A new chapter of solar energy conversion and storage?

Nov 13, 2012 by Kevin Hattori
Associate Professor Avner Rothschild.

(Phys.org)—Using the power of the sun and ultrathin films of iron oxide (commonly known as rust), Technion-Israel Institute of Technology researchers have found a novel way to split water molecules into hydrogen and oxygen. The breakthrough, published this week in Nature Materials could lead to less expensive, more efficient ways to store solar energy in the form of hydrogen-based fuels. This could be a major step forward in the development of viable replacements for fossil fuels.

"Our approach is the first of its kind," says lead researcher Associate Prof. Avner Rothschild, of the Department of . "We have found a way to trap light in ultrathin films of iron oxide that are 5,000 times thinner than typical office paper. This is the enabling key to achieving high efficiency and low cost. "

Iron oxide is a common semiconductor material, inexpensive to produce, stable in water, and – unlike other semiconductors such as silicon – can oxidize water without itself being oxidated, corroded, or decomposed. But it also presents challenges, the greatest of which was finding a way to overcome its poor properties. Researchers have struggled for years with the tradeoff between light absorption and the separation and collection of photogenerated charge carriers before they die out by recombination.

"Our light-trapping scheme overcomes this tradeoff, enabling efficient absorption in wherein the photogenerated charge carriers are collected efficiently," says Prof. Rothschild. "The light is trapped in quarter-wave or even deeper sub-wavelength films on mirror-like back reflector substrates. Interference between forward- and backward-propagating waves enhances the close to the surface, and the photogenerated are collected before they die off."

The breakthrough could make possible the design of inexpensive solar cells that combine ultrathin iron oxide photoelectrodes with conventional photovoltaic cells based on silicon or other materials to produce electricity and hydrogen. According to Prof. Rothschild, these cells could store solar energy for on demand use, 24 hours per day. This is in strong contrast to conventional photovoltaic cells, which provide power only when the sun is shining (and not at night or when it is cloudy).

The findings could also be used to reduce the amount of extremely rare elements that the solar panel industry uses to create the in their second-generation photovoltaic cells. The Technion team's light trapping method could save 90% or more of rare elements like Tellurium and Indium, with no compromise in performance.

Explore further: Recycling industrial waste water: Scientists discover a new method of producing hydrogen

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Sanescience
1 / 5 (3) Nov 13, 2012
These kinds of renewable energy storage designs are a distraction. You have massive loss of efficiencies if your using large heavy and power hungry systems to store hydrogen.

Direct production of fuel and chemicals from renewable energy will out-compete any such design.

Here is one way researches are directly producing fuel and chemicals: http://phys.org/n...765.html
triplehelix
1 / 5 (2) Nov 13, 2012
These kinds of renewable energy storage designs are a distraction. You have massive loss of efficiencies if your using large heavy and power hungry systems to store hydrogen.

Direct production of fuel and chemicals from renewable energy will out-compete any such design.

Here is one way researches are directly producing fuel and chemicals: http://phys.org/n...765.html


This makes hydrogen, aka, a fuel, didn't you read? And it is made completely from sunlight. Solar is the way to go, as it isn't running out anytime soon.

Also, using bacteria to make fuel breaks the 1st law of thermodynamics. You break a fuel down for energy, and get CO2, bacteria eat CO2 and make fuel-at a price. The bacteria uses energy fixing carbon bonds, as breaking carbon bonds makes energy. If the bacteria uses less energy making than breaking the carbon bond, congratulations, you have made a perpetual chemical engine, with over 100% energy efficiency. Bacterial fuels are nonsense.
antialias_physorg
4.3 / 5 (6) Nov 13, 2012
Also, using bacteria to make fuel breaks the 1st law of thermodynamics.

Erm. How about: No?
Bacteria require energy to break the CO2 bonds. They again require energy to fix it into usable forms (depending on how you engineered them this means sugars or methane or some other carbohydrate ... and their own cellular structure). That energy has to come from somewhere - either off the sludge you feed them or off of photosynthsis.

If the bacteria uses less energy making than breaking the carbon bond, congratulations, you have made a perpetual chemical engine, with over 100% energy efficiency

Good thing then that none do.
triplehelix
1 / 5 (3) Nov 13, 2012
Also, using bacteria to make fuel breaks the 1st law of thermodynamics.

