Why not use electricity directly instead of hydrogen

[HungryBunny]

Hi PhysicsForums,

I'm asking this as part of a small research project of mine in exploring hydrogen as an alternative energy source to fossil fuels.

Based on my limited understanding, hydrogen is a good alternative to fossil fuels (especially in cars) because the only waste product is water. However, the main problem is that obtaining hydrogen presently involves extraction from natural gas (a form of fossil fuel so it kind of defeats the purpose). I was looking at the possibility of obtaining hydrogen from electrolysis, which uses electricity that again comes from fossil fuel power plants. Some sources I've come across suggest that we can carry out the electrolysis of water using renewable energy sources like wind/nuclear/hydro.

Here is my question: since electricity is needed to break water down into H2 and O2, is it not wiser to just use that electricity obtained from wind/nuclear/hydro to directly power an electric car and bypass the electrolysis/hydrogen fuel cell completely? The reasons I can think of are: 1. recharging an electric car takes time while refueling hydrogen is quick, akin to traditional refueling 2. its more difficult to store and transport electricity (needs a battery I presume) than it is for hydrogen gas.

Do note that this is only a hypothetical research writeup for a module of mine (I don't actually have to carry out the research, and the idea need not actually really be feasible. This module focuses more on the process of idea generation and report writing etc), so I'm just assuming theoretically if obtaining hydrogen from electrolysis of water using renewable energy sources is feasible, which sounds great since water is abundant and renewable energy is well, renewable.

Thank you for your time!

 

[DrClaude]

The reasons I can think of are: 1. recharging an electric car takes time while refueling hydrogen is quick, akin to traditional refueling 2. its more difficult to store and transport electricity (needs a battery I presume) than it is for hydrogen gas.

As far as I know, that's basically it. You lose in efficiency by using hydrogen as an intermediary, but the idea would be that it would be as easy to use as gasoline. The main problem is that is way more dangerous than gasoline.

 

[russ_watters]

10 years ago we had a lot more threads on the potential for hydrogen replacing gasoline than we have today. I think the improving viability of hybrids and pure electrics, fracking unlocking vast new sources of oil and a lack of progress in hydrogen technologies explain why.

 

[insightful]

What keeps H₂ alive as a fuel is that 10 pounds can propel a fuel cell car 300 miles.

 

[Bystander]

10 pounds can propel a fuel cell car 300 miles

... of course, "scrubbing" it clean enough to use is far more expensive than it's worth ... or, will ever be worth.

 

[Vanadium 50]

What keeps H₂ alive as a fuel is that 10 pounds can propel a fuel cell car 300 miles.

Why is this a big thing? One kilo of hydrogen has the same energy as a gallon of gas. So one pound of hydrogen is the same as three pounds of gas. That let's your car be maybe 50 pounds lighter. Why is this a big thing?

 

[insightful]

Why is this a big thing?

No "range anxiety."

 

[jack action]

What keeps H₂ alive as a fuel is that 10 pounds can propel a fuel cell car 300 miles.

Why is this a big thing? One kilo of hydrogen has the same energy as a gallon of gas. So one pound of hydrogen is the same as three pounds of gas. That let's your car be maybe 50 pounds lighter. Why is this a big thing?

Yes but compared to the http://cleantechnica.com/2015/03/17/lighter-batteries-may-prove-tipping-point-electric-vehicles/, that is a big thing.

 

[Vanadium 50]

No "range anxiety."

I have a PHEV, and I don't have any range anxiety. Once every two weeks I use the gas engine. I use 92% less fuel than my previous car, and that means that in terms of reducing emissions, I already have 92% of the maximum possible gain. I don't see the need for heroics to get 8% more.

 

[insightful]

I have a PHEV, and I don't have any range anxiety.

I drive a Honda Insight and average 50 mpg...what's your point?

 

[Vanadium 50]

My point is that there are existing technical solutions for range anxiety. It's a solved problem.

 

[gmax137]

Yes but compared to the http://cleantechnica.com/2015/03/17/lighter-batteries-may-prove-tipping-point-electric-vehicles/, that is a big thing.

Hmm, OK, so if I want to carry say, 20 kg of H2, how much does the H2 tank weigh?

