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Power-to-Gas Enables Massive Energy Storage

PtG

A power-to-gas facility in Rozenburg, The Netherlands. Photo credit: Jared Anderson/Breaking Energy

Power-to-Gas (PtG) enables the natural gas pipeline network to be used for energy storage, resolving many of the integration issues that plague intermittent renewable energy sources such as wind and solar.

It is well known that finding a solution for scalable energy storage is critical in the pursuit of achieving a renewable energy future. While batteries, pumped-hydro, flywheels and other technologies have their merits, none are able to offer seasonal deep storage at the terawatt scale. Power-to-Gas is an elegant innovation that simply takes excess renewable electricity to create renewable hydrogen and methane for injection into natural gas pipelines or use in transportation. Existing gas pipelines can store hundreds of terawatt hours of carbon neutral methane for indefinite periods of time.

power to gas1

Germany has been pursuing the most aggressive renewable energy targets in the world under their Energiewende program. The Germans have been experiencing challenges in integrating large proportions of wind and solar power into the electric grid because peak power production periods do not correlate with peak demand, so there are sunny afternoons when solar PV is outproducing demand, and likewise windy nights when power production must either be curtailed or exported to neighboring countries at low prices. Adding to the technical challenge is the fact that wind and solar production can spike and drop off very quickly, with little warning, creating inefficiencies as grid managers scramble to match supply with demand.

Many technology pathways are being pursued towards the goal of broad-based energy storage to help meet the challenge of integrating renewables into the power grid. Batteries and flywheels are excellent for rapid discharge and frequency management but are not suitable for long-term storage. Pumped Hydro and Compress Air Energy Storage (CAES) offer longer-term storage but are fundamentally limited by the requirement of favorable geographies. Chemical conversion of electricity to gas allows the existing natural gas pipeline infrastructure to be leveraged for massive-volume, long-term, distributed storage that is cost competitive with other storage technologies. Additionally, the synthetic methane of hydrogen produced via PtG can be utilized as carbon-neutral transportation fuels or elsewhere in industry.

Germany has embraced PtG as a critical component in the Energiewende program. PtG enables German utility operators to manage the gas and power networks in tandem, shifting gas to power and power back to gas as needed throughout the day to match supply and demand. There are 30 PtG plants at various levels of commercial production throughout Germany and neighboring countries.

power to gas2

The suite of technologies being deployed to create PtG and technology innovation is rapid in the space. PtG begins with basic electrolysis, using electricity to split water, H2O, into its components hydrogen and oxygen. The oxygen has commercial value and is sold or utilized and the hydrogen can be deployed in three different ways.

Hydrogen can be injected directly into natural gas pipelines and analysis is ongoing to determine what proportions of hydrogen can be supported. Originally it was thought that no more than 5% hydrogen could be used, but depending on the pipeline engineering and downstream uses, ratios up to 12% have been achieved. Older cast iron and steel pipes don’t contain hydrogen well because they are embrittled by the hydrogen which can also leak through seams because it is much smaller than a methane molecule. Modern plastic pipes contain the hydrogen much more effectively and can take higher ratios, but users must be consulted to ensure their operations are not impacted by higher hydrogen ratios. This is an ongoing area of investigation and pipeline standards for direct hydrogen injection have not been established in Germany.

The second method for hydrogen use is methanation, reacting the hydrogen with carbon dioxide to create synthetic methane, or renewable natural gas. Natural gas is primarily methane, CH4, and synthetic methane is identical to fossil methane and can be blended or substituted with no limitations. The chemical process is known as the Sabatier reaction and is the inverse of methane stream reforming commonly used to produce industrial hydrogen from natural gas.

Methanation of CO2 is one of the many ways to utilize captured carbon dioxide for beneficial purposes and is not limited to use with excess renewable electricity. Any energy source could be used including nuclear power. It is entirely feasible that a dedicated nuclear power plant could be set up to do reverse combustion and convert CO2 and H2O into synthetic methane or synthetic liquid fuels that are ultra-pure and carbon neutral, but that is a discussion for a separate article.

The third method for utilizing methane and hydrogen generated via PtG would be use in transportation instead of pipeline injection. Compressed hydrogen, CNG, or LNG could be manufactured on site for direct use in vehicles as carbon-neutral clean fuels.

Two of the leading vendors of P2G solutions are Hydrogenics and ETOGAS. Hydrogenics has over 60 years’ experience manufacturing alkaline electrolyzers and is actively involved in numerous PtG projects in a number of countries. The technical challenge in using older generations of alkaline electrolysis has been the slow ramp up rate from a cold start which limits the flexibility and efficiency for grid integration. Newer generations of hardware have been designed that reduce cold start times from minutes to seconds and Hydrogenics is actively pursuing the market for grid frequency regulation that requires second-by-second reaction response times.

In 2013 ETOGAS inaugurated the world’s largest commercial PtG methanation plant in Werlte, Germany which was built in partnership with Audi and Siemens to produce synthetic natural gas. Audi markets the gas as e-gas and it is distributed via pipeline to CNG filling stations where it is sold as carbon neutral vehicular fuel.

The Werlte plant was constructed next to a biogas digester facility that provides the CO2 for methanation. Since methanation is an exothermic process, producing significant heat (approximately 300° C steam), the heat at the Wertle plant is sent back to the digester to facilitate the digestion process. The thermal energy from the methanation is valuable for industrial processes and creates many opportunities for systems integration with other processes. The Wertle plant has an electrical capacity of 6 MW and consumes 2,800 metric tons of CO2 to produce 1,000 metric tons of renewable natural gas per year. Though the Wertle plant is the largest commercial PtG plant in operation globally, it is still considered a demonstration plant.

There are a number of emerging PtG technologies coming along including Proton Exchange Membrane (PEM) electrolysis and biological methanation. Biological methanation uses bacteria to react the CO2 and hydrogen into methane instead of traditional catalytic methods, but these processes are still pre-commercial. PEM electrolysis is considered very promising, though not as mature as alkaline electrolysis. PEM is essentially a hydrogen fuel cell in reverse and consumes electricity to produce hydrogen rather than consume hydrogen to produce electricity. The advantage of PEM electrolysis is very rapid response times and expected cost reductions that couple with the development of hydrogen fuel cells for vehicles.

