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Fuel Cells

Converts the energy of hydrogen into electrical energy without the need for combustion

Diagram of how a fuel cell works.

Combined Heat and Power systems (CHP) describes a group of technologies that produce electricity and heat. Conventional approaches include, for example, a diesel engine with waste heat recovery. However, newer, more environmental technologies are fast developing. Smaller CHP units located in a building or home and using waste heat from generating electricity will be more efficient than generating electricity at a central plant where losses are high and the waste heat cannot be used. Producing electricity in your own home may not be that far away.

Fuel cell technology is under development that could permit a freezer chest-sized fuel cell to power an entire home. Fuel cells produce electricity through a chemical reaction rather than burning the fuel, and therefore have very low emissions. In residential applications, fuel cells are expected to eventually compete with current electricity generation, depending on costs of natural gas and electricity in a given region.

While fuel cells are not yet commercially available for residential use, they are available for large-scale power production, and may be commercially available for residential use within the next five years.

A fuel cell is a device that converts the energy of fuel into electrical energy without the need for combustion. A conventional power plant produces electricity by burning a fossil fuel that turns a generator. Fuel cells produce electricity by using hydrogen in a chemical process, in a similar way as a battery. Since hydrogen is almost always found combined with other elements, fuels such as natural gas, methane, propane, ethanol, gasoline, or other fuels are used to extract hydrogen for use in the fuel cell. When fossil fuels are used to produce hydrogen, other byproducts are produced, such as CO2 and in some cases small amounts of NOx, SOx, and particulate matter. These byproducts are much less than those produced by burning these fuels to produce electricity. Fuel cells are much less polluting and about twice as efficient as typical steam-turbine electricity production. Once the hydrogen is obtained, the fuel cells' only by-products are heat and water.

A fuel cell consists of two electrodes separated by a membrane. Hydrogen passes over one electrode and oxygen over the other. The electrode surface has a catalyst that splits the hydrogen gas into protons and electrons. The protons only can pass through the membrane and react with the oxygen and electrons on the other side to make water. The electrons cannot pass through the membrane and, in the process of bypassing the membrane, produce electricity for use in the home.

A 5 to 7 kW residential fuel cell prototype is about the size of a freezer chest and can provide enough electricity for a typical 2,000 square foot home. Waste heat from the fuel cell could be used to produce hot water or space heat for a home, thereby increasing the overall efficiency of the fuel cell system.

Fuel cells not only offer an efficient means of generating electricity from fossil fuels, but also have very low emissions. Up to 70 percent of the energy obtained from fuel can be converted to usable electric power and heat (compared with about 35 percent from a central power plant).


Energy Efficiency

Combined Heat and Power (CHP) systems installed in the home, whether based on fuel cells or a typical reciprocal engine, are more efficient than generating electricity and transmitting it to the home. When the waste heat is used in the home, the efficiency of the system rises to over twice that of central generating plants. This efficiency gain results in lower costs for energy. The greater the amount of the waste heat that can be utilized, the more cost savings that will be realized.

Environmental Performance

Fuel cell Combined Heat and Power systems have an improved environmental performance since the technology relies on chemical reactions rather than combustion. The chemical reaction does produce carbon dioxide which is a green-house gas pollutant, but in lower quantities than combustion with its inefficiency. In addition, typical pollutants s released in the combustion process are eliminated in the fuel cell operation. Other environmental benefits include higher efficiency resulting in lower fuel usage, lower noise pollution, and less water and land use typical of central generation plants. And an associated environmental benefit may be the pure water that is produced in the fuel cell chemical process when producing electricity.


Difficult

Fuel cells are currently expensive; residential-sized systems are under development and not commercially available. Residential trials are underway by some manufacturers. Long-term performance and standardized maintenance requirements and procedures are not yet established. Currently, a substantial overhaul of the fuel cell is required as often as every five years.


Initial costs for the Fuel Cell Combined Heat and Power systems are high and focused on the premium power market. This market tends to pay more for energy based on other attributes such as reliability, noise reduction, lower unplanned maintenance problems, or associated environmental benefits.


The operational costs for Fuel cell generation systems are dependent on the efficiency of the system. The curves below show the cost of electricity for different efficiency fuel cells relative to the natural gas costs. For example, a 50% efficient fuel cell will produce electricity at about 5 cents/kWh if the natural gas cost is 70 cents per therm. This cost does not include the purchase price of the fuel cell. In addition the fuel cell maintenance is very high with current technology.


National Electric Code (NEC) and National Fire Protection Association (NFPA) codes will apply to fuel cells used for residential applications. The regulations concerning the interconnection of fuel cells with the home electrical system are being developed, but are not yet standardized.


No field evaluations have been completed due to lack of commercialization of fuel cell systems for residential use.


When residential fuel cells are available, they may be installed in basements or outside. Connections for a fuel gas line and electrical supply to the home will be necessary. When using a fuel other than pure hydrogen, an exhaust vent will be required. Some fuel cells will require a drain for excess water. Other fuel cell designs will use all of the water produced by the fuel cell internally. Waste heat from the fuel cell may be used for hot water production or simply vented to the outdoors.


No information is available at this time


Fuel cells, when used to generate electricity while utilizing the waste heat, are a very clean and efficient energy supply for the home, especially when compared to other fossil fuel energy production methods. With fuel cells, weather-related electrical power outages will be minimized. Widespread use of fuel cells can decrease the need for large central generating plants, especially as communities continue to grow.

Installed costs in CHP mode today are over $6000/kW. Long-term target cost for residential fuel cells is $1500 per kW. Depending on the cost of the hydrogen source (such as natural gas), electricity from a 2-kW system at this cost could provide power at 8 to 10 cents per kWh over the lifetime of the fuel cell.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.