U.S. patent application number 11/641942 was filed with the patent office on 2008-06-26 for methods for fuel cell system optimization.
This patent application is currently assigned to BLOOM ENERGY CORPORATION. Invention is credited to Arne Watson Ballantine, Steven Edward Schumer.
Application Number | 20080152959 11/641942 |
Document ID | / |
Family ID | 39543303 |
Filed Date | 2008-06-26 |
United States Patent
Application |
20080152959 |
Kind Code |
A1 |
Schumer; Steven Edward ; et
al. |
June 26, 2008 |
METHODS FOR FUEL CELL SYSTEM OPTIMIZATION
Abstract
A method of operating a fuel cell system which includes
operating a fuel cell system at one or more operational modes,
wherein said fuel cell system is configured to operate at a
plurality of operational modes comprising: maximum power output,
maximum system efficiency, maximum reliability, maximum lifetime,
maximum return on investment or a mode combining any two or more of
the preceding.
Inventors: |
Schumer; Steven Edward; (San
Jose, CA) ; Ballantine; Arne Watson; (Menlo Park,
CA) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
BLOOM ENERGY CORPORATION
|
Family ID: |
39543303 |
Appl. No.: |
11/641942 |
Filed: |
December 20, 2006 |
Current U.S.
Class: |
429/428 ;
429/452 |
Current CPC
Class: |
H01M 8/04619 20130101;
H01M 8/04701 20130101; H01M 8/04753 20130101; H01M 8/04828
20130101; Y02E 60/50 20130101; H01M 8/0494 20130101 |
Class at
Publication: |
429/13 ;
429/19 |
International
Class: |
H01M 8/00 20060101
H01M008/00 |
Claims
1. A method of operating a ftiel cell system compri sing: operating
the fuel cell system at a first operational mode; and switching
from said first operational mode to a second operational mode,
wherein said first and second operational modes are different from
one another and each independently selected from a list of modes
comprising: maximum power output, maximum system efficiency,
maximum reliability, maximum lifetime, maximum return on investment
or a mode combining any two or more of the preceding.
2. The method of claim 1 wherein switching between the first and
second operational modes is carried out manually.
3. The method of claim 1 wherein switching between the first and
second operational modes is carried out automatically.
4. The method of claim 3 wherein the switching is carried out based
on data provided to the system.
5. The method of claim 4 further comprising the step of providing
data to the system.
6. The method of claim 4 wherein the data comprises: time-of-day
electric rate changes, fuel cost or CO.sub.2 emission levels.
7. The method of claim 1 wherein the system further comprises a
control system for storage and execution of settings for each
operational mode.
8. The method of claim 7 further comprising the step of activating
the control system to switch the operational mode of the fuel cell
from the first mode to the second mode.
9. The method of claim 1 wherein the first mode is maximum power
output.
10. The method of claim 1 wherein the second mode is maximum power
output.
11. The method of claim 1 wherein the first mode is maximum system
efficiency.
12. The method of claim 1 wherein the second mode is maximum system
efficiency.
13. The method of claim 1 wherein the first mode is maximum
reliability.
14. The method of claim 1 wherein the second mode is maximum
reliability.
15. The method of claim 1 wherein the first mode is maximum
lifetime.
16. The method of claim 1 wherein the second mode is maximum
lifetime.
17. The method of claim 1 wherein the first mode is maximum return
on investment.
18. The method of claim 1 wherein the second mode is maximum return
on investment.
19. The method of claim 1 wherein the first mode is a mode
combining two or more of maximum power output, maximum system
efficiency, maximum reliability, maximum lifetime, maximum return
on investment.
20. The method of claim 1 wherein the second mode is a mode
combining two or more of maximum power output, maximum system
efficiency, maximum reliability, maximum lifetime, maximum return
on investment.
21. A fuel cell system comprising: a computer system for directing
the operation of said fuel cell system, said computer system
comprising: a fuel cell stack; a processor; and a memory, coupled
to the processor, the memory comprising a plurality of instructions
executable by the processor, the plurality of instructions
configured to: operate the fuel cell system in a first operational
mode; and switch the fuel cell system to a second operational mode;
wherein said first and second operational modes are each selected
from an array of operational modes comprising: maximum power
output, maximum system efficiency, maximum reliability, maximum
lifetime, maximum return on investment or a mode combining any two
or more of the preceding.
