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Swiss team develops effective and low-cost solar water-splitting device; 14.2% solar-to-hydrogen efficiency

Using commercially available solar cells and none of the usual rare metals, researchers at the Swiss Center for Electronics and Microtechnology (CSEM) and École Polytechnique Fédérale de Lausanne (EPFL) have designed an intrinsically stable and scalable solar water splitting device that is fully based on earth-abundant materials, with a solar-to-hydrogen conversion efficiency of 14.2%.

The prototype system is made up of three interconnected, new-generation, crystalline silicon solar cells attached to an electrolysis system that does not rely on rare metals. The device has already been run for more than 100 hours straight under test conditions. The method, which surpasses previous efforts in terms of stability, performance, lifespan and cost efficiency, is published in the Journal of The Electrochemical Society.

crystalline Silicon (c-Si) solar cells show high solar-to-electricity efficiencies, and have demonstrated stabilities in excess of 25 years. Propelled by their attractive performance, they have continuously dominated the market since their inception, with a current worldwide market share greater than 85%. Their high production volumes have largely contributed to a price drop of 80% since 2008, currently reaching levels below $1 per watt peak.

… Recently, c-Si modules have been implemented in solar-hydrogen devices, demonstrating SHE [solar-to-hydrogen efficiency] of 9.7%. As the VOC of the presented c-Si cells is only ∼600 mV, four cells need to be connected in series to achieve stable water splitting performance. This results in lower operating currents and limited SHE efficiencies. Alternatively, c-Si-based heterojunction (SHJ) cells can reach VOC values in excess of 700 mV. These VOC values are the highest ones reported for silicon wafer-based technologies, and are predominantly obtained by an excellent interface passivation with a thin (∼5 nm) film of hydrogenated intrinsic amorphous silicon (a-Si:H) between the c-Si wafer and the oppositely doped emitter, forming the p-n junction. We demonstrate in this study that, thanks to their high VOC, three series-connected SHJ cells can already stably drive the water splitting reaction at unprecedented SHE.

—Schüttauf et al.
Epfl
Schematic overview of the solar-driven hydrogen generator. The SHJ module captures sunlight and converts it into electricity directly feeding the electrochemical membrane electrode assembly water-splitting unit. Water is fed in the anodic side, where it is oxidized and oxygen molecules are generated; the simultaneously produced protons migrate across the membrane to the cathode, where they are reduced into molecular hydrogen. The gases can then be collected and stored in their pure form. Schüttauf et al. Click to enlarge.

A 12-14 m2 system installed in Switzerland would allow the generation and storage of enough hydrogen to power a fuel cell car over 10,000 km every year.

—Christophe Ballif, co-author

In terms of performance, this is a world record for silicon solar cells and for hydrogen production without using rare metals.

The key here is making the most of existing components, and using a hybrid-type of crystalline-silicon solar cell based on heterojunction technology. The researchers’ sandwich structure—using layers of crystalline silicon and amorphous silicon—allows for higher voltages needed to power directly the microstructured Ni electrocatalysts. Nearly identical performance levels were also achieved using a customized state-of-the-art proton exchange membrane (PEM) electrolyzer.

The researchers used standard heterojunction cells to prove the concept; by using the best cells of that type, they would expect to achieve a performance above 16%.

The research is part of the nano-tera SHINE— project to develop an efficient and cost-effective hydrogen production system using sunlight and water.

Resources

  • Jan-Willem Schüttauf, Miguel A. Modestino, Enrico Chinello, David Lambelet, Antonio Delfino, Didier Dominé, Antonin Faes, Matthieu Despeisse, Julien Bailat, Demetri Psaltis, Christophe Moser, and Christophe Ballif (2016) “Solar-to-Hydrogen Production at 14.2% Efficiency with Silicon Photovoltaics and Earth-Abundant Electrocatalysts” J. Electrochem. Soc. 163(10): F1177-F1181 doi: 10.1149/2.0541610jes

Comments

HarveyD

This could become a smart and effective way to capture and store solar energy for rainy-cloudy days for the house and for future FCEVs.