System efficiencies and costs for PtG vary widely on a case-by-case basis and are closely tied to overall systems integration, particularly in the case of CO2 methanation. Under the best circumstances the life-cycle efficiencies are over 70%, but there are many methods for capturing CO2, many methods for utilizing industrial heat, and many methods for consuming methane, all of which impact full systems efficiency. And while synthetic natural gas is more expensive than fossil natural gas in the American market, SNG from PtG is entirely carbon neutral, which means that it can carry a price premium and earn credits under potential carbon emissions regimes. More importantly though, PtG offers the ability to decouple renewable electricity production from electricity demand and open up alternative industrial and transportation markets for renewable energy.

Despite the interest in Europe, there has been very little discussion of PtG in North America. American environmentalists seem to be so busy fighting hydrofracking and natural gas infrastructure that they are overlooking the incredible promise of renewable natural gas and PtG. There is one project going forward in Ontario, Canada, a 2.5 MW grid storage project by Hydrogenics. News of this project got the attention of the California power authorities (Cal ISO) who just recently signed a contract with NREL (National Renewable Energy Lab) to model the Western States Grid to identify PtG opportunities. California has some of the most aggressive renewable energy targets after Germany, and California authorities have come to recognize the potential for using PtG to help integrate renewables into the grid.

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Content Discussion

Math Geurts's picture
Math Geurts on December 6, 2014

Power-to-gas is an excellent solution as long as costs don’t matter.

Ed Dodge's picture
Ed Dodge on December 6, 2014

The way to bring costs down is to build it out.

Bob Meinetz's picture
Bob Meinetz on December 6, 2014

Ed, 70% efficiency for PtG sounded wildly optimistic, and Wikipedia lists round trip – including regeneration of electricity – at 49-64%. So while saying the tech enables “massive energy storage” may be technically correct, in the case of renewables we’re taking a meager input and cutting it in half just to overcome variability. Not much left over.

It’s hard to blame them, but this appears to be a fossil industry attempt to astroturf its product by injecting a little reconstituted renewable energy into the mix.

Ed Dodge's picture
Ed Dodge on December 6, 2014

Bob, who says this tech is limited to renewables? Nuclear power would work just as well (or better). We could build nukes whose entire function is to produce RNG instead of electrons. 

Secondly, there is a lot of potential systems integration around water treatment. The H2O inputs can be dirty water that require some kind of treatment otherwise. The combustion of natural gas produces clean water that returns to the hydrological cycle.

Third, we are not limited to old school alkaline electrolysis. There is a lot of cutting edge work going around PEM electrolysis, CO2 electrolysis and CO2 methanation.

Finally, our existing power production models are hardly models of efficiency. I have been writing elsewhere on improved power prodcution using CO2 turbine cycles to replace old school steam cycles. Plus how much efficiency do we lose every day by curtailing power production in order to match demand? By integrating PtG, there is no need to curtail power at all, just dump it back into the gas grid, of course there are always losses in every conversion step, but that needs to be balanced against other inefficient alternatives.

Efficiency needs to be judged within the context of overall system integration. There is an entire alternative model to be pursued around the recycling of CO2 and production of renewable natural gas. Methane molecules are every bit as renewable and desirable as electrons.

Math Geurts's picture
Math Geurts on December 6, 2014

Let’s wait untill the Germans have payed the bill for solving the problem that they create by adorating solar energy in a country far from the equator..

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

Power-to-gas with methane synthesis from captured CO2 sounds like a good idea; as end user of energy, we can continue business as usual, and our sustainability problems get fixed on the supply side (like sustainable electricity).  The only problem is that in the future low-carbon society that nearly all environmentalists agree that we must create, the amount of CO2 that can be captured is very small (about enough for aviation, from concrete making).

It turns out that there is another solution.  Making ammonia in the power-to-gas process is just as efficient as making methane with captured CO2 (and avoids the energy and economic cost of CO2 capture).  The only other required feedstock is nitrogen, which unlike CO2, can be easily and cheaply captured from the air (nitrogen is 80% of the air, CO2 is 0.0004%).

Ammonia is in many ways a better fuel than methane.  Because ammonia is a liquid under mild conditions, it can get around infrastructure chicken-and-egg problems by delivery to early adopters via truck or rail, whereas methane must travel via pipeline.

Ammonia beats methane as a transportation fuel.  Unlike liquid natural gas (LNG), it is not cryogenic, and can be stored indefinitely with no boil-off.  It has 25% higher energy density than compress natural gas (CNG), and requires 20 times lower pressure for storage (saving tank weight and cost, and allowing more space efficient non-cylindrical tanks).

Ammonia also beats other synthetic fuels for internal combustion engines.  It has triple the energy density of 5,000 psi hydrogen.  It burns cleaner than hydrogen (ammonia can be injected into the catalytic converter to remove NOx which forms from combustion of any fuel, especially hydrogen).   Like diesel, ammonia can be burned at high compression ratios for 20% higher efficiency than gasoline; it burns cleaner than gasoline, and much cleaner than diesel (which produces harmful soot particulates).

When it comes to seasonal energy storage (fuel for winter heating, summer cooling, or rescheduling over-production from spring wind & small hydro energy), ammonia is much more versatile than methane.  Methane storage requires special geology for underground storage (e.g. depleted gas fields or salt-formations).  Ammonia can be stored anywhere in warehouse-sized unpressurized refrigerated tanks, or residential sized lightly-pressurized unrefrigerated propane-like tanks.

The switch to ammonia fuel will require slightly different infrastructure than we now have. But that new infrastructure will be indefinitely sustainable, and won’t be dependent on the fossil fuel industry for operation, nor will it favor fossil fuel as the easiest primary energy source.

See NH3 Fuel Association

Hops Gegangen's picture
Hops Gegangen on December 6, 2014

 

And nukes dedicated to RNG could be placed far away from population centers that don’t want them in their back yards. We need a way to tap nuclear power.

