New Process Uses Sunlight to Split Water

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A University of Colorado Boulder research team has moved closer to what some call the Holy Grail of a sustainable hydrogen economy — splitting water with sunlight. 


The CU-Boulder team has devised a solar-thermal system designed to use a vast array of ground mirrors to concentrate sunlight onto a single point atop a central tower up to several hundred feet tall. The tower would gather heat to roughly 2,500 degrees Fahrenheit (1,350 Celsius) and then deliver it into a reactor containing chemical compounds known as metal oxides. As the 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.

The team showed that adding steam to the system would cause oxygen from the water molecules to adhere to the metal oxide surface, freeing up hydrogen molecules for collection as hydrogen gas. To get the steam, the concentrated sunlight beamed to the tower would heat the water to boiling. [Hydrogen: Future of Fuels Finally Drives Up | Video] Conventional theory holds that producing hydrogen through the metal oxide process requires 1) heating the reactor to a high temperature to remove oxygen 2) then cooling it to a low temperature before 3) injecting steam to re-oxidize the compound and release hydrogen gas for collection.

The innovation here is that no swing in temperature is required. The whole process can be undertaken at the same temperature, and can be driven by turning a steam valve on or off. With the new method, the amount of hydrogen produced to power fuel cells or for storage is entirely dependent on the amount of metal oxide (a combination of iron, cobalt, aluminum and oxygen), and how much steam is introduced into the system. The researchers envision building reactor tubes roughly a foot in diameter and several feet long, filling them with the metal oxide material and stacking them on top of each other. A working system to produce a significant amount of hydrogen gas would require a number of the tall towers, each with its own reactor, to gather concentrated sunlight from several acres of mirrors surrounding each tower. A paper on the National Science Foundation-funded research was published in the August 2 issue of Science. Editor's 

 

Written By: Jim Scott, University of Colorado Boulder
continue to source article at livescience.com

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    • In reply to #1 by Roedy:

      I guess the idea is you can store hydrogen more easily than electricity. I presume electricity is easier to distribute.

      Hi Roedy.

      Hydrogen storage is difficult, since to get a reasonable energy density means very high tank pressurization, which is heavy and/or costly, since using exotic materials like carbon fiber is very expensive for 3-5000 psi containers. High pressure tanks also preclude the kind of space efficient shapes found in gasoline tanks, and large tanks to get decent range are risky in serious accidents.

      The other considerations are that electricity is rather inefficient when distributed over power lines, and you have to generate the electricity, which in many places is a dirty business if using coal, oil, gas or nuclear means. Electric cars are still expensive and heavy, while the range, battery life, manufacturing and disposal are still big problems.

      Hydro-electric power stations are better, but the lack of locations and damage to the above-dam geography can be serious, as can a failure from earthquakes, etc. Wind and tidal turbines are good solutions, but there is still the NIMBY issue when built in denser population locations.

      There are no easy or cheap answers, but this solar-hydrogen proposal is another viable part of solving our massive problem, which needs good solutions soon, since any methods will take a lot of money and time to put into operation…. Mac.

  1. this really would put “zero emission” on a whole new level.

    There have already been plans in the past to use geothermal energy similarly to produce hydrogen, but the problem with geothermal energy as an energy source to split water has so far been that there are few places on earth where geothermal energy, at least in quantity, is readily and reliably available near the eath’s surface. Like Iceland or other volcanic regions.

    But using solar energy just might be feasible practically everywhere in sun-spoiled regions around the globe. There are extensive uninhabited arid deserts on four continents around 30 degrees both northern and southern latitude which would be perfectly suited for vast hydrogen producing facilities of this kind. Those regions might in the future become what the oil producing countries of our time have been for the last 100 years: simply put, the world’s power source.

