Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD OF COORDINATING AND STABILIZING THE DELIVERY
OF WIND GENERATED ENERGY
Field of the Invention
The present invention relates to wind generated energy systems, and in
particular, to a method of coordinating and stabilizing the delivery of wind
generated
energy, such as to a power grid.
Backaround of the Invention
Generation of energy from natural sources, such as sun and wind, has been an
important objective in this country over the last several decades. Attempts to
reduce
reliance on oil, such as from foreign sources, have become an important
national issue.
Energy experts fear that some of these resources, including oil, gas and coal,
may
someday run out. Because of these concerns, many projects have been initiated
in an
attempt to harness energy derived from what are called natural "alternative"
sources.
While solar power may be the most widely known alternative source, there is
also the potential for harnessing tremendous energy from the wind. Wind farms,
for
example, have been built in many areas of the country where the wind naturally
blows.
In many of these applications, a large number of windmills are built and
"aimed" toward
the wind. As the wind blows against the windmills, rotational power is created
and then
used to drive generators, which in turn, can generate electricity. This energy
is often
used to supplement energy produced by utility power plants and distributed by
electrical
power grids.
Wind farms are best operated when wind conditions are relatively constant and
predictable. Such conditions enable a consistent and predictable amount of
energy to
be generated and supplied, thereby avoiding surges and swings that could
adversely
affect the system. The difficulty, however, is that wind by its very nature is
unpredictable and uncertain. In most cases, wind speeds, frequencies and
durations
vary considerably, i.e., the wind never blows at the same speed over an
extended
period of time, and wind speeds themselves can vary significantly from one
moment to
another. And, because the amount of power generated by wind is mathematically
a
function of the cube of the wind speed, even the slightest fluctuation or
oscillation in
wind speed can result in a disproportionate change in wind-generated power.
For
example, a three-fold change in wind speed (increase or decrease) can result
in a
twenty-seven-fold change in wind-generated power, i.e., 3 cubed equals 27.
This is particularly significant in the context of a wind farm delivering
energy to
an electrical power grid, which is a giant network composed of a multitude of
smaller
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networKs. l hese sudden surges in one area can upset other areas and can even
bring
down the entire system in some cases. Because of these problems, in current
systems, wind farm power outputs are often difficult to deal with and can
cause
problems for the entire system.
Another problem associated with wind fluctuations and oscillations relates to
the
peak power sensitivity of the transmission lines in the grid. When wind speed
fluctuations are significant, and substantial wind power output fluctuations
occur, the
system must be designed to account for these variances, so that the system
will have
enough power line capacity to withstand the power fluctuations and
oscillations. At the
same time, if too much consideration is given to these peak power outputs, the
system
may end up being over-designed, i.e., if the system is designed to withstand
surges
during a small percentage of the time, the power grid capacity during the
greater
percentage of the time may not be used efficiently and effectively.
Another related problem is the temporary loss of wind power associated with an
absence of wind or very low wind speed in some circumstances. When this
occurs,
there may be a gap in wind power supply, which can be detrimental to the
overall grid
power output. This is especially important when large wind farms are used,
wherein
greater reliance on wind-generated power, to offset peak demand periods,
exists.
Because of these problems, attempts have been made in the past to store
energy produced by wind so that wind generated energy can be used during peak
demand periods, and/or periods when little or no wind is available, i.e., time-
shifting the
energy from when it is most available to when it is most needed. Nevertheless,
these
past systems have failed to be implemented in a reliable and consistent
manner. Past
attempts have not been able to reduce the inefficiencies and difficulties, as
well as the
fluctuation and oscillation problems discussed above, inherent in using wind
as an
energy source for an extended period of time.
Notwithstanding these problems, because wind is a significant natural resource
that will never run out, and is often in abundance in many locations
throughout the
world, there is a desire to develop a method of harnessing power generated by
wind, to
provide electrical power in a manner that allows not only energy to be stored,
but
enables the delivery of the energy to the power grid to be coordinated,
managed and
stabilized, to smooth wind power fluctuations and oscillations, while at the
same time,
filling in wind energy gaps prior to delivery, such that energy swings and
surges that
can adversely affect the power grid can be eliminated.
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Summary of the Invention
The present invention relates to a method of using and storing wind generated
energy and effectively coordinating, managing and stabilizing the delivery of
that energy
in a manner that enables wind power fluctuations and oscillations to be
reduced or
avoided, by smoothing and stabilizing the delivery of power to the grid, and
avoiding
sudden surges and swings which can adversely affect the power delivery system.
The
present method generally comprises a process that utilizes daily wind
forecasts and
projections to anticipate the wind conditions and characteristics for the
upcoming day,
and then using that data to effectively plan and develop a delivery schedule,
with the
objective of enabling the system to provide the longest possible periods of
time where
wind generated power output levels to the power grid can remain constant for
the
upcoming 24 hour period. In this respect, the present system contemplates
using
various types of energy generating systems, including those that can store
energy for
later use, and control systems that can determine how much energy is stored
and how
much is being used from storage at any given time.
In one aspect, the present system comprises windmill stations that are
dedicated
to various uses to determine how wind power is generated. The first of these
stations is
dedicated to creating energy for direct and immediate use by the power grid or
community (hereinafter referred to as "immediate use stations"). The second of
these
windmill stations is dedicated to energy storage using a compressed air energy
system
(hereinafter referred to as "energy storage stations"). The third of these
windmill
stations can be switched between the two (hereinafter referred to as "hybrid
stations").
The system is preferably designed with a predetermined number and ratio of
each type
of windmill station to enable the system to be both economical and energy
efficient in
generating the appropriate amount of energy for both immediate use and storage
at any
given time. These systems are preferably used in communities where there is a
need
for a large number of windmill stations, i.e., a wind farm, and/or access to
an existing
power grid, such that energy from the system can be used to supplement
conventional
energy sources.