 

Bob Meinetz's picture
Bob Meinetz on December 6, 2014

Ed, I agree there could be a lot of environmental value in creating RNG to replace fossil NG in our existing infrastructure. The catch is whether we can guarantee that the energy inputs are 100% carbon-free nuclear or renewables. If they’re not, we could very easily be worse off than before. Moreover, there would have to be a very good reason to justify not distributing that same nuclear electricity directly, incurring transmission losses of 10% vs. 45% for PtG. For powering “legacy” gas furnaces, water heaters, etc. it may well be environmentally advantageous.

If NG is being supplemented with RNG it will be extremely difficult to verify the carbon footprint of the fuel that comes out the end of the pipe (CCS suffers from a similar vulnerability). If it’s cheaper to simply pump fossil-sourced natural gas with a bit of RNG mixed in, there’s a high probability that’s what will happen. The world’s biggest business has demonstrated they have very little interest in reducing atmospheric carbon, but a lot in creating the appearance they are. For example, Chevron and Shell have spent millions hyping hydrogen because if it ever does become widely adopted it will give America’s 15,000 service stations a “clean” fuel to sell – despite the fact that well-to-wheels it results in more carbon emissions than gasoline.

Finally, methane molecules are not every bit as renewable and desirable as electrons. Some of them escape, and trap 25 times as much radiative energy as the CO2 molecules from which they were made.

Jeffrey Miller's picture
Jeffrey Miller on December 6, 2014

Ed,

This is interesting. I have a couple of questions. 

1. Methane is itself a powerful greenhouse gas. If we were to start making lots of methane using PtG, some of it would inevitably escape into the atmosphere from leaking pipes and so forth. How big a problem would this be? Has anyone tried to estimate this?

2. If syngas is made using CO2 captured from burning biomass, I can see how it would be carbon neutral. But the amount of biomass available for energy is pretty limited given the very low power density from plants (David Mackay estimates .5 to 1 watts per m^2 in Europe) and given that we need to reserve most farmland for food. How much does this constrain how scalable biomass derived (ie CO2 captured from burning biomass) synfuel can become? Do you have any Mackay style back of the envelope estimates for this?

3. If syngas is made from CO2 captured from burning a fossil fuel like coal or natural gas, then it cannot (it seems to me) be considered carbon neutral. It is true that by making the synfuel you are in a sense using the carbon twice and so getting more energy per unit of CO2 emission, but when you burn the synfuel, the carbon that you captured from burning a fossil fuel to make the synfuel is going into the atmosphere unless you also capture it. Do you agree?

4. I see the see the argument for using excess renewable capacity to make a fuel like syngas. But in your nuclear example, where you imagine a nuclear plant producing syngas, what would be the rationale for doing this? Is there anything that the syngas could do which could not be done more efficiently just using the electricity directly? Or, put differently, are there compelling reasons for making lots of syngas other than the desire to store energy to smooth out the production fluctuations of variable renewables?

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

Ammonia production facilities can also be located remote from the end user (including on wind farms).  Unlike methane, ammonia can be used in developing countries which lack pipeline infrastructure too; it can be delivered by truck to villages and sold in refillable tanks like propane.  

A simple device called a cracker uses a hot catalyst to convert ammonia (NH3) to a clean burning and non-toxic mixture of hydrogen and nitrogen which is suitable for indoor cooking, home heating, and certain fuel cells.

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

 in the case of renewables we’re taking a meager input and cutting it in half just to overcome variability.”

It’s often said that end-user demand variations also require that the grid handle variations.  The difference is that power-to-fuel starts getting interesting as a response to curtailment when solar and wind hit about 40% penetration, but not until nuclear hits 80% penetration.  The result of this difference is that in a sustainable future, if all curtailed electrcity was used to make fuel, with nuclear we’d only end up with enough fuel to replace diesel (e.g. heavy duty trucks, buses, etc); with renewables, a lot more synfuel shows up which makes the whole system less energy efficient and less affordable,  thus less probable.

Bob Meinetz's picture
Bob Meinetz on December 6, 2014

Nathan, you lost me on the last line:

a lot more synfuel shows up which makes the whole system less energy efficient and less affordable,  thus less probable.

It sounds like you’d be taking curtailed (wasted) energy and making something of value (synfuels) out of it, no?

Keith Pickering's picture
Keith Pickering on December 6, 2014

Ed,

Sorry to see that you (and everyone else in the P2G world) has missed a couple of big ideas. First, the US Navy recently created small amounts of aviation gasoline from seawater and electricity. A liter of seawater contains 120 times the amount of CO2 than a liter of air, mostly in ionic forms that can be easily separated. That plus H2 from electrolysis, and you combine with the Fischer-Tropsch process to create hydrocarbons of any desired length. The Navy’s research has been driven by a paper some years ago that proposed making jet fuel at sea via a nuclear-powered fuel factory ship. That study put the cost of the manufactured fuel at $6/gallon, but half of that was for the ship; if the reactor were beached, presumably it could be made for $3/gallon.

Another path-not-mentioned is putting biology to work, in a hybrid biofuel/synfuel system. It turns out that some forms of methanogenic archea (these are microbes more primitive than bacteria) will produce a lot of methane if you feed them electricity. Lab results have put the one-way efficiency of the system at 80%, and that’s just a first-cut, before-optimization number. 

And finally, the round-trip efficiency number in this case is deceptive, because you should never, ever, burn P2G methane (or hydrogen) to make electricity. The only thing you should ever be doing with that is transportation fuel, and winter heating.

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

Running power-to-fuel plants at low capacity factor (i.e. using curtailed electricity) always has higher capital cost (per unit fuel) than than running them baseload.  This means that they will have to buy the curtailed power at a discount (many studies assume the cost of curtailed power is nearly zero), which must be funded by increasing the cost of electricity to other users.

Renewable-rich systems must be greatly overbuilt, with much more curtailed electricity which must be given away.  Nuclear has the added advantage that it can supply urban areas with very low cost energy for district heating (space heating and domestic hot water, via piped hot-water networks), for winter heating at a time that solar is nearly worthless. 

