A fuel cell is a device that uses hydrogen (or hydrogen-rich fuel) and oxygen to create electricity by an electrochemical process. If pure hydrogen is used as a fuel, fuel cells emit only heat and water as a byproduct. Several fuel cell types are under development, and they have a variety of potential applications. Fuel cells are being developed to power passenger vehicles, commercial buildings, homes, and even small devices such as laptop computers.
Fuel cells have several benefits over conventional combustion-based technologies currently used in many power plants and passenger vehicles. They produce much smaller quantities of greenhouse gases that contribute to global warming and none of the air pollutants that create smog and cause health problems. In fact, if pure hydrogen is used as a fuel, only heat and water are emitted.
Fuel cells are more efficient than combustion-based technologies, and the hydrogen used to power them can be obtained from a variety of sources, including fossil fuels, renewable sources, and nuclear energy. Since the fuel can be produced from domestically available resources, fuel cells have the potential to improve national energy security by reducing our dependence on oil from foreign countries.
Although the potential benefits of fuel cells are significant, many challenges, technical and otherwise, must be overcome before fuel cells will be a successful, competitive alternative for consumers. These include cost, durability, fuel storage and delivery issues, and public acceptance.
A fuel cell is a device that uses hydrogen (or hydrogen-rich fuel) and oxygen to create electricity by an electrochemical process. A single fuel cell consists of an electrolyte sandwiched between two thin electrodes (a porous anode and cathode). While there are different fuel cell types, all work on the same principle
The amount of power produced by a fuel cell depends upon several factors, such as fuel cell type, cell size, the temperature at which it operates, and the pressure at which the gases are supplied to the cell. Still, a single fuel cell produces enough electricity for only the smallest applications. Therefore, individual fuel cells are typically combined in series into a fuel cell stack. A typical fuel cell stack may consist of hundreds of fuel cells.
Direct hydrogen fuel cells produce pure water as the only emission. This water is typically released as water vapor. Fuel cells release less water vapor than internal combustion engines producing the same amount of power.
Most fuel cells systems use pure hydrogen or hydrogen-rich fuels, such as methanol, gasoline, diesel, or gasified coal, to produce electricity. Both fuel types have advantages and limitations.
Most fuel cell systems are fueled with pure hydrogen gas, which is stored onboard as a compressed gas. Since hydrogen gas has a low energy density, it is difficult to store enough hydrogen to generate the same amount of power as with conventional fuels such as gasoline. This is a significant problem for fuel cell vehicles, which need to have a driving range of 300-400 miles between refuelling to be competitive gasoline vehicles. High- pressure tanks and other technologies are being developed to allow larger amounts of hydrogen to be stored in tanks small enough for passenger cars and trucks. In addition to onboard storage problems, our current infrastructure for getting liquid fuel to consumers cant be used for gaseous hydrogen. New facilities and delivery systems must be built, which will require significant time and resources. Costs for large-scale deployment will be substantial.
Fuel cell systems can also be fuelled with hydrogen-rich fuels, such as methanol, natural gas, gasoline, or gasified coal. In many fuel cell systems, these fuels are passed through onboard "reformers" that extract hydrogen from the fuel. Onboard reforming has several advantages
There are also several disadvantages to reforming hydrogen-rich fuels
High-temperature fuel cell systems can reform fuels within the fuel cell itself—a process called internal reforming—removing the need for onboard reformers and their associated costs. Internal reforming, however, does emit carbon dioxide, just like onboard reforming. In addition, impurities in the gaseous fuel can reduce cell efficiency.
The design of fuel cell systems is quite complex and can vary significantly depending upon fuel cell type and application. However, most fuel cell systems consist of four basic components
Though they are not discussed here, most fuel cell systems include other components and subsystems to control fuel cell humidity, temperature, gas pressure, and wastewater.
The first component of a fuel cell system is the fuel processor. The fuel processor converts fuel into a form useable by the fuel cell. If hydrogen is fed to the system, a processor may not be required or it may only be needed to filter impurities out of the hydrogen gas.
If the system is powered by a hydrogen-rich conventional fuel such as methanol, gasoline, diesel, or gasified coal, a reformer is typically used to convert hydrocarbons into a gas mixture of hydrogen and carbon compounds called "reformat." In many cases, the reformat is then sent to another reactor to remove impurities, such as carbon oxides or sulfur, before it is sent to the fuel cell stack. This prevents impurities in the gas from binding with the fuel cell catalysts. This binding process is also called "poisoning" since it reduces the efficiency and life expectancy of the fuel cell.
Some fuel cells, such as molten carbonate and solid oxide fuel cells, operate at temperatures high enough that the fuel can be reformed in the fuel cell itself. This is called internal reforming. Fuel cells that use internal reforming still need traps to remove impurities from the unreformed fuel before it reaches the fuel cell.
Both internal and external reforming release carbon dioxide, but less than the amount emitted by internal combustion engines, such as those used in gasoline-powered vehicles.
Energy Conversion Device - The Fuel Cell Stack
The fuel cell stack is the energy conversion device. It generates electricity in the form of direct current (DC) from chemical reactions that take place in the fuel cell. The fuel cell and fuel cell stack are covered under Fuel Cell Components and Function.
Current Inverters Conditioners
The purpose of current inverters and conditioners is to adapt the electrical current from the fuel cell to suit the electrical needs of the application, whether it is a simple electrical motor or a complex utility power grid.
Fuel cells produce electricity in the form of direct current (DC). In a direct current circuit, electricity flows in only one direction. The electricity in your home and work place is in the form of alternating current (AC), which flows in both directions on alternating cycles. If the fuel cell is used to power equipment using AC, the direct current will have to be converted to alternating current.
Both AC and DC power must be conditioned. Power conditioning includes controlling current flow (amperes), voltage, frequency, and other characteristics of the electrical current to meet the needs of the application. Conversion and conditioning reduce system efficiency only slightly, around 2 to 6 percent.
Heat Recovery System
Fuel cell systems are not primarily used to generate heat. However, since significant amounts of heat are generated by some fuel cell systems—especially those that operate at high temperatures such as solid oxide and molten carbonate systems—this excess energy can be used to produce steam or hot water or converted to electricity via a gas turbine or other technology. This increases the overall energy efficiency of the systems.
Fuel cells are classified primarily by the kind of electrolyte they employ. This determines the kind of chemical reactions that take place in the cell, the kind of catalysts required, the temperature range in which the cell operates, the fuel required, and other factors. These characteristics, in turn, affect the applications for which these cells are most suitable. There are several types of fuel cells currently under development, each with its own advantages, limitations, and potential applications. A few of the most promising types include
The important issues of concern today are environmental pollution and energy conservation. In India, these issues are more significant, in view of the alarming rise in pollution levels due to automobiles in the metropolis and the need to conserve fast depleting oil resources. The need for use of Electric Vehicles (EV) has been well recognised. A significant step in this direction has been the introduction of Battery Operated Vehicles (Electric Vehicles), which are pollution free, eco-friendly with zero emission. Unlike the conventional cars that use petroleum fuels to power internal combustion engines, the electric car is run by a direct current electric motor powered by a rechargeable battery pack. Electric vehicles are used today in sizeable numbers for specialised applications, viz., industrial, recreational, road transports.
To promote, support, accelerate the development and rapid commercialisation of Battery Powered Vehicles, as an alternative to petrol/diesel operated vehicles, by providing financial and technical assistance to the prospective developers.
The running of Battery Powered Vehicle is not only pollution free but eco-friendly too and yields benefits such as