Fuel Cells Explained

Fuel Cell Benefits

  • Environmental
  • High Efficiencies
  • Combined Cooling, Heat & Power (CCHP)
  • Reliability
  • Power Quality
  • Permitting Ease
  • Modularity
  • "Distributed Generation-ness"

Environmental Acceptability

The environmental benefits of fuel cells are some of the main motivating forces in their development. These benefits include the zero- or near-zero-emission of criteria pollutants (NOx, SOx, CO, and hydrocarbons) and very low noise emissions.

Environmentally friendly fuel cell properties could eliminate consumer contempt for power generation close to their houses and businesses. While most consumers probably would prefer to have conventional electricity generated at a location far from their homes due to the noise and pollution, the benign nature of fuel cells makes them non-offensive even if placed in residential communities.

Chart: Fuel Cell system efficiencies

High Efficiencies

Depending upon fuel cell type and design, fuel-to-electricity efficiency ranges from 30 to 60 percent (LHV). For hybrid fuel cell/gas turbine systems, electrical conversion efficiencies are expected to achieve over 70 percent (LHV). When byproduct heat is utilized, the total energy efficiency of fuel cell systems approaches 85 percent.

As shown in Figure 3, stand-alone fuel cell systems have the capability of reaching efficiencies greater than 50 percent, even at relatively small sizes (e.g., 10 kW). Hence, fuel cell systems could reduce the impact of electricity production on global climate change by reducing the amount of greenhouse gases emitted into the atmosphere per kilowatt-hour of power. They would also reduce resource depletion and dependence on fossil fuels by allowing more power to be harnessed from an same amount of fuel.

Combined Heat and Power (CHP) or Combined Cooling, Heat and Power (CCHP) Capability

Combined Heat and Power or combined cooling, heat and power capability diagram

High-quality heat is available for co-generation, heating, and cooling. Fuel cell exhaust heat is suitable for use in residential, commercial, and industrial co-generation applications.

The figure to the right compares conventional generation to CHP. On the left we see that the purchase of power from the grid must be supplemented with an onsite boiler to provide the same heating needs as what a fuel cell's waste stream (heat) could provide at no extra cost or investment.

The heat from a fuel cell can be used for a variety of purposes:

  • Boilers: Two thermal loads for a boiler plant are make-up water and return water.If a boiler distribution system is maintained properly, make-up water requirements will likely be low.For high make-up water requirements, pre-heating boiler make-up water represents a good application for a fuel cell power plant.Load characteristics will depend on the loads on its thermal loop, time of year, and site specific factors.
  • Domestic Hot Water(DHW) is usedfor a variety of purposes including showers, laundry, kitchen loads, etc.In dormitories or hotels, thermal loads typically peak in the morning and evening periods with little or no demand in the middle of the day and night.
  • Space Heating Loops.Hot water space heating loops generally operate at temperatures that require the high-grade heat exchanger Thermal utilization is to the months where space heating is required.
  • Swimming pools have both make-up water requirements (due to evaporation and spillage) and pool reheat requirements.The thermal load demand will vary depending on whether the pool is indoors or outdoors, the ambient temperature and humidity, the wind velocity, whether the pool is covered or not, the pool size and other site specific variables.
  • Absorption Cooling Thermal Loads: Using a high-grade heat exchanger option, the fuel cell power plant can provide heat to an absorption chiller to provide cooling to a building. Absorption chillers create a thermal load for a fuel cell when no other loads are available. If electric rates are high in the cooling season, then displaced cooling using an absorption chiller can be cost-effective. Sites with longer cooling seasons or requiring continuous cooling (hospitals, etc.) are the best candidate sites for this technology


Courtesy of Broad USA

Reliability

Fuel cells are assumed to be superior to the grid because they are on site and subject to fewer disruptions (e.g. storms knocking down wires). With no moving parts, fuel cells will have less instances of failure than mechanical systems.

Today, the long-term performance and reliability of many of the fuel cell systems has not been significantly demonstrated to the market.Research, development and demonstration of fuel cell systems that will enhance the endurance and reliability of fuel cells are currently underway. The specific RD&D issuesin this category include: (1) endurance and longevity, (2)thermal cycling capability, (3) durability in installed environment(seismic, transportation effects, etc.), and (4) grid connection performance.

Power Quality

Fuel cell electrical output canbe configured to be computer grade. For example, systems have been configured to provide 99.9999+ percent uptime. Furthermore, fuel cell power plants can be set up in a range of electrical outputs. Individual fuel cell systems also can be arranged in series to meet increasing load demands.

Permitting Ease

Permitting and licensing schedules are short due to the ease of siting. Furthermore, fuel cell power installations are exempt from air emission permitting requirementsin many U.S. states and provide flexibility under many federal, state and local air pollution standards.

Modularity

The fuel cell is inherently modular. It operates at near constant efficiency, independent of size and load. The fuel cell power plant can be configured in a wide range of electrical outputs, ranging from single kilowatt sizes up to multi-megawatt systems.

Distributed Generation

Distributed Generation (DG) refers to generation at or near the site of use (for example, at a near a building requiring power). Fuel cells are a form of DG, and can contribute to the establishment of a DG market because of their characteristics as described above. Instead of an electricity distribution infrastructure based on centralized power plants routing power through wires over long distances, fuel cells and DG make it attractive to spread small power plants throughout an electrical grid or a geographic area.

Such a configuration could:

  • Reduce pollution
  • Increase local and system reliability
  • Increased power quality due to a potential freedom from troublesome frequency variations, voltage transients, dips, and surges. A fuel cell can be an attractive alternative to expensive uninterruptible power supplies, power-line filters, or energy storage systems used to condition grid electricity.
  • Increase efficiency by reducing the distance electricity would have to travel from source to consumer.
  • Reduce system maintenance cost (no transmission and distribution wires)
  • Increased flexibility in system design, expansion and growth
  • Reduction in customers' outage costs and experiences
  • Increased response to changing loads
  • Cogeneration benefits (heat capture)
  • Reduction in time to respond to customers needs - fuel cell construction is quicker than central station units and large transmission improvements, making it easier to match incremental capacity additions to load growth. This reduces opportunity cost and risk relative to investing in large central station units.
  • Customers are spending money installing power quality devices to alleviate power fluctuations, or bargaining for damage payments from generators. Fuel cell installations may mitigate or eliminate these situations.

From a global perspective, system reliability (availability) is extremely important for DP penetration in rural energy development. Remote locations need systems that will not breakdown and can be left unattended.

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Fuel Cells Explained

 


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