A 2000+ sq-ft. roof top unit could eventually supply enough (converted-stored) energy for a well constructed house + one or two FCEVs (for 50 to 75 KM each/day) where/when the home compressed H2 tanks are large enough.

Davemart

I don't think the optimal way to use this is by storing it at the house.

Arrays local to petrol stations would work fine though, and the hydrogen can be stored there, perhaps as a hydride.

But the NG pipeline network can also store large quantities of hydrogen, mixed in with the methane:

http://www.greencarcongress.com/2010/05/tgc-20100511.html#more

For winter use salt caverns and depleted NG fields can provide enormous amounts of additional storage capacity.

Hyundai points out that fuel cell cars and buses actually clean the air due to their needing to pump it through their system to provide oxygen:

'According to local industry leader Hyundai Motor Co., a fuel cell electric vehicle can collect up to 20 milligrams of fine dust for every kilometer it travels.

An FCEV is a type of hybrid vehicle that uses a fuel cell and a battery to power an electric motor instead of an engine. Because its fuel cell requires oxygen, the car purifies air for oxygen and thus gathers fine dust in the process.

Considering that a diesel passenger car produces 10 milligrams of fine dust for every kilometer traveled, each FCEV can help purify air polluted by two diesel vehicles, the automaker claimed.

The study apparently shows that though both electric vehicles and fuel cell cars emit no greenhouse gases, fuel cell cars could be a better option as they could also help get rid of fine dust, which has become a serious health hazard globally.'

https://fuelcellsworks.com/news/study-suggest-fuel-cell-vehicles-may-be-a-solution-to-reducing-fine-dust/

Exhaust pipe emissions are not the only source of particulates.
Tyre wear makes a contribution, which increases massively with 'ludicrous' acceleration:

'PM2.5 emission from tire dust was calculated as 3.7 mg/km/vehicle.
Emission of tire dust was shown by a quadratic function on acceleration.'

http://www.nanoparticles.ch/2015_ETH-NPC-19/Poster/44_Tonegawa.pdf

As can be seen from the graphs there, 4000 lb cars accelerating extraordinarily rapidly are going to generate way, way more than this average.

So fuel cell cars and buses can help mop up the pollution not only from diesels and ICE, but from inappropriately fast accelerating electric cars too.

electric-car-insider.com

Harvey, how difficult do you think it will be to get a 10,000 PSI compressor and tank permitted for residential use?

Have you ever been nearby such a compressor? They are not quiet.

They are also not cheap, or maintenance free.

HarveyD

Every current FCEV has on-board 10,000 PSI tanks sitting in the home garage. Home H2 tanks could be as save if not saver.

Of course, FCEV owners without home installation could fil up weekly or so at the local H2 station.

Small home H2 compressing unit could easily be insulated to keep noise and vibration down to acceptable levels.

Davemart

The Linde ionic compressor is very low maintenance:

file:///C:/My%20Documents/General%20Info/Science%20and%20Technology/Hydrogen/Ionic%20Compressors/hydrogen-technologies-the-ionic-compressor-90-fo-eng-358503.pdf

However it does produce around 75 Db (A) at 5m

So for home storage to work really hydrides, ethanol etc would be needed.

The petrol station model works just fine for hydrogen though, and of course those buying PHEV FCEV's like the coming Daimler can plug in at home.

Whilst running on the battery though it would not be cleaning the air as a pure FCEV does.

On high pollution days PHEV FCEV drivers will be requested to keep their fuel cells running, and avoid their batteries!

Davemart

There is little point in paying for and carrying around a huge battery in any case, or even in the PHEV configuration, if the NREL is right and hydrogen from renewables comes in at around $1.14kg:

http://www.greencarreports.com/news/1105642_hydrogen-cost-could-equal-50-cent-gasoline-with-renewable-energy-study

After allowing for the increased efficiency over petrol, that is equivalent according to my link to gasoline at around 50 cents/gallon, but from all renewables and without pollution at point of use, or much of it anywhere in the chain.

