DonDeeHippy
Member
Thanks pushme and martin for your take ill put this with the others of don't know yet but a good idea , not quote it in a argument quite yet 
Are hydrogen tanks superior to batteries?
- Thread starter Martin Williams
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NeilBlanchard
Well-Known Member
You are not correct on the efficiency of batteries. And your beloved hydrogen is much less efficient.
You can have up to 9 (or more?) Powerwalls together, if you want more capacity. Each is a bit over 13kWh, and would drive an EV about 52 miles - that is one heck of a long driveway!
You don't even need batteries to charge an EV - just put it into the grid, and then take it back out later. Or, plug in during the day, when your car is home. A big battery EV lasts all week.
Pushmi-Pullyu
Well-Known Member
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Pushmi-Pullyu
Well-Known Member
So far as I know, the only one which is actually being produced for sale is the Simple Fuel system, which is capable of generating H2 and dispensing it into a FCEV. You can buy one for $250,000 - 300,000, depending on whether it can produce 5 kg or 10 kg per day. Cheap at the price, right?
From InsideEVs news: "IVYS Simple Fuel Station Offers Homemade Hydrogen For $250,000"
To be fair, if -- if -- the high-pressure electrolyzer Martin described is actually practical, that might bring down somewhat the cost of similar systems made in the future.
If you don't need to compress it that much, if you were to (like a H2 fueling station) hold it at "only" 500 PSI instead of the 10,000 PSI needed to fully fill a fool cell car, then surely it could be done more cheaply.
There are systems which use electrolysis and H2 storage for stationary energy storage, including some made for home use; but I don't know that any of them are being produced in sufficient quantity to have a list price. I get the impression they're more the experimental type.
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Pushmi-Pullyu
Well-Known Member
Still flogging the deceased equine of trying to claim that batteries are not a much, much better, significantly more efficient, and almost infinitely more practical way to store energy than H2, eh Martin?
Round-trip efficiency for stationary H2 energy storage is only about 50%, worse than even your lowball figure for battery storage. And the batteries are far cheaper, too, as well as likely to last as long. Any type of H2 storage system is likely to have a "DO NOT REFILL AFTER" date, just like fool cell cars, and for the same reason: Any metal fittings in long-term contact with compressed H2 become embrittled over time.
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Pushmi-Pullyu
Well-Known Member
Reality check: Try between 8% and 15%, depending on how close to full the pack is. Average efficiency should be somewhere around 88-90% efficiency, yielding a round-trip efficiency of about 77-81% efficiency. If it's not that efficient, then it was built poorly.
And the Earth is flat, and let's hear it for "clean diesel" too! Whee! Isn't being a EV-bashing science denier fun?
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Pushmi-Pullyu
Well-Known Member
Mea culpa, that was an error on my part; that should have been propane, which can be effectively stored at low compression.
Storing methane (or natural gas, which is mostly methane) in a vehicle as a fuel -- as CNG (Compressed Natural Gas) -- requires pretty high compression; 3000 - 3600 PSI. Not as high as H2 certainly, but still pretty high compared to propane.
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Martin Williams
Active Member
I am correct on the round trip efficiency of batteries. I have just double checked it, and suggest you do too. Yes you could have nine powerwalls at £4,500 apiece but I doubt if you'd ever recover that investment and the efficiency would be even worse You'd could also use 7,000 laptop batteries. My point is nobody makes a car charging domestic battery system or a domestic hydrogen filling system yet.
As to plugging into the grid, indeed you could. In fact you'd probably have to! The point of using a home hydrogen system is that you WOULDN'T have to. Transferring the energy into a car as hydrogen is quick and can be done at your convenience, not that of the car. Plugging into the grid is not that easy. You have to find a charging point. It also cost you more.
Martin Williams
Active Member
I think Pushmi is confusing what is meant by 'efficiency'. I was talking about round trip efficiency. Yes, you might lose 10% of the energy on charging in the form of heat in the charger and the battery, but you also lose energy in heating in the battery when discharging. So you only get 80% back of what you put in.