 

[jack action]

Hmm, OK, so if I want to carry say, 20 kg of H2, how much does the H2 tank weigh?

Not an expert on hydrogen tanks, but I'm guessing less than 700 kg (1543 lb), a lot less.

But for gas, I know that 70 L of gas weights 50 kgf and you can add about 20 kgf for the tank, fuel pump and other fuel delivery accessories. Still way below the 725 kgf (1600 lb) of a battery pack.

 

[russ_watters]

My point is that there are existing technical solutions for range anxiety. It's a solved problem.

Apparently there are people who don't like the solution. I think for some it is because 92% isn't good enough.

 

[CWatters]

The best way to approach this subject is to realize that what cars need is an energy storage mechanism, be it a gas tank, a hydrogen tank, a battery, a fly wheel or a twisted rubber band. They are all energy storage mechanisms with different energy densities. Both the mass and volumetric energy density matters..

Wikipedia has a good page on energy density that includes info on just about every type of energy storage system, everything from Uranium to a Ham and cheese sandwich...

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

Some of the data includes any "containment" required (such as the tank) but some doesn't.

 

[Gullik]

Do note that this is only a hypothetical research writeup for a module of mine (I don't actually have to carry out the research, and the idea need not actually really be feasible. This module focuses more on the process of idea generation and report writing etc), so I'm just assuming theoretically if obtaining hydrogen from electrolysis of water using renewable energy sources is feasible, which sounds great since water is abundant and renewable energy is well, renewable.

Thank you for your time!

Just to answer this. It's already being done large scale on Iceland.

http://www.sciencedirect.com/science/article/pii/S0360319909001992

(sorry for barely related article, tablet and not on University network)

 

[gmax137]

Not an expert on hydrogen tanks, but I'm guessing less than 700 kg (1543 lb), a lot less.

But for gas, I know that 70 L of gas weights 50 kgf and you can add about 20 kgf for the tank, fuel pump and other fuel delivery accessories. Still way below the 725 kgf (1600 lb) of a battery pack.

Sorry, I'm not trying to be argumentative here, but... That 10 pounds of H2 you say can carry you 300 miles: at atmospheric pressure, it occupies over 1900 ft3. To put it into your car, you need to compress it. If you compressed it to fit in the same space as you current gasoline tank (say, 25 gallons), the tank pressure would be over 8400 psi. For the metric guys, that's 58 MPa or 580 bar... A tank at that pressure will have walls several inches thick and weigh probably over 1500 pounds. Of course, you could use a bigger tank at lower pressure, with thinner walls, so there's probably some optimum size for the tank. But any reasonably sized tank (that fits into your car) is going to be a hefty piece. Liquefying the H2 (like they do with propane) isn't an option, as far as I know.

 

[Greg Manko]

The reason you would use electrical energy to create hydrogen to use in a car comes down to how far you can go on one "fill".
With hydrogen you can go much farther because batteries simply can't - and likely won't - contain anywhere near the energy.
Hydrogen is tricky to work with and store. Because the molecule is so small, you must use very thick tanks with an inner rubber coating, or you lose gas through the sides of the tank! So storage of large amounts is difficult and expensive. Once we perfect the technology, I wouldn't be surprised to see hydrogen fuel cell cars being used.
Right now, fossil fuels are the most affordable and we are set up to handle it, so I can't see it going away anytime soon - it'll just be used more efficiently

 

[jack action]

Sorry, I'm not trying to be argumentative here

Please do, I know nothing about hydrogen and I love to learn.

That 10 pounds of H2 you say can carry you 300 miles: at atmospheric pressure, it occupies over 1900 ft3. To put it into your car, you need to compress it. If you compressed it to fit in the same space as you current gasoline tank (say, 25 gallons), the tank pressure would be over 8400 psi. For the metric guys, that's 58 MPa or 580 bar...

See, I never thought about that and turns you are right. Will go to bed a little bit more knowledgeable tonight.

A tank at that pressure will have walls several inches thick and weigh probably over 1500 pounds. Of course, you could use a bigger tank at lower pressure, with thinner walls, so there's probably some optimum size for the tank. But any reasonably sized tank (that fits into your car) is going to be a hefty piece. Liquefying the H2 (like they do with propane) isn't an option, as far as I know.

