Fuel cells convert fuel into electricity through an electrochemical process instead of combustion of the fuel. William Grove invented the first fuel cell in Great Britain in 1839 and people have been trying to make them economical ever since. The technology went on to power all onboard electronics for the U.S. space program since the 1960s.
Since then, various fuel cell chemistries have been developed. This has resulted in products suitable for a wide range of applications. Interest in fuel cells has continued growing due to a world-focus on efficiency and pollution. Fuel cells pack high efficiency into small packages with almost zero sulfur oxide, nitrogen oxide and carbon monoxide pollution. In theory, fuel cells are better than piston engines, gas turbines and steam engines.
A typical Internal Combustion Engine (ICE) generator set (genset) burns fuel in an engine to turn a shaft connected to a generator, spinning a magnet in a wire coil and “pushing” electrons out. This process uses combustion and results in significant greenhouse emissions. The fuel efficiency also varies greatly depending on the type of genset used. The theoretical maximum efficiency of an engine is called the Carnot limit. So, the larger the difference between the peak temperature in the engine and the exhaust temperature, the greater the efficiency. Unfortunately as peak temperatures climb to get more efficiency from an engine, so does the production of nitrogen oxides. Nitrogen oxides may be a minor greenhouse gas, but they are a major contributor to eye-stinging urban smog. With tough emissions restrictions, engine manufacturers go to great lengths and expense to reduce nitrogen oxide emissions.
Best Gensets today:
Gas turbines have historically achieved a maximum 38% efficiency. But the exhaust from a gas turbine is quite hot and can be used for making steam to drive a third kind of engine – a steam engine. Steam engine-generators have achieved as much as 40% efficiency. Coupling a gas turbine – operating on the Brayton Cycle – to a boiler and steam engine using the Rankine Cycle, you get a combined cycle power generator.
Best Combined Cycle Power Generators:
Smaller Gas Turbines:
There are a variety of Fuel Cell types but in general they:
Some 2 kW fuel cells have achieved 60% efficiency in converting the energy in natural gas to electricity. And some fuel cell providers have claimed efficiencies of 70%, but this is for fuel cells which require high purity hydrogen. The 70% efficiency claim does not include the energy required to split out hydrogen from natural gas or water. Including those losses, the net efficiency drops to between 25% and 30%.
At efficiencies of 60% in small units, fuel cells can provide power at the home, office or factory much more efficiently than can the utilities with all the losses in the power lines going from big power plants to the meter. Where there is no utility, fuel cells can provide power at double the efficiency of small engine-gensets.
Fuel cells convert chemical energy in fuels to DC electric power using an electrochemical process – not through combustion. Similar to how a battery operates, a fuel cell is recharged by a fuel used to run a chemical “pump”. The “pump” moves electrons from one side of a barrier (which becomes positively charged) to the other side (which becomes negatively charged). It does so continuously until the fuel supply is exhausted.
There are many types of legacy fuel cells such as proton exchange membrane (PEM), molten carbonate fuel cells (MCFC), direct methanol fuel cells (DMFC) and solid oxide fuel cell (SOFC). The table below lists characteristics of these various fuel cell approaches. These technologies use expensive precious metals, corrosive acids or hard-to-contain molten materials and have marginal performance. Most of these fuel cells generate electricity by moving fuel through the electrolyte. Solid oxide fuel cells differ in that they move oxygen from air through the electrolyte.
|Fuel Cell Type||Proton Exchange Membrane (PEM)||Molten Carbonate Fuel Cell (MCFC)||Direct Methanol Fuel Cells (DMFC)||Phosphoric Acid Fuel Cells||Solid Oxide Fuel Cells (SOFC)|
25-35% (including losses to create hydrogen)
|Start-up Time||Seconds (not counting the Reformer)||Hours||Seconds||Hours||
Recognized as having the greatest potential out of all of the fuel cell technologies.
Use of hydrocarbon fuels still produces carbon dioxide (a greenhouse gas). But SOFC power generation produces significantly low levels of carbon dioxide. Since fuel cells produce electricity through a chemical process versus combustion, there are virtually no nitrogen oxide (NOx), sulfur oxide (SOx) or carbon monoxide emissions. This adds up to unparalleled efficiency – less fuel to produce the same electricity.