Each immediate use station preferably has a horizontal axis wind turbine
(HAWT) and an electrical generator located in the nacelle of the windmill,
such that the
rotational movement caused by the wind is directly converted to electrical
energy via
the generator. This can be done, for example, by directly connecting the
electrical
generator to the rotational shaft of the wind turbine so that the mechanical
power
derived from the wind can directly drive the generator. By locating the
generator
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downstream of the gearbox on the windmill shaft, and by using the mechanical
power of
the windmill directly, energy losses typically attributed to other types of
arrangements
can be avoided.
The energy storage stations are more complex in terms of bringing the
mechanical rotational energy from the high above ground nacelle down to ground
level
as rotational mechanical energy. Likewise, each energy storage station is
connected to
a compressor in a manner that converts wind power to compressed air energy
directly.
The horizontally oriented wind turbine of each energy storage station
preferably has a
horizontal shaft connected to a first gear box, which is connected to a
vertical shaft
extending down the windmill tower, which in turn, is connected to a second
gear box
connected to another horizontal shaft located on the ground. The lower
horizontal shaft
is then connected to the compressor, such that the mechanical power derived
from the
wind can be converted directly to compressed air energy and stored.
The compressed air from each energy storage station is preferably channeled
into one or more high-pressure storage tanks or pipeline storage system, where
the
compressed air can be stored. Storage of compressed air allows the energy
derived.
from the wind to be stored for an extended period of time. By storing energy
in this
fashion, the compressed air can be released and expanded by turbo expanders at
the
appropriate time, such as when little or no wind is available, and/or during
peak
demand periods. The released and expanded air can then drive an electrical
generator, such that energy derived from the wind can be used to generate
electrical
power on an "as needed" basis, i.e., when the power is actually needed, which
may or
may not coincide with when the wind actually blows.
The present invention contemplates that the storage tank, pipeline system,
and/or related components, and their masses, can be designed to absorb and
release
heat to maintain the stored air at a relatively stable temperature, even
during
compression and expansion. For example, when large storage tanks are used, the
preferred embodiment comprises using a heat transfer system made of tubing
extending through the inside of each tank, wherein heat transfer fluid (such
as an
antifreeze) can be distributed through the tubing to provide a cost-efficient
way to keep
the temperature in the tank relatively stable.
The present system can also incorporate other heating systems, including
heating devices that can be provided with the storage tanks that can help
generate
additional heat and pressure energy, and provide a means by which the
expanding air
can be prevented from freezing. Alternatively, the present invention also
contemplates
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using a combination of solar heat, waste heat from the compressor, combustors,
and
low level fossil fuel power, etc., to provide the necessary heat to increase
the
temperature and pressure of the compressed air in the storage tank. The
present
system also contemplates that the cold air created by the expansion of the
compressed
air exhausting from the turbo-expander can be used for additional
refrigeration
purposes, i.e., such as during the summer where air conditioning services
might be in
demand.
It can be seen that the immediate use stations discussed above can be used to
produce electricity directly from the windmill stations for immediate delivery
to the
power grid. On the other hand, it can be seen that the energy storage stations
can be
used to time shift the delivery of wind generated power, so that wind
generated power
can be made available to the power grid even at times that are not coincident
with when
the wind actually blows, i.e., even when no wind is blowing, and/or during
peak demand
periods. The coordination and usage of these stations enables the current
system to
provide continuous and uninterrupted power in a stabilized manner to the power
grid,
despite fluctuations and oscillations in wind speed, by coordinating and
managing the
flow of energy from the various stations to the power grid.
The present system preferably incorporates hybrid windmill stations that can
be
customized and switched between energy for immediate use, and energy for
storage,
i.e., a switch can be used to determine the levels of energy dedicated for
immediate
use and storage. In such case, the ratio between the amount of energy
dedicated for
immediate use and that dedicated for storage can be further changed by making
certain
adjustments, i.e., such as by using clutches and gears located on the hybrid
station, so
that the appropriate amount of energy of each kind can be provided. This
enables the
hybrid station to be customized to a given application at virtually any time,
to allow the
system to provide the appropriate amount of power for immediate use and energy
storage, depending on wind availability and energy demand at any given moment.
Using these three types of windmill stations, the present system is better
able to
allocate wind-generated energy to either immediate delivery to the power grid,
or
energy storage and usage, depending on the wind conditions and needs of the
power
grid. That is, the hybrid stations can be used in conjunction with the
immediate use
and energy storage stations to provide the proper ratio of power which would
enable
large wind farms to be designed in a more flexible and customized manner,
e.g., so that
the appropriate amount of energy can be delivered to the grid at the
appropriate time, to
meet the particular demands of the system. In short, using a combination of
the three
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types of windmill stations enables a system to oe more specincany aaapiea ana
customized so that a constant supply of power can be provided for longer
periods of
time.
The wind patterns in any particular location can change from time to time,
i.e.,
from one season to another, from one month to another, and, most importantly,
from
day to day, hour to hour, and minute to minute. Accordingly, these
fluctuations and
oscillations must be dealt with in conjunction with energy storage for the
system to
provide continuous power at a more constant rate.
The present invention contemplates that daily wind forecasts be obtained for
the
particular area where the wind farm is located, to project the wind conditions
and
characteristics for each upcoming day. These wind forecasts are intended to be
based
on the latest weather forecast technologies available to approximate as
closely as
possible the actual expected wind conditions over the course of the upcoming
24-hour
period. While these forecasts may not be entirely accurate, they can provide a
very
close approximation of the expected wind conditions, sufficient for purposes
of planning
and developing the wind delivery schedules, that will enable the system to
continually
operate.
Once each daily forecast is obtained, the present method contemplates using
the data to formulate an energy delivery schedule for the upcoming day, based
on the
forecast, with the objective of creating the longest possible periods of time
during which
the wind generated power output level to the grid can remain constant. For
example, in
the preferred embodiment, it is desirable to have no more than about three
constant
power output periods during any given day, such that there would be less than
three
changes to the rate of power output being supplied to the power grid on any
given day
(although up to as many as 7 or so constant power periods can be provided if
necessary). By enabling the system to provide longer periods when the wind
generated
power output is constant, the present system enables power surges and swings,
such
as those caused by wind speed fluctuations and oscillations, to be reduced and
in some
cases eliminated altogether.
