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Solar Power Produces Hydrogen Fuel

Excess Solar Energy Can Be Stored for Use in Hydrogen Fuel Cells.

A major drawback to the use of solar-electric power is that it is only produced while the sun shines, but modern society uses electricity around the clock. A new technique is under development that would effectively allow the excess solar energy to be stored as hydrogen for later use in fuel cells to produce electricity.

There are a number of techniques available to get electricity from solar power. When clouds or geography blocks the sun from shining on the solar power facility, the flow of electricity stops. Small-scale facilities can store excess electricity in batteries or even flywheels, but these are not effective for large-scale power generation facilities.

Photo-Disassociation of Water

Electricity can be used to convert water into oxygen and hydrogen. The hydrogen can then be used in a fuel cell to produce electricity and water. The energy losses involved in the process of producing the electricity, converting it into hydrogen fuel, and then re-producing electricity, make this inefficient at best. 

Photoelectrolysis of water can also convert solar energy into the chemical energy of oxygen and hydrogen (Schwerzel in Solar Energy, Hautala Ed). This produces hydrogen directly, eliminating one of the steps. This has not increased the efficiency much to date. One problem is that the two gasses are not physically separated in the process of their production. A pure-hydrogen feed is needed for fuel cells. 

A research team in Germany is working with a new catalyst to increase the efficiency of the photo-disassociation process (Ritterskamp, Angew. Chem. Int. Ed). The catalyst is titanium disilicide (TiSi2), a semi-conductor material that absorbs light over a wide range of the solar spectrum. This allows for a more effective use of the available sunlight. 

Physical Separation of Hydrogen and Oxygen

What increases the efficiency of hydrogen production is that this catalyst provides an easy method for the separation of oxygen and hydrogen. In the presence of sunlight at temperatures of 55 to 80° C, hydrogen gas is produced and can be removed from the cell by flushing with nitrogen gas. The oxygen gas remains absorbed on the catalyst bed. 

Once hydrogen production stops, the light is removed from the system. The catalyst bed is heated to 100° C and the oxygen is flushed from the system. The system is then cooled back to 55 to 80° C. Light is then applied to the system and hydrogen generation resumes.

 A Practical Hydrogen Generator

Optimization work continues on this process and we are years away from a practical hydrogen generator. Even so we can imagine how such a generator system would work at a solar-electric power generation facility. The details would probably vary some depending on the type generation facility, but general idea would remain the same. 

A portion of the facility would be set aside for hydrogen generation. The amount would depend on where the facility was located. More hydrogen would be required for a facility that had more cloudy days. A smaller amount would be required for a facility located in sunny desert regions. 

When the sun shines on the facility, the hydrogen would be collected from the solar-hydrogen cells and stored under pressure. The oxygen generated would probably be vented to the atmosphere. When the sun stopped shining the hydrogen would flow to fuel cells to be converted back into water and electricity. The water would be recycled. 

An efficient solar-hydrogen generator would allow for around the clock operation of a solar-electric generation facility. Hydrogen produced during sun-lit hours would feed fuel cells to produce electricity during hours of darkness.

Further Reading

  • Bioinorganic Chemistry: http://ewww.mpi-muelheim.mpg.de/bac/index_en.php
Submitted by SuperGreenMe on Oct 31, 2008