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reading this article about Germany planning to store renewable energy as hydrogen gas, i'm left wondering why they deem so great this plan, compared with other alternatives like ammonia as a energy carrier for storage?

Is there a comparison chart between the different processes to store electric energy in chemical format?

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4 Answers 4

Making ammonia is an absolute bugger because nitrogen is so unreactive. The normal route is the Haber process, http://en.wikipedia.org/wiki/Haber-Bosch, but this requires high pressures and temperatures.

Hydrogen is easy to produce from electricity, and I guess that's why it's the first choice for storage of energy generated by unreliable sources like wind or solar. If there were an industrial scale process for using electricity to make something more easily stored, like methane, I guess that would be a lot easier to store. However I don't know of any such process that works outside the lab.

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What is exactly the engineering detriment due to the fact that it is so unreactive? High pressure and temperature tanks are entirely feasible, I think the real question is how the process scales to large production rates. Then again, there could be poor conversion efficiencies due to this Nitrogen chemistry, which would impact the energy balance of the process and present a much more fundamental barrier than just requiring high capital costs. I'm not a chemical engineer but I am captivated by their facility design :D –  Alan Rominger Apr 23 '12 at 16:26
I'm not sure what you're asking Alan. Ammonia has been made with the Haber process for about a hundred years so it's obviously a feasible way of making ammonia, but it's energy intensive and expensive. –  John Rennie Apr 23 '12 at 16:45
Energy intensity as an argument doesn't make sense since we're discussing ammonia as an energy medium. Regarding the cost, if I could convert electricity into a liquid fuel at 85% efficiency, it would be fantastically competitive. Cost of the electricity, for one, only matters relative to the value of the liquid fuel. The capital cost is still there, so it would be consistent to argue that the Nitrogen chemistry particulars lead to high facility capital costs, but you have not argued that. –  Alan Rominger Apr 23 '12 at 17:26
Hmm, I don't have figures for how energy efficient the Haber process is, but bearing in mind that it requires 200 atm at 500C I'd guess the plant running and maintenance costs are high. The capital costs are indeed very high, though that is a one off. –  John Rennie Apr 23 '12 at 18:13

(I tried to post this response with chart and links, but I'm new here, so the system won't let me include images or more than two links. Please cut and paste the other links to view them in your browser.)

This diagram from the NH3 Fuel Association (taken from www.nh3fuelassociation.org/about-us--why-nh3) (scroll down the page) may answer part of your question: it compares ammonia with hydrogen and various other fuels. It shows that ammonia contains twice as much hydrogen energy as pure hydrogen (see "H2 Density" column), so, assuming efficient conversion and cracking processes, it can certainly make more sense to store hydrogen as ammonia.

MattZ ... the website you link to used to be the official site for the NH3 Fuel Association, but they changed their name and the url you cite has since been taken over by spiderbots. Please visit http://www.nh3fuelassociation.org for links to the various studies you mention. Please also note that an updated version of their website will be relaunched in a few weeks.

As to why Germany plans to store hydrogen ... ammonia's toxicity may make it politically complicated for governments to promote, and more needs to be done to establish safe handling standards and address confidence issues for ammonia. The argument for hydrogen in Germany may also be a local one: if there is no need to transport the energy carrier long distances, then hydrogen may do fine. As I understand it, in Germany, they're planning on keeping and using it more or less in place. This wouldn't be the case if transporting large distances: the benefits of the existing ammonia infrastructure - pipelines, storage, safety, training - may outweigh the cost of building a new hydrogen infrastructure from scratch.

Addressing Martin Beckett's points, re: toxicity, ease of handling, and emissions ...

