas (oxidizes readily) and compressed hydrogen gas is so reactive it becomes explosive in its speed of oxidation.  Even if compressing hydrogen were the only option of storage (it isn’t – see below), it is still a better option than liquid petroleum fuels.  For instance, a gas tank is ruptured, the liquid flows down to the ground from the tank and the fumes above the liquid can ignite to create an explosive result (note how Hollywood loves to show this is car chases with cars exploding).  Many of the Hindenburg survivors were below the dirigible when it caught fire, because hydrogen is lighter than air (the reason it was used to lift the dirigible) and all the fire went straight upwards from the point of ignition.  Another minor drawback of hydrogen is that volume for volume with energy efficiency it needs more space than say, gasoline.  So, a hydrogen fuel tank would take up four times the size of a fuel tank than a gasoline tank for the same distance to be travelled.  This, however, is a minor nuisance considering that there are at least six ways to store hydrogen, except for high pressure tank storage, that are safe from catastrophic explosion problems

The hydrogen gas can be stored in high-pressure cylinders up to 800 bar (11, 500 psi), however, with more energy use can be used to store liquid hydrogen (safe from explosion) in cryogenic tanks, yet this requires insulated tanks of course.  Hydrogen gas can be adsorbed onto nano-porous materials with a large specific surface area.  The advantage here is that the gas is at atmospheric (ambient) pressure and therefore the gas is non-flammable until released form the adsorbed surface at a slow rate.  Depending on the material used, it may be necessary for the storage containers to be under some elevated pressure (up to 1500 psi, yet still non-flammable).  The gas can be stored in a lattice metal matrix as a metal hydride under atmospheric pressure, again non-flammable until slowly released.  Metal hydrides because of their chemical make-up Metal hydrides because of their chemical make-up are highly effective at storing large amounts of hydrogen in a safe and compact way.  Finally hydrogen can be chemically bonded in at ambient pressure initially being adsorbed at higher pressure and released using elevated temperature, or using metals and alloys are capable of reversibly absorbing large amounts of hydrogen.   volumetric densities of hydrogen are found in metal hydrides.  The chemical bonding technology is showing valuable options in using hydrogen as a future fuel.   

The major advantages of hydrogen as a fuel are that by converting chemical potential energy directly into electrical energy, hydrogen fuel cells avoid the “thermal bottleneck” (a consequence of the 2nd law of thermodynamics).  This makes the generation of hydrogen from renewable energy environmentally friendly.  Fuel cells have few drawbacks and are very efficient, have no moving parts to wear out and produce no pollution. 

Iceland transport Infrastructure – To show the possibilities of using hydrogen as a viable transportation fuel, Shell energy company is helping Iceland move to renewable energy.  With its abundance of geothermal and hydroelectric power, Iceland is leading the way to demonstrating how hydrogen fuel can be used for both storage and especially transport.  The Icelandic bus fleets now use hydrogen fuel cells and the government is ramping up the system to fuel all Icelandic cars with hydrogen fuel.  All locals will be able to go to a regular gas station and fill up on hydrogen like they would with regular gasoline.  Economist insist that moving to a hydrogen fuel economy is too expensive, but Iceland is bucking this fallacy and is fast becoming the model for how renewable energy can exist in highly developed countries.    

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