How Are Fuel Cells Different From Batteries?

Topics: Batteries, Fuel Cells, Energy Storage

Jahnavi Sajip
Author : Jahnavi Sajip on June 5, 2018

Batteries and fuel cells can both be used as power supplies when the utility service is not available, and both supply electricity without a rotating generator. However, there are important differences in the internal construction and capabilities of fuel cells and batteries. In simple terms, a battery delivers energy it has previously stored, while a fuel cell converts the energy from a fuel to electricity.

Conventional generators also produce electricity from fuels, but fuel cells generate it directly through a chemical reaction. On the other hand, generators depend on fuel combustion inside their pistons to produce a rotational motion, and the voltage supply comes from the interaction of two magnetic fields in the rotor and stator.


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Comparing Batteries and Fuel Cells

A key operating difference between batteries and fuel cells is that batteries have a charge and discharge cycle, while fuel cells produce electricity continuously, as long as their fuel is available.

  1. Batteries are useful in applications where they can be recharged. This can be accomplished with the power grid supply or with a renewable generation system. When combined with renewable generation, batteries enable a power supply that is independent from external sources.
  2. Fuel cells are a better option when there is no way to recharge batteries. For a given amount of energy, a fuel cell and its respective tank are much more compact and lighter than an array of fully charged batteries.

Note that a fuel cell can be refueled while operational, since the tank is separate. On the other hand, a battery cannot be charged and discharged simultaneously. The only exception are flow batteries, which have properties of both conventional batteries and fuel cells:

  1. Energy is stored as a charge difference between two electrolyte tanks.
  2. Electricity is produced when these electrolytes interact through a membrane in the flow battery.

How Can Fuel Cells Reduce Building Emissions?

Fuel cells have been designed for various fuels, including propane, natural gas, diesel and hydrogen. However, they can produce electricity twice as efficiently as a conventional electric generator, without noise or vibration. The emissions of a fuel cell are also much lower than those of other generation systems:

ELECTRICITY GENERATION SYSTEM TYPICAL CO2 EMISSIONS PER MWH
Coal-fired generator 1000 kg
Oil-fired generator 750 kg
Natural-gas-fired generator 500 kg
Fuel cell 400 kg

In the case of hydrogen fuel cells, there are no CO2 emissions for the simple reason that the fuel input contains no carbon (pure hydrogen gas). The only by-products are water vapor and heat. The drawback of this technology is that hydrogen is very difficult to store and handle.

Types of Fuel Cells

There are many ways to build a fuel cell, all accomplishing the same result: producing electricity from a fuel through a chemical reaction. Each type of fuel cell comes with advantages and limitations.

TYPE OF FUEL CELL

BRIEF DESCRIPTION

PROS

CONS

Proton Exchange Membrane (PEM)

Uses a polymer electrolyte. One of the most developed and common fuel cell types.

- Compact
- Long life
- Quick response
- Mature technology
- Expensive
- Complex
- Uses specialized fuel

Alkaline Fuel Cell (AFC)

Uses an alkaline solution as the electrolyte. Preferred type of fuel cell for aerospace applications.

- High efficiency
- Low cost manufacturing and operation
- Simple system with no compressors
- Mature technology
- Bulky
- Requires pure hydrogen and oxygen
- Pollutant sensitivity limits applications

Molten Carbonate Fuel Cell (MCFC)

Uses a molten carbonate solution as the electrolyte.

- High efficiency
- Fuel compatibility
- Suitable for large-scale applications, and combined heat and power (CHP)
  • - Susceptible to corrosion
  • - Slow start
  • - Short life

Phosphoric Acid Fuel Cell (PAFC)

Uses phosphoric acid as the electrolyte. First type of fuel cell to become commercial.

- Tolerates fuel impurities
- Suitable for large-scale applications and CHP
- Susceptible to corrosion
- Bulky
- Low efficiency
- Short life

Solid Oxide Fuel Cell (SOFC)

The electrolyte is a solid oxide or ceramic.

- High efficiency
- Fuel compatibility
- Suitable for large-scale applications and CHP
- High temperature
- Susceptible to corrosion
- Slow start
- Short life

Concluding Remarks

Fuel cells allows the production of electricity from fuels without combustion, at a higher efficiency than conventional generation systems and with reduced emissions. Since they operate above room temperature, their heat emissions can be recovered for space heating and domestic hot water applications.

When deciding between batteries and fuel cells, consider the energy inputs available - batteries need recharging and fuel cells need a compatible fuel. Get a qualified professional opinion to determine which system works best for you, or perhaps you can benefit from both.

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