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

“…electricity will be first to go fossil free well before transport heating aviation or industry

The way I look at it, fossil fuel importing developing countries will be first to go fossil free.  Since oil is the most expensive fuel to import, it will be a high priority to replace with a domestic replacement.  Electricity from Chinese and Indian nuclear plants is already cheap enough for synfuel to compete with imported oil (at least until the recent, likely temporary price drop).  Imported liquified natural gas will likely never gain a foot hold in poor countries.  Only when countries become wealthy enough to value clean air above cheap energy will they consider replacing coal.

Power-to-fuel and ammonia fuel can and have been demonstrated in prototypes and pilot projects.  Efficiency improvements due to widespread public acceptance of  very small computer driven taxis or carpooling in computer driven taxis can only be demonstrated by doing it.  I’ll believe it when I see it (not just a few cars, but >50% market share, which is what it would take to make a real difference for personal cars;  for heavy trucks, power-to-fuel is still the best answer).

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

I suspect that CO2 extraction from seawater is only practical (and environmentally friendly) for mobile systems like ships.  The natural mixing just isn’t fast enough, especially at the GWatt scale.

In a college energy systems class, we studied OTEC (ocean thermal energy conversion), and those systems must be mobile also, otherwise they find themselves surrounded by a region of depleted water (even at the 100 MW scale, IIRC).

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

Right, syn-fuel from power-to-fuel will never be cost effective for electricity generation. 

However, note that the real-world retail value of electricty and gasoline are usually about the same in the US (10 ¢/kWh is the energy equivalent of $3.40 per gallon of gasoline equivalent).

Note also, (as a result of the Carnot equation from thermodynamics), high temperature nuclear plants couple to thermo-chemical hydrogen synthesis can make hydrogen at the same efficiency as they can make electricity (e.g. about 50%).  Converting hydrogen to ammonia will loose about 10-20% of the energy (as would compressing the hydrogen thru a pipeline and then into tanks), but then distributing electricity costs more than distributing liquid fuel. 

 

Ed Dodge's picture
Ed Dodge on December 6, 2014

Keith,

I am well aware of the Navy’s work, I just haven’t got around to writing an article, its on my list. At one time I was in touch with the primary researcher.

I have also written about some biotech methods for CO2-to-synfuels. It all seems promising.

I try to keep my articles at around 1000 words give or take, so I try to make each topic concise and can’t go down each tangent, even if they are relevant.

Ed Dodge's picture
Ed Dodge on December 6, 2014

The whole argument that methane leakage is bad tells me that we should put some investment in tightening up our pipeline infrastructure, which has the benefit of keeping more molecules available to be used. I don’t accept the argument, at all, that methane leakage means that we should not use methane.

If CO2 being used is captured CO2, what difference does it make if it comes from coal or biomass? The only thing that matters is the net going into the atmosphere. We need robust carbon capture and utilization regardless of the original carbon source.

Make power or making synfuels from nuclear power are not mutually exclusive options. We can have both. Electricity is great but we can not run all of industrial society off electrical power. We require hydrocarbons for the forseeable future to fuel high horsepower vehicles and for industrial heat.

Jeffrey Miller's picture
Jeffrey Miller on December 6, 2014

“The whole argument that methane leakage is bad tells me that we should put some investment in tightening up our pipeline infrastructure”

I was just asking a question, not making an argument. There is no question that methane leakage is bad. What’s not clear to me is how big an issue it would be if synfuel production were to become widespread.

“If CO2 being used is captured CO2, what difference does it make if it comes from coal or biomass?”

If the synfuel is going to burned to heat buildings, run cars, or for industrial processes (where it cannot be captured), it matters a great deal. If the original source of the CO2 is captured fossil fuel emissions, the net result of making and burning the synfuel will be be net carbon emissions into the atmosphere. 

Ed Dodge's picture
Ed Dodge on December 6, 2014

You may not have made the argument that we should not use methane, but it is one of the primary arguments that is made against using natural gas.

We are not going to stop using hydrocarbons, industrial society absolutely requires them. But we can lower net carbon emissions by a combination of electrification of everything possible, maximizing efficiency across the board, optimize around methane where we need to combust, lowering the fossil carbon content of methane by increasing the ratio of renewable methane. And we need a robust CO2 capture and pipeline infrastrcuture to keep excessive quantities of CO2 going in the atmosphere. We also need comprehensive land management practices to sequester carbon in the soil.

Ed Dodge's picture
Ed Dodge on December 6, 2014

Nathan, you do great analysis, you just need to jump from the NH3 camp to the CH4 camp. We have an enormous and functioning natural gas infrastrcuture already in place, you cannot say the same for ammonia.

Ed Dodge's picture
Ed Dodge on December 6, 2014

One big problem with ammonia compared to methane is that ammonia is toxic, irritating and corrosive. It is very nasty if exposed to you. Methane is completely non toxic to the body, in fact our bodies produce it naturally.

LNG has an excellent safety record and is in wide use today as a bulk volume fuel for container ships, trucks and heavy equipment, soon it will power railroad locomotives. Aside from LNG being cold enough to burn it is not a hazard to your body. I love watching LNG safety videos where they pour it out at their feet, breathe in the fumes or pour it in a glass of water and drink the water. LNG is way safer than any of the other hydrocarbon fuels we routinely deal with every day. Never a major spill at sea despite 40 year commercial track record.

Nathan Wilson's picture
Nathan Wilson on December 6, 2014

Wait, I never said ammonia from nuclear and renewable energy was cost competitive in the US today;  I admit that it isn’t (neither is synthetic methane).

But I think that if fully developed (with US technology), it could be economical in China, India, and other developing nations, whose future energy demand will dwarf ours anyway.  They can’t out-bid rich nations for access to the world oil markets, so they’ll switch to domestic synfuel.  If we develop the technology for clean syn-fuel, they’ll use it, otherwise they’ll stick with proven coal-to-liquids technology, which China already has.

However, today’s US natural gas prices are not sustainable.  They are being suppressed by a temporary demand imbalance, as it is a co-product of oil extraction (and “natural gas liquids” which are propane and butane), which produces most of the profits.  Today’s oil price is even too low for energy companies to make money in the US.  That means they will invest less in drilling new wells, and future supply will drop and prices will stabilize.  At the same time, the market for US gas will expand (transportation, chemicals, and power plants under the future EPA CO2 rules), which will re-balance oil and gas prices.  