  2. I’ve always been skeptical about Hydrogen as an alternative fuel. I’m admitting up front what I’m about to say in this comment are just impressions and intuitions and I’m more than willing to be proven wrong. For one thing any alternative energy source that George Bush promotes I’m automatically skeptical of. But it always seemed like Hydrogen was the energy solution people like Bush would trot out because unlike some other alternative energy sources that could actually be used now it was always at least ten years away at a minimum. Also, my understanding is it essentially requires the same kind of infrastructure that gasoline does. So where as electric cars would put a huge dent in Exxon’s business model, Hydrogen would be a natural thing for them to want to transition to, they could eventually transform gas stations into hydrogen stations.

    Having said all that this looks very cool and even if some of my suspicions turn out to be correct I think we are so far behind what we should be doing to address climate change we need to investigate every viable alternative.

    • In reply to #3 by Red Dog:

      I’ve always been skeptical about Hydrogen as an alternative fuel.

      Me too. [Ammonia](http://www.intechopen.com/books/hydrogen-energy-challenges-and-perspectives/ammonia-as-a-hydrogen-source-for-fuel-cells-a-review has most of it advantages and very few of its disadvantages. It is more energy dense and much more transportable. Though low octane it has been used successfully in IC engines. It works in fuel cells. Solar thermal techniques are being proposed for its manufacture and its use in a closed loop solar thermal energy storage system. New, sustainable sources for ammonia production are being developed including biomass. It is the most used chemical feedstock and at present consumes 1 to 2 % of all our energy. Making fertiliser feedstock in deserts also has an attraction. Attention on hydrogen may be better directed to NH3.

      I, nevertheless, wish this project well, also. It looks well thought through.

  3. This appears to be a variation on the solar-thermal electric power towers, but producing hydrogen instead of electricity.

    http://breakingenergy.com/2013/04/03/concentrated-solar-power-tower-technology-hits-milestone/
    The last of 14 Concentrated Solar Power (CSP) receiver panels and heat shields have been installed at the Crescent Dunes Solar Energy project, and construction of the 10,400 articulating mirrors, or heliostats, on the 1600-acre heliostat field is underway in Tonopah, Nevada. PWR has provided the worldwide exclusive license to SolarReserve, a developer of large-scale solar energy projects based in Santa Monica, Calif., for the molten salt power tower and heliostat technologies.

    PWR developed technology for the receiver panels, as well as critical components for the molten salt power tower. It also supplied the technology for the receiver structure, onto which the heliostats will direct sunlight. When commissioned in 2014, the 110-megawatt project will be the nation’s first commercial-scale, molten salt solar power tower and world’s largest plant with fully integrated energy storage system, able to provide enough energy to supply 75,000 homes 24/7.

    It would be interesting to see a comparison of the figures, comparing the direct production of hydrogen fuel from a metal oxide reactor, with hydrogen production from the electrolysis of water, or the direct use of electricity or heat.

  4. I know I’m going out on a limb here but…

    If hydrogen powered apparatus (automobiles, generators, heaters, garden tools, etc) one day become mainstream, perhaps that would also provide us a way to collect the product of its combustion: water. The world supplies of fresh water are deemed to become scarce in the future. Couldn’t we kill two birds with the same rock by doing this? Reduce emissions AND save water?

    You drive your car all day/week and when you come home, you pull out the exhaust collection canister and bring it inside your home where there is a water storage and purifying system. The system itself would be powered by hydrogen and would collect its own combustion water as well.

  5. A couple of questions come to mind. First, the places where you get the most sunlight also seem to be places where there is little or no water. The residents of those areas may object to however much of their scarce water will be not just used temporarily, like to cool a reactor, but utterly consumed. The water that enters such a solar power plant cannot be released ‘down stream’ to be used by someone else. It is gone for good. As to the other by-product, oxygen, there is certainly a market for that. But both hydrogen and oxygen require energy-consuming devices to compress/liquefy and store for shipment to their respective markets. What is the energy equation here ? Could such a power plant be located inside a modest city, where the output could be used right there, to refuel public transit and taxis ? Maybe. How big a facility (area) would be required ? I imagine there is not a lot of sound or chemical pollution to bother the neighbours. Maybe the price of local hydrogen as a fuel would make it atttractive.

