(liquid?) it takes to generate 1 KW?Or would efficiency be based on Terms, or BTU's, per gallon of hydrogen (# 0f BTU's and /or Therms in a gallon of Hydrogen).
A fuel cell is just used for holding the fuel, not making energy. You would need information on the apparatus that is generating the energy from hydrogen. Asking how efficient a fuel cell is is like asking how many miles to the gallon your gas tank gets in your car.
Liquid hydrogen has an energy density of 10.1 MJ/l (9,500 BTU/l). Gasoline has much more: 34.6 MJ/l (33,000 BTU/l). But that's not really a useful measure, since the price of a gallon of gasoline and the price of a gallon of liquid hydrogen are very different. We're used to thinking of it in gallons only because we ordinarily buy gas by the gallon, and it's always gas we buy. If you look in terms of weight, for example, liquid hydrogen is 143 MJ/kg, and gas is only 46.9 MJ/kg. Efficiency is hard to compare. A fuel cell is about 80% efficient with the energy it gets. A gas engine is about 25%, and they actually operate near their theoretical efficiency for their size. Bigger, hotter engines are more efficient for internal combustion engines. In fact, that's one good reason to stop using them. It would be better to build a giant power plant that burned the very same gasoline to make hydrogen, because that power plant can be up to 60% efficient. Even if the resulting fuel cell is only 80% efficient, the net result is 48% efficiency, twice what you get from a gas engine.
it's hard to say, first of all because 1KW isn't an amount of energy, it's a rate. One kilowatt-hour is a unit of energy. It's really hard to say, since there are no native sources of Hydrogen. No Hydrogen mines. Typically you break up Methane, CH4, to get Hydrogen. So there's a lot of waste right there. Even if a fuel cell was 100% efficient it could never make up for the inefficiency of reforming methane, about 60%. Then there's the CO2 problem, reforming methane makes twice as much CO2! Then there's the cost of purification, as fuel cells die very quickly if the Hydrogen isn't made 99.8% pure by removing the sulfur and other nasties found in oil and gas products. You could guess that subtracts another 15% from the efficiency. Then if you want liquid Hydrogen, get out the checkbook, as liquefying Hydrogen is immensely energy intensive. It takes about half a kwH to liquefy one kwh of LH2. As a guess that will drop the overall efficiency of getting liquid Hydrogen down below 30%. And you haven't even gotten the LH2 to the fuel cell yet! So I guess the bottom line is it doesnt matter how efficient the fuel cell is. Even if it was 100% efficient the 30% efficiency of making LH2 makes the overall efficiency lower than a diesel engine (50%).
but I'm no way an expert on these things. fuel type kWh/litre kWh/US gallon kWh/imperial gallon %age gasoline/gas/petrol 10.1 37.9 45.9 1 diesel 8.9 33.7 40.5 88% ethanol 5.9 22.2 26.8 58% methanol 4.9 18.8 22.3 48% butanol 8.1 30.7 36.8 80% Liquid hydrogen* approx. 2.22 approx. 8.4 approx.10.1 22% *Liquid hydrogen has approximately one-third the energy of gasoline/gas/petrol. So you about 5 times the volume of hydrogen to do the same amount of work as gasoline etc can do. Of course, if you're good with sums, you'll be able to convert both the energy measure and the liquid measure to whatever you prefer. There are plenty of unit conversion sites on the net.
by way of fact they are no longer as good as oil based fuels. subsequently good is defined as a mixture of potential density, ease of use, secure practices and fee. subsequently a tank of petrol or diesel gets you a first rate distance (a minimum of a few hundred kilometres), that's rather consumer-friendly so you might apply basically requiring you to open the tank and stick the nozzle in to refuel and not taking long to realize this, to no longer point obtainable is an entire distribution device obtainable, it would not tend to pose plenty danger in an accident (outdoors of Hollywood Ca, us of a, automobiles do exactly no longer catch hearth or explode very frequently) alongside with being of life like fee (or a minimum of those human beings who do no longer very own Hummers think of so) and many times basically undercut via possibilities by way of tax incentives (biodiesel many times calls so you might interrupt the regulation to be greater low-fee, and if adequate human beings initiate doing it then do initiate handing out fines). Now technologies ought to advance the possibilities to the factor at which possibilities exchange into workable or maybe favored yet we are no longer there yet and there is an exceedingly good danger that the alternative for fossil gasoline derived transportation fuels would be synthetic hydrocarbons (i.e. what we are utilising now, only synthetic with warmth (probable from a Gen IV reactor) and CO2 from the ambience particularly of pumped out of the floor).