After a simple search, apparently they can go well below the 1500 lb mark rather easily. From 45 kg (@145 L) to 215 kg (@55 L) for 3 kg of H₂ (130 mi range) and from 90 kg (@320 L) to 222 kg (@200 L) for 7 kg of H₂ (435 mi range). The source is from 2002 and there seems to be room for improvement.

But any reasonably sized tank (that fits into your car) is going to be a hefty piece.

Yeah, they don't say how much they cost ...

 

[rootone]

As things stand the most easy to use and longest range power supply for a vehicle is still hydrocarbons, directly or indirectly
If there was a way to dump the carbon, even producing useful carbon products as a result that would be wonderful.
So far though, we are still stuck with burning the carbon into CO2 to get energy out, which is a problem.

 

[BobPixel]

Excellent question, it would be great if more people asked it!

Since there is no freely occurring hydrogen here on Earth, it's less of a fuel and more of an energy storage element. The "follow the money" mantra works for this power source: who will profit the most? Is it the same mega-corporations that have given us oil spills, fracking, and a warming climate?

Do we really want more of the same types of consequences from the economics of externalizing the costs of production?

 

[CraigHB]

Hydrogen is a really good fuel having excellent energy density and essentially zero emissions. The problem is storing it. Extremely high pressure is required to make it practical which leads to some technological barriers. For one a delivery system. Then there's the cost and mass of tanks to store it. There's some considerable hazard in handling a flammable gas at high pressure for the general public. Of course when gasoline first came on the scene with the advent of the combustion powered car people had similar concerns and debates over storing gasoline.

Fuel cells are also a very promising technology, but they have their issues too. The stack has to be quite tall to handle the voltages required to power a car. At this point catalysts are expensive so a stack of several hundred cells is cost prohibitive as a consumer product. Also fuel cells can run on a variety of fuels, but any fuel other than hydrogen doesn't provide a solution since there are still environmentally unfriendly emissions.

I think the solution can be found in electricity, but batteries are expensive and don't last indefinitely. In terms of technological development I think batteries are closest to the solution for a pollution free way to store energy for the masses. However, that simply shifts the burden of pollution free energy production to the electrical grid. Though electric cars get the problem half way solved. The rest is left to a clean method of generating electricity.

 

[Vedward]

If hydrogen is used in Otto cycle engines (regular automotive engines), it will burn air. Unfortunately air is mostly nitrogen, so some nitrogen will also burn, creating NOx compounds, a pollutant. It would be best to use it as a fuel for fuel cells, to generate electricity for electric cars, then the exhaust will be only H2O, not any pollutants.

 

[Vedward]

Also, fuel cell costs are decreasing, in the near future they may be able to match Diesel engines to power Railroad Locomotives for capital & operating costs. Watch out for hydrogen power in the future, but automobiles may be a way off for now.

 

[Algr]

And then another runner in the race is road transmission: Store small amounts of power in the car, and once you get on the highway, draw electricity from wires in the road.

 

[mheslep]

Why is this a big thing?

I think the assumption is that hydrocarbon combustion is off the table in some zero emissions transportation future, so that the remaining comparison is the range enabled by some kWh of battery versus that enabled by some kilos of hydrogen.

The latest comprehensive MIT study posits that refueling time, not necessarily range, will hinder wide adoption of battery vehicles. A standard gasoline pump delivers chemical energy at a rate of maybe 10 MW to the vehicle tank, an entire station perhaps 200 MW. An H2 station could deliver at similar power levels. That's not going be replicated in the near decades by the grid, EV chargers and connected batteries.

Pg 270

...One of our specific findings on the use of electricity in transportation is that, without additional technological breakthroughs, pure BEVs are likely to be limited to modest sales volumes. One major reason is the long recharging time for this technology, which better vehicle batteries will not significantly reduce. Drivers are accustomed to refueling gasoline vehicles for more than 400 miles of travel in about five minutes. Gasoline refueling occurs at a rate of chemical energy transfer through the pump outlet of about 10 MW. For the equivalent recharging rate (400 miles of range in five minutes) 2–3 MW of electrical power would be required.40 This power requirement is more than an order of magnitude higher than even the fastest (Level 3) charging stations (~100 kW). Even if the associated battery cooling and durability challenges could be overcome, rapidly switching on 2–3 MW of charging power would place significant demands on the electricity distribution system: equivalent to the average power demand of more than 2,000 homes or 1 million square feet of commercial building space. Therefore, BEVs, in our judgment, are unlikely to replace very many gasoline-fueled cars in the near- to mid-term, due to the combination of challenges from battery capacity, cost, driving range, and the practical constraints on recharging times.

