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New technique for turning sunshine and water into hydrogen fuel


August 5, 2013

Artist's conception of a commercial hydrogen production plant that uses sunlight to split water  to produce clean hydrogen fuel (Image: University of Colorado Boulder)

Artist's conception of a commercial hydrogen production plant that uses sunlight to split water to produce clean hydrogen fuel (Image: University of Colorado Boulder)

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A new technique developed by a University of Colorado Boulder team converts sunshine and water directly into usable fuel. The technique involves concentrating sunlight in a solar tower to achieve temperatures high enough to drive chemical reactions that split water into its constituent oxygen and hydrogen molecules. In this way, the team says it should be able to cheaply produce massive amounts of hydrogen fuel.

The 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. The reduced metal oxide now gains a chemical composition that makes it ready to bind with oxygen atoms. Introducing steam into the reactor, which can also be produced by heating water with sunlight, causes the compound to draw oxygen atoms out of the water molecules, leaving behind hydrogen molecules that can be collected as hydrogen gas.

While the concept of using an array of mirrors to concentrate sunlight into a single point at the top of a tall tower is nothing new, being the same technique used in solar thermal tower power plants, there are certain key differences here. Typically, sunlight is concentrated about 500 to 800 times in standard solar power tower designs to reach temperatures of about 500º C (932 º F) and 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.

"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," says Charles Musgrave, Professor of Chemical and Biological engineering at CU-Boulder.

To 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. While it isn't too different in principle from using a magnifying glass to focus sunlight onto a piece of paper to get it to burn, this setup allows the reflected sunlight to be concentrated by up to 2,000 times. "We are trying to use sunlight to drive chemical reactions that require higher temperatures than combustion," says Musgrave.

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.

Though there aren't any working models, conventional theory dictates that a change in temperature is necessary to make the two different reactions occur – a high temperature for reducing the oxide and a low temperature for re-oxidation. Instead, the introduction or the absence of steam is used to drive the different reactions and certain unique properties of the metal oxide compounds used makes this possible.

"We determined that both reactions could be driven at the same temperature of about 2,500° F (1,371° C)," Musgrave told us. "Even though we run at a constant and lower temperature we still generate more hydrogen than competing processes."

Alan Weimer, the research group leader at CU-Boulder says that eliminating the time and energy required for temperature swings lets them make more hydrogen in a given amount of time. To produce even more hydrogen fuel they'd only need to increase the amount of material in the reactor. "In many respects, our approach is out of the box where prior work was inside of the box using the temperature swing," he adds.

According to the team, huge solar plants spread across many acres could produce much more fuel per acre than biofuels for the same amount of acreage. Another advantage that this process has over other renewable technologies, such as wind and photovoltaics, is that it directs sunlight to directly drive chemical reactions to produce fuel for use in combustion engines or fuel cells. In contrast, photovoltaic processes first convert sunlight into electricity, reducing overall efficiency.

"Our objective is to produce hydrogen (H2) at $2/kg H2," Weimer tells Gizmag. "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." The 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.

Though the technology has the potential to be a game-changer in pushing the hydrogen economy forward, commercialization might still be several years away thanks to continuing stiff competition from fossil fuels.

The National Science Foundation and the U.S. Department of Energy supported the research and a paper on the system was published in the Aug. 2 issue of Science.

Source : University of Colorado Boulder

Update: This story was amended on Aug. 7, 2013 to correct an error in figures given to us that related to land area required to generate 100,000 kg of hydrogen per day. We were originally told it was 120,000 acres, when the correct figure is 1,200 acres. Our apologies.

About the Author
Lakshmi Sandhana When Lakshmi first encountered pig's wings in a petri dish, she realized that writing about scientists and imagineers was the perfect way to live in an expanding mind bubble. Articles for Wired, BBC Online, New Scientist, The Economist and Fast Company soon followed. She's currently pursuing her dream of traveling from country to country to not only ferret out cool stories but also indulge outrageously in local street foods. When not working, you'll find her either buried nose deep in a fantasy novel or trying her hand at improvisational comedy. All articles by Lakshmi Sandhana

Usually in steam generation there is sludge leftover, look at any steam boiler. At what pressure will the steam operate?