They calculated this before these results from Switzerland, of course.

gorr

I said long time ago here to start Making synthetic gasoline near my home with these solar panels and put this gasoline for sale at a better price than actual petroleum gasoline without state taxs.

Davemart

A BEV is only as clean as the electric grid, and solar power for home charging relies on offset, not really charging from solar at all.

The electric grid will not become entirely clean for a very long time.

Hydrogen from solar can short circuit this, as a hydrogen supply chain could be set up separate from the general grid.

On top of that, electric cars especially the fast accelerating Tesla's churn out substantial particulate pollution, as I have detailed above.

Fuel cell cars can not only counter their own particulate pollution from tire wear, but absorb that from other cars and sources.

So the whole energy chain from fuel cell cars is much cleaner than from BEVs, and far less CO2 intensive, and can clean up city air.

They are demonstrably the better solution in my view.

Big Al

It appears to me that any kind of electricity could be used to produce hydrogen this way, not necessarily solar electricity!

ai_vin

High pressure tanks or metal hydrides? How about high pressure metal hydrides?
http://www.iphe.net/docs/Meetings/Lucca_Italy_05/Daigoro_Mori.pdf

Also, Liquid Organic Hydrogen Carriers (LOHC) look promising.

Engineer-Poet
the NG pipeline network can also store large quantities of hydrogen, mixed in with the methane

The storage capacity of NG pipelines is small, and the fraction of energy that hydrogen can store in them is vastly smaller due to the much lower volumetric energy density.  Anyone who repeats this bit of nonsense is either innumerate, deluded or a shill for the scammers.

What this scheme needs is a way to produce, not molecular hydrogen, but NADH from NAD.  NADH can convert CO2 into methanol using well-understood enzymes.  Methanol is safely storable at ambient conditions.

I'm not even sure low efficiency is a big problem with this scheme.  No efficiency is stated for the PV cells, but I'd guesstimate 20-22%.  If power is first tapped off for vehicle charging demand, a PHFCV would run first on direct electric power with excess diverted to MeOH production.  At perhaps 10% total efficiency, a system on a 150 m² roof receiving 3 kWh/m²/day of collector would capture... calculator... 16.4 MWh of storable energy.  That' s about 56 million BTU or 560 therms.

That much looks good, the rest comes down to resource requirements and cost—and we know that those are pretty dismal for PV systems.  It might look better if excess wind power can also be dumped to it.

Davemart

EP said:

'The storage capacity of NG pipelines is small, and the fraction of energy that hydrogen can store in them is vastly smaller due to the much lower volumetric energy density. Anyone who repeats this bit of nonsense is either innumerate, deluded or a shill for the scammers.'

And anyone who adopts this wholly intemperate mode of address without the slightest attempt to provide any substantiation for their argument is not only a fool, but a deeply arrogant one.

'Power-to-gas systems may be deployed as adjuncts to wind parks or solar-electric generation. The excess power or off-peak power generated by wind generators or solar arrays may then be used at a later time for load balancing in the energy grid. Before switching to natural gas, the German gas networks were operated using towngas, which for 50–60 % consisted of hydrogen. The storage capacity of the German natural gas network is more than 200,000 GWh which is enough for several months of energy requirement. By comparison, the capacity of all German pumped storage power plants amounts to only about 40 GWh. The storage requirement in Germany is estimated at 16GW in 2023, 80GW in 2033 and 130GW in 2050.[4] The transport of energy through a gas network is done with much less loss (<0.1%) than in a power network (8%). The storage costs per kilowatt hour are estimated at €0.10 for hydrogen and €0.15 for methane.[5] The use of the existing natural gas pipelines for hydrogen was studied by the EU NaturalHy project[6] and US DOE.[7] The blending technology is also used in HCNG.'

https://en.wikipedia.org/wiki/Power_to_gas

So the storage potential of the NG grid is large relative to many current storage mechanisms, although not as large as the salt caverns and depleted NG fields which can also be used.

