Fuel Cells, the Hydrogen Economy and

(y)our Energy Future

S.A. KleinSolar Energy Laboratory

Dept. of Mechanical Engineering University of Wisconsin - Madison

Slide courtesy of Don Aitkens

The Problem - Hubbert’s Peak

Global Warming• Available data suggests that the average temperature is

increasing.• Increased levels of carbon dioxide in the atmosphere is the

explanation for the increase

Mauna Loa, Hawaii

Source: Keeling and Whorf, Scripps Institution of Oceanography.

U.S. DOE Energy Policyhttp://www.eere.energy.gov/hydrogenandfuelcells/presidents_initiative.html

...Bush has already proposed $1.2 billion in research funding so that America can lead the world in developing clean, hydrogen-powered automobiles

The Bush Administration’s fiscal year 2007 budget request includes $289 million for research to support the President’s Hydrogen Fuel Initiative.

Objectives

• Brief review different fuel cell concepts• Characteristics of hydrogen as a fuel• Fuel cells for transportation vehicles• Fuel cells for stationary distributed power• Projections of our energy future

What is a Fuel Cell?

Converts chemical energy to electrical power - like a batteryElectrochemical process - Avoids Carnot limitationsFuel is continuously supplied to electrodesCharge carriers: 2 2

3, ,H CO or O+ − −

Proton Exchange Membrane

(PEM)

Phosphoric Acid Fuel Cell

(PAFC)

Molten Carbonate Fuel Cell (MCFC)

Solid Oxide Fuel Cell

(SOFC)

Operating Temperature

80°C (200°F)

200°C (400°F)

650°C (1200°F)

600-1000°C (1100-1800°F)

Expected Early Market

Available

1992 Reintroduction

(2007) Pre-

commercial

Available (small

systems)

System Electric Efficiency

Ranges (HHV)*

20-45%

35-40%

40-60%

30-70%

Size Range 0.1 – 250 kW 200-400 kW 250 kW – 3 MW

1 kW – 1 MW

System Cost (est.)

Cost Target

$1,500 -3,000/kW

$25-50/kW

$6,000/kW

$1,800/kW

$4,000 – 10,000 /kW

$400/kW

? $400-$800 /kW (2010)

Applications

Stationary Vehicles Portable

Stationary / Cogen

Stationary / Cogen Marine

Stationary / Cogen

Portable *System efficiency depends on fuel type, fuel processing method, and manufacturer’s design

Major Types of Fuel Cells

Fuel Cell Technology Issues• Life: (Target = 40,000 hrs or ~5 yrs with <10% degradation)

- Reliability: Electrical shorts, catalyst performance, acid loss etc.- Materials: corrosion, catalyst poisoning, sintering, etc.

• Economics: (Target < $1,000 stationary, $50/kW transport.)- Current system cost: $1,500 – $6,000/kW- Competition (microturbines, stationary engines)- Lower costs needed for automotive - 100 hp (75 kW) →$75,000). Internal combustion engines are < $50/kW

• Systems Integration:- Controls & integration with conventional equipment

• Fuels: (Major reason for developmental delays)- Reforming and associated efficiency/cost impacts- Distribution and storage of H2

Characteristics of HydrogenThe development of a “hydrogen economy” is advocated

Advantages of Hydrogen• Low to zero emissions• Compatible with all fuel cell types• Reduces dependence on imported petroleum (possibly)Disadvantages of Hydrogen• Low energy storage density• Poor transport characteristics• Not naturally available

Hydrogen MethaneMolar Mass [kg/kmol] 2 16

Heating Value [MJ/kmol] 241.8 802.29Heating Value [MJ/kg] 121 50

Density at 25 C, 1 bar [kg/m3] 0.081 0.647Volumetric heating value [kJ/m3] 9755 32364Auto-Ignition Temperature [°C] 572 632

Where does Hydrogen Come From?Hydrogen is not a fuel

• Electrolysis of water (4% of current production) – Efficiency (η) is 70-80% (20-30% based on source energy)– Electricity from: Wind, solar or nuclear energy– DOE cost goal: $2.85/gal gasoline equiv. (1 kg H2) by 2010

• Reformation of CH4 (96% of current production)– η ≈ 77% – Endothermic– CO is still present– DOE cost goal: $1.50/gal gasoline equiv. by 2010

• Other methods – Biomass-derived– Biological– High temperature thermochemical e.g., ZnO reduction

Reforming: CH4 + H2O 3H2 + CO (800°C ΔH = 206.16 kJ/mol CH4)

Shift: CO + H2O H2 + CO2

(300°C ΔH = -41.15 kJ/mol CO)

http://www.eere.energy.gov/hydrogenandfuelcells/

$2.00-3.00/gal equiv by 2015

Energy Needed to Compress HydrogenCompress to same energy density for storage and transport

(332 bar)

(100 bar)Current pipelinepressure

This is a thermodynamic limit;no storage medium can require less energy.