Erm. How about: No?
Bacteria require energy to break the CO2 bonds. They again require energy to fix it into usable forms (depending on how you engineered them this means sugars or methane or some other carbohydrate ... and their own cellular structure). That energy has to come from somewhere - either off the sludge you feed them or off of photosynthsis.

If the bacteria uses less energy making than breaking the carbon bond, congratulations, you have made a perpetual chemical engine, with over 100% energy efficiency

Good thing then that none do.


Right, and that "sludge" they eat is miraculously made right?

You want to farm literally tonnes of bacteria to mass produce a fuel, youre going to have to give them food, which is going to have a carbon footprint bigger than the CO2 they absorb, otherwise, you are breaking the 1st law of thermodynamics. The concept is possible, mass production.No
antialias_physorg
5 / 5 (4) Nov 13, 2012
Right, and that "sludge" they eat is miraculously made right?

No. It might be some waste product - but it does contain useable energy for the bacteria. I.e. if you have the waste anyhow then you may as well use it to turn a part of the energy still in there into fuel (another approach is to burn the stuff in thermo-powerplants. So it's pretty obvious that there IS still energy in there)

But the most sustainable way is to use bacteria that rely on photosynthesis to put the energy in their products. How do you think the energy we get out of the food we eat gets into the plants in the first place?

The concept is possible, mass production.No

I didn't say it was sensible for mass production (It may be. farming ocean spaces for phytoplankton may be economically feasible. But I haven't crunched the numbers on that.)
I'm just saying that your commment about 'breaking thermodynamic laws' is wrong.
triplehelix
1 / 5 (2) Nov 13, 2012
I know it doesnt physically break the law of thermodynamics, that is my point. My point is either it does not work on a mass production scale, or it is breaking the law of thermodynamics. Your choice is you can be wrong, or very wrong.

The issue is photosynthesis isn't the only requirement to make fuel, again, you cant break the law of thermodynamics, you cant burn fuels, make CO2, and make it back into fuel without using energy for this process. This usage is going to be more than what you get out, because, as states before, you cant break the law of TD. Making fuel from CO2 will always require more energy than you get from breaking the carbon bonds in the fuel in the first place, lazers, chemically, biologically, molecules have a minimal energy requirement to form, and give exact energies out when broken. The process will get less and less efficient with each turnover of fuel>co2>fuel>co2. Its not perpetual, nothing is, it will require additional fuel, and that's a limited resource.
triplehelix
1 / 5 (2) Nov 13, 2012
The reason fossil fuels give such high yields of energy is because its the Earths very own Battery. It has taken hundreds of millions of years to get all that oil, and we drain it and use it within 200 years. Massive yield! Imagine no fossil fuels, none. We have bacteria, it turns CO2 into hydrocarbon fuel, to feed the bacteria we need to make its food, which inevitably has a carbon dioxide footprint, and energy expenditure. The fuel is made, burnt for energy, back to CO2. The bacteria grabs the CO2 back, and once again we need to feed the bacteria. You will always need an outside source of energy to allow the metabolism of the fuel. You're using (indirectly) fuel....to make fuel!! Its insane! we dig up oil so the farmer can use his tractor so he can grow crops, so these crops can feed animals to give us the raw materials for nutrient agar. We then make fuel, bringing us back to step 1, only due to the law of TD, it isnt 100% efficient, and we have lost energy.
triplehelix
1 / 5 (2) Nov 13, 2012
The only way around this, is if the outside fuel is from biofuels, as you then have renewable oil based fuel from the sun to the plant, which requires little maintenance, little technology, and its food is naturally in the ground and fertilizer from animals excrement. The issue here is, we have now removed the need for bacterial fuels because we've made a buttload from biofuel. Why burn fuel for energy to make a product, for this product to feed a bacteria to make fuel, at less than 100% efficiency, you're losing "fuel"! lol. Again, fossil fuel yields are so high because it is millions of years worth of energy condensed into our current burn rate of 200, maybe 250 years. Making fuel in "real time" does nothing! Solar is the only way forward for energy requirements.
antialias_physorg
5 / 5 (4) Nov 13, 2012
you cant burn fuels, make CO2, and make it back into fuel without using energy for this process.
And I think no one ever claimed you could.
Maybe you missed the word 'solar' in the heading of the article?