22. A fuel cell system comprising: a fuel cell stack; and a means
for: operating the fuel cell system at a first operational mode;
and switching from said first operational mode to a second
operational mode, wherein said first and second operational modes
are different from one another and each independently selected from
a list of modes comprising: maximum power output, maximum system
efficiency, maximum reliability, maximum lifetime, maximum return
on investment or a mode combining any two or more of the
preceding.
23. A method of operating a fuel cell system comprising: providing
a fuel cell system comprising a fuel cell stack and a control
system; storing in the control system a list of operational mode
parameters which correspond to a maximum power output mode, a
maximum system efficiency mode, a maximum reliability mode, a
maximum lifetime mode, a maximum return on investment mode and a
mode combining any two or more of the preceding; and executing a
first operational mode from the list of operational mode parameters
stored in the control system to operate the fuel cell system in the
first operational mode.
24. The method of claim 23, further comprising executing a second
operational mode different from the first operational mode from the
list of operational mode parameters stored in the control system to
operate the fuel cell system in the second operational mode.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is directed to fuel cell systems and
operation thereof.
[0002] Fuel cells are electrochemical devices which can convert
energy stored in fuels to electrical energy with high efficiencies.
High temperature fuel cells include solid oxide and molten
carbonate fuel cells. These fuel cells may operate using hydrogen
and/or hydrocarbon fuels. There are classes of fuel cells, such as
the solid oxide regenerative fuel cells, that also allow reversed
operation, such that oxidized fuel can be reduced back to
unoxidized fuel using electrical energy as an input.
SUMMARY OF THE INVENTION
[0003] Embodiments of the present invention describe methods of
operating a fuel cell system comprising: operating a fuel cell
system at one or more operational modes, wherein said fuel cell
system is configured to operate at a plurality of operational modes
comprising: maximum power output, maximum system efficiency,
maximum reliability, maximum lifetime, maximum return on investment
or a mode combining any two or more of the preceding. In a specific
embodiment, a fuel cell system comprises: a computer system for
directing the operation of said fuel cell system, said computer
system comprising: a processor; and a memory, coupled to the
processor, the memory comprising a plurality of instructions
executed by the processor, the plurality of instructions configured
to: operate the fuel cell system in a first operational mode; and
switch the fuel cell system to a second operational mode; wherein
said first and second operational modes are each selected from an
array of operational modes comprising: maximum power output,
maximum system efficiency, maximum reliability, maximum lifetime,
maximum return on investment or a mode combining any two or more of
the preceding.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0004] Currently available fuel cell systems are typically
optimized for performance based on one or possibly two parameters.
The most typical parameters being maximum output power and customer
load. Several problems accompany such performance
optimizations.
[0005] First, when fuel costs are high, operation at a maximum
power setting (or operating to meet all customer load demands) may
be a poor choice economically, thereby reducing the economic
benefits expected of the system.
[0006] Second, given the typical shape of the efficiency curve of a
fuel cell system, operating at a maximum power setting when the
need for reduced CO.sub.2 emissions is in effect, is an
inappropriate choice, particularly when in violation of the
conditions under which the system has been licensed for
operation.
[0007] Finally, if it is desired to maintain the longest possible
economic lifetime or reliability of the equipment (of the fuel cell
system), then operating at a maximum output power or following a
load profile will not be satisfactory.
[0008] The embodiments of the present invention overcome the
aforementioned problems by providing a flexible approach to
operating a fuel cell system. Namely they provide the ability
operate at one or more different operational modes. For instance,
all settings are adjusted to optimize to an operational mode of the
fuel cell system such as maximum return on investment.
[0009] Whereas previous fuel cell generator systems operate
strictly to generate power at a specified output level or to
generate power following a varying load profile, embodiments of the
present invention enable optimization of system output to a number
of key variables. For example, this system allows the optimization
of the system output to maximum return on investment. This ensures
that the fuel cell generator equipment purchased is best utilized
for return on investment.
[0010] Accordingly, in one aspect of the present invention a fuel
cell system is configured to operate at one or more different
operational modes.
[0011] In another aspect, a fuel cell system is configured to
switch between at least two different operational modes.