The manner in which the daily schedules are planned and carried out utilizes
the
windmill stations discussed above, as well as a valve control system for
controlling the
amount of energy that is stored and used from storage. The system contemplates
being able to control the amount of wind generated power output levels at any
given
time by implementing an appropriate number of immediate use and energy storage
stations for generating energy, and by converting the appropriate number of
hybrid
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stations, and then controlling how much energy is supplied directly to the
power gna,
and how much is provided via energy storage, using compressors and expanders,
at
any given moment in time. The controls are also necessary to maintain proper
levels of
energy in storage, based on continually updating the wind forecasts, so that
the system
never runs out of stored energy. Based on wind forecasts, it is possible
during any
given day to anticipate the need for additional energy in storage (such as
when it is
expected that the power needed may exceed the power supplied during the
upcoming
24 hour period), and when it is not needed (such as when it is expected that
there will
be sufficient wind to provide direct energy during the next 24 hour period).
Brief Description of the Drawings
FIGURE 1a shows a flow-chart of a horizontal axis wind turbine system
dedicated to generating energy for immediate use;
FIGURE 1 b shows a flow-chart of a modified horizontal axis wind turbine
system
dedicated to storing energy in a compressed air energy system;
FIGURE 2a shows a flow-chart of a hybrid horizontal axis wind turbine system
for generating electricity between immediate use and energy storage;
FIGURE 2b shows an example of a pressure release valve system;
FIGURE 3 shows a wind histogram for a location in Kansas during the month of
November 1996;
FIGURE 4 shows six daily wind histories for the period between November 1 and
November 6, 1996 at the same Kansas site;
FIGURE 5 shows a comparison between the Nordex N50/800 and a computer
model;
FIGURE 6 contains two charts showing two potential delivery schedules for
November 1, 1996;
FIGURE 7a contains two charts showing an 87/13 ratio between immediate use
and energy storage, the top chart comparing the constant output periods with
the
wind/power availability curve, and the bottom chart comparing the constant
output
periods with the amount of power supplied into storage, both for the same
November 1,
1996 day;
FIGURE 7b contains two charts, the top chart showing the amount of energy in
storage over time, and the bottom chart showing the pressure and temperature
curves
in storage, both for the same November 1, 1996 day;
FIGURE 8a contains two charts for November 5, 1996 at the same site showing
a 60/40 ratio between immediate use and energy storage, the top chart
comparing the
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constam output penoas wnn me mnaipower avauae~uny curve, ana um uuucrm cmm
comparing the constant output periods with the amount of power supplied into
storage;
FIGURE 8b contains two charts for November 5, 1996, the top chart showing the
amount of energy in storage over time, and the bottom chart showing the
pressure and
temperature curves in storage;
FIGURE 9a contains two charts for November 6, 1996 at the same site showing
a 50150 ratio between immediate use and energy storage, the top chart
comparing the
constant output periods with the wind/power availability curve, and the bottom
chart
comparing the constant output periods with the amount of power supplied into
storage;
FIGURE 9b contains two charts for November 6, 1996, the top chart showing the
amount of energy in storage over time, and the bottom chart showing the
pressure and
temperature curves in storage; and
FIGURE 10 is a chart showing the daily delivery schedules for the three days,
indicating the number of immediate use and energy storage windmills that were
operational, based on the settings of the hybrid stations, and the number of
storage
tanks used and the cost of generating the power each day.
Detailed Description of the Invention
The apparatus portion of the present invention comprises three different types
of
windmill stations, including a first type having a horizontal axis wind
turbine that
converts rotational mechanical power to electrical energy using an electrical
generator
and providing energy for immediate use (hereinafter referred to as "immediate
use
stations"), a second type having a horizontal axis wind turbine that converts
mechanical
rotational power to compressed air energy for energy storage (hereinafter
referred to as
"energy storage stations"), and a third type that combines the characteristics
of the first
two in a single windmill station having the ability to convert mechanical
rotational power
to electrical energy for immediate use and/or energy storage (hereinafter
referred to as
"hybrid stations"). The present system is designed to use and coordinate the
three
types of windmill stations described above so that a predetermined portion of
the wind
generated energy can be dedicated to energy for immediate use and a
predetermined
portion of the energy can be dedicated to energy storage.
The following discussion describes each of the three types of windmill
stations,
followed by a description of how to coordinate the windmill stations for any
given
application:
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H~ immeaiate use Stations:
Figure 1a shows a schematic flow diagram of an immediate use station. The
diagram shows how mechanical rotational power generated by a windmill is
converted
to electrical power and supplied as electrical energy for immediate use.
Energy derived
from the wind can be converted to electrical power more efficiently when the
conversion
is direct, e.g., the efficiency of wind generated energy systems can be
enhanced by
directly harnessing the mechanical rotational movement caused by the wind as
it blows
onto the windmill blades to directly generate electricity.
Like conventional windmill devices used for creating electrical energy, the
present invention contemplates that each immediate use station will comprise a
windmill tower with a horizontal axis wind turbine located thereon. The tower
is
preferably erected to position the wind turbine at a predetermined height, and
each
wind turbine is preferably "aimed" toward the wind to maximize the wind
intercept area,
as well as the wind power conversion efficiency of the station. A wind
turbine, such as
those made by various standard manufacturers, can be installed at the top of
the tower,
with the windmill blades or fans positioned about a horizontally oriented
rotational shaft.
In this embodiment, a gearbox and an electrical generator are preferably
located
in the nacelle of the windmill such that the mechanical rotational power of
the shaft can
directly drive the generator to produce electrical energy. By locating the
electrical
generator directly on the shaft via a gearbox, mechanical power can be more
efficiently
converted to electrical power. The electrical energy can then be transmitted
down the
tower via a power line, which can be connected to other lines or cables that
feed power
from the immediate use station to the grid or other user.
