Solid oxide fuel
cells are comprised of an electrolyte, a cathode, and an anode. They combine
air and fuel to drive a continuous electrochemical process that produces a
reliable supply of electricity. Fuel cells do not operate through combustion as
most energy-producing mechanisms that use combustible fuels do, but through
chemistry. Specifically, they convert chemical energy into electrical energy,
molecules to electrons. The largest and most efficient natural gas turbines
that utilize combustion are able to achieve up to 63% efficiency in combine cycle
where the waste heat from combustion is utilized to run a steam turbine. Fuel cells
utilize reduction-oxidation reactions in which electrons move from one fuel, hydrogen,
natural gas, propane, or even gasoline and diesel to the oxygen component of
the system, which is derived from the air. The solid oxide fuel cell (SOFC) “uses
a solid ceramic separator, which allows the cell to operate at high
temperatures (700 °C or 1300 °F) at which ordinary fuel cell separators would
melt. The higher temperature both accelerates the reaction between the fuels
and allows the cell to produce hydrogen internally. In this way, solid oxide
fuel cells can use a common fuel like natural gas, at 60% efficiency,
comparable to combustion turbines.” The ceramic separator is electrolyte.
The materials coating the electrolyte make up the anode and cathode.
Source: Solid-oxide Fuel Cells: Using familiar fuel in a new way. Michael R. Gerhardt. Harvard. Blog. November 16, 2015. Solid-oxide Fuel Cells: Using familiar fuel in a new way - Science in the News (harvard.edu)
SOFCs are currently
limited to stationary deployments rather than use in transport since the high operating
temperatures required make startup time impractical and make long term stability
of cell materials uncertain. There are two main stack designs for the cells:
planar and tubular. (Bloom’s Series 10 is stackable)
The SOFC does
not need the great size, capacity, and cost of a combined-cycle gas turbine system
to achieve 60% efficiency but can get there on a much smaller scale and at much
less cost. Efficiency can also be increased to up to 85-90% by utilizing the waste
heat from the SOFC to heat buildings and to cool them via evaporation cooling. While
a SOFC still produces CO2 the exhaust is just CO2 and water, so it is much easier
to capture CO2 from a SOFC than from a natural gas power plant which has many
other combustion components.
Unfortunately,
there are some disadvantages of SOFCs that have limited their deployment. Cost
is a big issue, particularly cost of materials such as the ceramic materials
that separate the fuel anode from the oxygen cathode in the system. The high
operating temperature also presents some potential safety issues so shielding
components are necessary. Another problem is the time it takes the system to
get up to those high operating temperatures. SOFC advantages and disadvantages
are summarized below.
Bloom Energy’s Series 10 Solid Oxide Fuel Cells
On July 24,
2023, Bloom Energy announced the availability of their new Series 10 Solid
Oxide Fuel Cell Systems. Bloom Energy describes the Series 10 module as a “10MW
fuel cell offering with a five-year, flat-rate contract shipped in just 50
days, disrupting the traditional electricity-buying model.” The speed of
deployment compared to other forms of green energy is a big selling point as is
the buying model. Customers are not bound to long term contracts which gives
them options for the future. “The offer includes maintenance and 24/7
monitoring. Optional add-ons include microgrid and combined heat and power
(CHP) compatibility.” The modules are tailored for data centers, healthcare
facilities, and utilities. The modules can operate on hydrogen or natural gas,
including renewable natural gas, or a blend of hydrogen and natural gas. Bloom has
95% of U.S. market share for stationary fuel cell technology. Bloom shows a
deployed Series 10 array on their website. It looks like it contains cells banked
together in 10 different sets and some associated room for the fuel and connection
components with a total land footprint of 182’ x 107’. A 10MW solar array would take up to 100 acres
and due to capacity factor would have less than 20% of annual output as the Series
10 in many areas and be available only part of the time. Thus, SOFCs are far
more practical for facilities from a land use/land availability perspective. In
many cases there wouldn’t be enough space for facilities to go solar. Bloom handles
removal of the systems as well in its turnkey process. The only thing that
varies is fuel costs but when determined are offered at a fixed rate. The costs
of natural gas is not expected to fluctuate much in the next decade and a five-year
fixed rate is doable. Hydrogen prices could vary but likely not by much and
again a five-year rate is safe to do. The modules can be combined at any size from
hundreds of kilowatts to 10MW. Bloom Energy currently has 1GW deployed overall
at hundreds of locations. Rates are as low as 9.9 cents per KWh. There is some
variability by region due to fuel cost differences and local taxes.