If US consumers accept CNG vehicles in large numbers, I expect industrial natual gas prices to hit $10/mmbtu, and still consumers would pay only half the cost of gasoline at the pump.  This will mean the US can resume building nuclear plants for electricity (rather than burning more natural gas), we’ll have leverage to convince China to reduce CO2 emissions, and they’ll do it by making syn-fuel from nuclear power.

Nathan Wilson's picture
Nathan Wilson on December 7, 2014

Thanks, but I don’t see how syn-methane can be helpful in the US.  The oil & gas companies are far too powerful here for me to seriously contemplate any future without them.  It would hurt their future for them to endorse nuclear power by buying-in.  So the only low carbon transportation future for us I can see is one built around CC&S.  The only transportation fuel that works with CC&S is ammonia.

If we subsidize/mandate our way to 10% ammonia penetration in heavy-duty trucks, and leave personal cars using gasoline and batteries, the oil companies can brag to the public about being green, with an ammonia blend that is 20% sustainable (the rest fossil derived), and not feel that their future is threatened (we could pretend that ammonia is too dangerous for consumers, although the overall safety is the actually same as that of gasoline, the tradeoff of toxicity vs. flammability is about equal).

At the same time, that would refine the technology for other countries to use to eliminate imported oil altogether.

On the other hand, developing syn-methane would only encourage other countries to develop methane distribution infrastructure (which costs even more than ammonia infrastructure: ammonia can travel by truck or rail, plus a given pipeline can carry 1.5 times more energy as liquid ammonia compared to gaseous methane).  With that plan, they’ll also need a coal industry to provide CO2.  Once they have methane and coal infrastructure and industry, they too will have fossil fuel lock-in.  And poor countries will certainly not use CC&S.

Roger Arnold's picture
Roger Arnold on December 6, 2014

Keith, I don’t want to throw too much cold water on your enthusiasm for the Navy’s approach, because I actually support it — after a fashion. I hope it succeeds. But the challenges shouldn’t be understated. It’s going to be extremely capital intensive, and that $6.00 a gallon equivalent, in my opinion, is wildly optimistic — even when you have the advantage of virtually free power from HEU-fueled military reactors.

A liter of water may contain 120 times more CO2 than a liter of air, but its mass is 1000 times greater. Is it really easier to extract CO2 from 8 tons of water than from one ton of air? It’s not obvious — not to me anyway.

Also, the removal involves splitting seawater into acid and base fractions. That’s most efficiently done using bipolar membrane electrodialysis. It involves running an electical current through the seawater. Unfortunately, seawater is not a very good conductor. Its conductivity is only about 5 S/m (Siemens or inverse ohms per meter). That means that one volt across opposite faces of a one meter cube of seawater will drive a current of 5 amps. That’s 0.5 ma / cm^2, about 1000 times less than the current density at which commercial electrolysis or fuel cells operate. To extract CO2 from seawater at any halfway reasonable efficiency, the cells will have to be operated at really low current densities. They will have to be huge; hence the very high capital cost. 

Maybe there’s some better way to do the extraction that I don’t know about, or one will be developed. But I’ve read the NRL papers, and the the approaches they’re playing with all based on electrochemistry. They all suffer from similar current density limitations. So I’m not holding my breath.

Bob Meinetz's picture
Bob Meinetz on December 7, 2014

Roger, what evidence do you have that self-drive cars, hyped since the 1920s, are on the verge of mass adoption?

Our houserobot can’t even drive a regular car. She ran over our e-cat, then drove through the garage wall. Like General Motors’ 1956 Motorama Firebird II she has an electronic brain – but that didn’t seem to help.

 

Roger Arnold's picture
Roger Arnold on December 7, 2014

RR, you’re a pretty smart guy. I know from many other comments you’ve posted that you have a decent grasp of science. So why do you insist on posting such asinine comments?

Nobody is asserting that synthetic methane can be produced at scale and at prices that will undercut the stuff that we get from wells. The issue is large-scale energy storage. What do we do with the surplus power that’s available when the wind is strong or the sun shining brightly? Where do we get power to make up for the missing output when the wind and sun aren’t cooperating? You can argue that PtG isn’t the most efficient solution — that we only get back about 40% of the surplus power that we used to make the synthetic gas. That’s accurate, and justified if you can suggest better alternatives. But getting back 40% of what was surplus for use when it’s needed is certainly better than just spilling it and then living with rolling blackouts when we don’t have enough. There’s nothing “bonkers” about it.

Perhaps you’d like to argue that putting ourselves in a  position where we need to worry about large scale energy storage is bonkers, when we could be deploying clean load-following nuclear capacity. That’s a different kettle of fish, and I’d probably agree with you about that. But that’s not what you said. You just wildly attacked the whole concept of fuel synthesis. That behavior, to me, is bonkers.

Roger Arnold's picture
Roger Arnold on December 7, 2014

Meh. Ocean currents in most places are sufficient to keep a large stationary OTEC plant supplied with warm and cold water. I’m pretty sure that’s not a real problem. You do have to pay attention to the placement and depth of intake and outlet ports. However the real problem remains capital cost. The thermal efficiency of “conventional” OTEC (to the extent that there is such a thing) is so low that the volume of flow through the heat exchangers (boilers, superheaters, and condensers) is huge.

There may be ways to address that problem and make OTEC competetive. But that’s a matter for a different article.

Engineer- Poet's picture
Engineer- Poet on December 7, 2014

getting back 40% of what was surplus for use when it’s needed is certainly better than just spilling it and then living with rolling blackouts when we don’t have enough. There’s nothing “bonkers” about it.

But can you afford to store it?  At 40%, your €0.10/kWh wind energy going in costs €0.25/kWh on the way out, plus amortization, interest cost on the purchased power and O&M.  Olkiluoto will cost less than half that.

The problem is those who insist that humanity has to survive with the energy from the wind and sun.  These were inadequate two centuries ago, and pathetically so with today’s vastly larger population.  There’s a way to make solar a 24/7 power source, but the same people who want us to “go green” absolutely hate the idea of solar collectors in space.

Perhaps you’d like to argue that putting ourselves in a position where we need to worry about large scale energy storage is bonkers, when we could be deploying clean load-following nuclear capacity.