[0012] In another aspect, a fuel cell system is operated at a mode
selected from an available list of modes.
[0013] In another aspect, a fuel cell system is operated at a mode
based on data provided to the system.
[0014] In yet aspect, a fuel cell system is configured to
automatically switch from one operational mode to another different
mode based on data provided thereto.
[0015] In yet another aspect, a fuel cell system is configured with
a control system for automatically selecting between operational
modes.
[0016] In still another aspect, a fuel cell system is configured
with a computer system for automatically selecting between
operational modes.
[0017] Embodiments of the present invention describe a fuel cell
system control method whereby it is possible to select from
multiple criteria for system operation. The controller of the fuel
cell system will optimize system operation against these criteria,
to achieve the following operational modes: maximum power output,
maximum system efficiency, maximum reliability, maximum lifetime,
maximum return on investment or a mode combining any two or more of
the preceding.
[0018] Maximum output power generally describes a state of the fuel
cell system wherein the system outputs the maximum possible output
power without damage. For instance, system controls are adjusted to
make changes, such as increasing the fuel cell temperature and/or
increasing the fuel flow rate to the upper end of their allowed
range.
[0019] In the maximum efficiency mode, the fuel system operates at
the maximum possible overall efficiency. For example, the control
system constantly monitors stack voltages, inverter power losses
and auxiliary component loads and selects both thermal and electric
conversion levels to be at the level where system efficiency is
optimized. This output power will almost always be less than the
maximum output power of the system and it will also be less than
the minimum output power of the system because of the shape of the
curve of fuel cell efficiency, electric power conversion efficiency
curve, and auxiliary component power losses. Typically, fuel cell
efficiency decreases with increased power, at the higher limits.
Fixed power auxiliary devices have a decreasing negative impact on
efficiency the higher the output power of the system is. Losses
such as pump, blower, and resistive heating losses will increase
continuously as the output power of the system is increased.
[0020] In the maximum reliability this mode, the fuel cell system
is operated in a mode where age-related and thermal effects are
minimized while maintaining and acceptable load for the customer.
In this mode, the controller will isolate outputs which, for
example, are paralleled to increase load-sharing of 25 KW modules.
Thus, an efficiency loss may be incurred. However, by isolating
outputs, the reliability of each individual output is
increased.
[0021] Similar to maximum reliability mode, the maximum lifetime
mode optimizes control parameters, such as stack temperature,
reformer temperature, power level, humidity, and gas fuel flow in
order to achieve the longest lifetime of components, such as the
fuel cell stacks, hot box metal components, and auxiliary
components such as the inverter or air blowers. In this mode, the
temperature parameter in particular would be minimized to the
lowest possible value for sustained operation in order to minimize
the degradation rate of fuel cell components.
[0022] In maximum return on investment mode, the fuel cell system
adjusts its output in order to obtain a maximum return on system
investment. One or more of several key inputs based on the customer
installation are maintained through system lifetime: cost of fuel;
opportunity and lost-business costs; grid stability or fraction of
capacity; cost or credit of CO.sub.2 (or other) system emissions;
cost of system hardware; and cost of replacement electricity from
the grid (as a function of yearly season and time of day). The
system is then configured with upper and lower limits on key system
parameters such as output power and stack temperatures. The system
is also configured with limits on key external factors such as grid
power cost, grid stability, and loss of power risk. The control
system optimizes system parameters to minimize the cost of power
generation throughout the projected lifetime of the system.
[0023] In one embodiment, a combined mode is used wherein two or
more of said operational modes coincide via the same system
settings. For example, maximum efficiency and maximum lifetime are
both optimized with the same settings. This might involve operating
at a temperature which maximizes lifetime, but at a power level
which maximizes efficiency.
[0024] In another embodiment, a method of operating a fuel cell
system involves the steps of operating the fuel cell system at a
first operational mode and switching from said first operational
mode to a second operational mode. Said first and second
operational modes are different from one another and each
independently selected from a list of modes comprising maximum
power output, maximum system efficiency, maximum reliability,
maximum lifetime, maximum return on investment or a mode combining
any two or more of the preceding.