Even though, this system is still never going to provide more energy out than in (losses always occur).. Hydrogen (and petroleum) are just energy carriers, not an original source of energy, that would be the sun (in combination with the earth's gravitational energy providing the processing reactor for oil etc) .

It is the Cost per gallon equivalent which matters (price point).

Remember, we never have to manufacture Rock Oil, petroleum suffers from massive inefficiencies in its creation / manufacture, fortunately for us it was laid down in the strata a long time ago. (Sure we do make some synthetic fuels, as in synthetic diesel, and methanol, but that is still using a resource we didn't have to create (methane) ).

If this can produce more fuel than the equivalent acreage with agriculture, it may be a goer, as long as the backers are willing to invest.

Noting also, that places which are most suitable for solar thermal energy, may not be so good for intensive agriculture.

Just sayin.


"With the aid of a solar thermal plant, the team believes that they can generate 100,000 kg (222,460 lb) of hydrogen per day" Sigh... we gizmag readers do love projected yields with no area/cost information. Since we are gizmag readers, I suppose we could extrapolate how much land area that would take v time to make that much based on amplifying sunlight 2000 : 1. Any takers? I already have a headache.

Craig Jennings

I see a lot of negative vibes floating around. 100,000kg or 10,000kg is irrelevant. The point is it can continue the process as long as there is light. Hydrogen is expensive. A plant like this would pay for itself within a year.

In simple principles, a solar furnace with stainless steel mirrors is only going to have a carbon footprint for smelting the steel and fabricating the various metal parts. From a monetary point, it can also be fabricated very inexpensively.

Beyond that, the run ongoing requirement will just be the water for the turbine and washing the mirrors.

In the case for the water splitting, concept, its just bumping up the temperature. All it will cost environmentally is the water required to make the product. Initial fabrication will be about the same.

Ongoing maintenance is chicken feed, and fabrication of hydrogen is also going to be as expensive as the water required to make it.

As far as discussions around land area required for the task, it really depends how well the lenses focus. Nothing stops the designer from incorporating a second set of lenses at the focal point for a refined focus.


@Nairda How do you know that it would pay for itself within a year? Do you have documenetd sources of build cost and ongoing costs versus output?


One does not need all that acreage if you use 10 meter diameter water filled lenses and redirect all the focal points to one location.

waleed Al Gharabally

I love gizmag and always enjoy the articles re alternative energy stratagems, however, this seems counter-intuitive. When corn was initially utilized to make ethanol the price of corn as cattle feed and/or human food sky rocketed. Now we are using water to make energy. I presume that this will have to be non-salt water and very pure to avoid interfering with the chemical reactions cited. The amount of potable water available is limited and the cost of it will likely similarly go up. The availability will also likely go down.


I'm curious where the water is drawn from. The sea? Aquifers? What water purification systems are needed before it goes into the system?

Considering the volume of hydrogen produced and the relatively inexpensive materials (although I'm curious what those metal oxides are) involved, I can see this project paying for itself in a few years.

This is the next step in concentrated solar power plants. Previously, pilot plants focused light to heat a medium (water, molten salts, oils). This goes through a heat exchanger to produce steam for the turbine and then produces electricity.

The capital investment for those CSP are large, because of heat exchangers, large medium storage tank, auxiliary heating systems, turbines. Not to mention corrosion problems with molten salts.

All in all, this is a positive step going from a CSP system that utilizes specific heat, to one utilizing chemical energy (skipping over a step that uses latent heat). It delivers an energy carrier which is energy dense per kg.

Fretting Freddy the Ferret pressing the Fret

let's see - New York City has 5,602 buses and a land area of 195,000 acres. So if we replace all the buildings in the city with mirrors, we will be able to generate about enough fuel to run the buses for the people who are no longer there. Economics of scale - even with desert land prices are not favorable towards a cost effective solution


Has hydrogen storage and haulage been worked out? Last I knew it was really hard and expensive to store hydrogen being the smallest element with ability to leak out. How does hydrogen storage and haulage factor into the cost?