Agreed.  Nuclear power gets rid of most of the human impact of energy, and eliminates the issue of rolling blackouts as well.  Paradoxically, by providing steam for high-temperature electrolysis (90% efficiency is now available, it seems) it can provide H2 for storable fuel at a highly competitive price… simultaneously eliminating most of the need for storage.  That also gives you your answer to “can’t turn them down”; by diverting steam and electricity on demand, the net electric output can be varied to suit even without changing the reactor output power.

FWIW, if the landfill gas is being mined for CO2, it could be converted to methanol instead of methane.  Both can be stored as liquids at room temperature, and MeOH is arguably a better motor fuel than either methane or gasoline.

Hops Gegangen's picture
Hops Gegangen on December 7, 2014

 

One thing I’ve learned working in the international railroad industrsy is that there are countries in which one cannot install modern railroad signalling equipment because people will steal the copper wires to sell for scrap.

Good luck proving electricity, let alone nuclear reactors.

Ed Dodge's picture
Ed Dodge on December 7, 2014

The gas companies are embracing RNG. Much of my data on this subject comes from the natural gas industry. They are not dumb, they recognize that all the methane naturally forming and venting from landfills and sewage treatment can be their product. And RNG is carbon neutral (by legal standards) and so it carries a price premium. There is no pushback from fossil natural gas players against RNG. Clean Energy Fuels, T. Boone Pickens retail LNG company, is marketing ‘Redeem’ which is bio-LNG and it is nearly 20% of the product they move.

And why wouldn’t poor countries use carbon capture? Rich countries need to develop it, but once it works why would use not expand?

Jeffrey Miller's picture
Jeffrey Miller on December 7, 2014

Ed,

You claim that PtG methane (made with low carbon electricity) is carbon neutral at least five times in your article and you make this claim without any qualification about the source of the CO2 used to make the syn-methane:

“Additionally, the synthetic methane of hydrogen produced via PtG can be utilized as carbon-neutral transportation fuels or elsewhere in industry.”

“It is entirely feasible that a dedicated nuclear power plant could be set up to do reverse combustion and convert CO2 and H2O into synthetic methane or synthetic liquid fuels that are ultra-pure and carbon neutral, but that is a discussion for a separate article.”

“Compressed hydrogen, CNG, or LNG could be manufactured on site for direct use in vehicles as carbon-neutral clean fuels.”

“Audi markets the gas as e-gas and it is distributed via pipeline to CNG filling stations where it is sold as carbon neutral vehicular fuel.”

“And while synthetic natural gas is more expensive than fossil natural gas in the American market, SNG from PtG is entirely carbon neutral, which means that it can carry a price premium and earn credits under potential carbon emissions regimes.”

You also note that methanation is a beneficial way to use captured CO2:

“Methanation of CO2 is one of the many ways to utilize captured carbon dioxide for beneficial purposes and is not limited to use with excess renewable electricity.”

You could forgive the reader of your piece from coming away with the impression that syn-methane is in fact carbon neutral. 

But is it true that syn-methane is carbon neutral? Let’s follow the carbon.

Suppose I burn a kilogram of coal to make electricity. In the process I create ~3 kg of CO2. I want my electricity to be carbon neutral, so I capture this CO2 and sell it to you. You take my CO2 and use electricity from your windmill to make syn-methane. You then sell your syn-methane back to me a premium claiming that it is carbon neutral. I burn the syn-methane to heat my house and feel good because I’m carbon neutral. All good, except that at the end of the day, 3 kg of fossil CO2 went into the atmosphere. This is not carbon neutral at all, and you shouldn’t (I think) make it sound like it is. 

What would be carbon neutral? If you sold me your windmill derived hydrogen and I burned that, that would be carbon neutral. Or if you bought the CO2 to make your syngas from a biomass facility (like Audi evidently does at their pilot plant), that would be carbon neutral (but there are constraints on how much CO2 is available from biomass). 

Is this just a technical quibble? No, it’s not. If we are using fossil fuels as the source of the CO2 for the syngas and we make a lot of syngas, then we’re going to be emitting lots of CO2 which the IPCC tells us is not a good idea. 

We can do most of what we want to do directly with electricity from nuclear power. To the extent that we still need some liquid hydrocarbon fuels, syn-fuel using CO2 from biomass may be a good option. I’d prefer to let the market sort that out with a significant carbon fee+div, starting small and going up 10% a year. 

Bob Meinetz's picture
Bob Meinetz on December 7, 2014

Jeffrey, “amen”. Great post. 

On edit: At best we’re improving the energy yield on our original carbon by re-using it for storing renewable energy. The problem, in this energy chain at least, is that it requires fossils at all. Any efficiency losses or renewable production shortfalls will be compensated by burning more NG, and when consumption is more profitable than conservation, that will be the rule more than the exception.

Thomas Garven's picture
Thomas Garven on December 7, 2014

And could some of those reactors please be High Temperature Gas Cooled Reactors [HTGR] with the secondary side using super critical CO2 [sCO2].  We can put about 10 [2000MWt] here in Southern Arizona so we can use the low temperature secondary side heat for desalination using low temperature draw solution salt technology.  

 

Thank you in advance. 

Ed Dodge's picture
Ed Dodge on December 7, 2014

At the end of the day it is about building systems that incentivize carbon capture and utilization, and CO2 methanation is one method to potentially use a lot of CO2, as a form of CO2 recycling.

Going forward, if coal were to be the source of the CO2 for PtG, then it would be up to regulators to determine how “carbon-neutral” it is. The technology does not care, and I don’t believe this issue has ever been addressed by an authoritative body.

I would argue that synfuels generated from captured carbon and PtG should be classified as carbon neutral becuase we want to incentivize the technology. Otherwise we are just back to the same old business case that virgin fossil fuels are cheaper and therefore we should use them and continue to dump the waste. I am working to build the case for waste conversion.

How about if the CO2 has been recycled multiple times? Does it really matter if it came from coal at one point?

We are not going to stop using substantial quantities of hydrocarbons. We can electrify light duty transport and home heating. But heavy duty transport and industrial heat, and likely lots of power gen, will continue to run on hydrocarbons, and biomass does not provide remotely close to the required quantities. That is why we need carbon capture, and which is why we need solutions for doing something useful with the CO2, like recycling it.