The waste heat is due to current through the internal resistance of the cells, and as the heat generated is proportional to the square of the current, fast charging becomes more and more inefficient as you increase the speed. Thus if you charge a battery slowly over - say - ten hours with a heat loss of 100 Watts, you lose a total of 1kWh. If you double the current over five hours, the rate of energy loss will be 400 Watts, meaning that the total loss will be 2kWh. Reducing it to 2.5 hours will give you losses of 4kWh. At 1.25 hours it goes up to 8kW and so on. Fast charging is VERY inefficient.
Batteries used by people like Tesla are designed not for round trip efficiency, but for maximum energy density, for obvious reasons. There ARE lithium batteries that have better round-trip efficiencies - approaching 90% if you charge them carefully - but they hold less energy per kg, so are not so good for cars. Tesla's Powerwall uses his car batteries, partly because the units can be made more compact and saleable, but probably more because Tesla is making car batteries anyway, and the user is unlikely to worry about lower round-trip efficiency.
Well, there is an answer for NeilBlanchard. The cost is ludicrous of course, but I imagine a billionaire wanting power on his remote island paradise might consider it as a possibility. I suspect the key to these things becoming less expensive comes down to getting rid of the compressor. If it can be reduced to an electrolyser and a tank, then the cost can be made far lower perhaps to the level where ordinary mortals can afford it. Honda seems to have a practical demonstrator of this sort of approach.
As to filling your car without the need for pumping it in, I think the key to this would be for the system to have a combination of a bigger tank running at higher pressure. As is well known, for a given mass of gas at constant temperature, the pressure times the volume is a constant. So if the dispenser has a tank the same size as that of the car, containing gas at 140MPa, then the result of connecting it to a car's tank at zero pressure would be both tanks pressurised to 70MPa. If the dispenser's tank were twice the volume of the car's, then you would need it to be pressurised to only 105MPa to fill the car's tank to 70MPa, and so on.
The waste heat is due to current through the internal resistance of the cells, and as the heat generated is proportional to the square of the current, fast charging becomes more and more inefficient as you increase the speed. Thus if you charge a battery slowly over - say - ten hours with a heat loss of 100 Watts, you lose a total of 1kWh. If you double the current over five hours, the rate of energy loss will be 400 Watts, meaning that the total loss will be 2kWh. Reducing it to 2.5 hours will give you losses of 4kWh. At 1.25 hours it goes up to 8kW and so on. Fast charging is VERY inefficient.
Batteries used by people like Tesla are designed not for round trip efficiency, but for maximum energy density, for obvious reasons. There ARE lithium batteries that have better round-trip efficiencies - approaching 90% if you charge them carefully - but they hold less energy per kg, so are not so good for cars. Tesla's Powerwall uses his car batteries, partly because the units can be made more compact and saleable, but probably more because Tesla is making car batteries anyway, and the user is unlikely to worry about lower round-trip efficiency.
So far as I know, the only one which is actually being produced for sale is the Simple Fuel system, which is capable of generating H2 and dispensing it into a FCEV. You can buy one for $250,000 - 300,000, depending on whether it can produce 5 kg or 10 kg per day. Cheap at the price, right?
Well, there is an answer for NeilBlanchard. The cost is ludicrous of course, but I imagine a billionaire wanting power on his remote island paradise might consider it as a possibility. I suspect the key to these things becoming less expensive comes down to getting rid of the compressor. If it can be reduced to an electrolyser and a tank, then the cost can be made far lower perhaps to the level where ordinary mortals can afford it. Honda seems to have a practical demonstrator of this sort of approach.
As to filling your car without the need for pumping it in, I think the key to this would be for the system to have a combination of a bigger tank running at higher pressure. As is well known, for a given mass of gas at constant temperature, the pressure times the volume is a constant. So if the dispenser has a tank the same size as that of the car, containing gas at 140MPa, then the result of connecting it to a car's tank at zero pressure would be both tanks pressurised to 70MPa. If the dispenser's tank were twice the volume of the car's, then you would need it to be pressurised to only 105MPa to fill the car's tank to 70MPa, and so on.
NeilBlanchard
Well-Known Member
Batteries are MUCH cheaper, AND more efficient, than a hydrogen system.
Therefore batteries are better than hydrogen.
This whole thread is moot.
