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What is an electrolyzer?
How does hydrogen fit in small scale
renewable energy systems?
How do PEM fuel cells work?
What is an electrolyzer?
One way to make hydrogen is to use a source of electrical power to run an electrolyzer. An electrolyzer is a device which uses electricity to dissociate hydrogen and oxygen from water molecules. The electrolyzer contains an electrolyte solution such as potassium hydroxide (KOH), or a solid polymer electrolyte.
An electrolyte is a chemical compound that is ionized: its atoms or molecules have lost electrons and are electrically charged. Thus, the electrolyte substance is electrically conductive.
When power is applied to an electrolyzer, the electrodes transmit the charge through the electrolyte. This weakens the bond between the hydrogen and oxygen in the water molecules in an electrolyte solution, and thus releases hydrogen and oxygen gas. The oxygen gas can either be processed and stored, or released into the atmosphere. The hydrogen gas is then passed through a gas processing system. It can then be used as a fuel, or be stored for later use.
How does hydrogen fit in small scale
renewable energy systems?
One of the problems with generating electricity from renewable energy sources such as solar and wind is that they do not produce a constant supply of power, so, the power generally needs to be stored. Typically, batteries are charged by a PV panel or wind generator, and then power is drawn as needed from the batteries. However, battery storage is limited in its efficiency.
During time periods when sun or wind is abundant, batteries are likely to be charged quite quickly to capacity, and without some alternative storage, the excess power generated is simply lost. Batteries also need to be cycled (used and recharged) regularly - they cannot store the power for an extended period of time. Plus, disposal of spent batteries is problematic due to toxic non-biodegradable materials they contain.
Hydrogen can be used either as a supplement to or a substitute for batteries in solar and wind power systems. As a supplement, once the batteries are fully charged, the power is switched to an electrolyzer which generates hydrogen gas. The gas is processed, and then can be stored indefinitely. It can be used on site to power a fuel cell generator to create electricity and heat, or be burned like propane; or it can be fuel for fuel cell powered vehicles.
How do PEM fuel cells work?
There are several types of fuel cells, but PEM (proton exchange membrane) fuel cells show the most promise for small scale power use.
 PEM Fuel Cell
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PEM fuel cells use a catalyst and a membrane to dissociate hydrogen atoms in order to generate electricity. The hydrogen is fed into the fuel cell and onto a catalyst layer that facilitates the hydrogen electrons and protons to separate. Behind the catalyst is a membrane. The membrane allows the protons to pass through, but the electrons cannot, and instead are routed through an external circuit to an electrical load (motor, light bulb, etc.). Then, the electrons continue on to the other side of the membrane where they recombine with the protons and oxygen atoms to create water.
Fuel cells contain no moving parts, and when powered by hydrogen, the only by-products are water and heat. Fuel cells are not difficult to construct, and except for the catalyst and membrane, they can be constructed from commonly available materials.
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