Toxicity: certainly, yes it is toxic, but rather than dismiss ammonia for this fact alone, it is worth expanding the view of our risk analysis. For instance, it's easy to argue that the death rate from our current fuel use poses far greater and more unacceptable toxicity (tailpipe emissions cause approximately 21,000 early deaths and 3,000 lung cancer deaths every year in the US alone, according to the Clean Air Task Force, from 2005 (www.catf.us/resources/publications/view/83). Exploring alternatives with an open mind is worthwhile. See Quest Analytics' Risk Analysis (PDF) from 2009 (www.energy.iastate.edu/Renewable/ammonia/downloads/NH3_RiskAnalysis_final.pdf), which compares the risks of NH3, LNG and gasoline in automobiles, and concludes that "the hazards and risks associated with the truck transport, storage, and dispensing of refrigerated anhydrous ammonia are similar to those of gasoline and LPG." Don't take my word for it - read the Risk Analysis.

Handling: ammonia is easier to handle than hydrogen, because it doesn't require high pressure (saving significant money and reducing risk of explosion) and also because of the hydrogen embrittlement problem: hydrogen is such a small atom it leaches into steel and causes it to fracture, requiring a more expensive storage / pipeline (en.wikipedia.org/wiki/Hydrogen_embrittlement). Farming and refrigeration industries have been handling ammonia safely for decades. Perhaps we need to define "safely." I don't have access to FACT's full database, but they record global industrial accidents. Two quick searches showed that in the last four years there has been one fatal accident involving ammonia, but three fatal accidents involving hydrogen. Search the FACT database here: www.factsonline.nl/browse-chemical-accidents-in-database. If anyone has access to more precise data, I'd be very grateful to learn more. Comparing ammonia to any other energy carrier should be done rationally, without a "scare factor". Another advantage to ammonia: it stinks. This makes it unfavorable at a simple level but actually offers a crucial benefit: the early warning signal. If you have a hydrogen leak, you won't know until it's too late (and you can't add a smell to the hydrogen, or it won't function in fuel cells). If you have an ammonia leak, you'll know.

NOx emissions: true if you're using it carelessly and inefficiently, but not true if you have a balanced input (correct proportions of oxygen / ammonia to produce a clean, stochiometric reaction), and catalytic converter to remove emmissions. See the Hydrogen Engine Center (www.hydrogenenginecenter.com/aspx/news/news.aspx) for detailed examples of successfully using ammonia for internal combustion engine and genset power. Ammonia is also an important ingredient in many systems that clean tailpipe emissions - for Diesel Exhaust Fluid, see BlueSky (www.blueskydefna.com) - so any proper ammonia fuel system is designed to clean emissions using the onboard fuel.

John Rennie: there are green ammonia projects out there, well beyond the labs, using renewable electrochemical ammonia synthesis, not just Haber-Bosch, in much the same way as the German project is producing hydrogen. This eliminates the natural gas feedstock and can reduce electricity consumption (because it mitigates the high temperatures and pressures necessary for the H-B process) despite relying upon electrolysis to provide the hydrogen - efficiency advances are being made all the time. For a few up-and-running examples, see:

Freedom Fertilizer: freedomfertilizer.com/Nitrefinery.html

GreenNH3: www.greennh3.com/

Wind To Green: www.conocophillips.com/EN/tech/energyprize/Pages/IngramSwearengen.aspx

University of Minnesota (they built its ammonia plant, but I can't find a more up-to-date link than this one: www.license.umn.edu/Products/Ammonia-Production-without-Molecular-Hydrogen-for-use-in-Fertilizer-Production__Z07182.aspx

Let me know if I can provide more details. Best, TB.

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@trverbrown, I agree that industrial pretty much anything can be handled safely if you are careful. I just didn't see Ammonia filling stations as terribly likely ! –  Martin Beckett Apr 23 '12 at 21:35

Ammonia is also toxic, tricky to handle and burning it is going to generate a whole bunch of the same nitrous-oxides you get from fossil fuels.

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Actually, Ammonia IS a better energy storage option than hydrogen. there are a ton of studies and a few demonstration projects that have already shown this - www.nh3fuelassociation.org

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thanks MattZ. Care to elaborate or give us a summary? –  lurscher Apr 10 '12 at 17:33
Is this spam or a troll? www.ammoniafuelnetwork.org has no connection I can see with a serious discussion of energy storage. The home page has all sorts of rubbish about melatonin. –  John Rennie Apr 10 '12 at 17:46

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