Such challenges haven't deterred Aldo Steinfeld and his team at the Swiss Federal Institute of Technology, Zurich. They have a system which is already sucking CO2 out of the atmosphere to feed a synthetic fuel process.
The team's reactor again uses a large parabolic mirror to concentrate solar heat onto a chamber – this time containing calcium oxide. Once it reaches 400 °C, air is pumped into the chamber, and the heat causes the calcium oxide to react with CO2 to form calcium carbonate.
Next, the calcium carbonate is then heated again, this time to 800 °C, at which point it releases a pure stream of CO2 and reverts back to calcium oxide.
This stream of CO2 is piped into a second reactor. Here, a solar concentrator is used to heat zinc oxide to 1700 °C, causing it to release oxygen molecules, leaving metallic zinc. The temperature is then lowered and CO2 and steam are pumped in, which react with the pure zinc to form syngas, a mixture of hydrogen and carbon monoxide, – and zinc oxide once again. The team has previously experimented with a 10-kilowatt prototype, and is planning to test a 100-kilowatt version early next year.
Finding ways to use the sun's energy to create fuel should be one of the highest-priority areas for clean-energy technology research, says Ken Caldeira of the Carnegie Institution of Washington at Stanford University in California. "This area holds out the promise for technologies that can produce large amounts of carbon-neutral power at affordable prices, which can be used where and when that power is needed," he says.
"It is one of the few technology areas that could truly revolutionise our energy future."
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