The present invention contemplates that the immediate use stations are to be
used in connection with other windmill stations that are capable of storing
wind energy
for later use as described in more detail below. This is because, as discussed
above,
the wind is generally unreliable and unpredictable, and therefore, having only
immediate use stations to supply energy for immediate use will not allow the
system to
be used to provide power output at a constant rate. Accordingly, the present
invention
contemplates that in wind farm applications where multiple windmill stations
are
installed, additional energy storage stations would also be installed and
used.
B. Enerq S~toraae Stations.
Figure 1 b shows a schematic flow chart of an energy storage windmill station.
This station preferably comprises a conventional windmill tower and horizontal
axis
wind turbine as discussed above in connection with the immediate use stations.
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-- ~itcemse, the wmd turbine is prereraaiy iocatea at me top or me mnamm mwe~
ana
capable of being aimed toward the wind as in the previous design. A rotational
shaft is
also extended from the wind turbine for conveying power.
Unlike the previous design, however, in this embodiment, energy derived from
the wind is preferably extracted at the base of the windmill tower for energy
storage. As
shown in Figure 1 b, a first gearbox is preferably located adjacent the wind
turbine in the
nacelle of the windmill, which can transfer the rotational movement of the
horizontal
drive shaft to a vertical shaft extending down the windmill tower. At the base
of the
tower, there is preferably a second gearbox designed to transfer the
rotational
movement of the vertical shaft to another horizontal shaft located on the
ground, which
is then connected to a compressor. The mechanical rotational power from the
wind
turbine on top of the tower can, therefore, be transferred down the tower, and
converted
directly to compressed air energy, via the compressor located at the base of
the tower
or somewhere nearby. A mechanical motor in the compressor forces compressed
air
energy into one or more high pressure storage tanks or pipeline system located
on the
ground. With this arrangement, each energy storage station is able to convert
mechanical wind power directly to compressed air energy, which can be stored
for later
use, such as during peak demand periods, andlor when little or no wind is
available.
The energy storage portion of the present system preferably comprises means
for storing the compressed air energy, such as in storage tanks or a pipeline
system.
Reference can be made to U.S. Application Serial No. 10/263,848, filed on
October 4,
2002, for additional information regarding the storage tank, heating and other
apparatuses and methods that are capable of being used in connection with the
present
invention, and to the U.S. Provisional Application filed by applicants on May
30, 2003,
entitled "A Method of Storing and Transporting Wind Generated Energy Using a
Pipeline System," and the related non-provisional application filed on June 1,
2004, for
additional information regarding the pipeline system for storing and
transporting wind
generated energy which can be used in connection with the present invention.
The
storage facility is preferably located in proximity to the energy storage
stations, such
that compressed air can be conveyed into storage without significant pressure
losses.
Various size storage facilities can be used. The present system contemplates
that the sizing of the storage facilities can be based on calculations
relating to a number
of factors. For example, as will be discussed, the volume size of the storage
facility can
depend on the number and ratio of energy storage and immediate use stations
that are
installed, as well as other factors, such as the size and capacity of the
selected wind
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ruromes, the capacity or me seiecrea compressors, me avanapuiry or wina, me
exrenz or
the energy demand, etc.
Any of the many conventional means of converting the compressed air into
electrical energy can be used. In the preferred embodiment, one or more turbo-
expanders are used to release the compressed air from storage to create a high
velocity airflow that can be used to power a generator to create electrical
energy. This
electricity can then be used to supplement the energy supplied by the
immediate use
stations. Whenever stored wind energy is needed, the system is designed to
allow
compressed air in the storage tanks to be released through the turbo-
expanders. As
shown in Figure 1b, the turbo-expanders preferably feed energy to an
alternator, which
is connected to an AC to DC converter, followed by a DC to AC inverter, and
then
followed by a conditioner to match impedances to the user circuits.
The present invention contemplates that the storage facilities be designed to
absorb and release heat to maintain the stored air at a relatively stable
temperature,
even during compression and expansion. For example, when large storage tanks
are
used, the preferred embodiment comprises using a heat transfer system made of
thin
walled tubing extending through the inside of each tank, wherein heat transfer
fluid
(such as an antifreeze) can be distributed through the tubing to provide a
cost-efficient
way to keep the temperature in the tank relatively stable. The tubing
preferably
comprises approximately 1 % of the total area inside the tank, and copper or
carbon
steel material. They also preferably contain an antifreeze fluid that can be
distributed
throughout the inside of the storage tank, wherein the tubing acts as a heat
exchanger,
which is part of the thermal inertia system. The storage tanks are preferably
lined by
insulation to prevent heat loss from inside.
The present system can also incorporate other heating systems, including
heating devices that can be provided on top and inside the storage tanks that
can help
generate additional heat and pressure energy, and provide a means by which the
expanding air can be prevented from freezing. In some cases, although not in
the
preferred system, the present invention can use a combination of solar heat,
waste heat
from the compressor, combustors, low-level fossil fuel power, etc., to provide
the
necessary heat to increase the temperature and pressure of the compressed air
in the
storage tank. The present system also contemplates that the cold air created
by the
expansion of the compressed air exhausting from the turbo-expander can be used
for
additional refrigeration purposes, i.e., such as during the summer where air
conditioning
services might be in demand.
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C: -- Hybrid Stations:
Figure 2a shows a hybrid station. The hybrid station is essentially a single
windmill station that comprises certain elements of the immediate use and
energy
storage stations, with a mechanical power splitting mechanism that allows the
wind
power to be allocated between power for immediate use and energy for storage,
depending on the needs of the system.
Like the two stations discussed above, a conventional windmill tower is
preferably erected with a conventional horizontal axis wind turbine located
thereon.
The wind turbine preferably comprises a horizontal rotational shaft having the
ability to
convey mechanical power directly to the converters.
