Fuel Cells

Size Range

0.01 MW to 10 MW

Technology

Fuel cells use the chemical energy created upon the oxidation of hydrogen to produce heat and electricity with a by-product of water See figure below. When hydrogen enters a fuel cell, a catalyst on the anode divides the hydrogen into H+ (hydrogen ion) and e- (electron). The negatively charged electrons flow through an external load to the cathode, whilst the hydrogen ions pass through the electrolyte to the cathode, where they combine with oxygen and the electron to produce water and release energy (heat) - see equations 1& 2 below. The voltage produced by a single fuel cell is small. However, fuel cells can be organised into stacks to provide power as required. Fuel cells are thus an ideal modular technology.

Fuel Cell Schematic
	1. H2 -> 2H+ + 2e- 2. 2H+ + 2e- + 2O2 -> 2H2O + energy

Fuel cells fall into two categories: low-temperature and high-temperature. Low temperature fuel cells (e.g. phosphoric acid) have been around for over 35 years, and are therefore reliable technologies. High-temperature fuel cells (e.g. molten carbonate and solid oxide) operated at a temperature of roughly 540ºC, and are real emerging technologies.

Performance and Efficiency

Low-temperature fuel cells	High-temperature fuel cells
Rapid start-up. Low operating efficiencies	Start-up time up to 8 hours Up to 50% fuel to electric efficiency today Theoretical possibilities of up to 60%. By-product heat is 260 to 370ºC, suitable for most thermal uses.

Fuel Types

Hydrogen can be derived from reforming natural gas or propane.
Hydrogen can also be obtained through electrolysis of water, powered by renewable energy sources.
Low-temperature fuel cells require externally reformed hydrogen.
High-temperature fuel cells can reform fuel internally.

Applications

Commercial, Residential

Low-temperature fuel cells can be used in transport applications, because of their rapid start, while high-temperature fuel cells are suitable for stationary power.
Large fuel cell applications can be used in small industrial and commercial applicationsincluding sectors such as electronics or food processing.
Small fuel cells can be used in domestic setting, providing heat and electricity for a single or number of homes.
Low-temperature fuel-cells are suitable for back-up power, while high-temperature power for facitlities with more constant power requirements.

Advantages and Disadvatages

Advantages	Disadvantages
Fuel cells can provide heat for a wide range of applications. High electrical efficiencies under varying load. No moving parts, except fans. Low emissions. Quiet operation.	With the exception of PAFC, no fuel cells are yet fully commercially viable; Largely unproven technology; No existing infrastructure for large-scale supply of hydrogen.

Economic Performance

Cost Range for Fuel Cells
Installed Capital Cost ($/kW)		3,500 – 5,000
Operating and Maintenance ($c/kWh)		0.5 – 5.0
Levelized Cost ($c/kWh)
8000hrs/year		9.0 – 11.5
4000hrs/year		14.5 – 19.5
Source: WADE, 2006

The current installed capital cost of a fuel cell are still high, due to the materials used and lack of mass-production. There have been significant and continuing reductions in the cost of balance of plant, and in production costs of the fuel cells. O&M costs and lifetimes for fuel cells remain somewhat speculative, due to lack of operational experience.