    • In reply to #6 by rod-the-farmer:

      A couple of questions come to mind. First, the places where you get the most sunlight also seem to be places where there is little or no water. The residents of those areas may object to however much of their scarce water will be not just used temporarily, like to cool a reactor, but utterly consu…

      what if you just transport sea water into those deserts from the nearest sea or ocean? If crude oil and gas can be pumped through pipelines over thousands of miles with today’s technology, then pipelines could also be built to get water to places that have plenty of sun but little water.

    • In reply to #6 by rod-the-farmer:

      A couple of questions come to mind. First, the places where you get the most sunlight also seem to be places where there is little or no water. The residents of those areas may object to however much of their scarce water will be not just used temporarily, like to cool a reactor, but utterly consumed.

      Firstly I’m a bit skeptical about this myself also, are large amounts of aluminum and iron oxide going to be consumed or oxided in this process, requiring more power to revert them back? If so that makes it not so sustainable but possibly a good way of generating say enough power to store a few days worth of power for overcast days etc. Heating salts with solar arrays can generate electricity for about a day but if this works then you could potentially store enough to back up for longer.

      As for completely consuming water, its more re-distributed (if used in fuel cells in cars the water will come out of the tailpipes). However you are right it will not be available to the residents. However how is this different from cooling towers on coal and nuclear powerplants? Deserts at least here in Australia don’t have a lot in the way of residents. If used at the powerplant to provide base load power utilising fuel cells to turn it back into electricity then the water could be recycled could it not. Even if used to power gas turbines could the gases not be cooled in radiators and used again? But granted there do seem to be some problems. I don’t think these problems would seem to big if it was a massive oil find discovered somewhere, look at the engineering problems associated with deep sea drilling.

  6. Is this a case for unintended consequences? The suggestion to transport sea water makes the most sense, we reap two rewards the minerals and the energy. But what happens to the oceans if we begin to extract water to produce energy as evaporation rates increase due to climate change? Salt concentrations rise killing off more species in the oceans, sky falling kinda stuff?

    Another unintended consequence may be cheaper energy and the benefits derived from cheaper energy.

    • In reply to #8 by Zontor:

      The suggestion to transport sea water makes the most sense, we reap two rewards the minerals and the energy.

      First of all, the use of seawater is unlikely, as it is corrosive when used in machinery. – Although desalination plants are used in some countries and they can be solar powered.

      But what happens to the oceans if we begin to extract water to produce energy

      The volume of water needed to split into gases is quite small compared to the volumes of gas involved.

      as evaporation rates increase due to climate change? Salt concentrations rise killing off more species in the oceans, sky falling kinda stuff?

      There is a negligible chance of seawater becoming more concentrated. It is already becoming much more diluted because of global warming causing melting ice caps. There is also the fact, that once hydrogen is burned as a fuel, it returns to being water.
      The danger to oceans is in CO2 acidification. http://ngm.nationalgeographic.com/2011/04/ocean-acidification/liittschwager-photography

  7. Was I asleep in my thermo classes? The energy contained in the produced hydrogen can’t be greater than that collected by the solar panels, no matter how ingeniously it was done. So the problem is back to square one: until photovoltiacs are efficient and inexpensive enough, we’re nowhere. Also, the hydrogen — how do intend to transport it? It’s BP is so low that as liquid is out of the question I imagine. As a highly compressed gas? — the Hindenburg and Challenger were nothing compared a rail full of compressed hydrogen tankcars exploding in an accident (guaranteed to happen) — I would love to see it. As metal hydrydes — this just might work.

    • In reply to #19 by david.strumfels:

      Was I asleep in my thermo classes? The energy contained in the produced hydrogen can’t be greater than that collected by the solar panels, no matter how ingeniously it was done.

      That is the point! It collects the energy from a whole field of computer controlled motorised heliostats (mirrors). It has nothing to do with “solar panels”. It works on chemical reactions driven by heat.

      So the problem is back to square one: until photovoltiacs are efficient and inexpensive enough, we’re nowhere.

      None of the systems here have anything to do with photovoltaics. Both the OP and my comment @4 refer to solar thermal heliostat systems.

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