That is using comparable metrics, not your wholly undefined 'small'

You have become more obsessive as your favoured alternatives have lagged.

Do try to act like a normal human being occasionally, as I quite like you, when you are not being a complete tedious prat.

william g irwin

Guys, please remember how old and leaky our NG delivery system is. I am told by folks that maintain the pipes that, especially in cities, there is still many miles of cloth wrapped wood pipe delivering NG. Ouch! Significant money is needed to update and maintain our aging NG pipeline infrastructure.
On top of that, the very small molecular structure of H2 makes it very hard to contain - much harder than NG - so that makes an increase in H2 content even more of a leakage problem in pipe distribution with NG.

Engineer-Poet
anyone who adopts this wholly intemperate mode of address without the slightest attempt to provide any substantiation for their argument

Anyone who disputes this oft-substantiated claim without any attempt to check it out for themselves is an ignoramus, and a deeply arrogant one.

Natural gas pipelines may handle up to 10% H2 without major technical difficulties (larger fractions reduce the molecular weight too much so that e.g. compressors cannot achieve their rated output pressure).  At 10% H2 by volume, the energy content of the hydrogen is less than 4%.  This is nigh-trivial.

H2 may not be storable in underground reservoirs containing sulfate rocks because of bacterial metabolism of sulfate to H2S.

Before switching to natural gas, the German gas networks were operated using towngas, which for 50–60 % consisted of hydrogen.

That was when distribution was local (no LD pipelines or compressor stations) and all appliances were specified for town gas.  This is no longer the case.  Ironically, the claim about the storage capacity of the German NG network is unreferenced—yet you accept it uncritically.  The capacity of reservoirs is by volume, not by energy, and substituting H2 for methane slashes it by 7% for every 10% H2.

You have become more obsessive as your favoured alternatives have lagged.

You mean "as the Greens have doubled down on failure that SHOULD have forced them to reconsider."

Do try to act like a normal human being occasionally

I am fed up with fools.  The world can no longer endure their mistakes; had you been forced to bet on your favored options, you would have lost and would be out of the game now.

Davemart

william:

The post I referenced was for the German NG network, as they are going into it heavily right now, and the figures happened to give an insight relatively quickly without wading through lots of other information extraneous to that immediate part of the issue.

It is of course not the only reference I rely on for the subject.

Here is a substantial study for the case of the US grid:
http://www.nrel.gov/docs/fy13osti/51995.pdf

Yep, it would need a certain amount of patching, but is no worse than much other US infrastructure - and as my link said, the old town gas was 50% hydrogen, and they managed to pump it around very successfully with much more primitive technology.

Davemart

EP:

Your assumption that that is the only reference I rely on is as unfounded as your notion that I had not investigated the matter in the first place.

And you expose yourself terribly by making absolutely daft comments that 4% of the NG grid by energy AT ANY ONE
TIME is in some way trivial relative to other forms of storage in use.

The link I provided when you have still given none assuming that others will be so overawed by your brilliance that none are needed for your worshippers to accept what you say, indicated that the German's are planning an energy flow of 16Gw by 2023 which compares to their total pumped storage of 40 GWh, so is as respectable amount at that early stage, with much more to come.

And I can't be bothered to provide a second level of references to the size of the German NG network to prove your notion that I rely solely on that one is an example of your replacing logic with assumptions.

You hold forth and expect to be taken seriously without one solid reference.

If you are tired of putting up with fools, it seems you are tired of life, as you are an excellent example, and an oafishly ill mannered one with a megalomanic misconception of your own intellect and understanding.

No one at all will be interested in any discussion with you on any subject whatsoever, or give an fig for your opinion.