The energy is certainly there to transform even low yield photosynthesis bacteria into workable amounts of fuel (AFAIK photosynthsis is about 3% efficient and the sun provides enough energy for all our needs many times over. )

It has taken hundreds of millions of years to get all that oil, and we drain it and use it within 200 years.

And only a very small part of the biomass on Earth got transformed into fossil fuels. Most of that stuff just goes round and round.

it turns CO2 into hydrocarbon fuel, to feed the bacteria we need to make its food

Make its food? What's wrong with sunlight (and water)? Have you ever seen a plant? Do you need to 'make' its food? No.
triplehelix
1 / 5 (2) Nov 13, 2012
I loved the article, the original poster said this was useless and only way forward was bacterial fuels and posted a link. You then came along and agreed with him. I agree with the article completely because you directly get energy and a fuel source from the sun with a panel just sitting there, with effectively no maintenance, excellent!

Yes a small amount of biomass got transformed. My point is making fuel in real time doesnt work as nothing is over 100% efficient. The only way to get over 100% efficiency (loophole) is use 100 years worth of fuel making in 10 years, issue is, the poor people living in poverty for 90 years.

You need to make a bacterias food, a bacteria isnt a plant. Even then, plants still need carbon sources...Put a plant in deionised water, watch it die!

We seem to be discussing different things here, im talking about bacterial farming, requiring a food source. Youre talking about plants....
triplehelix
1 / 5 (2) Nov 13, 2012
Even if plants did need just water, lets go down this route. The plant itself needs no food, but biofuels are needed, so thousands of acres are needed. Sure it rains sometimes, but often extra water is required. This water is pumped for miles, using energy. Extra water is needed in the infrastructure because thousands of acres of new biofuel land has been made, requiring resevoirs to be built, requiring energy. This makes jobs, these people need to get to work, they drive cars, increasing fuel consumption even more. Because they have jobs they can then afford luxury digital consumables, increasing their electricity usage, and carbon footprint. A>B>C>D. A doesnt go directly to D, that doesn't mean B and C can be ignored. Nothing apart from electron configuration emission is 100% effective. Again, the reason fossil fuels give large yields are because we're using it faster than it was made. A simple mathematical loophole in efficiency.
antialias_physorg
5 / 5 (3) Nov 13, 2012
The only way to get over 100% efficiency is use 100 years worth of fuel making in 10 years,

Which isn't over 100% efficient because you're conveniently omitting that the 100 years worth of fuel also had to be generated at some point. Laws of thermodynamics only apply to CLOSED systems. You can't just open a system and claim that theromdynamic laws get violated. They're not applicable to open systems.

plants still need carbon sources

CO2 from the air? Maybe you should look up the word 'plant' on wikipedia before going on.

You need to make a bacterias food

You don't need to make anything. Just take whatever is already there and you don't need anymore. Why is this so hard to understand? You use energy sources that are there for free. sun, wastes and wastewater, bacteria/algae that feed on whatever is handy and multiply by themselves. As long as you get out more than YOU put in (i.e. because the free sources fill up your energy balance) it's all good.
Lex Talonis
1 / 5 (4) Nov 13, 2012
Jesus - the love child of god and his daughter, can do it.

Any guy that spends 2000 years in low earth orbit without an oxygen supply - until he comes back one day, eventually, soon - he can do anything.

Sanescience
1 / 5 (1) Nov 13, 2012
triplehelix: um, wow.

At risk of feeding a troll, I'll admit I meant to say hydrocarbon fuel, not to imply hydrogen isn't a fuel.

The rest of you statements exhibit enough confused thinking that I'm not even going to try and untangle them.

I'll add a quick thought for those who understand the issues involved. The efficiency of electrolysis can potentially be pretty high. However hydrogen gas takes enormous effort to concentrate, store, and transport. Resulting in an *effective* efficiency that is very low.

