e-News #90: Fuel Cells

October 29, 2013
 
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Fuel Cells Fuel Alternative Energy Options

The Rise of Fuel Cells

The greatest exposure most of the public has to today’s fuel cell technology likely is through transportation markets. In large part, this is because the federal government in 2003 proposed the Hydrogen Fuel Initiative, an attempt to develop fuel cell technologies to make fuel-cell vehicles cost effective. This initial push was further supported through the Energy Policy Act (EPACT) legislation of 2005 which changed U.S. energy policy by providing incentives for energy production of various types.

Although the public’s familiarity with fuel cells might reside primarily with vehicles, it is the stationary use of fuel cells to power portions or the entirety of buildings that may provide the greatest potential for the technology.

What are Fuel Cells?

A fuel cell is a device that converts the chemical energy from a fuel – most commonly hydrogen – into electricity through a chemical reaction with oxygen or another oxidizing agent. Although many might think of fuel cells as batteries, they are not. Fuel cells require a constant source of fuel and oxygen to operate, and they can produce electricity for as long as fuel and oxygen are provided.

Fig1 Fuel Cell Assembly DOE EERE
Figure 1: A fuel cell assembly demonstrating the functionality of fuel cells.
Image courtesy of DOE EERE.

There are three main components to a fuel cell: a reformer, a stack, and an inverter.

  • Reformer: The reformer portion of a fuel cell “strips” hydrogen from the actual fuel source, such as natural gas or water. This process can be completed through chemical reactions that break down the fuel into gaseous hydrogen molecules. Hydrogen then is stored at pressure and becomes ready for use in a fuel cell.
  • Stack: The stack is the core of what defines this technology. An example of a stack assembly is shown in Figure 1. It consists of an anode, electrolyte membrane, cathode, and bipolar plates. At its simplest, the anode interacts with the provided fuel source – hydrogen gas – to generate ions and electrons. The ions travel through the electrolyte membrane to the cathode, but the electrons cannot pass through the electrolyte and create the electric current of the fuel cell before being returned to the cathode. The cathode then catalyzes oxygen with the ions and returned electrons, and this combination then is exhausted from the cathode side as water and lost as waste heat. All these components are necessary to facilitate the proper reactions, even though minor variations in fuel cell designs may affect the way that the chemistry of combining hydrogen and oxygen is completed. The movement of electrons mentioned in the stack component is where the usable voltage is generated from the cell, and a typical fuel cell produces from 0.6 V to 0.7 V. The total power produced for effective use in a particular application then can be multiplied by assembling individual cells in series to yield higher voltages and/or in parallel configurations for a higher current to be supplied.
  • Inverter: This stage of the process is often only necessary in utility grid applications or those that require a clean alternating current (AC) power source. It is purely a transformer that converts and cleans the direct current (DC) produced by the fuel cell to AC for transmission or direct use in a facility.

Fuel Cell Design Options

Through years of fuel cell development, a number of variations have developed to fit their niche applications. Table 1 lists the primary types by fuel source, noting some of their base characteristics. The modular capacity ratings range from 1 kilowatt to 10 megawatts depending on the design, but can be staged or expanded in the event that additional power or replacement and upgrades become necessary.

Proton Exchange Membrane Fuel Cells: This is the most common cell researched for passenger vehicles and the transportation sector. It operates at a relatively low temperature which enables safer use in a single vehicle. The physical properties allow for a higher power density which also helps reduce equipment size. The closer the ratio of size and capacity when compared to the internal combustion engine, the greater opportunity there is to become a viable solution for that application.

Phosphoric Acid Fuel Cells: This type of cell operates at a slightly higher temperature than PEMFCs and for that reason is unsuitable for vehicle use, but it becomes more effective as a stationary power source for an office building, data center, or other grid-tied facility.

Solid-Oxide Fuel Cells: Solid oxide is increasingly the most popular style for use in stationary power systems. Such a high operating temperature helps facilitate cleaner chemical reactions and enables quality hot water, if not steam generation, to be possible for additional heating capacity for a building .