Hydrogen requires 3 to 4 times as much energy as methane for compression

Energy Needed for Pipeline Transportfor equivalent energy flow rates at 100 bar

Hydrogen requires ~ 2-7 times as much transport energy

2

2L vP f W V Pdρ

Δ = = Δ& &

Other Transport Options• Liquefaction

Normal boiling point of H2 is 20.4 KTheoretically, only 3.3% of the energy in the fuel is required to

cool and condense from 25°C Actually > 30% of fuel energy is required due to low COP

• Truck Transport1

Receiver at 40 bar, truck transport at 200 barStandard tank truck can carry 3.2 tons and deliver 2.9 tons of

methane At 200 bar, only 320 kg of hydrogen are carried with 288 kg

delivered40% of the fuel energy is required to deliver H2 200 km

1from Eliasson and Bossel, “Future of the Hydrogen Economy”, http://www.efcf.com/reports/

Fuel Cell VehiclesHyundai DaimlerChrysler

Ford General Motors

Disadvantages of Fuel Cells for Vehicles• Hydrogen as Fuel

large high-pressure tanks and limited distance on tanknew infrastructure required for refilling

• Liquid Fuels requires reforming (perhaps not with methanol)CO must be eliminatedlower efficiencypoor time response

• Difficult Design Problemsize, shocks, temperature extremes, transientsreformation, storage, safetyreliability...

• Why isn’t CNG (methane) used extensively for cars?Equiv. energy cost of CNG = $1.32/gal w/o taxes, (1.22 therm/gal)CO2 output is 80% of that from gasoline

Hydrogen Volume Required for Transport Fuel

0

100

200

300

400

500

600

700

800

900

0 50 100 150 200 250 300 350

Specific Energy (Wh/kg)

Ener

gy D

ensi

ty (W

h/l)

Lead-Acid

Ni-Cd

Ni-MH

Li-Ion

ZMPAg-Zn

Battery TechnologyTwo Centuries Of Progress

Battery TechnologyTwo Centuries Of Progress

Lighter Weight

Sm

alle

r Siz

e

1801 VoltaZn-Cu

1839 Fuel Cell1859 Pb Battery1899 Ni-Cd1973 Li-Metal1975 Ni-MH1979 Li-Polymer

1990Sony

Li-Ion

2000BellcorePlasticLi-Ion

Battery development generally proceeds from small sizes to larger sizes as the technology matures.

Source: Tarascon and Dave Foster, U. of Wisc

Energy Storage Density

Energy Storage Density

Disadvantages of Fuel Cells for Vehicles• Hydrogen as Fuel

large high-pressure tanks and limited distance on tanknew infrastructure required for refilling

• Liquid Fuels requires reforming (perhaps not with methanol)CO must be eliminatedlower efficiencypoor time response

• Difficult Design Problemsize, shocks, temperature extremes, transientsreformation, storage, safetyreliability...

• Why isn’t CNG (methane) used extensively for cars?Equiv. energy cost of CNG = $1.32/gal w/o taxes, (1.22 therm/gal)CO2 output is 80% of that from gasoline

Fuel Cells for Stationary Power

• Simpler than vehicular applications • Can be operated directly from natural gas• May be able to use waste heat (cogeneration)

thereby improving overall efficiency• Transient operation is less important• Balance of system is important• Careful system optimization is required

Source: Shell Oil

World oil production will peakbetween 2004-2008 according toKenneth Deffeyes1.

(1018

J)

1 The Impending World Oil Shortage, Princeton Univ. Press

Concluding Comments+ There is increasing pressure on our conventional energy reserves+ There is evidence supporting global climate change induced by

CO2 from combustion+ A hydrogen economy has been proposed with fuel cells providing

energy for transportation and stationary applications

− Hydrogen is not available and it is not an ideal fuel− If used, hydrogen must be generated from renewable fuels and

used locally− Fuel cells can improve efficiency and lower emissions, but not

significantly if conventional fuels are used to produce hydrogen− Large expenditures for changing to a hydrogen economy do not

appear to be warrantedClearly – challenges lie ahead

Quiz

A. Water heater uses much less energyB. Water heater uses about the same energyC. Water heater uses much more energyD. They cannot be compared…

How does the energy use for the typical family vehicle compare with that for the typical hot water heater?

What are the Driving Forces For Fuel Cell Development?

• InfrastructureDifficulty in siting new plantsCost and efficiency losses (5-8%) in transmission Power quality and dependability issues

• Higher EfficiencyEfficiency is reduced by fuel processingFuel is relatively inexpensive and plentiful (now)

• Lower emissionsWhat is the cash value of reduced pollutants?Regulatory considerationsGlobal warming and political consequences

• "The less you know, the better it looks"