But of course that has got you out of engaging with the fact that your opinions as to the future direction of energy have obviously been trashed by the information which has come to light in the last few years, and you have not got the guts or integrity to face that, so your refuge is childish ill manners so that you have an excuse not to admit that your arguments have been shown to be worthless.

How cowardly.

How foolish.

How sad.

SJC

Some would rather criticize than propose constructive solutions. Proposing solutions would subject THEM to criticism.

ai_vin

OK, from Dave's link; https://en.wikipedia.org/wiki/Power_to_gas

"The storage capacity of the German natural gas network is more than 200,000 GWh" & "Grid injection without compression - A gas mixing plant ensures that the proportion of hydrogen in the natural gas stream does not exceed two per cent by volume, the technically permissible maximum value when a natural gas filling station is situated in the local distribution network. The electrolyser supplies the hydrogen-methane mixture at the same pressure as the gas distribution network, namely 3.5 bar."

Running some numbers: 2% of 200,000 is 4,000 but even with hydrogen's lower energy content I still get 1,600 Gwh. And the storage requirement in Germany is estimated at ONLY 16GW in 2023, 80GW in 2033 and 130GW in 2050?

Have I got those numbers right Dave?

ai_vin

Correction: The energy density of methane gas at 1 bar is .037 MJ/l and that of hydrogen is .01 MJ/l. 4,000 divided by 3.7 is about 1081 - less than the 1,600 I stated above.

Davemart

Hi al:

I try to avoid doing too many calculations myself, and those decimal places are tricky!

A lot of the links when I researched this some years ago are dead now, but here is an extant one giving the figures:

https://www.gtai.de/GTAI/Navigation/EN/Invest/Industries/Smarter-business/Smart-energy/power-to-gas,t=germanys-gas-network-infrastructure-the-advantage,did=547396.html

'Germany's generous gas network reserves - more than 400,000 km of pipeline connecting natural gas reservoirs with a total storage volume of 23.5 billion cubic meters and a further 15.2 billion cubic meters in planning - allow for provision of approximately one sixth of annual domestic electricity generation.

Put another way, Germany's extant gas network provides energy storage capacity of approximately 220 terawatt hours - or a three thousandfold capacity increase on Germany's current pumped storage levels (assuming a base efficiency level of 55 percent).

As such, power-to-gas represents a major energy storage opportunity, as the gas network's current storage capacity of around 210 terawatt hours allows it to serve both a renewable energy storage and distribution function in the future while discharging the burden on the power network and making the recovery of CO2 from fossil fuel sources for material use possible.

Power-to-gas also contributes to the stabilization of the power system by providing negative and positive regulating energy through targeted on-off switching. Germany is unique in the fact that hydrogen can be fed into the in-situ gas grid in significant quantities (up to 30 percent grid capacity in some regions).

Germany enjoys another unique advantage: the presence of salt caves in wind-intensive regions which are already being used for natural gas storage purposes.'

So the near enough figure is:
'loads!;-)

That is for the NG, but the percent of hydrogen is a moveable target, as critical connectors can be upgraded as needed - see my link to the NREL for the gory details in the case of the US.

The target for hydrogen storage in 2023 is low not because of problems putting it in the network, but because they are still developing and taking cost out of the electrolysis from renewables to supply the hydrogen.

It is also of interest that storage in underground salt caverns is ALREADY taking place, so the notion that sulphate formation is a show stopper and such storage will never take place is polemical nonsense, which is not to say that the problem is non-existent, of course.

Davemart

I should have qualified salt cavern storage to note that it is currently NG, not hydrogen, being stored.

I assume that methane would also encounter any potential problems due to sulphur.

Davemart

More on separation of hydrogen back out from an NG network, and interestingly:

'A certain percentage of hydrogen is already added to the natural gas as an additional energy source – up to a maximum of 4% in Austria and even as high as 10% in Germany, depending on the region. Technologically, feeding hydrogen into the natural gas network is not a problem and the general natural gas customer does not even notice. But anyone who would like hydrogen can now have it specifically filtered out from this natural gas/hydrogen mixture.

http://phys.org/news/2016-04-hydrogen-natural-gas-network-greener.html#jCp

-So your 2% of the NG network capable of being hydrogen instead is pretty conservative in many areas of Germany, Al! ;-)

ai_vin

It's not MY 2% Dave. I got it from your wikipedia link. And I was going for the most conservative number I could get to show that even a low estimate results in about 10 times more storage than they are asking for.