I wonder if its any cheaper for the same amount of energy gain to instead of using mirrors to focus sunlight on a single tower, to rather use fresnel lens to focus light on a spot (not a tower), similar to what a magnifiying glass. Since the lense takes sunlight and focuses it to a smaller point, where as the mirrors take light and reflect it, which one is more energy efficient. I would think the fresnel len system would take less space and generate similar power levels. Perhaps someone could add more to this speculation.


Something does not add up here. 120,000 acres is 188 sq miles!

Divide it all out and you get about 1000 ft squared ( 1 million sq ft) per bus.

Rocket bus?


one could reduce temp and pressures with a silica-glass boiler and making the focus point broader,then filling the glass container with superfine stainless steel wool increasing surface area to water boiling points with much finer control...just saying

science ninja

Most of these commenters ignore the crux of this system: sunlight is free. Get with it, folks.


Yes, the sunlight is free, but putting it to use is the expensive part of the equation! Just look at what happened in India when Coca Cola went in there and started making their health destroying soft drinks! The cost and availability of fresh water went off the charts in BOTH directions!! The people of India lost while Coca Cola gained! The benefits of a few jobs are far outweighed by the damage done to the people and the environment. Of course the Hydrogen will fall back down to Earth as H2O again, but how long will it take for it to get back into this portion of the loop?? What will be the cost of purifying the water to where the reactants aren't poisoned and rendered inert?? What will be done with those compounds that are taken out of the feed stock, especially if they are toxic in nature?? And how about hydrogen making things brittle? How many fittings need to snap off of a piping system and people get injured or killed before it's realized just how much of a fool's errand this is???


Expanded Viewpoint

I agree with bobtannica's statements as these were the first questions that entered my mind when reading the article. Using ethanol as a source of energy has only pushed up food prices. Using water as a source of energy will only push up prices as well. Not just the cost to the everyday consumer for home use, but also the cost to people who raise livestock or farmers who need the water for irrigation. The problem with most of these alternative energy strategies is that all they do is transfer the expense away from the energy source and on to any number of things, like food prices, drinking water prices, etc. A $2 per gallon gas / hydrogen equivalent sounds attractive, but when it adds $2 to the cost of other goods and services, in the end you have a greater cash outlay than you did before with the old energy source.

Also, where does the water come from? If it comes from the sea I imagine you will have to clean it up before it can be used in the process described in the article. If it comes from our fresh water sources that means less water for us to drink. There is a good documentary called "Blue Gold: World Water Wars" on youtube that delves into the problem of shrinking fresh water supply. Living in the western United States, I know all to well the bickering that occurs between states when it comes to water rights and this has been going on for decades.

Something else that concerns me about pumping water out of the ocean is that once its gone, i's gone. I imagine if the hydrogen were to be used for only buses, trains, etc. that the strain on the ocean wouldn't be too bad. If we started using this hydrogen for fuel in our personal cars and to create electricity, etc. at first the effects of removing that much water from the world's oceans wouldn't be noticeable, but over time the effects would accumulate and start to effect marine habitats, as well as oceanic currents, which would have a direct effect on weather patterns. Water can be produced, but it's a tricky and potentially explosive process. And guess what? You need hydrogen to do it. Realistically you can have one or the other, but not both.

ALso, how would these changes to the water level of the oceans effect the phytoplankton in the oceans which produce half of the worlds oxygen? We'd be running low on water and oxygen. That wouldn't be fun.

I realize that these are extreme examples, but my point is that we can't let our excitement about the next "It" alternative fuel source cloud our judgement when it comes to the possible consequences down the road. Humanity inherently thinks with a short term frame of mind. How many times has that gotten us in trouble in the past and the present? Short term fixes always cause long term headaches that seem to compound the problems we face in the end. We need to stop wasting our time on energy sources that just transfer the expense to other things and focus on energy sources that are sustainable. I'm all for hydrogen and any other fuel / energy source as long as it doesn't effect water, oxygen or food.

John Public

@MD @bobtannica

Your comparisons to agriculture/ethanol are not valid because unlike agriculture/ethanol, this process only requires sunlight and water, not viable farming land. You can build these things in the desert or other areas not suitable to agriculture, therefore there is no competition.

