As a follow up to my article on scam water devices, I thought it would be useful to do one on hydrogen and water powered cars. One of the problems with being involved in renewable energy research, in particular fuel cells, is you’ll occasionally get someone who comes up to you and says, well hydrogen comes out the back of the fuel cell car yes? And hydrogen comes from water, so why not split the water again and feed the hydrogen into the fuel cell and you’ll have a car that can run on water…..hmmmm….,.Because that would be “perpetual motion”.
Now okay, I realise most people reading this will likely say like duh! obviously that won’t work. But I’ve heard this often enough that I really do feel the need to put together a post on it. I mean a year or two ago we had one of our degree students (not exactly the brightest one I might add) come by and ask if he could borrow an electrolysis machine so he could test the idea out (he was advised to start off with a 2nd level chemistry textbook then get back to us). So there is enough of this BS out there that it deserves debunking.
A fuel cell is not 100% efficient, they are usually about 40-60% efficient, although if we capture the heat (in a CHP application) this can jump to 90%. But as regards practical electrical efficiency, you’re talking about 50%, once we account for the balance of plant. By comparison a petrol engine is only about 25% efficient. Making hydrogen from electricity means electrolysis. There are various different hydrogen production processes, some of which can yield efficiencies as high as 75%, but for practical purposes (e.g. something you could fit in a car) you are probably talking about 40-60% efficiency. Let’s assume the higher figure of 60%. You’ll need to compress the hydrogen to get it into the tank, that’s going to be about 80-90% efficient, assuming you opt for a pressure below 350 bar. If you go for a much higher pressure (and most FCEV’s store hydrogen at 700 bar), then you’ll need to expend more energy compressing it. And as the hydrogen will get rather hot, you’ll need an multi-stage compression system with an innercooler. Although its worth pointing out that this step can be skipped if we opt for a static application and run at a much lower pressure.
So adding up our efficiencies we get 0.5×0.6×0.9 = 27%. In other words even if you devoted all of the electricity the fuel cell generated purely to hydrogen production, you’d end up with less than a third the energy you started off with. There is no way such a system could work.
I would note that overall cycle efficiency of hydrogen can be higher than I’ve indicated here. A paper by Bartolozzi etal (2013) illustrates the different options in more detail. But in summary, if we opt for more energy efficient means of hydrogen production, run everything at a lower pressure, recycle the waste heat (given that much of the losses represents waste heat), you can achieve much higher efficiencies. This is the point of static applications such as Fuel cells CHP plants, or simply burning hydrogen in a conventional boiler, as a substitute fuel for natural gas. Personally, I reckon the main use for hydrogen in the future will likely be static applications, mostly for winter heating or backing up the grid, with hydrogen fuelled vehicles essentially filling a niche between electric vehicles and biofuel powered vehicles. The extend to which hydrogen vehicles will be used depends to what extend the range issue with BEV’s can be resolved and how much biofuels we can sustainably produce. Keeping in mind that when I say “vehicle” I extend that to planes and ships. But clearly as regards water powered cars, 27% cycle efficiency is the best you could get…although the term “static energy sinkhole” is perhaps a more accurate description than “water powered car”.
Ah, but at this point you’ll be told, that there’s this special “additive” that you mix into the water that will solve everything (which no doubt some quack will sell you over the internet). But for that to work the additive would have to raise the efficiency of the electrolysis process to higher than 100% and ultimately impart more energy into the system per unit mass than the hydrogen….and hydrogen has the highest calorific value of any known substance in the universe!…which is kind of the whole reason for using hydrogen in an fuel cell in the first place!
Quite simply put, if this magical “additive” actually existed, you’d be better off ditching the hydrogen tank, the fuel cell and the electrolysis process and coming up with a chemical fuel cell (e.g. like a flow battery) that ran directly off this “additive”. Furthermore our “additive” will have a production cycle, which will involve the consumption of energy. And its pretty reasonable to assume this will not be 100% efficient, indeed its doubtful it could match the efficiency of hydrogen production (again that’s kind of the point of using hydrogen!).
If such a device worked, nevermind powering a car, you could use it to generate electricity, solve world hunger and create a post scarcity society. And as for all the conspiracy theories, would companies hide such a technology if it existed? Of course not, they’d patent it and then make trillions. The fact is that water is basically the left over ashes of a hydrogen fire. Saying you can run a car off of water is equivalent to taking the ashes from a log fire and trying to glue them back together again. If such a simple answer to all of the world’s energy problems existed, don’t you think we’d be using it?