Therefore batteries are better than hydrogen.
This whole thread is moot.
TeslaInvestors
Active Member
Battery efficiency: Don't forget the vampire drain. It get be 20% - 30% overnight in cold weather.
How does it affect the efficiency? The 80% Martun quotes is assuming you use up the charged battery quickly. But that's not how it works, especially for long range EVs. I suspect you will lose 20% extra just due to vampire drain over a week.
How does it affect the efficiency? The 80% Martun quotes is assuming you use up the charged battery quickly. But that's not how it works, especially for long range EVs. I suspect you will lose 20% extra just due to vampire drain over a week.
Martin Williams
Active Member
I am unconvinced that battery cars are cheaper than hydrogen ones with the same range. I suppose you could take Tesla's most efficient car, stuff it to the gills with yet more flashlight batteries, and achieve similar mileage to the Mirai or the Clarity, but it would cost a lot more.
The killer point, however, is not efficiency but convenience.
Give the consumer a car which gives him the same availability as his ICE car, all the advantages of an electric car, and no need to have to plug it in every time you park, to fiddle about with cables, and worry about how long it takes to charge, or whether the batteries are degrading, or whether he can put the heater on and still get home, and I think you will see which technology prevails.
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Pushmi-Pullyu
Well-Known Member
I don't know if you actually believe this ridiculous EV-bashing FUD or if you're just "playing dumb". Either way, you're trolling. Vampire drain has nothing to do with the apparent energy loss from letting the battery pack freeze. If you warm the battery back up, that "lost" capacity magically reappears!
What's really going on with a frozen li-ion battery is that batteries use a chemical reaction, and as is typical for chemical reactions, that process is greatly slowed when it gets below a certain temperature, which for li-ion chemistry is the freezing point of water, or within 5 degrees of that temperature. Discharging the battery under those conditions doesn't produce nearly as much power as it does when the battery is warmer. But of course, if that frozen battery is warmed up, then discharging it will produce power just as well as it did before it was frozen. So it's not that the energy stored in the battery is actually lost if it's frozen, it's just that the battery is very inefficient at producing power in that state.
If the car's battery pack is called upon to run the battery heater to warm itself up, then this of course will cause some loss of stored energy. That's why it's always advised that if your plug-in EV is left out in the cold when it's going to freeze overnight, then you should plug it in so it can run the battery heater without draining the battery.
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Plug-in EVs left out overnight without powering the battery heater might indeed lose 20-30% of their range, but that's not just because of the frozen battery. That's a combination of the battery pack having to warm itself up, plus the extra energy consumed by running the car's cabin heater, defrosters, and other increased power demands in very cold weather.
* * * * *
It should be noted that gasmobiles also lose MPG in bitterly cold weather -- I think that's typically about 15-20%? -- but of course dedicated EV bashers like "TeslaInvestor" want us to forget that!
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Pushmi-Pullyu
Well-Known Member
Apparently for you, diesel has prevailed, since that's what you're driving. All your arguments in favor of fool cell cars haven't even convinced you to buy one yourself!
And if hydrogen fuel plus fuel cells are so great, then why is your narrowboat powered by batteries? Hmmm?
Martin Williams
Active Member
Alas, not so. You need energy to 'warm it up' and that is 100% lost.
It isn't. It is powered by diesel.
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Pushmi-Pullyu
Well-Known Member
I covered that in my comment. Do I need to dumb it down for you to understand that the energy needed to warm up the battery won't come from the battery if you plug the car in?
I think you're just "playing dumb" again.
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Martin Williams
Active Member
It doesn't matter where the energy comes from. If you have to supply energy to get the energy out, it is lost energy. It would be pretty hard to have it plugged in as you drive off on a chilly morning anyway. Energy needed to warm it up then would HAVE to come from the battery.
Martin Williams
Active Member
Regarding narrowboats, I think a battery powered boat would probably be quite practical. There is no requirement to keep the weight down, indeed the reverse because they have several tons of ballast in them anyway. Lead acid would work fine, and the power needed to keep them gliding along at below the speed limit of 4mph is small.