Like the energy storage station, the hybrid station is adapted so that wind
energy
can be extracted at the base of the windmill tower. As schematically shown in
Figure
2a, the wind turbine has a rotational drive shaft connected to a first gearbox
located in
the nacelle of the windmill, wherein horizontal rotational movement of the
shaft can be
transferred to a vertical shaft extending down the tower. At the base of the
tower, there
is preferably a second gearbox designed to transfer the rotational movement of
the
vertical shaft to another horizontal shaft located at the base.
At this point, as shown in Figure 2a, a mechanical power splitter can be
provided. The splitter, which will be described in more detail below, is
designed to split
the mechanical rotational power of the lower horizontal shaft, so that an
appropriate
amount of wind power can be transmitted to the desired downstream converter,
i.e., it
can be adjusted to send power to an electrical generator for immediate use,
and/or a
compressor for energy storage.
Downstream from the mechanical splitter, the hybrid station preferably has, on
one hand, a mechanical connection to an electrical generator, and, on the
other hand, a
mechanical connection to a compressor. When the mechanical splitter is
switched fully
to the electrical generator, the mechanical rotational power from the lower
horizontal
shaft is transmitted directly to the generator via a geared shaft. This
enables the
generator to efficiently and directly convert mechanical power to electrical
energy, and
for the electrical power to be transmitted to the user for immediate use.
On the other hand, when the mechanical splitter is switched fully to the
compressor, the mechanical rotational power from the lower horizontal shaft is
transmitted directly to a compressor, to enable compressed air energy to be
stored,
such as in a high-pressure storage tank. This portion of the hybrid station is
preferably
substantially similar to the components of the energy storage station, insofar
as the
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mechanical power generated by the hybrid station is mended to be directly
converted
to compressed air energy, wherein the stored energy can be released at the
appropriate time, via one or more turbo-expanders. Like the previous
embodiment, a
high-pressure storage tank or pipeline system is preferably located in close
proximity to
the windmill station so that compressed air energy can be efficiently stored
in the tank
for later use.
As will be discussed, the hybrid stations are preferably incorporated into
large
wind farm applications, and installed along with other stations for immediate
use and
energy storage. In such case, the compressor on each hybrid station can be
connected
to centrally located storage facilities, such that a plurality of energy
storage and hybrid
stations can feed compressed air into them. In fact, the system can be
designed so
that all of the hybrid stations and the energy storage stations can be
connected to a
single storage facility.
The mechanical power splitter, which is adapted to split the mechanical power
between power dedicated for immediate use and for energy storage, can comprise
multiple gears and clutches so that mechanical energy can be conveyed directly
to the
converters. In one embodiment, the mechanical splitter comprises a large gear
attached to the lower horizontal drive shaft extending from the bottom of the
station, in
combination with additional drive gears capable of engaging and meshing with
the large
gear. A first clutch preferably controls each of the additional drive gears to
move them
from a first position that engages (and meshes with) the large gear, to a
second
position that causes them not to engage the large gear, and vice verse. This
way, by
operation of the first clutch, an appropriate number of additional drive gears
can be
made to engage (and mesh with) the large gear, depending on the desired
distribution
of mechanical power from the lower drive shaft to the converters.
For example, one system can have one large gear and five additional drive
gears, wherein the first clutch can be used to enable the large gear to
engage, at any
one time, one, two, three, four or five of the additional drive gears. In this
manner, the
first clutch can control how many of the additional drive gears are activated
and
therefore capable of being driven by the large gear (which is driven by the
lower
horizontal drive shaft), to determine the ratio of mechanical power to be
conveyed to
the appropriate energy converter. That is, if all five additional drive gears
are engaged
with the large gear, each of the five additional drive gears will be capable
of conveying
one-fifth or 20% of the overall mechanical power to the energy converters. If
only three
of the additional drive gears are engaged with the large gear, then each
engaged
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additional drive gear will convey one-third or 33.33% of the mecnantcal power
generated by the windmill. If two drive gears engage the large gear, each will
convey
one half or 50% of the transmitted power, etc.
The mechanical splitter of the present invention preferably has a second
clutch
to enable each of the additional drive gears to be connected downstream to
either an
electrical generator (which generates energy for immediate use) or an air
compressor
(which generates compressed air energy for energy storage). By adjusting the
second
clutch, therefore, the mechanical power conveyed from the large gear to any of
the
additional drive gears can be directed to either the electrical generator or
compressor.
This enables the amount of mechanical power supplied by the windmill station
to be
distributed and allocated between immediate use and energy storage on an
individual
and adjustable basis. That is, the amount of power distributed to each type of
energy
converter can be made dependent on the adjustments that are made by the two
clutches, which determine how many additional drive gears engage the large
gear, and
to which energy converter each engaged additional drive gear is connected.
Those
connected to the electrical generator will generate energy for immediate use,
and those
connected to the compressor will generate energy for storage.
Based on the above, it can be seen that by adjusting the two clutches of the
mechanical power splitter mechanism, the extent to which energy is dedicated
for
immediate use and energy storage can be adjusted and allocated. For example,
if it is
desired that 40% of the mechanical power be distributed to energy for
immediate use,
and 60% of the mechanical power be distributed to energy for storage, the
first clutch
can be used to cause all five of the additional drive gears to be engaged with
the large
gear, while at the same time, the second clutch can be used to cause two of
the five
additional drive gears (each providing 20% of the power or 40% total) to be
connected
to the electrical generator, and three of the five additional drive gears
(each providing
20% of the power or 60% total) to be connected to the compressor. This way,
the
mechanical splitter can divide and distribute the mechanical power between
immediate
use and energy storage at a predetermined ratio of 40/60, respectively.
In another example, using the same system, if it is desired that all of the
mechanical power be distributed to immediate use, the first clutch can be used
to cause
the large gear to engage only one of the additional drive gears, and the
second clutch
can be used to connect the one engaged additional drive gear to the electrical
generator, i.e., so that all of the mechanical power generated by the windmill
station will
be conveyed for immediate use. Likewise, if it is desired that all of the
mechanical
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power be distributed to energy storage, the second clutch can be used to
connect the
one engaged additional drive gear to the compressor, i.e., so that all of the
mechanical
power generated by the windmill station will be conveyed for storage.