 

[mheslep]

I have a PHEV, and I don't have any range anxiety. Once every two weeks I use the gas engine. I use 92% less fuel than my previous car, and that means that in terms of reducing emissions, I already have 92% of the maximum possible gain. I don't see the need for heroics to get 8% more.

I agree, and my combustion vehicle uses perhaps a third the fuel of my first combustion vehicle.

But US Science Adviser John Holdren insists we're not doing enough to prevent climate catastrophe: "...require global carbon emissions of carbon dioxide ... close to zero by 2100". Furthermore, Obama has repeatedly stated that there is no greater "threat to future generations than climate change". Perhaps they'll round up all the combustion engines, both straight or hybridized, and put them in camps.

 

[mheslep]

... If you compressed it to fit in the same space as you current gasoline tank (say, 25 gallons), the tank pressure would be over 8400 psi. For the metric guys, that's 58 MPa or 580 bar... A tank at that pressure will have walls several inches thick and weigh probably over 1500 pounds.

Just a bit outside. Mirai 70 MPa (10kpsi) tanks for 5kg H2 reportedly have mass 87.5 kg (193 lbs). Three layer tanks: glass fiber surface, carbon fiber middle, plastic layer inner.

 

[Vanadium 50]

Well, if we decide we want to reserve hydrocarbon use for elites to fly their private jets to Davos and decide how much the little people need to sacrifice, well that's not a technological decision.

The technology exists today to have zero net carbon emission cars. Right now.. Cars like the Ford Focus Energi have enough battery power for a one-way trip to work for most commuters. For longer trips, they can be paired to a flex fuel gasoline engine that burns alcohol. If your alcohol comes from fermenting corn, and your electricity comes from nuclear or hydro, you've done it.

Indeed, this is an application where the lower energy density of ethanol makes very little difference. I put 2 gallons or so in every month. Would 2.5 gallons make any difference?

 

[Mark Harder]

What keeps H₂ alive as a fuel is that 10 pounds can propel a fuel cell car 300 miles.

Thanks for pointing out that hydrogen is a fuel, not an energy source. People often confuse the two. Thus, hydrogen's superior utility is as a fuel. Speaking as an avid reader, nothing more, if it can be produced cleanly and the energy and economic costs of storing, transporting, compressing it (whether physically, or chemically, i.e. binding to a solid-state carrier) etc. outweigh its advantages over hydrocarbons, then there are clear advantages over hydrocarbon fuels:
When it burns, it produces water, nothing else. It burns over a wide range of fuel/air relative concentrations, i.e. lean/rich ratios. This makes it easier to design internal combustion engines for transportation applications, where the engine must satisfy large variations in demand. It needn't be burned to supply energy usefully. Hydrogen- oxygen fuel cells work quite nicely and far more efficiently than any heat engine can. There may be other pluses; I can't think of them now.
One downside people like to bring up is its safety. Being the lightest molecule, it possesses a high diffusion constant, and it is viscosity is also extremely low. These make designing leak-proof fittings rather tricky, and it's flammability over a range of hydrogen/air mixtures makes leaks even more dangerous. However, the safety issue need not be a deal-breaker. Hydrogen is used as rocket fuel and technologies for handling it are well known.
I've often wondered if H₂ could be a partial answer to a problem that alternative energy sources seem to have. The energy produced when demand is low is difficult to store up for times when demand is high. If a source of water is near a wind, ocean or hydroelectric project, the 'excess' electricity produced when demand is low could be directed toward electrolyzing water and storing the hydrogen. When demand is high, the stored hydrogen could generate electricity in fuel cells or by combustion. Long transportation of the fuel is thus avoided.
According to something I read decades ago, this concept was used to power a satellite. When the satellite was between sun and earth, solar panels produced enough energy to electrolyze some water on-board. The H₂ and O₂ were stored and used to generate electricity in fuels cells when the satellite was in the sun's shadow. It seems a bit complicated compared with using storage batteries for electric storage. Perhaps it was a proof-of-concept exercise. At the time (early '80s I believe), I don't think there were any lightweight storage batteries like the Li-based ones we have today. Perhaps that was why the idea seemed so attractive.