Molten Carbonate Fuel Cells: Perhaps the most important quality of this arrangement is that such a wide variety of fuels can be used in addition to pure hydrogen. These cells are very similar to solid oxide, but they operate at slightly lower temperatures. The greatest benefit here is that material costs are reduced for production due to some additional material leniency from the reduced operating temperature compared to Solid-Oxide.

Implementation Concerns

The issues with fuel cells may vary based on chosen applications. There are different criteria when applying the technology to vehicles or as facility power stations. Here is a look at the most prominent concerns relating to their use to supply building power.

  • Cost: Fuel cells contain many components that are costly and make their use prohibitive. Fuel cell membranes, precious metal catalysts like platinum, gas diffusion layers, and bipolar plates make up nearly 70 percent of a system’s cost.
  • Temperature: Reducing operating temperature, and thus limiting the amount of expensive specialty materials required, can limit some of this problem with automotive fuel cells. However, it then becomes important to consider the loss of Combined Heat Power (CHP) potential that might also be available, particularly in stationary fuel cell applications.
  • Durability: There is a balance to be achieved when designing for fuel cell cost. Higher-priced materials may allow for extended life of components, especially in the stack where the fuel conversion happens. For example, platinum is required as a catalyst due to its ability to handle the high temperatures in SOFCs without significant degradation. This is an expensive material and, when combined with the need to replace stack assemblies over time due to chemicals degrading components, is one of the largest drivers of a high life-cycle cost for fuel cells.

 

Table 1: Comparison List of Fuel Cell Variants.
Source: ASHRAE-HVAC Systems and Equipment.
Fuel Cell TypeProton Exchange Membrane (PEMFC)Phosphoric Acid (PAFC)Solid-Oxide (SOFC)Molten-Carbonate (MCFC)

Size Range

500W-250kW

100-200kW

1kW-10MW

250kW-10MW

Efficiency at LHV

30-40%

40%

45-60%

45-55%

Efficiency at HHV

27-36%

36%

40-54%

40-50%

Average Operating Temperature

200°F

400°F

1800°Fw

1200°F

Heat Recovery Potential

140°F water

Hot water

Hot water or steam

Hot water or steam

Fuels Used

Hydrogen

Hydrogen

Hydrogen
CO

Hydrogen
Carbon Monoxide
Natural Gas (Methane)
Propane
Landfill Gas
Marine Diesel
Coal Gasification

 

Fuel Cells in Use

The combined number of commercial buildings and industrial facilities in the U.S. exceeds 5 million, and their combined annual energy costs exceed $202 billion. With such a significant footprint, and with significant energy costs, there is the potential for substantial savings in energy use with the use of fuel cells, especially when transmission losses are factored in.

Commercial facilities, especially data centers and hospitals, often require a greater level of consumption and for longer periods of time. Data centers, in their basic form, are primarily multiple rows of server racks that operate at a constant load to maintain processing power. Hospitals also are required to operate at a consistent occupied level for nursing staff and patients, medical storage, and HVAC systems that support these areas. These 24/7 operations are ideal candidates for fuel cells. Their constant electric load profile fits well with a fuel cell that runs at a consistent level once started, and limited deviations from this configuration will optimize fuel cell lifetime. The added benefit of applying a fuel cell is the option to include some CHP function. This could be applied directly to heating needs in the space.

Fig2 400Kw Fuelcells Google Bloom Energy
Figure 2: 400kW of fuel cells in servers at Google’s main Mountain View, CA campus.
Image courtesy of Bloom Energy.

Sometimes it requires a primed test bed to validate the performance of new technologies. Google’s expansive Mountain View, California, campus can be considered an energy-intensive operation, but also one that has been considered carbon neutral since 2007.

