The latest idea for producing hydrogen efficiently and without emissions drawbacks uses the sun in a setup that looks a lot like the big power-tower concentrating solar power plants that are nearing completion in the American Southwest.
With the new discovery out of the University of Colorado Boulder, heat generated from the reflected light of thousands of mirrors pointed at the top of tower is used to drive chemical reactions that split water into its oxygen and hydrogen components.
“We have designed something here that is very different from other methods and frankly something that nobody thought was possible before,” research group leader Alan Weimer of the chemical and biological engineering department at Boulder said in a statement. “Splitting water with sunlight is the Holy Grail of a sustainable hydrogen economy.”
Splitting water in any fashion that is affordable and an emissions winner is definitely a big focus of research these days. The old less-than-green technique for producing hydrogen is to reforming from natural gas by stripping out the hydrogen atoms. However, renewable electrolysis – the use of renewable electricity to produce hydrogen by passing an electrical current through water – is getting increasing attention. Wind in particular is seen as powering these systems.
There’s a pretty sizeable demonstration in Germany nearly ready to start operation, and in Minnesota, a company says that by taking advantage of “lower value” nighttime wind energy – lower value because grid operators often don’t need it the electricity in the overnight hours – they can produce hydrogen at a low enough cost to make their operation viable.
With the Colorado scheme, the researchers say a big breakthrough is doing away with the large temperature swings (which are both energy and time intensive) in standard two-step, metal oxide-based solar thermal water-splitting cycles. Here’s how CU breaks down the process:
- Sunlight is concentrated by an array of mirrors to the top of a very tall tower.
- The tower gathers heat generated by the mirror system to roughly 2,500 degrees Fahrenheit (1,350 Celsius).
- The heat is delivered into a reactor containing chemical compounds known as metal oxides.
- As a metal oxide compound heats up, it releases oxygen atoms, changing its material composition and causing the newly formed compound to seek out new oxygen atoms.
- With the addition of steam to the system — which could be produced by boiling water in the reactor with the concentrated sunlight beamed to the tower — oxygen from the water molecules adheres to the surface of the metal oxide, freeing up hydrogen molecules for collection as hydrogen gas.
So when might we see such a system put into action on a commercial basis? When there’s a real price on carbon emissions.
“With the price of natural gas so low, there is no incentive to burn clean energy,” said Weimer, who is also the executive director of the Colorado Center for Biorefining and Biofuels. “There would have to be a substantial monetary penalty for putting carbon into the atmosphere, or the price of fossil fuels would have to go way up.”