A process like direct electric consumption by a bio converter at the the proposed 90% efficiency into hydrocarbon fuels that can be stored in a low tech container and transported using current infrastructure will have a much higher effective efficiency.
djr
5 / 5 (1) Nov 14, 2012
triplehelix - read your previous statement again - "Also, using bacteria to make fuel breaks the 1st law of thermodynamics" Your statement is false - using bacteria to make fuel does not break the 1st law of thermodynamics. Again - your statement is false. Commenting on a science web site - with blatantly false statements makes you look foolish.

Now - as far as the efficiency issue - I think sanescience is correct in bringing up the subject of efficiency. A major problem facing solar currently is how to store the power in order to match supply and demand curves. Storage increases the cost of the energy - so obviously affects the competitiveness of solar. If these researchers are on to something - the day the cost of solar power - plus the cost of storage is below grid parity - we escape gravity. We are building an 800 MW solar plant in California - build time 2 years http://cleantechn...-begins/ This train cannot be stopped.
Eikka
1 / 5 (1) Nov 14, 2012
A major problem facing solar currently is how to store the power in order to match supply and demand curves. Storage increases the cost of the energy - so obviously affects the competitiveness of solar.


To put the same thing quantatively, the top efficiency attainable by fuel cells or compound turbines at the moment peaks off at 60%

That means any stored hydrogen is necessarily at least 1.7 times more expensive than the direct cost of the solar energy before accounting for the cost of the equipment. If solar energy is at grid parity today, it must become half as expensive still before it starts to make economic sense to store any of it.

And to be relevant on a national scale as a year-round energy source, you need to store energy on the scale of more than 10 TWh, which corresponds to approximately 600 million tons of liquefied hydrogen.

Out of that, you can expect to lose about 30 million tons just by leaking. That is problematic because free hydrogen is a greenhouse gas.
djr
not rated yet Nov 14, 2012
you need to store energy on the scale of more than 10 TWh" Do you have a source for this number eikka? Are you talking globally, or about one specific country? To run totally on wind and solar - we will need a lot of storage. Hydrogen is not the only option. There are many research projects going on - looking for optimal storage solutions - pumped hydro is already being used. If you balance wind - solar - geothermal - with some good demand management - I think the storage issue is becoming very manageable. Look at where Germany is headed.
Eikka
1 / 5 (1) Nov 15, 2012
you need to store energy on the scale of more than 10 TWh" Do you have a source for this number eikka? Are you talking globally, or about one specific country?


It's a gross estimate based on an educated guess. Here's the reasoning:

A country the size of Germany uses about 500 TWh of electricity a year. The amount of solar energy available varies between seasons, and some of the energy would need to be stored to be used in the winter months.

It's reasonable to assume that the seasonal variation in production is more than 10% unless you're right on the equator. On that scale, 10 TWh of energy represents 2% of your energy flow, which is not enough to solve the variability problem, but it wouldn't be insignificant in helping it.

As a rule of thumb for any grid-scale storage technology, you have to be in the terawatt-hour territory to make a difference, even for small nations of few million people.
Eikka
1 / 5 (1) Nov 15, 2012
To put things in perspective, there's a distributed container of energy that exists right now that contains multiple terawatt-hours of energy.

There are 254 million passenger vehicles in the United States. Let's assume that each carries on average 5 gallons of fuel in its tank. That means 1.27 billion gallons of gasoline, which has 33 kWh of energy per gallon.

That comes out at 42 TWh.

All of that will be consumed within a week, so if you wanted to have a strategic reserve of three months worth, you would actually need to store 504 TWh worth of gasoline.
antialias_physorg
not rated yet Nov 15, 2012
Do you have a source for this number eikka?

I have a source for germany which says that 100% renewables grid would require 3 days worth of storage - which would mean about 5.1TWh of energy or three of these granite energy storage systems:
http://eduard-hei...are.html
Eikka
1 / 5 (1) Nov 15, 2012
I have a source for germany which says that 100% renewables grid would require 3 days worth of storage


That's only to account for the immediate hourly and daily variation in production and consumption. It doesn't account for the seasonal variation in supply and demand.

