Renewable energy notes for me power system engg

1. FUEL CELL
A Fuel Cell is an electrochemical energy conversion device that combines hydrogen and
oxygen to produce electricity (DC electricity), with water and heat as its by-product. Since
conversion of the fuel to energy takes place via an electrochemical process, not combustion. It is
a clean, quiet and highly efficient process- two to three times more efficient than fuel burning.
CONSTRUCTION
Anode
- Negative post of the fuel cell.
- Where the fuel "oxidizes", and releases electrons.
Cathode
- Positive post of the fuel cell.
- Where oxygen (usually from the air) "reduction" occurs.
Electrolyte
- Proton exchange membrane (PEM).
- Specially treated material (thin permeable polymer sheet), only conducts positively
charged ions.
Catalyst
- Usually a powder of platinum at anode and nickel at cathode is coated thinly onto carbon
paper or cloth.
- The platinum-coated side of the catalyst faces the PEM.
- Speedup the chemical reaction

2. WORKING PRICIPLE
Oxidation
 At the anode of the cell, a catalyst (platinum powder) is used to separate the proton
from the electron in the hydrogen fuel.
Reduction
 At the cathode of the cell, a second catalyst (nickel) is used to recombine the protons,
electrons, and oxygen atoms to form water.
On the anode side, hydrogen gas (H2) is forced through catalyst.
 When H2 molecule comes contacts platinum catalyst, it splits into two H+ ions and
two electrons (e-).
2H = 2H+ + 2e-
 Electrons are conducted through the anode.
 The positive hydrogen ions (H+) migrate across the electrolyte towards the cathode.
On the cathode side, oxygen gas (O2) is forced through catalyst
 Forms two oxygen atoms, each with a strong negative charge.
 Negative charge attracts the two H+ ions through the membrane, Combine with an
oxygen atom and two electrons from the external circuit to form a water molecule
(H2O).
2H+ + 2e- + O = H2O
 A single fuel cell generates a tiny amount of direct current (various from 0.7 to 1.4
volt).

3. TYPE OF FUEL CELL
Fuel cell type PEM AFC PAFC DMFC MCFC SOFC
Name
Proton
Exchange
membrane
Alkaline Phosphoric
Acid
Direct Methanol
Molten
Carbonate
Solid Oxide
Applications
Vehicles,
Mobile,
combined
heat and
power
production
Space
Applications
Large scale
combined heat
and power
production
Mobile
applications
from micro to
small
scale
Medium to
large scale
combined heat
and power
production, up
to MW
All sizes of
combined heat
and power
production, up
to multi MW
Operating
Temp(oC)
50-100 50-200 about 220 About 70 About 650 500-1000
Reactant Ion H+ OH- H+ H+ CO32- O2-
Fuel Hydrogen Hydrogen Hydrogen Methanol
H2, CO and/or
CH4
H2, CO and/or
CH4
Cell
component
Carbon-based Carbon-based Graphite based Carbon-based Stainless based Ceramic
Catalyst Platinum Platinum Platinum
Platinum/
ruthenium
Nickel Perovskites
Electrical
efficiency
40-50% 60% 37-42% 30-40% > 50% > 50%
Cell life time < 3000 hours < 5000 hours > 5000 hours < 3000 hours > 10000 hours > 10000 hours
Anode
reaction
H2 = 2H+ + 2e- H2 + 2(OH)- =
2H2O + 2e-
H2 = 2H+ + 2e- CH3OH + H2O =
CO2 + 6H+ + 6e-
H2 + CO3- - =
H2O + CO2 + 2e-
H2 + O- - =
H2O + 2e-
Cathode
reaction
½O2 + 2H+ +
2e- = H2O
½ O2 + H2O +
2e- = 2(OH)-
½O2 + 2H+ +
2e- = H2O
3/2 O2 + 6H+ +
6e- = 3H2O
½O2 + CO2 +
2e- = CO3 - -
½O2 + 2e- = O-
-

4. Benefits of Fuel Cell technology
 Environmental Benefits
o Fuels cells can reduce air pollution today and offer the possibility of eliminating
pollution in the future
 Environmental Benefits of Fuel Cell Power Generation
o A fuel cell power plant may create less than one ounce of pollution per 1,000
kilowatt-hours of electricity produced
o Conventional combustion generating systems produce 25 pounds of pollutants
for the same electricity
 Environmental Benefits of Fuel Cell Vehicles
o Fuel Cell Vehicles with hydrogen stored on-board produce ZERO POLLUTION in
the conventional sense
o The only byproducts of these Fuel Cell vehicles are water and heat
 Battery replacement/alternative
o Fuel Cell replacements for batteries would offer much longer operating life in a
packaged of lighter or equal weight
o Additionally, Fuel Cell replacements would have an environmental advantage
over batteries, since certain kinds of batteries require special disposal treatment
 Military Applications
o Fuel Cell technology in the military can help save lives because it reduces telltale
heat and noise in combat
o Handheld battlefield computers can be powered for 10 times longer with Fuel
Cell power meaning soldiers could rely on their computers in the field for longer
periods of time

5. Challenges to Fuel Cell Technology
 Cost
o The cost of fuel cells must be reduced to compete with conventional technologies.
o Conventional internal combustion engines cost $25-$35/kW; a fuel cell system
would need to cost $30/kW to be competitive.
 Durability
o Durability of fuel cell systems has not yet been adequately established.
o The durability standard for automobiles is approximately 150,000 miles and the
ability to function under normal vehicle operating conditions.
 Reliability
o For stationary systems 40,000 hours of reliable operation in a temperature range
of -35 degree Celsius to 40 degrees Celsius will be required for market
acceptance.
 System Size
o The size and weight of current fuel cell systems must be reduced to attain market
acceptance, especially with automobiles.
Applications
 Transportation
o All major automakers are working to commercialize a fuel cell car
o Trains, planes, boats, scooters, forklifts and even bicycles are utilizing fuel cell
technology as well
 Stationary Power Stations
o Over 2,500 fuel cell systems have been installed all over the world in hospitals,
nursing homes, hotels, office buildings, schools and utility power plants

6. o Most of these systems are either connected to the electric grid to provide
supplemental power and backup assurance or as a grid-independent generator
for locations that are inaccessible by power lines
 Telecommunications
o Due to computers, the Internet and sophisticated communication networks there
is a need for an incredibly reliable power source
o Fuel Cells have been proven to be 99.999% reliable
 Micro Power
o Consumer electronics could gain drastically longer battery power with Fuel Cell
technology
o Cell phones can be powered for 30 days without recharging
o Laptops can be powered for 20 hours without recharging
ADVANTAGES
 The fuel cell converts its fuel directly to electric power.
 No cooling water is needed so it can be located at any desired place.
 As it does not make noise. It can be readily accepted in residential areas.
 The fuel cell takes little time to go into operation.
 The land requirement is considerably less compared with conventional power plants.
 Possibly the greatest advantage of the fuel cell is its high operating efficiency.
 The maintenance charges are low as there are no moving parts and outages are also less.
 Fuel cells have an overload capacity of 50 to 100% for a short duration.
 In H2-O cell, the reaction product is water which is portable.
 The weight and volume of the fuel cell is considerably low compared to other energy
sources.
DISADVANTAGES
 Technology currently expensive
 Pure hydrogen is difficult to handle
 Requires refilling stations, storage tanks, …

7. Prepared by
R. RamaRaj, KCET
J. S. Sakthi suriya raj, KCET
K. Selva Narayanan, KCET