A previous posting, “Fuel Cell Vehicles”, reviewed the basics of the fuel cell and the fuel cell vehicles. At the end of that posting, it was said that: “There are a lot of things going for H2 powered fuel cell vehicles except the economics.”
What does that mean? There are two factors that make H2 non-competitive versus other alternatives. Factor one is that hydrogen (H2) is very costly to produce, and distribute. The second are the physical characteristics of H2 that increase the cost of distribution and use.
Hydrogen is costly to produce.
H2 is not a “natural resource” that can be mined or pumped out of the ground like coal, oil or natural gas. There are no H2 mines or deposits. Instead it must be extracted from some other compound containing H2, e.g., water (H20) or natural gas (CH4). Energy must be expended to break the chemical bond in order to make the separation and collection of H2. Often additional expenditures are needed to remove impurities that result the separation. These impurities, e.g. sulfur compounds, can damage the fuel cell if not removed.
The lowest cost method of producing H2 is steam methane reforming (SMR). SMR output is H2, CO and CO2 with a small amount of unreacted natural gas. A water gas shift reaction can produce more H2 and CO2 while reducing CO. Scrubbers are then used to take out CO2, CO, CH4 and sulfur from the gas stream.
Another way to produce H2 is by electrolysis. A simple laboratory devise for splitting water into H2 and O2 is shown in the illustration below.
Illustration source: Creative Commons
The illustration shows a battery supplying an electrical current that is passed through water from the cathode to the anode. The current causes the water to split into H2 and O2 molecules. Hydrogen and Oxygen evolve with the H2 collecting at the cathode and the O2 collecting at the anode.
Limited quantities of hydrogen are currently produced from electrolysis, since electrolytic hydrogen is relatively expensive, with approximately 80 percent of the operating cost being the cost of electricity. Electrolysis is economically feasible for uses requiring small amounts of hydrogen, extremely pure hydrogen or when power costs are low.
There is little data on electrolysis and the data that can be found, is often laboratory on semi-works sourced that is investigating the use of H2 in fuel cells. Three sources of data are summarized in the following:
The Florida Solar Energy Center discusses economics as follows:
’’ The cost of hydrogen production is an important issue. Hydrogen produced by steam reformation costs approximately three times the cost of natural gas per unit of energy produced. This means that if natural gas costs $6/million BTU, then hydrogen will be $18/million BTU. Also, producing hydrogen from electrolysis with electricity at 5 cents/kWh will cost $28/million BTU — slightly less than two times the cost of hydrogen from natural gas. Note that the cost of hydrogen production from electricity is a linear function of electricity costs, so electricity at 10 cents/kWh means that hydrogen will cost $56/million BTU.”
The price of Natural Gas used in the Florida Solar Energy Center notes essentially matches today’s prices. Today the US natural gas cost at the Henry Hub is $3.44/million btu. The delivered cost to an industrial user is not reported. Estimating that it might be doubled would make $6/million btu probably reasonable.
An 8 September posting by Green Car Congress titled “ITM Power reports its estimated cost of producing hydrogen via electrolysis down significantly from last year” reports prices per kg of H2 at $6.44/kgH2. This company manufactures and sells small electrolysis units. It appears that they are targeting H2 production and sales to fuel cell cars. The units are designed to be portable or permanently set up for production and sales.
Electrolysis is just one of this company’s product lines. The available data from this company is electrolysis unit performance. No economic data accompanied the sites I examined.
As with the three cases above, it is difficult to know what is included in the cost numbers. Hydrogen from the Norsk Hydro and Florida Solar Energy Center electrolyses designs exits at about 1 bar. Norsk Hydro does indicate compression to several levels but it is not clear that anything beyond the electrolyser is included the cost of manufacturing of the H2. ITM however makes it clear that their cost does include purification and compression.
The following table is incomplete and surely will leave you with some questions. But one thing you can surmise from it is the cost of H2. Most of the literature on H2 for fuel cells, calls H2 an energy carrier rather than an energy source. It is a costly energy carrier.
|Data||ITM||Fla Sol Energy Ct||Norsk Hydro|
|elect for above cost ¢/kwh||5||5||?|
|syst eff kwh/kg||55||54||47|
|syst eff kwh/kg ideal||39||39|
|syst pressure bar||700(?)||1||1|
|daily capacity kg/day||446||1080|
One kilogram of H2 has about the equivalent energy as one gallon of gasoline. Further, the fuel cell is about twice as efficient as an ICE vehicle. So, if the ITM number of $6.44/kg is real, then that works out to be about the same as $3.22/gallon of gasoline. However, look at the price of electricity= 5¢/kwh. Where can you get that? ITM’s study is based upon intermittently supplied wind farm electricity and in some cases, “stranded power” meaning the wind farms are too far away from the grid or a major user, so they sell power cheaply. An industry cannot be built on those rare occurrences. Beyond that, wind farms, without subsidies, are not viable. Subsidies are being reduced and will likely soon be only a distant memory—I hope.
The chart below shows the electrical prices across the US. Note that the populated areas, where most of the vehicles are, on this map are the ones with the highest electrical prices.
Thus, both the US and the UK price of a kg of H2 would be at least twice the figure shown by ITM and more likely nearly three times that price using the Florida Solar Energy Center’s analysis discussed earlier. That says the price expressed as gasoline equivalent would not be $3.22 but rather at least $6.44 and more likely near $10/kwh.
Physical Characteristics H2
Because of the low density of H2 requires that the pressure in the fuel storage tank must be 10,000 psi to get 350 miles between refuelings. That was discussed in the previous posting. There are some research institutes that say using Ammonia Borane for storage could surmount the need for these exceptionally high pressures. Ammonia borane could be a chemical hydrogen storage material that uses the elements nitrogen and boron to chemically bind hydrogen. According to a Sigma-Aldrich posting:
“In these chemical hydrogen storage materials, hydrogen is ‘discharged’ by a chemical reaction and the hydrogen is ‘recharged’ by a chemical processing pathway. This makes them unique compared to metal hydride materials or carbon sorbent materials where the hydrogen release and uptake is controlled by temperature and pressure. “
This technology has been around for nearly ten years, and I have not seen any cost analysis, nor an indication of the fuel storage tank size necessary to hold enough H2 in the ammonia borane to allow 350 miles range between refueling.
See the Material Safety Data Sheet for H2 here. Flammability range from 4% to 74% is about as wide as you find for any flammable gas. A personal note, for much of my working career, I worked in plants handling hydrogen from 12,000 psi down to atmospheric pressure. The precautions we took were extraordinary; such precautions that I doubt will be flexible enough to employ in service station levels.