Bright idea: Make H when the Sun shines, and H when it doesn't

German boffins design solar reactor that, er, works at night

Researchers in Cologne, Germany, have successfully demonstrated a solar reactor known as CONTISOL, which promises to be able make hydrogen day and night while running on little more than air and sunlight.

Hydrogen is often touted as a zero carbon fuel and promises a future free of potentially nasty emissions.

However, the reality is that generating hydrogen normally requires prodigious amounts of energy to drive the thermal chemistry required. Thermal energy that usually requires the burning of fossil fuels.

The fossil fuel element can be removed (or at least reduced) by switching to a reforming reaction produced by running methane and steam through a catalyst and heating to over 800°C using Concentrated Solar Power (CSP), producing carbon monoxide and hydrogen.

The boffins at the German Aerospace Center (DLR) have published the results of research that describes a novel concept, CONTISOL, for dealing with the main issue associated with solar reactors. Namely, what to do when the sun doesn’t shine.

CONTISOL takes the form of a cylinder cut with numerous rectangular channels, with each row of channels being either coated with a catalyst to perform the required chemistry, or clear to allow the heated air to pass through. Solar heated air is passed straight through the cylinder, heating it up for the required reaction before being stored for later use when sunlight is unavailable.

The use of air as a method for transferring heat is an unusual one, and benefits from stability at high temperatures. Heat storage in chemical or latent mediums are also options. Finally, air is abundant, so can be vented when it cools, and any leaks are unlikely to be catastrophic.

Generating hydrogen using CONTISOL would require a field of solar mirrors, a tower, a receiver for the heated air and a thermal storage system for when the sun is not shining on the mirrors.

The team at DLR have demonstrated the technology working in the laboratory at 5kW using an artificial sun and simulated heat storage. At least 1MW will be required to work at an industrial level, which is well within the bounds of today's technology. The Ivanpah Solar Power Facility in the Mojave desert, for example, has a capacity of nearly 400MW, though not everyone has an arid landscape at their finger tips.

Fans of James Bond movies may be remembering ‘The Man With The Golden Gun’ at this point, which also featured a solar energy plant, only with helium rather than hydrogen as a significant plot point. Focussing the energy of the sun at a solar reactor to make hydrogen seems a better use of thermal power than blowing up Bond’s unfortunate seaplane.

And unlike Scaramanga’s energy beam, CONTISOL should keep working even when the sun goes in, at least if the boffins have got their equations right. ®

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