The present system contemplates that any number of additional drive gears can
be provided to vary the extent to which the mechanical power can be split. It
is
contemplated, however, that having five additional drive gears would likely
provide
enough flexibility to enable the hybrid station to be workable in most
situations. With
five additional drive gears, the following ratios can be provided: 50/50,
33.33/66.66,
66.66/33.33, 20/80, 40/60, 60/40, 80/20, 100/0, and 0/100.
By using the clutches on the mechanical power splitter, each hybrid station
can
be adjusted at different times of the day to supply a different ratio of power
between
immediate use and energy storage. As will be discussed, depending upon the
power
demand and wind availability forecasts, it is contemplated that different
ratios may be
necessary to provide a constant amount of power to the user for extended
periods of
time, despite unreliable and unpredictable wind conditions. This system is
designed to
enable those ratios to be easily accommodated. Other systems for splitting the
power
are also contemplated.
D. Control and Valve Mechanism:
The present system preferably comprises a system to control the operation of
the windmill stations, the clutches on the hybrid stations, the amount of
compressed air
being fed into and out of storage, the operation of the compressors, the
operation of the
turbo-expanders, etc. The control system is preferably able to set the total
number of
windmill stations that are to be in operation at any given time, including how
many
immediate use stations are operated, how many energy storage stations are
operated,
and how many hybrid stations are operating in immediate use mode, and how many
are
operating in energy storage mode. This way, at any given time, the total
amount of
energy to be supplied by the system, and how the energy is allocated between
immediate use and energy storage, can be accurately controlled and adjusted.
For example, if a system has a total of 50 windmill stations, with 20
immediate
use, 20 energy storage, and 10 hybrid stations, the operator can determine how
many
stations will be dedicated for immediate use, on one hand, and storage, on the
other
hand, by using the control system to determine how many of the immediate use
and
energy storage stations will be in operation, and how many of the hybrid
stations will be
set to either immediate use or energy storage mode. For example, if it is
determined
that power from 28 immediate use windmill stations are needed for a particular
period,
CA 02527597 2005-11-29
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fhe -system can run all 20 of the immediate use stations, ana convert a or the
~i a nypna
stations to immediate use mode. At the same time, if only 16 of the energy
storage
stations are needed during the same period, 16 of them can be placed in
operation, and
the other 4 can be shut down, or the energy supplied by them can be
disconnected or
vented.
The control system is also preferably designed to be able to maintain the
level of
compressed air energy in storage at an appropriate level, by regulating the
flow of
compressed air into and out of storage. Compressed air is introduced into
storage via
compressors, and released from storage via turbo-expanders.
On the releasing end, a valve system, like the one shown in Figure 2b, can be
provided to allow a predetermined amount of compressed air to be released
through
the turbo-expanders at any given moment. Figure 2b shows an example of a
storage
tank with three couplings attached to three turbo-expanders, wherein valves
can be
used to allocate an appropriate amount of air through the turbo-expanders. The
chart
shows 5 different valve sequences, each associated with a particular pressure
amount
in the storage tank.
Valve sequence A is suited for 600 psig. According to this sequence, only
valve
numbers 3 and 5 are closed, and all others are open. In this manner, air
flowing
through valve 1 enters into the first turbo-expander, and can be converted to
electrical
energy, via the first alternator. Also, because valves 2 and 4 are open, some
of the
compressed air enters into the second and third turbo-expanders, and can be
converted to electrical energy via the second and third alternators. Beoause
valves 3
and 5 are closed, only air flowing through valve 1 is used.
Valve sequence B is suited for 300 psig. According to this sequence, only
valve
3 is open, and the other release valves, i.e., 1 and 5, are closed. In this
manner, air
flowing through valve 3 enters into the second turbo-expander, and can be
converted to
electrical energy via the second alternator. Also, because valve 4 is open and
valve 2
is closed, some of the compressed air can enter the third turbo-expander, and
be
converted to electrical energy via the third alternator. The first alternator
remains
unused because valves 1 and 2 are closed.
Valve sequence C is suited for 100 psig. According to this sequence, only one
valve, i.e., number 5, is open. In this manner, air flowing through valve 5
enters into the
third turbo-expander, and can be converted to electrical energy via the third
alternator.
The first and second turbo-expanders and alternators remain unused.
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when tnere is no pressure in the ZanK see vawe sequence u~, um vam~~ dm
closed, in which case compressed air energy introduced into the tank from the
compressors can build up over time, to help increase pressure in the tank.
Similar
controls are used in connection with the compressors to enable the tank to be
filled, i.e.,
to determine the rate at which compressed air will enter into storage via the
compressors. The controls preferably enable the amount of pressure in the tank
to be
maintained and moderated.
The controls can also be used to operate the heat exchangers that are used to
help control the temperature of the air in the tank. The controls determine
which heat
exchangers are to be used at any given time, and how much heat they should
provide
to the compressed air in the storage tanks.
The control system preferably has a microprocessor that is pre-programmed so
that the system can be run automatically, based on the input data provided for
the
system, as will be discussed. The present invention contemplates that an
overall
system comprising immediate use, energy storage and hybrid stations can be
developed and installed, wherein depending on the demands that are placed on
the
system by the area of intended use, a predetermined number of immediate use,
energy
storage and hybrid stations, can be in operation at any one time. This enables
the
present system to be customized and adapted to accommodate various wind
forecasts
during different times of the year, where wind conditions can vary
significantly.
E. Method:
The present method will now be discussed using an example, based on actual
wind conditions found at a site in Kansas during November of 1996 provided by
Kansas
Wind Power LLC. This period was selected because it contained wind histories
that
were varied enough to show how the present method can be applied in different
circumstances.