 

Mark Heslep's picture
Mark Heslep on December 7, 2014

NatGas at $4/mmbtu = 1.4 USA cents per KWh

You need electricity at 1 cent / KWh”

This means P2G is unlikely to work as a primary, frequently used backup, not that it can never be used.  If a way to can be found to use stored P2G for a couple week long wind outages that occur during the year, then the high price of the gas alone is not prohibitive. For the diurnal, frequent backups go to batteries or other energy limited but affordable means.   However, the problem of affording  a large spinning gas thermal fleet maintained and ready in which to burn that gas remains.

Jeffrey Miller's picture
Jeffrey Miller on December 7, 2014

“At the end of the day it is about building systems that incentivize carbon capture and utilization, and CO2 methanation is one method to potentially use a lot of CO2, as a form of CO2 recycling.”

No. At the end of the day, it’s about not dumping greenhouse gases into the atmosphere. If we end up re-releasing captured fossil fuel CO2 into the atmosphere by making syn-gas that we will then burn, we are not being carbon neutral.

“Going forward, if coal were to be the source of the CO2 for PtG, then it would be up to regulators to determine how “carbon-neutral” it is.” 

No. Regulators don’t determine how carbon neutral anything is. The laws of physics do. That said, I can easily imagine an interested industry lobby convincing regulators to declare PtG carbon neutral (regardless of the source of the CO2) so that the industry can call itself green and also charge more for their product, as you suggest in your comment to Nathan some companies already do (although it sounds like ‘Redeem’ may use carbon from plants and so be genuinely carbon neutral). 

“I, would argue that synfuels generated from captured carbon and PtG should be classified as carbon neutral becuase we want to incentivize the technology.”

You seem to be saying that we should pretend something is carbon neutral when it’s very clearly not (in general) carbon neutral because if we pretend that it is, we will “incentivize the technology” and it that must be good thing. In other words, the end (“incentivizing” PtG, even when it is not carbon neutral) justifies the means (fooling people about it being carbon neutral). I find this line of argument disturbing. If we don’t use language accurately and try to deal with problems like carbon pollution with honest accounting and analysis, it is unlikely that we solve them.

“How about if the CO2 has been recycled multiple times? Does it really matter if it came from coal at one point?”

The end uses you specified for syn-gas –  transportation and industrial heating – don’t lend themselves to carbon capture so there would be no multiple times recycling. The other big use you mention – power to gas and back to power – is inefficient and it would be even less so if in the last stage you had to recapture the carbon. If you had a kwh of electricty and you turned it into gas at 70% and then back to electricity at 50% you’d have 35% left over. If you used a third of that electricity to capture the carbon, you’d be left with less than a quarter of the energy you started with. It seems like a stretch to me to believe that power->gas->power would be worth the trouble.

 

Mark Heslep's picture
Mark Heslep on December 7, 2014

Suppose I burn a kilogram of coal to make electricity. In the process I create ~3 kg of CO2. I want my electricity to be carbon neutral, so I capture this CO2 and sell it to you. You take my CO2 and use electricity from your windmill to make syn-methane. You then sell your syn-methane back to me a premium claiming that it is carbon neutral.”

The idea behind P2G is a backup for intermittent power sources like solar and wind, which otherwise have no capacity value.  Replace solar or wind (or hydro/nuclear) in the above and then what happens to your argument.

Jeffrey Miller's picture
Jeffrey Miller on December 7, 2014

Bob,

I agree – there could be some gains in energy yield for a fixed amount of carbon. That is not, however, at all the same as ‘carbon-neutral’. I think this kind of thing looks most promising when applied to carbon capture from biomass where the whole thing could really be carbon neutral. 

Roger Arnold's picture
Roger Arnold on December 7, 2014

The comments nesting level has gotten rather deep, making it hard to read new replies. I’m posting this at the top level, but it’s a followup to various comments below on the issue of whether PtG (or P2G, whichever you prefer) is “carbon neutral”.

I agree with Ed, that one must look at the system as a whole. The question to ask is what advances the long term goal of eliminating the transfer of fossil carbon to the atmosphere. I believe that PtG does that.

As to whether it’s “technically” carbon neutral if the CO2 it’s using comes from coal, that depends on how one chooses to frame the analysis. If carbon capture at the coal-fired power plant is taken as “given”, and the question is how to dispose of the captured carbon, then no, PtG is not carbon neutral. It’s allowing fossil carbon that would otherwise be pumped into a deep saline aquifer for permanent sequestration to instead be released into the atmosphere — albeit after doing some useful work and satisfying a portion of the demand for fuel.

If, OTOH, one frames the choice as being between “capture and use for PtG” vs. “no capture”, then PtG is clearly carbon neutral. It has not increased the amount of fossil carbon that ends up getting into the atmosphere.

I think the latter framing is more realistic than the former, because reality is that carbon capture will never be voluntarily implemented in the absence of a market for captured CO2. Incumbent interests have amply demonstrated that they have the power to forestall any effort to define CCS as an inherent cost of using fossil fuels. The only places where carbon capture is being implemented are those where the captured CO2 has economic value for enhanced oil recovery. And that’s a limited market.

Nathan Wilson's picture
Nathan Wilson on December 7, 2014

Yes, as nuclear power-to-fuel is developed, I think the efficiency going from reactor coolant to fuel will eventually approach 45%.

When I said liquid fuels have lower distribution costs than electricity, I’m talking about transportation fuel, which has nearly constant year-round demand, and the end-user provides the last-mile of delivery.  Fuel for heating is valued-added, as the supplier must store it seasonally, which adds to the cost, and it uses pipeline infrastructure which has poor capacity factor, due to seasonal demand.  The poor capacity factor and last-mile of delivery are part of why electricity is expesive to distribute.

Nathan Wilson's picture
Nathan Wilson on December 7, 2014

Ok, what about dumping CO2-depleted water into the ocean?  Is that acceptable environmentally?