For example: http://www.usna.e...rage.pdf

As shown in the Appendix, data from the United
States over the period 2000–2007 [5] indicate that had all
the electrical energy come from solar collectors, it would
have been necessary to store from 21% to 27% of the annual
consumption; and had it all been from wind, 5%–13% of
annual consumption would have been required; and if it had
been half from solar and half from wind, 7%–16% of annual
consumption would have been required.
Eikka
1 / 5 (1) Nov 15, 2012
That is of course assuming that there exists a wide supergrid to shuttle the electrical power across the United States to level off the differences between states. In a smaller country such as Germany, the variations in output are greater.
Eikka
1 / 5 (1) Nov 15, 2012
It's also interesting to note that:

These estimates of storage capacity
are greatly increased when conversion losses are considered.
For example, based on the efficiencies in [25],
when solar electricity is converted to hydrogen by
electrolysis and then reconverted to electricity via a
combustion turbine, 50% of the annual production of
electricity would have to be sent to the electrolysis unit, and the storage would have to hold hydrogen having an
energy content of 34% of the annual production


antialias_physorg
5 / 5 (1) Nov 15, 2012
That's only to account for the immediate hourly and daily variation

The article claimes that they used a simulation and historical weather data of the entire European continent (and also factored in a European grid. I.e. if all European nations went 100% renewable then each nation would need their equivalent of similar storage spaces). since the grid allows for overcapacity in one region to be shifted to another region the 'seasonal variation' is quite negligible (on days when you have less sunshine you usually have more wind - especially off shore)
Eikka
1 / 5 (1) Nov 15, 2012
The article claimes that they used a simulation and historical weather data of the entire European continent (and also factored in a European grid


Then I simply have to judge them incredible, because all the other similiar studies over similiarily large regions that I have seen point to a much larger portion of required energy storage than <1%

The US example of 50/50 solar and wind requires an average of 8% of the annual production to be stored and stockpiled for later use. That is roughly ten times more than what your article claims is needed, and that is still only for electric power. You need as much if not more for direct heating needs, and to power transportation systems and cars.
antialias_physorg
not rated yet Nov 15, 2012
What do you mean by less than 1%? Less than 1% of yearly production? Sure that makes sense - because what happens in reality is NOT that production goes to zero over an entire continent (or more if you include solarthermal powerplants in northern Africa which are planned) - ever.

So 3 full days worth of storage means that you can have weeks and weeks of 'sub par' production at a stretch where you just need to feed in a little extra every day.

With the amount of suny days you have in areas where photovoltaics are viable and the amount of windy days for many places where windfarms are planned the chance that ALL of them produce sub par output for such a long time is nil.

And then there are the biogas and waste-thermo powerplants which can be run at full capacity during that time to take up some of the slack.
Sanescience
1 / 5 (1) Nov 15, 2012
Until I see a working small scale version for a couple years studied to estimate maintenance costs and susceptibility to environmental damage or protest groups, I'm a skeptic.
Eikka
1 / 5 (1) Nov 16, 2012
So 3 full days worth of storage means that you can have weeks and weeks of 'sub par' production at a stretch where you just need to feed in a little extra every day.


That "little extra" for weeks and weeks is a fantasy. Solar and wind vary much more than that. Three days is about the absolute minimum you need to make it through the daily variations, when wind power can easily die down for 3-4 days and solar output is practically zero in January, and at night of course.

It doesn't address the 3-5 months of winter when your solar energy output is down and energy demand is up. The demand approximately doubles from summer to winter, which means you NEED to store large amounts of energy.

And then there are the biogas and waste-thermo powerplants


The amount of available biogas and energy from waste is actually very marginal. I remember I once calculated the available biogas from all lavatory waste in Sweden, and it is just enough to power about 10,000 cars
Eikka
1 / 5 (1) Nov 16, 2012
What you also didn't take into account is that your storage mechanism isn't just for covering gaps in production. It's there to capture the energy when it comes in, and then distribute it out steadily. That means you won't have 3 days of energy stored at all times, more like 1 or 1½ days because you need headroom for the incoming energy.

Especially with wind power, the energy comes in at large bursts because of statistical relationships with wind speed and probability distributions. You get half the output energy in 1/7th the running time on average, which means your storage system spends most of its time waiting for that one windy day per week.

What happens when you get a whole windy week?

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