Figure 3 shows what is commonly called a wind histogram for the site. This
chart represents an actual wind history taken at an actual location. In
general, this
chart shows the average number of times or occurrences the wind reached a
certain
speed (when measured afi hourly intervals) during the month of November 1996.
The
wind history is designed to enable a study to be made of the average wind
speeds at
any given location, during any given time, from one season of the year to
another.
This information can be useful, for example, in helping to formulate a
solution for
the entire year, which can be based on the best and worst case scenarios
presented by
the studies. Figure 3 shows that the peak number of occurrences for any
particular
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wind speed measurement was about 43, which occurred when the wind velocity
reached about 9 meters per second. Stated differently, during the month of
November,
when measured every hour, the wind speed was about 9 meters per second more
often
than it was at any other speed, i.e., for a time estimated to equal about 43
hours (43
occurrences multiplied by one hour intervals equals 43 hours). Another way to
look at
this is that the wind was blowing an average of about 9 meters per second
during an
average of about 43 measurements taken at hourly intervals during the month.
The chart also shows that the wind speed was below 2 meters per second for
only a few occurrences during the month. Likewise, the chart shows that the
wind
speed was above 18 meters per second maybe once. Stated differently, what the
chart
shows is that the wind blew at below 2 meters per second and above 18 meters
per
second for only a few hours during the entire month of November, which is
helpful in
determining the proper equipment and method to be used in connection with the
site.
What this also means is that depending on what kind of wind turbines are
selected, the chart can predict the amount of time that the wind turbines
would be
operational and functional during the month to produce energy. For example, if
it is
assumed that the wind turbines that are selected are designed to operate only
when the
wind speed is between 3 meters per second and 15 meters per second, due to
efficiency and safety reasons, it can be predicted that during any given day
during the
month of November those wind turbines would be operational for most, but not
all, of
the time.
In an actual application, more than one month will have to be investigated and
studied. Indeed, such a determination generally comprises a cost verses
benefit
analysis, and energy efficiency study, that takes into account the
availability of wind
during the worst and best case scenarios over the course of an entire year,
and the
demands that are likely to be placed on the system at that location year
round.
The amount of wind generated power produced by the wind turbines during the
above mentioned period will then depend on the wind speed at any given time
during
the period. In general, the wind power to be derived by a wind turbine is
assumed to
follow the equation:
P=C~*0.5*Rho *A*U3
Where
C, = Constant (which is obtained by matching the calculated power with the
dimensions of the wind turbine area and wind speed performance)
Rho = Density of air
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A = Area swept by wind turbine rotors
U = Wind Speed
This means that the amount of wind power generated by the wind is proportional
to the
cube of the wind speed. Accordingly, in a situation where the wind turbines
are fully
operational within the velocity range between 2 meters per second and 18
meters per
second, the total amount of wind power that can be generated will be a direct
function
of the total wind speed between those ranges.
On the other hand, various wind turbines are designed so that the wind power
output remains relatively constant during certain high wind velocity ranges.
This can
result from the windmill blades becoming feathered at speeds above a certain
maximum. For example, certain wind turbines may function in a manner where
within a
certain velocity range, i.e., between 13 and 20 meters per second, the wind
power
generated remains constant despite changes in wind speed. Accordingly, in the
above
example, during a period where the wind speed is between 13 meters and 18
meters
per second, the amount of wind power generated by the wind turbine would be
equal to
the power generated when the wind speed is 13 meters per second. Moreover,
many
wind turbines are designed so that when the wind speed exceeds a maximum
limit,
such as 15 meters per second, the wind turbines will shut down completely, to
prevent
damage due to excess wind speeds. Accordingly, the total amount of energy that
can
be generated by a particular windmill must take these factors into
consideration.
Figure 3 also compares the actual number of occurrences with averages
determined by the Weibull distribution over a period of time. In this respect,
it should be
noted that wind histograms for wind speeds are typically statistically
described by the
Weibull distribution. Wind turbine manufacturers have used the Weibull
Distribution
association with the "width parameter" of k=2.0, although there are sites
wherein the
width parameter has attained a value as high as k=2.52.
While it is desirable to know how often, on the average, certain wind speeds
actually occur during the year, it is also important for purposes of the
present invention
to know when the various wind speeds will occur during the day, i.e.,
forecasted on a
daily basis, and the magnitude of those wind speeds, so that they can be used
to
formulate daily energy delivery schedules, which is one of the goals of the
present
invention. To develop a system that can be applied on a daily basis, it is
necessary to
obtain daily wind speed forecasts and predictions in advance of the upcoming
day, to
enable a plan or schedule to be established which can be applied the next day.
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In this respect, Figure 4 shows daily wind histories that have occurred during
a
particular week in the same November time frame at the same site. Figure 4
shows a
compilation of measurements taken over a period extending from November 1,
1996 to
November 6, 1996. This particular chart shows the wind speeds that were
measured at
hourly intervals throughout each day during that period.
The line that represents November 1, for example, starts after midnight with
the
wind blowing slightly under 7 meters per second and ends at before midnight
with the
wind blowing slightly under 8 meters per second. During that day, the wind
fluctuated
very little, with some of the lowest measurements, of about 4 meters per
second,
occurring in the morning hours, with a peak (spike) of about 7 meters per
second
occurring at about 2:00 p.m. The wind speeds then increased toward midnight.
The line that represents November 2, on the other hand, shows the wind to be
more varied. The wind starts just after midnight at slightly below 8 meters
per second,
and begins to slow down to a low of about 2 meters per second at about 10:00
a.m. and
continues at a low level. Then beginning at about 5:00 p.m., the wind starts
to pick up,
ending the day with wind speeds of close to 13 meters per second by midnight.
The next day, November 3, the wind continues to stay relatively high, while
fluctuating up and down, reaching a low of about 9 meters per second at about
8 a.m.,
and reaching a peak of about 15 meters per second at about 1 p.m. On this day,
the
wind began after midnight at slightly below 13 meters per second, and ended
with wind
speeds of slightly below 11 meters per second by midnight.
