Powered by the Sun: Sun-Made Hydrogen Fuel

solar2It’s been known for some time that our future may hinge on the successful development of solar power. Despite it being a clean, renewable alternative to traditional, dirtier methods, the costs associated with it have remained prohibitive.  Which is why, in recent years, researchers and developers have been working to make it more efficient and bring down the costs of producing and installing panels.

But a new technique developed by the University of Colorado Boulder may have just upped the ante on solar-powered clean energy. Using concentrated sunlight in a solar tower to achieve temperatures high enough to drive chemical reactions that split water into its constituent oxygen and hydrogen molecules, the team claims that solar energy may now be used to cheaply produce massive amounts of hydrogen fuel.

hydrogenfuelThe team’s solar thermal system concentrates sunlight off a vast array of mirrors into a single point at the top of a tall tower to produce very high temperatures. When this heat is delivered into a reactor full of metal oxides, the oxides heat up and release oxygen. This leaves the reduced metal oxides in a different state and ready to bind with new oxygen atoms.

Steam is then introduced into the reactor, which can also be produced by heating water with sunlight. This vaporized water then interacts with oxides, which draw oxygen atoms out of the water molecules leaving behind hydrogen molecules. These molecules can then be collected and harvested as hydrogen gas, and placed in storage containers for export.

solar_beadsGranted, the concept of using solar energy and heat to create hydrogen fuel is not new. Earlier this year, teams from the University of Delaware and Harvard already proposed using solar arrays and small panels (artificial leaves) to separate hydrogen from water. And solar thermal tower power plants have been in use in some parts of the world for years now.

But there are several key difference that set the University team’s concept apart. In a standard solar power tower, sunlight is concentrated about 500 to 800 times to reach temperatures around 500º C (932 º F) to produce steam that drives a turbine to generate electricity. However, splitting water requires temperatures of around 1,350º C (2,500º F), which is hot enough to melt steel.

hydrogenfuel-2To get those kinds of temperatures, the team added additional mirrors within the tower to further concentrate the sunlight onto the reactor and the active material. But the big breakthrough came about when the team discovered certain active materials that allowed both these chemical reactions (reducing the metal oxide and re-oxidizing it with steam) to occur at the same temperature.

As Charles Musgrave, Professor of Chemical and Biological engineering at CU-Boulder, explains it:

You need this high temperature both to give you the driving force to drive the chemical reactions and also the kinetics to make the reactions go fast enough to make the process practical. We determined that both reactions could be driven at the same temperature of about 2,500° F (1,371° C). Even though we run at a constant and lower temperature we still generate more hydrogen than competing processes.

Though they have yet to produce a working model, the concept has a big advantage over other methods. By eliminating the time and energy required for temperature swings, more hydrogen fuel can be created in any given amount of time. Another advantage it has over other renewable technologies, such as wind and photovoltaics, is that it uses sunlight directly to produce fuel rather first converting sunlight into electricity, which reduces overall efficiency.

solar_array1The team believes that a site with five 223 m (732 ft) tall towers and about two million sq m (21.5 million sq ft) of heliostats on 485 ha (1,200 acres) of land could generate 100,000 kg (222,460 lb) of hydrogen per day, which is enough to run over 5,000 hydrogen-fuel cell buses daily. Or as Alan Weimer, the research group leader, put it:

Our objective is to produce hydrogen (H2) at $2/kg H2. This is equivalent to about US$2/gallon (3.7 L) of gasoline based on mileage in a fuel cell car versus a combustion engine today.

Not a bad substitute for gasoline then, is it? And considering that the production process relies on only the sun – once the multi-million dollar infrastructure has been built of course – it will be much more cost effective for power companies than offshore drilling, frakking and pipelines currently are. Add to that the fact that its far more environmentally friendly, and you’ve an all around winning alternative to modern day fuels.

Source: gizmag.com

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