HYDROGEN FUEL CELLS CURRENT AND FUTURE DESIGNS USE AS AN ENERGY STORAGE DEVICE RENEWABLE VS. CO2 GENERATING DISTRIBUTION METHODS AND COSTS SAFETY
Molecular Hydrogen Facts • Three times energy content of gasoline (120 Mj/kg vs. 44Mj/kg) • Cost of liquefying it is 30 to 40% of its energy content • Pipelines are 50% greater diameter than for gas (for equivalent energy transmission rate), so more $. • Distribution doubles cost of production ($1.03/kg). • Flammable concentration has a wide spread from 4% to 75%.
Types of Fuel Cells • Phosphoric Acid fuel cells: only commercially available. Since 1991, 250 units sold (until 2004). $4500/kW • Proton Exchange Membrane fuel cells. Vehicle transportation method because 25kW to 150kw size. Beta testing at $1500/kW by UTC Fuel Cells. • Solid Oxide fuel cells. Currently operate using natural gas, but could use H. Unlike those above, no noble metals. Can operate up to 1000 c.
Molecular Hydrogen Generation • Three different scales of generation: Central Station, Midsize, and Distributed. • Central Station: 1,080,000 kg/day would support 2M cars. Distributed by pipeline. Generated by fossil fuel or nuclear energy. • Midsize: 21,600 kg/day would support 40k cars. Distributed by cryogenic truck. Generated by natural gas or biomass • Distributed: 480 kg/day would support 800 cars. No distribution system needed. Renewable fuels used.
Hydrogen Generation • Electrolysis: from fossil fuels or renewable energy sources • Fossil Fuels requires carbon sequestering (next slide) • Hydroelectric, Nuclear Energy, Photovoltaic, grid based energy, wind power, have either periodic generation, which may not match usage, or have constant generation, which does not match usage. • Energy storage at peak times is a problem for these energy sources that hydrogen generation could solve. • Cost for all distributed (renewable) sources is two to five times cost of gasoline (2004)
Carbon Dioxide Sequestering • No advantage to Hydrogen production from fossil fuels as far as reducing Carbon Dioxide is concerned. Yet this is the cheapest method to generate Hydogen. • Currently, only 4% of Hydrogen is from electrolysis; the rest is from coal, oil and natural gas, which contains about 10% CO2 as well as the Hydrogen. • Norway injects CO2 into saline aquifer. • Los Alamos study of CO2 injection into magnesium formations (Peridotites, serpentinite, Gabbro, and Basalt) • Costs about $8 per ton of CO2 disposed. Permanent and no legacy problems for future generations.
CO2 and Hydrogen from fossil fuels • Small increase in cost to capture CO2 when hydrogen produced by fossil fuels. • Using coal as feedstock, sulfur captured along with CO2. • CO2 sequestering and storage costs about $4.00/barrel of oil, $24/ton of coal, $0.54/cubic feet of natural gas. • New infrastructure required to transfer CO2 from H2 production to storage. • Deep ocean already stores CO2, may give it up with warming. • World’s biological storage now 700 billion tons. To double this storage would require doubling vegetation.
Hydrogen production technologies • From natural gas. Already import natural gas. H conversion from methane by steam reforming, produces CO too. If natural gas costs $6.50/Btu, H costs $3.51/kg • From Coal. Enough to last 200yrs. Produces the most CO2 for the same H. Gasification produces syngas. Research may get costs to $0.90/kg. • From nuclear energy. Water splitting by electrolysis or thermochemical process. Need temps of 700 to 1000 c. No CO2. No cost estimates. • Electrolysis. Most expensive. Use proton exchange membrane( PEM) or liquid electrolyte (KOH).
Hydrogen production--Renewable fuels • From wind energy. Electrolyze water. Wind is the most cost effective renewable energy source: $0.04 to $0.07/kWh costs about $6.64/kg per H2 if grid back up used. • From Biomass. Only 0.2 to 0.4% of solar energy converted to H2. Costs $7.05/kg by gasification, not including fertilizers and land degradation. • From Solar energy. Either by electrolysis (Photo voltaic) or using photoelectrochemical cell (in a early stage of development). Cost now is $28.19/kg and solar energy is only available 20% of the time.
Hydrogen safety • Small leak more flammable than for gasoline, but more likely to disperse, so ignition less likely. • Static spark can ignite, so ground during transfer. • Detonation more likely than with gasoline because of wider flammable concentration and higher flame speed. • Need high pressure to transfer efficiently: 5-10k psi. • Odorless, burns with a blue flame. Small molecule precludes adding scent molecule.