To summarize, Series
10 provides resilience, quick deployment, reliability, short-term power
contract, cost predictability, cost optionality, monitoring and maintenance, low
emissions, no pollutants, quiet operation, modular and easily sized for purpose
when needed, ability to add CHP, freedom from outages in a microgrid mode, and
low space footprint. That is quite a lot of practical value. Utilities can also
provide the systems to their customers where applicable. When pipelined gas is
used Bloom acquires certified responsibly sourced natural gas, renewable
natural gas (processed biogas from landfills, wastewater, agriculture, and
anaerobic digestors), or hydrogen. When using pipelined gas, the system processes
the gas, reforming it by removing sulfur and other components. When using
hydrogen there is no need for processing, of course. Hydrogen availability and
cost is not yet worked out. The system can use blends up to 100% hydrogen.
The table
below from Bloom’s 2019 White Paper shows an example of how a 1MW fuel cell can
displace far more CO2 emissions than an equivalent 1MW solar PV array. Most of
this simply has to do with capacity factor, or rate of utilization, where the
solar panels can only operate when the sun is out with lower output in winter.
The fuel cell can provide full-time energy, here given an avg. 95% utilization
rate compared to 13.4% for the solar array. The grid-tied fuel cell can sell
energy back to the grid when needed, thus displacing more emissions. Thus, much
like a charged battery, it can be far superior to wind or solar as a
distributed resource.
Research is
ongoing for SOFSs with one goal being to develop systems that can run at lower
temperatures. This would reduce thermal stress and materials costs. It could
also extend operational life. It would also increase efficiency. Low -temperature
SOFCs would require less insulation and they would have faster heat up and
start times. 3D printing is being explored in manufacturing, one reason being
to increase the surface area where reactions can occur. Automakers are also
researching SOFCs for use with existing gasoline or diesel engines.
References:
Series
10: Changing the Way Business Buys Power. Bloom Energy. The
New Series 10: Changing the Way Business Buys Power - Bloom Energy
How
Fuel Cells Reduce Carbon Emissions As Effectively As Renewables. Bloom Energy.
White Paper. April 2019.
How
solid oxide fuel cells provide reliable power and drive decarbonization. Wood
MacKenzie. September 20, 2023. How
solid oxide fuel cells provide reliable power and drive decarbonization | Wood
Mackenzie
Solid-oxide
Fuel Cells: Using familiar fuel in a new way. Michael R. Gerhardt. Harvard.
Blog. November 16, 2015. Solid-oxide
Fuel Cells: Using familiar fuel in a new way - Science in the News
(harvard.edu)
Advantages
and Disadvantages of Solid Oxide Fuel Cell. Aspiring Youths. Advantages
and Disadvantages of Solid Oxide Fuel Cell (aspiringyouths.com)
Solid
oxide fuel cell: Decade of progress, future perspectives and challenges. Mandeep
Singh, Dario Zappa, and Elisabetta Comini. International Journal of Hydrogen
Energy. Volume 46, Issue 54, 5 August 2021, Pages 27643-27674. Solid
oxide fuel cell: Decade of progress, future perspectives and challenges -
ScienceDirect
Bloom
Energy Launches Series 10 Net-Zero Compliant Solution, Accelerating Adoption of
Clean Power Generation. July 24, 2023. Bloom Energy. Bloom
Energy - Bloom Energy Launches Series 10 Net-Zero Compliant Solution,
Accelerating Adoption of Clean Power Generation
Solid
Oxide Fuel Cell. Wikipedia. Solid oxide fuel
cell - Wikipedia
A
review on cell/stack designs for high performance solid oxide fuel cells. Bora
Timurkutluk, Cigdem Timurkutluk, Mahmut D. Mat, Yuksel Kaplan. Renewable and
Sustainable Energy Reviews. Volume 56, April 2016, Pages 1101-1121. A
review on cell/stack designs for high performance solid oxide fuel cells -
ScienceDirect
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