Transcript HYDROGEN FUEL CELLS - University of California, Irvine

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.