In July of 2008, Google installed a series of solid oxide fuel servers that contain thousands of fuels cells. Each individual cell is capable of producing about 25 W, enough to power a light bulb. The fuel cells are aggregated together to create a stack, about the size of a loaf of bread; a few stacks combined could power an average home. The stacks then are combined together to form a power module, and multiple modules are assembled into a complete server.

Through the first 18 months following the installation, the cells had 98 percent availability and the four 100 kW servers 
delivered 3.8 million kWh of electricity to offset campus use. Systems of this size generally pay for themselves within a 3- to 5-year window from startup.

Fuel Cell Benefits

Fuel cells are not classified as a renewable energy technology since they primarily still utilize hydrocarbon fuels as the source of their reformed hydrogen. However, they are generally fit for comparison as an alternative to grid-provided power, as would be solar photovoltaic (PV) or wind systems, by way of their use. This is evidenced by the growing trend to develop localized electric power, called distributed generation.

Some benefits that fuel cells can provide in the right building application include:

  • Cells can utilize a renewable fuel. Landfill gas or marine grade biodiesel can be used with fuel cells to help them become a more truly renewable system.
  • Like other renewable technologies, there is reduced or eliminated transmission losses. According to Energy Information Administration (EIA), data, national, annual electricity transmission and distribution losses average about 7% of the electricity that is transmitted in the United States. This distributed generation approach significantly reduces these losses. Some fuel cells still require a connection to a natural gas supply provided by a utility, but the generation of electric power becomes local. This then can be supplemented with other renewables to help mitigate traditional peak building loads.
  • Fuel cells are a scalable, modular solution. As exhibited in the Google, Inc. installation of fuel cell servers, the technology can be expandable to meet current or future site needs by adding additional servers.
  • High operating temperatures allow for combined heat and power (CHP) integration. The CHP integration allows for increased overall efficiency ratings by collecting some of the waste heat generated by this unit to heat water for domestic or limited process heating uses throughout a building.
  • Continuous power can be provided. Unlike typical wind and PV installations, there are no intermittent power drops due to weather conditions or seasons. Fuel cells provide a constant rated stream of electricity as long as they have the fuel and water to maintain their chemical reactions.

Utility Incentives

The California Public Utilities Commission’s Self Generation Incentive Program (SGIP) is one of the longest-running and most successful distributed generation incentive programs in the country with 544 completed projects and a total capacity of 252 MW.

Since its inception in 2001, the SGIP has evolved significantly. It no longer supports solar photovoltaic technologies, and it also has been modified to include energy storage technologies, to support larger projects, and to provide an additional 20% bonus for California-supplied products.

The SGIP program is administered by Pacific Gas & Electric, Southern California Edison, Southern California Gas, and the California Center for Sustainable Energy on behalf of San Diego Gas & Electric. Utility representatives can provide more detailed information regarding SGIP opportunities, but some quick facts on the program follow.

  • Incentives for adopting fuel cells, CHP or electric, are $2.03/W.
  • For projects 30 kW or larger, 50 percent of incentive will be received up-front; 50 percent will be received based on actual kWh production over the first 5 years. For projects under 30kW, 100 percent of the incentive will be paid up front.
  • Systems must be sized according to customer’s electricity demand, be new, and be in compliance with all applicable performance and safety standards.
  • Fuel cells must be covered by a minimum ten-year warranty covering labor and replacement costs.

Although fuel cells are still considered an emerging technology, they are proving to be a formidable and increasingly popular option for implementation as part of comprehensive renewable energy strategies and distributed generation design schemes.

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e-News is published by Energy Design Resources (www.energydesignresources.com), an online resource center for information on energy efficiency design practices in California.

Savings By Design (www.savingsbydesign.com) offers design assistance and incentives to design teams and building owners in California to encourage high-performance nonresidential building design and construction.

Energy Design Resources and Savings By Design are funded by California utility customers and administered by Pacific Gas and Electric Company, Sacramento Municipal Utility District, San Diego Gas and Electric, Southern California Edison and Southern California Gas Company, under the auspices of the California Public Utilities Commission.

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