Engineer- Poet's picture
Engineer- Poet on December 7, 2014

If, OTOH, one frames the choice as being between “capture and use for PtG” vs. “no capture”, then PtG is clearly carbon neutral. It has not increased the amount of fossil carbon that ends up getting into the atmosphere.

It hasn’t decreased it either.  The fossil carbon involved would still be taken from the ground and put into the atmosphere.  If we’re not actually going to stop the dumping, we’re going to wind up with the same devastating climate change, ocean acidification, etc.  Delaying the schedule by a few years changes little.

If carbon capture will never be voluntarily implemented for its own sake, then we must eliminate carbon entirely.  This means nuclear power, which is why I’m such a staunch advocate.

Nathan Wilson's picture
Nathan Wilson on December 7, 2014

No, computer vision is not adequate for computer driven cars yet.  

Then there is always the issue that human drivers can recognize and fix a wide range of issues (e.g. ice on the windshield, wheels stuck in the mud, pedestrians in the way, …) that computers can’t, hence the initial round of computer cars will likely only be adequate for niche applications, a situation which could persist forever.

Bob Meinetz's picture
Bob Meinetz on December 7, 2014

Roger, regarding

If, OTOH, one frames the choice as being between “capture and use for PtG” vs. “no capture”, then PtG is clearly carbon neutral. It has not increased the amount of fossil carbon that ends up getting into the atmosphere.

This is only the case if the energy which is being stored has been generated completely carbon-free, i.e. nuclear or renewables, because something on the order of 45% of PtG stored energy will be wasted due to efficiency losses. Assuming PtG will be storing energy from the current generation mix on a grid, that will average out to 70% fossil fuels nationwide, so carbon emissions will be 31.5% (.45 x .7) higher than non-stored generation.

If PtG is applied only to the output of a nuclear plant, windfarm, etc. there are no carbon emissions to start with. But assuming the energy we lose through inefficiencies must be replaced by the current grid mix, we’re replacing 70% of the waste with fossil energy – giving our “carbon-free’ windfarm 31.5% of the footprint of fossil fuel generation.

Nathan Wilson's picture
Nathan Wilson on December 7, 2014

why wouldn’t poor countries use carbon capture?

Because it’s cheaper not to.  For building new electric power plants, a nuclear plant is cheaper than coal with carbon capture, nuclear is also cheaper than solar+wind with coal-w/carbon-capture backup.  For building a nuclear syn-fuel plant, making ammonia is cheaper than methane, unless you already have free CO2 available.

Now if they have plentiful fossil gas, then they could save money by using fossil gas for transportation fuel and nuclear (or gas) for electricity.  If they build out the gas-fired power plants first, then decide to add nuclear, it still makes more sense economically (and for energy efficiency) to write-off the gas-to-electricity plants, use the nuclear plants for electricity, and the fossil gas for transportation fuel.

The only scenario I see for syn-methane is for greenwashing a few percent of a fossil fuel industry you have no intention of phasing-out.

Jeffrey Miller's picture
Jeffrey Miller on December 7, 2014

Roger,

One thing that I hope we can all agree on is that honest accounting demands that the company that captures the carbon from the fossil fuel that it burns and the company that makes syn-gas using this carbon cannot both claim to be carbon neutral. That would be like Green Mountain Power telling its customers that it produces renewable electricity while at the same time selling its renewable energy credits to polluters in other states so that they can also claim the credit. Carbon polluters love this kind of shell game and the regulators are often quite happy to go along with it, but this produces rather obvious problems if we are actually interested in reducing carbon emissions rather than just pretending to do so. 

In this context, I suggest that we restrict the acronym CCS to the practice of capturing carbon emissions and sequestering them on geological timescales. This is what people who appeal to CCS as an important carbon reduction strategy mean when they refer to CCS.  

We will need a new acronym to describe the process of capturing carbon emissions from fossil fuels temporarily, using them to make methane, and then re-emitting them when we burn the methane. How about CCTS, for “capture and temporary storage”? 

I don’t deny that CCTS has some advantage over no storage at all in that you get to use the same carbon twice, but we should not pretend that CCS = CCTS. They are very different since in the former case fossil fuel carbon is sequestered and in the latter it is not. I am frankly skeptical that CCTS will do very much to help get our emissions to where they need to be. That is presumably one reason why the gas companies are OK with CCTS. If we are serious about carbon reductions, we have to act against the interests of the fossil fuel companies. There is no way around that. This may be politically impossible, but if so, we should be preparing our kids and grandkids for a drastically different world. 

 

Nathan Wilson's picture
Nathan Wilson on December 7, 2014

I would agree that ammonia is likely more hazardous than LNG (gasoline is also worse than LNG), and ammonia’s toxicity will be a PR problem that must be overcome.  I don’t think there is a legitimate safety problem  at least two major studies have found that ammonia is just as safe as gasoline, which is to say, safe enough (of all the risks encompassed by our transportation system, driver error, not fuel safety is the main issue, the next big one is probably air pollution, which ammonia helps).  Ammonia is also produced and excreted by our bodies (so chronic low doses from worker exposure are harmless), and unlike gasoline is not carsinogenic.

I think LNG’s boil-off problem makes it non-viable for indoor storage (i.e. garage kept cars).  I don’t believe the infrastructure for LNG has a meaningful headstart on ammonia, since we already use huge amounts of ammonia for fertilizer and even have 3000 miles of ammonia pipeline nationwide and 800 retail outlets for ammonia in Iowa alone. see this presentation.

Here is a presentation on ammonia safety, which claims that ammonia is no worse than gasoline (the higher toxicity is offset by the lower fire/explosion hazard), and better than LPG.

Roger Arnold's picture
Roger Arnold on December 7, 2014

Environmentally? More than acceptable, it would be desirable. The depleted water would initially be moderately alkaline. Over time, it would absorb CO2 from the atmosphere, and return to a more normal pH. But in the meantime, it would help to counter ocean acidification. 

In this case, however, you may be right that a mobile facility would be needed. Not so much to keep it supplied with non-depleted water, but to enable the depleted water output to be adequately diluted. I believe the alkalinity in the freshly depleted seawater is high enough to be harmful to some forms of sea life if not diluted with unprocessed seawater. I haven’t done any calculations on that, however, and could be wrong.

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