As far as power concerns go for things such as purifying water or perhaps bringing water in via pipeline (if built in desert)... The article already mentioned combing a solar thermal plant, you just use that (or other traditional solar methods) to supply an adequate amount of power for the hydrogen production and auxiliary tasks.

Another idea is to have these things built on offshore platforms not unlike oil rigs. Being offshore you obviously have an adequate supply of water. If needed, the desalination could be built right onboard the platform. And with being offshore, you have three potential modes of power generation to operate the plant... wind, solar, tidal.


small start on what we need if you figure acreage to the 62 million vehicles in the us alone. you would need about half the land mass of are entire country.


Sunlight is not free! It's called land and people fight and die for it.The government owns land out here in the west and I certaintly don't want solar plants harming the desert tortoises or marring the landscape.The problem of H2 storage and transport is being worked on we use a lot of it today from petro chemical to food production. In fuel cells it would be very efficient.This process is pretty cool that it doesn't waste the heat.It would not pay for itself for many years if ever ,the government would have to help which is sometime warranted. H2 today comes from natural gas which is very cheap Very high temperature nuclear plants can make H2 with less impact on the land. The West is running out of water and very pure water is required for either process.If we took it from the ocean you would never notice it as when you use it it turns back to water.I do support research in this area as it can be produced carbon free in the future like this or nuclear and is a good energy carrier

Paul Bedichek

Hydrogen burned in an engine combines with oxygen in the air and produces water.

What you need to know about fuels is the stoichiometric ratio or how many units of air per unit of fuel produces the most complete combustion.

Natural gas: 17.2 Gasoline: 14.7 Propane: 15.5 Ethanol: 9 Methanol: 6.4 Hydrogen: 34 Diesel: 14.6

The non-oxygen components of air contribute nothing* to the combustion process. What they do is act as a working fluid, enhancing the gas expansion caused by the heat from the oxygen/fuel burning.

If air was pure oxygen and only the amount of oxygen required to burn the fuel was admitted to an engine, it wouldn't work very well because there wouldn't be enough gas expansion to move the pistons or spin the turbine blades.

To run an engine on hydrogen requires 34 times as much air as it does hydrogen, no matter how the hydrogen is generated. Just cracking water into its components then burning them won't work. A huge amount of other gasses from outside air have to be run through.

See the Mythbusters episode where they rigged the test by completely blocking off the carb inlet. They should have just stuck the tube into the open carb like they did from the hydrogen tank, which ran the engine. Most likely their electrolytic generator wouldn't have been producing enough hydrogen, not for that big V8. If it's not going to work, let it not work on its own without deliberately taking steps to ensure it won't work.

*Running too lean leaves 'excess' oxygen to do things like combine with nitrogen, which produces nitrogen oxide (NOx, which is not Nitrous Oxide). NOx can combine with water vapor and produce a very dilute nitric acid. The same process produces sulfur dioxide which makes a very dilute sulfuric acid. (I bet the sulfur from onions mixing with human tears makes stronger sulfuric acid than is produced from S02 from engine exhaust.) Part of what catalytic converters do is break down SO2 and NOx in the exhaust. Now there's a company advertising "nitrogen enriched" gasoline. Why put more nitrogen in the fuel when that's what is 70% of air and causes enough problems making NOx that catalytic converters have to break down?

Gregg Eshelman

If these solar systems were all over the world providing the maximum energy we could reasonably expect from them, how much water what they use up, in a day?

How long would it be before they used up all the fresh water on Earth?

Would be slowly but permanently, lowering our water supply, on Earth?


I am in favor of any sustainable form of energy that does not lay waste to the earths environment. It will be nice to see what the real numbers are. We all must remind our selves about the urgency of getting off fossil fuel and nuclear fuels as we use them today. The earth will not die because of us, the earth will allow us to destroy enough to destroy our selves. Have a good day.


The corrected figure of 1,200 acres seems so much the more credible that it has been lowered by a factor of 100 versus the formerly published of 120,000 -- yet WhoIsBramStoker finds out that an astounding one million square foot would still be required for powering a single bus...