The fly in the ointment - as usual - is charging them. I suppose the Canal and River Trust could install charging points, but as boaters tend to moor out in the countryside where there is no power available it would be very expensive to do this over well over 2,000 miles of canal. Solar panels are another possibility but it's not possible to collect enough power to run the boat, even on a sunny day. Much of the network is shaded by trees too, which don't help, and anyway, the canals wiggle about so the panels would not be pointing the right way most of the time.
So probably hydrogen would, overall, be less expensive. Unfortunately, there are no facilities for filling up with this along the towpaths either. So, diesel will continue to be used for the foreseeable future. One might speculate about using solar cells and a high differential pressure electrolyser to charge up a tank during periods when it is not in use, but I think that is pretty unlikely to happen for a very long time, if ever.
Interestingly, it would probably be worthwhile recirculating the water emerging from the fuel cell to be used again by the electrolyser were such a system to be devised. Canal water is pretty mucky, and you really need distilled water for electrolysis, so reusing it would make sense. The canal water could be used for condensing the steam that emerges from the fuel cell, so you don't really have a refrigeration problem to worry about.
However, for the time being, diesel is the standard. Mine is a 4 cylinder Vetus (a marinised Mitsubishi!) I use supercapacitors to start it in order to avoid hammering the battery, but vintage 100-year-old single cylinder engines are highly prized by enthusiasts who pay well over £10,000 to acquire one. These things are hand cranked to start, and thump away at about 50 to 100 rpm as they have done since the early part of the 20th century, whilst their owners polish the brasswork, oil the bearings and generally fondle them as they worry about where to get spares from. Not my idea of fun, but they seem to enjoy it.
The fly in the ointment - as usual - is charging them. I suppose the Canal and River Trust could install charging points, but as boaters tend to moor out in the countryside where there is no power available it would be very expensive to do this over well over 2,000 miles of canal. Solar panels are another possibility but it's not possible to collect enough power to run the boat, even on a sunny day. Much of the network is shaded by trees too, which don't help, and anyway, the canals wiggle about so the panels would not be pointing the right way most of the time.
So probably hydrogen would, overall, be less expensive. Unfortunately, there are no facilities for filling up with this along the towpaths either. So, diesel will continue to be used for the foreseeable future. One might speculate about using solar cells and a high differential pressure electrolyser to charge up a tank during periods when it is not in use, but I think that is pretty unlikely to happen for a very long time, if ever.
Interestingly, it would probably be worthwhile recirculating the water emerging from the fuel cell to be used again by the electrolyser were such a system to be devised. Canal water is pretty mucky, and you really need distilled water for electrolysis, so reusing it would make sense. The canal water could be used for condensing the steam that emerges from the fuel cell, so you don't really have a refrigeration problem to worry about.
However, for the time being, diesel is the standard. Mine is a 4 cylinder Vetus (a marinised Mitsubishi!) I use supercapacitors to start it in order to avoid hammering the battery, but vintage 100-year-old single cylinder engines are highly prized by enthusiasts who pay well over £10,000 to acquire one. These things are hand cranked to start, and thump away at about 50 to 100 rpm as they have done since the early part of the 20th century, whilst their owners polish the brasswork, oil the bearings and generally fondle them as they worry about where to get spares from. Not my idea of fun, but they seem to enjoy it.
DonDeeHippy
Member
I noticed ice vehicles where mentioned for loss of efficiency in the cold to is hydrogen effected by cold or do they work the same in freezing conditions. Id imagine it would be hard to freeze hydrogen.
Martin Williams
Active Member
I think fuel cells need to reach an operating temperature which may take some time, measured in a few tens of seconds I imagine. Bit like ICE car, which, by the way, once they warm up are more efficient in cold conditions. The air is denser then and contains more oxygen per unit volume than at warmer temperatures. You may have noticed improved mileage travelling at night due to this, although the difference is pretty small.
If the hydrogen condenses, you are dead and no longer care much! At 70MPa. I think its about -220 degrees centigrade, by which time the air would be liquid too! Most likely starting the car would be the least of your problems!
If the hydrogen condenses, you are dead and no longer care much! At 70MPa. I think its about -220 degrees centigrade, by which time the air would be liquid too! Most likely starting the car would be the least of your problems!