Fuel cells are electrochemical systems that consume a fuel to produce electrical power with by-products of heat and water. Fuel cells have no moving parts and operate much like a battery that does not require recharging, producing quiet, reliable power, with efficiencies higher than internal combustion engines.
Progress has been made in fuel cell technology since previous Fundamental series descriptions appeared in Energy and Power Management. Interest continues to increase because of energy supply and weather disruptions. Fuel cell installations are now covered in sections of the national electric code (NEC).Fuel cells are expected to play an important role as a solution are to our nation’s reliance on imported oil. New tax incentives provided by the Energy Policy Act (EPAct 2005) further stoke interest.
The new regulations provide tax credits for qualifying fuel cell systems “placed in service” in 2006 and 2007. The credits are for 30% of the cost, up to $1000 per kW of power that can be produced. To qualify, systems must have an efficiency of at least 30% and must have a capacity of at least 0.5 kW.
In addition, EPAct 2005 (Section 807) established the Hydrogen Technical and Fuel Cell Advisory Committee (HTAC). HTAC will provide technical and programmatic advice to the Secretary of Energy on the Department of Energy’s (DOE) hydrogen research, development, and demonstration efforts.
Types of Fuel Cells
The types of electrolyte used in a fuel cell distinguishes and designates the different types. Phosphoric-acid fuel cells (PAFC) (shown in the diagram) have a high potential for use in small stationary power-generation systems. They operate at a higher temperature than PEM fuel cells and have a longer warm-up time.
Operation
In a fuel cell, hydrogen and oxygen combine to produce water and electricity. Hydrogen enters the fuel cell anode, and oxygen enters the cathode. The hydrogen presses through the electrolyte to get to the oxygen. A catalyst (sometimes in the form of a coating on the anode) helps separate the gas into electrons and hydrogen ions (protons). Only the protons can pass through the electrolyte to the cathode side of the cell. The electrons cannot pass and flow to an electrical load through an external circuit.
As oxygen flows into the fuel cell cathode, a coating on the cathode helps the electrons, hydrogen ions, and oxygen combine to form water and heat. The electric direct current continues as long as fresh hydrogen flows into the anode.
Individual cells are built-up in ‘sandwiches,’ called stacks, to provide a sufficient level of power. The number of cells in a stack dictates the total voltage. The surface area of each cell controls the total current. The total power generated is the product of the total voltage and the total current.
Challenges
The oxygen required for a fuel cell comes from the air. However, hydrogen is not that readily available and has limitations that makes its use impractical for many applications. There are no hydrogen pipelines coming into buildings to feed fuel cell generators. Hydrogen is not easily stored and distributed; therefore, it will be many decades before a transition to a hydrogen economy is possible.
Fuel cells that can use other, more readily available fuels will be required during the transition.
Promising fuels include natural gas, propane, kerosene, and methanol. The fuels have some distribution networks in place that can help them penetrate the market. The principal advantage of natural gas is the existing extensive infrastructure, but homes in rural areas have propane tanks.
The Nippon Oil Corporation (NOC) will soon begin installation of 1-kilowatt kerosene-fueled residential fuel cell cogeneration units in Japan.
Peugeot has unveiled the smallest fuel cell currently available for cars and pledged further research to halve the price by 2010. The Genepac fuel cell is 80-kW and can run for 500 kilometers (310 miles).
Commercial Building
An Anchorage, AK, postal facility has five 200-kW units; it was the first to use a multiple fuel cell unit controlled by an electric utility. The postal facility sells excess power to the utility at the avoided fuel cost the utility pays independent power producers. The installation uses a high-speed switching control system that allows the fuel cell power plant to run when grid power is not available.
Future maintenance costs will include replacing the fuel cell stacks at the end of their useful life, estimated at a minimum of 40,000 hours. Operating the stacks 75% loaded is expected to increase life to 48,000 hours. A new stack costs $250,000, but reconditioned stacks may be available at a lower cost. Reliability has exceeded 97%, and availability ranged from 97.2 – 99.8% during a six-month data collection period.
Another fuel cell was installed in conjunction with a district heating system in Dinslaken, Germany. The fuel cell has logged more than 15,000 hours of operation since commissioning. The power is supplied to the local grid that serves 73,000 people and the waste heat is used to supplement the district heating system, providing uninterrupted service to half a million residential users supplied by this power source.
During unusual winter weather, the installation continued to operate and supply electricity despite 75 grid disturbances that occurred because of a sudden winter freeze. Customers served by the fuel cell unit never lost power despite the severe weather.
Fuel cells have higher efficiency (up to 80% when waste heat is recovered) than central power plants (about 35% for the US utility power grid), and internal combustion engines (25 – 30%). Fuel cells offer decentralized, reliable power, independent of the vulnerable power grid. In remote areas where there are no power lines, fuel cells are now competitive and where the cost of downtime is high, they are finding applications as backup power sources.
Currently, the main disadvantage is the high cost of manufacturing. Economies of scale and high volume production facilities should eventually reduce the cost.
Test Your Knowledge
1. Fuel cells are less efficient than internal combustion engines.
2. PAFCs are used primarily in:
a. In small stationary power-generation systems
3. EPAct 2005 provides:
a. No incentive for installing fuel cells
b. A future tax credit for fuel cells installed after 2007
c. A tax credit for installing fuel cell systems in 2006 or 2007
4. Disadvantages of using fuel cells today include:
a. Their high initial cost
b. The high cost of replacement stacks
5. Reformers are:
a. Not usually needed in fuel cell installations
b. Used to decontaminate the hydrogen derived from other fuels
c. Remove the oxygen from fuel cells
Answers:
1. Fuel cells are less efficient than internal combustion engines.
2. PAFCs are used primarily in:
a. In small stationary power-generation systems
3. EPAct 2005 provides:
c. A tax credit for installing fuel cell systems in 2006 or 2007
4. Disadvantages of using fuel cells today include:
5. Reformers are:
b. Used to decontaminate the hydrogen derived from other fuels