Davemart

Al:

I simply meant 'your figure' in the sense that it was the one you, very sensibly, used, as even that low figure proves the case.

The notion that the NG network does not 'really' store energy arises from the fact that in order to retain enough pressure to drive the network, of course most of it must be left in situ.

It does however provide a very large working reserve,and in fact the pressure is allowed to drop somewhat when demand is high.

None of that really affects the storage of hydrogen though, as the small percentage needed can be added and withdrawn at will.

That means that large amounts of hydrogen can be generated from renewables, transported in the NG pipelines and extracted where it is needed, at a filling station, for instance.

That is aside from the use of salt caverns and depleted NG fields allowing the amount in the network to be topped up.

Here is an analysis of salt cavern storage for the UK, including costs:

http://www.eti.co.uk/wp-content/uploads/2015/05/3380-ETI-Hydrogen-Insights-paper.pdf

Right now salt caverns are in use:

'Salt caverns are man-made underground
holes created by washing salt out of large
geological structures made of almost pure
salt. As shown in Figure 2 a well is drilled
down into the salt field. Water is pumped
down, dissolves the salt, and the brine
removed for use or disposal. They are used
throughout the world to store natural gas
and other hydrocarbon products. The UK
stores about 10,000 GWh of natural gas
alone (enough to keep the country running
for a few days). H2 is also currently stored in
a small number of salt caverns in the UK and
the USA, supporting chemical plants and oil
refineries. The largest single store (USA) holds
over 100GWh of H21.'

So there is nothing speculative about the technology.

Studies show that NG fields can also be used, with a particular field analysed in depth:

'A. Amid, D. Mignard and M. Wilkinson from the University of Edinburgh have just published a study in the International Journal of Hydrogen Energy, looking into the possibility of using depleted natural gas reservoirs for pressurised hydrogen storage. As of January 2013, a total of 688 natural gas storage facilities were operated worldwide with a combined working gas capacity of 377 billion m3, so if it proved technically feasible there would certainly be scope to take advantage of these spaces.

The researchers’ analysis foresaw three technical problems. First, that the remnant methane in reservoirs would contaminate the hydrogen. Second, that micro-organisms could feed on the hydrogen while it is in storage; and third, that the hydrogen will leak from its prison.

The team’s modelling was based on a partially depleted natural gas reservoir in the Southern North Sea, off the coast of Yorkshire. Their findings were,

Contamination: That initial injection cycles could see some methane contamination, but this was ‘not a serious concern’, and the contaminants would be cleansed over multiple cycles. Hydrogen sulphide could prove an issue, and reservoirs should be chosen to minimise the amount of sulphate reducing bacteria.

Consumption: There would be some loss of hydrogen as it is converted to methane and biomass, but the worst case scenario would put this at no more than 3.7% of the hydrogen.

Leakage: Hydrogen is more diffuse than methane, and so we could expect some leakage, but it is unlikely to be more than 0.035% of the stored hydrogen after 12 months.

In conclusion, the assessment found that there is no insurmountable technical barrier to this plan, given current technology. However it would be a major undertaking, with an average power in the order of 4–5 GW required during a six month injection cycle to fill the reservoir to capacity, provided that cushion gas is already present.'

https://fuelcellsworks.com/news/a-feasibility-study-of-storing-hydrogen-in-depleted-gas-reservoirs/

ai_vin

Looks good. BTW earlier I mentioned "Liquid Organic Hydrogen Carriers" and I wonder if you've looked into that at all. LOHCs make storing & transporting hydrogen as easy as diesel.

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