Is CA-Boulder surreptitiously trying to discredit its own innovative hydrogen production system? And if so, is Big Oil to be seen behind?

And, BTW, why is there no other comment on WhoIsBramStoker's revelation?


Hydrogen alone is a lousy fuel even if cheaply generated it is still bulky, leaky, and makes many metals brittle. However the hydrogen coming out of the reactor will be hot and the hydrogen can be attached to other stuff to make better fuel. Carbon would be best for generating easily stored and transported fuel, but nitrogen is always available and while Anhydrous ammonia is bulkier it is much easier to handle being a liquid at non cryogenic temperatures. Hydrazine like Anhydrous ammonia can be burned in an ICE or fuel-cells (without the difficulties of hydrocarbons) and has a nice density with the plus of being a room temperature liquid but is notably toxic. Ammonia has the joke in the deck that it can be mixed with water and piped to its destination and be fairly easily removed from the water if you have both moving in the same direction anyway. The land area required to generate 100,000 kg of hydrogen per day is 1,200 acres.

The condition of the water you start with is immaterial it has to be turned into super hot steam first leaving the salt and other minerals behind.

re; MD While technically true that petroleum is only an energy carrier because it is compressed and fossilized sunlight, Don't be a jackwad.

re; Gregg Eshelman I've seen the Mythbusters episode. the hydrogen efficiency enhancer bit was a slander. The device is not intended to simply replace gas or diesel but instead the small amount of hydrogen is supposed to speed the burn of the fuel so that the heat is generated sooner so that the engine captures more of the available energy. Not having tried it I don't know that it works but the theory is good.


here is the bottom line folks, all of the techniques should be investigated and financed by a international fund provided by the industrialized nations, because we are the ones using up all of the energy. probably about 1000 to a million times as much as the un industrialized nations. yet they have to suffer from us screwing up everything. if the ideas were revied by international per review of scientiest / engineers AND the results given away FREE to everyone we could solve a lot of the worlds conflict in one swoop. damn the capitalist ROI, it is the life of our world that is at stake.


Overall I'm still in favor of steam turbines generating electricity, as they are by their nature reasonably closed cycle and a more mature technology and does not require a continuous high flow of water as hydrogen production does.

Battery energy density will only improve, so beating the dead horse with internal combustion of any material is ultimately just nostalgia for those trying to cling to the past.

For me the sign that civilization is progressing is when there does not appear to be an insidious ulterior motive to energy projects. For this, the push for hydrogen generation through any means is a way to prolong internal combustion into the next century. Same same with the new high temperature nuclear reactors that produce hydrogen on tap. It also produces weapons grade material, like old reactors.

So for our century, I will be at peace when I see Thorium and pebble bed nuclear reactors replacing conventional, and solar concentrators (generating electricity) floating on large pontoons 5km off the coast.


{shrill whistle}

Okay, folks, back away from the paranoia.

90% of the Continental United States has a layer of subsurface brackish water. Ask anybody that drills water wells for a living, come on, it ain't Rocket Science.

We manufacture H2 gas with sunlight, and use either pipelines to get it to market or canisters of charred chicken feathers.

There are several ways to do this.

The SIMPLE way is to just store the H2 gas underground in large, low-pressure tanks and burn it to make electricity on demand.

Another possibility is moving our heavy industry out West right next to the power source. If you check, most of our Aluminum smelting is done right next to HydroElectric plants.

But the Gas to Liquid technology might be the easy access technology you're looking for.

You can make synthetic hydrocarbons with CO gas and H2 gas, and end up with Methanol.

Just fine for running our cars on.

And for everybody that panicked about running out of water, PLEASE bonk yourself on the head...

When you burn H2 gas you get H2O, WATER.

So we start with brackish, salty water.

We use solar energy to purify it with Reverse Osmosis.

We convert it to H2 gas.

We either ship the H2 gas, store it in a balloon and burn it for power at night, or convert it to Methanol.

The net amount of water in the world doesn't change.

Honestly, sometimes I'm embarrassed by people jumping at shadows.

William Carr
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