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Publication Title | Solar Hydrogen Production by Electrolysis

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Hydrogen

Solar Hydrogen

Production by

Electrolysis

Walt Pyle, Jim Healy, Reynaldo Cortez ©1994 Walt Pyle, Jim Healy, Reynaldo Cortez

Why would anyone want to produce hydrogen at home? Hydrogen can be used as a

non-toxic energy storage and transport medium. Hydrogen that is made from water using solar energy is a sustainable and renewable home energy supply. Make hay (or hydrogen) while the sun shines. Then use the stored hydrogen to produce heat and electricity on demand, day or night!

We got excited about solar hydrogen production during the seventies and the first oil shocks. What happened between the seventies and nineties? For the most part we worked with thermolysis (splitting water with concentrated solar heat) and photoelectrolysis (splitting water in a liquid solar cell). We also followed the work of other hydrogen pioneers, such as Roger Billings and his associates, who produced and used hydrogen in home appliances and vehicles.

The article by Richard Perez about the Schatz PV Hydrogen Project (HP #22, pp. 26–30) and a subsequent visit to Humboldt State University’s Trinidad Marine Laboratory launched us into designing and making a “home-sized” system based on electrolysis of water. Electrolysis is the competition for thermolysis and photoelectrolysis at this juncture.

Hydrogen and oxygen can be produced from water using electricity with an electrolyzer. This article describes the installation and operation of a 12 cell Hydrogen Wind Inc. 1000 Watt electrolyzer. This electrolyzer can produce 170 liters/hour (6 cubic feet/hour) of hydrogen and 85 liters/hour (3 cubic feet/hour) of oxygen (at standard temperature and pressure).

In addition, we describe a homebrew purification and storage system for the hydrogen and oxygen produced by the electrolyzer. With proper after-treatment, the gases produced can be stored safely. The purified hydrogen and oxygen can be used in fuel cells (to produce direct current electricity) and catalytic burners (for heating and cooking) without poisoning or damaging the noble metal catalyst materials. The gases can also be used for welding and cutting, as well as for motor vehicle fuel.

!!!!Safety First!!!!

Making and storing hydrogen and oxygen is not kid’s stuff — this is “rocket fuel”! Use flashback flame arrestors on the hydrogen and oxygen outlets from the electrolyzer. Secure dangerous caustic from small prying hands. Make sure your gases are pure before storing them. More on safety follows.

How Much Hydrogen Do I Need?

This varies tremendously from household to household, depending on how well the Demand Side Management job has been done. We can run our Platinum Cat space heater for about three hours on a cubic meter of hydrogen. The amount of gas needed can be estimated from the energy consumption of any appliance. Amanda Potter and Mark Newell’s article in HP #32 (pp. 42–45) describes the operation of an electrolyzer and shows how to calculate the amount of gas needed to run appliances. See articles on hydrogen space heating in HP #34, hydrogen cooking in HP #33, and making electricity from hydrogen with a fuel cell in HP #35.

How Much Power Does It Take?

A cubic meter (35.3 cubic feet) of hydrogen gas takes about 5.9 hours to produce in this electrolyzer, when operated at its rated input power of 1000 Watts. This means the energy required to produce a cubic meter of hydrogen and 0.5 cubic meter of oxygen is about 5.9 kW-hr. This translates to an efficiency of 51%, where 3 kW-hr/m3 equals 100% efficiency at 20°C. Typical industrial scale plants operate at about 4.5 kW-hr/m3 or 67% efficiency at high current density. The efficiency is better at lower current density.

What Is Needed to Produce Hydrogen at Home?

Our system includes the following components and sub-systems (see the block diagram next page):

• Solar electric power and/or utility grid power • Power Controller

• Electrolyzer

• Hydrogen Purifier

• Oxygen Purifier

• Hydrogen and Oxygen Storage Tanks

• Electrolyte Storage Tank and Transfer Pump • Makeup-water Purifier

32 Home Power #39 • February / March 1994

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