[0025] As previously noted, a benefit of the present invention is a
flexible approach to operating a fuel cell system. In sequential or
multiple mode operation methods, the fuel cell system is flexibly
operated based on the desired benefits to the end user and/or
supplier of power. This method will permit automatic, permissive
switching among the modes discussed above. If, for example, the
fuel cell system is operating in the maximum output power mode, the
control system can be so configured as to automatically respond to
such events as, but not limited to, time-of-day electric rate
changes by changing to maximum return on investment mode. These
events, provided as data to said fuel cell system, or controller
for the system, may further include other externally supplied
market signals such as price of spot-market such as natural gas,
for systems which operate on natural gas.
[0026] In some cases, user definable control modes might be
included. In these modes, the matrix of parameters limits, the
matrix of costs, and the matrix of system responses could be
manipulated by the customer in order to obtain an optimization
which the customer's circumstances dictate.
[0027] The user settings could be triggered to change on a time of
day basis for use in peak-shaving. This might be particularly
appropriate in installations where billing rates change at discrete
times and cost of power is unacceptably high.
[0028] The control system could be configured to recognize and
diagnose situations where a change in system configuration may lead
to, for example, an improved return on investment condition. For
instance, if three 25 KW hot box modules were installed, but base
load exceeds 100 KW and CO.sub.2 emissions costs are great, the
control system could flag for the user the advantage of installing
a fourth 25 KW hot box module.
[0029] Operation of the fuel cell system may be carried out
manually or automatically. Both types of operation are further
described below. For instance, a particular group of settings may
be associated with one of the operational modes wherein activation
of said settings can be carried out in one step. Preferably, the
settings are constantly monitored and adjusted to achieve the
optimal state of the system, be it maximum power output, maximum
system efficiency, maximum reliability, maximum lifetime, maximum
return on investment or a mode combining any two or more of the
preceding.
[0030] In manual operation, a human operator may change the
operational mode of the fuel cell system by using a control system
such as a computer or a control panel, based on the desired
benefits as previously discussed. As in some embodiments, displayed
or printed data pertaining to events such as fuel cost, or
electricity cost may be used by the human operator in selecting the
most appropriate mode.
[0031] In automatic operation, the control system such as a
computer or a dedicated logic chip (or circuit) is configured to
store operational mode parameters and execute an operational mode
from of list of: maximum power output, maximum system efficiency,
maximum reliability, maximum lifetime, maximum return on investment
or a mode combining any two or more of the preceding. Data
pertaining to events previously described would be received by the
control system and positively (switch to new mode) or negatively
(stay at the same mode) acted upon.
[0032] Therefore, another method involves operating a fuel cell
system equipped with a control system by activating said control
system to switch the operational mode of the fuel cell from a first
mode to a second mode.
[0033] In embodiments of the present invention wherein operational
modes are switched between two or more different ones, any
combination can result. That is, the first, second, third, etc.
modes are each independently chosen from the list of operational
modes previously described. This obviously can result in a very
large number of combinations or permutations.
[0034] In another embodiment, a fuel cell system includes a fuel
cell stack and a computer system for directing the operation of
said fuel cell system. Said computer system preferably comprises a
processor, and a memory coupled to the processor. The memory stores
a plurality of instructions (corresponding to operational modes)
executed by the processor, to operate the fuel cell system in a
first operational mode. If need be, the computer system can switch
the fuel cell system to a second operational mode. Of course the
number of times the switching occurs is potentially limitless. Said
first and second operational modes are each selected from maximum
power output, maximum system efficiency, maximum reliability,
maximum lifetime, maximum return on investment or a mode combining
any two or more of the preceding.
[0035] The computer system may be equipped to receive data
pertaining to, but not limited by, time-of-day electric rate
changes or fuel cost. Upon receipt of the data, the computer system
may select to switch or not switch modes based on how it is
programmed. The data may be provided from the internet, entered
manually by the operator provided from other data sources.
[0036] The foregoing description of the invention has been
presented for purposes of illustration and description. It is not
intended to be exhaustive or to limit the invention to the precise
form disclosed, and modifications and variations are possible in
light of the above teachings or may be acquired from practice of
the invention. The description was chosen in order to explain the
principles of the invention and its practical application. It is
intended that the scope of the invention be defined by the claims
appended hereto, and their equivalents.
* * * * *