 

[Bystander]

However, there hasn't been enough Pt mined and refined in all history.

 

[CraigHB]

Batteries are well on their way in development right now and I think they have the most potential (there's a pun there) to provide a zero emission future. As stated there's a big problem with the time it takes to recharge. There's a big difference putting a car on a charger for several hours versus fulling a tank of fuel in a few minutes. Though it's possible advances will allow very high charge rates, I don't think it will ever be possible to charge a battery in only a few minutes. There's simply a limit to the current a wire can carry. It's always going to take at least a couple hours to recharge even with currents at the limit of what wires can carry and what sources can supply. It's not going to be possible to put energy back into a battery any faster than it can be taken out.

I've thought for some time that a really good solution might be the combination of a fuel cell and a storage battery. In that case a fuel cell can run long term at a relatively low power output to keep batteries charging. Batteries can provide energy at a much greater rate than a fuel cell can provide standing alone. That allows the car to reach high peak power outputs as required. The two could provide range even further than a gasoline car having a tank of fuel plus the energy capacity of a battery. When the car is resting, the fuel cell can keep running to supply charge to the battery. Though this again falls back to the high cost of fuel cells. They're just too expensive for public consumption right now. Though we may be only one breakthrough away from a cheap consumer level fuel cell.

There is the argument that we've already passed the point of no return in terms of pollution and climate change. That should not be a reason to give up though. The sooner we stop adding unnatural chemicals to the atmosphere, the less time it will spend in an unnatural state and the sooner it will return to a natural state. I'm no expert on climate change, but I don't believe it's a situation where once it goes over the edge it never comes back. I think we're still pretty far from a situation where the climate has run away for good.

 

[gmax137]

Just a bit outside. Mirai 70 MPa (10kpsi) tanks for 5kg H2 reportedly have mass 87.5 kg (193 lbs). Three layer tanks: glass fiber surface, carbon fiber middle, plastic layer inner.

Sounds similar to the tanks jack action linked to above. When I wrote my post, I was thinking steel cylinder tanks; that shows you how easy it is to be stuck in the existing paradigm. Still, the tanks in your link (near 200 pounds for 5 kg H2) show the storage of hydrogen is more difficult than gasoline.

By the way, how do you guys embed a link to a previous post?

 

[phans]

It seems that a solution to all the long recharge times that batteries have, at least for automotive applications, is to standardize on two or three battery sizes/capacities with standardized connections (physical & electrical), and then build cars that can use them. If this is done smartly, it would then be possible to build automated battery-swapping-stations. You'd drive in, stop for a few minutes, and drive out with a fully charged battery. You'd receive a credit for any unused charge on the battery you drove in with and pay for the net gain. Taken a little further, a smart gasoline provider (Exxon/Mobil, Shell, ...) could add a battery-swap bay to its existing gas stations. In this scenario you wouldn't even own a battery, you'd just pay to use one. Like swapping propane tanks for your gas grill, except the automotive battery swap could/would be automated. This needs no new technology, just smart use of what we already have. Forget your battery-charging-station network, Tesla, build automated drive-thru battery swapping stations!

 

[CraigHB]

If this is done smartly, it would then be possible to build automated battery-swapping-stations.

That would be a solution to the charging time problem. It's not without some logistical issues itself. The battery is the most expensive part in an electric car. There would be some large initial costs to build stations and stock batteries in the numbers required to make it practical.

Right now battery technologies and form factors vary widely. Companies generally don't like to share technology so getting them to work together on a battery standard would not be an easy thing to do. Especially since the battery is a big point of competition in electric cars determining range, cost, and performance.

Companies are typically pretty obsessed with minimizing production costs. When dealing with the hundreds of Amps these batteries supply, coming up with a reliable quick release connector and battery housing that can handle thousands of cycles is an engineering problem. It creates extra costs that would not be there but for some kind of quick change standard.

Battery stations are definitely a possible solution, but like any distribution system there's costs involved and some entity has to saddle them.