On November 4, the wind continues to fluctuate, reaching a peak of about 13
meters per second, but begins to subside, reaching a speed of about 5 meters
per
second by midnight.
On November 5, the day begins shortly after midnight with winds reaching as
low
as 2 meters per second, but then begins to increase dramatically, with winds
reaching a
peak of about 14 meters per second by about 4 p.m. The wind speed continues to
stay
relatively high and reaches about 12 meters' per second at midnight.
On the next day, the wind fluctuates again, reaching another peak of about 14
meters per second at about noon, and then begins to subside, reaching a low of
about
7 meters per second by midnight.
What this chart tracks are the wind speeds that actually occurred during the
first
week of November 1996 at the site. In the present invention, however, wind
speed
forecasts are obtained for a particular site, so that each day's anticipated
wind speeds
are predicted at least one day in advance. That is, while Figure 4 shows
examples of
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wind histories, the present invention contemplates using wind speed forecasts,
which
are similar in content to the histories, except that they are projections for
the future, not
records of the past. Such forecasts can be developed from data obtained from
weather
bureaus and other data resources, and using the latest weather forecasting
technologies. The present invention contemplates that relatively accurate
forecasts can
be developed, particularly when made within 24 hours before the forecasted
day.
Once the data is obtained, the wind speed forecasts that are similar to the
wind
histories for the upcoming day are prepared, which can be used to determine
the daily
power delivery schedules that should be implemented to maintain a relatively
constant
power output level for the longest possible periods during the upcoming 24
hour period.
Again, the objective is to deliver power to the power grid using a reduced
number of
constant power output level periods per day, i.e., preferably three or less,
although up
to about 7 or more can be acceptable as will be discussed. This allows for the
number
of times that the delivery output level will have to be changed to be
minimized, thereby
placing less stress and work on the switching mechanism.
For purposes of this example, three of the six days in November 1996, i.e.,
November 1, 5 and 6, have been chosen for their extreme varied wind speeds,
which
are helpful in showing various aspects of the present method. Days where wind
speed
variations are high require the use of stored energy to smooth the delivery of
energy to
the grid, whereas days that have fewer wind speed variations typically do not.
These
three days will be studied and plotted to show how the present method can be
applied
to determine a daily delivery schedule that can satisfy the stated objectives.
Before discussing the development of the delivery schedules, it is pertinent
to
discuss the selection of the wind turbines, which will determine the power
output
capacity for each windmill station, and therefore, play a role in the design
of the daily
delivery schedules. In this respect, it is important to note that the overall
design of the
wind farm, including the total number of windmill stations that are to be
installed, can be
based on the criteria that have been explained in Applicants' previous
application,
which has been incorporated herein by reference. In the particular example
shown
here, Applicant has selected the Nordex N50/800 wind turbine, the performance
of
which is being compared to a computer model in Figure 5. This product has been
chosen for this example, but any conventional wind turbine could have been
used. The
selected wind turbine has a 50 meter diameter blade, a 50 meter tower height
and a
swept area of 1,964 square meters. It turns on at 3 meters per second, and has
a
design wind speed of 14 meters per second. This size was selected because the
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power generation capacity is suited for large applications, such as 100 to
1,000 MW
wind farms, while at the same time, the product is small enough to be
transported by
truck and rail.
The example storage facility has also been designed with 62 storage tanks,
each
being 60 feet long and 10 feet in diameter, with a rating of 600 psig. This
allows for the
use of standard off-the-shelf components and hardware, which can reduce the
overall
cost of installation. The design takes into account the worst case scenarios,
i.e., days
where the most number of tanks are required, to determine the total number of
tanks
that are needed for the wind farm at the site under consideration. The
pipeline system
can similarly be designed with the appropriate storage capacity, based on the
size of
the pipe, and its length.
The methodology applied in formulating a delivery schedule for each upcoming
day involves at least the following three design considerations that relate to
how much
energy is generated by the immediate use stations, and how much is generated
by the
energy storage stations (including the hybrid stations that have been
converted to one
or the other):
1. The peak pressure in storage should not exceed 600 psig;
2. At any moment in time, the pressure in storage should never be less than
100 psig; and
3. Pressure in storage at the end of each day should equal or exceed that at
the
beginning of each day, if possible.
Based on these considerations, an iterative process is preferably used to
determine how many of each type of windmill station should be in operation at
any
moment in time. Using the methodologies discussed in the previous application,
and
the concepts discussed herein, the design that has been chosen for this
example is as
follows: 24 immediate use stations, 6 energy storage stations, and 19 hybrid
stations.
This enables the system to be adjusted within a range of between a maximum of
43
immediate use windmills (24 immediate use stations and 19 hybrid stations
converted
to immediate use), and a maximum of 25 energy storage windmills (6 energy
storage
stations and 19 hybrid stations converted to energy storage). In general, more
immediate use stations are used when there are fewer variations in wind speed,
and
more energy storage stations are used when there are more variations in wind
speed.
The system also has the ability to shut off or otherwise vent power from any
of the
windmill stations, so that the appropriate ratio between immediate use and
energy
storage can be obtained at all times, if necessary.
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Figure 6 shows two different delivery schedules that have been developed for a
24-hour period on November 1, 1996. Both charts compare the constant output
curve
(shown by the two straight lines) with the wind/power availability curve. The
difference
between the two schedules relates to how many immediate use and energy storage
stations have been placed in operation during the day. The first chart
represents a
system with a setting where 87% of the total wind generated power is delivered
to the
grid directly from the immediate use stations, and 13% of the power is
processed
through storage. The second chart represents a setting where 40% of the wind
generated power is delivered to the grid from the immediate use stations, and
60% of
the power is processed through storage.
In both examples, each delivery schedule has been developed to provide two
constant power output periods, one lasting 20 hours, and the other lasting 4
hours.
This was primarily based on the shape of the wind speed curve on that day,
which
shows that the wind speed fluctuated around 5 meters per second during the
first 20
hours, and then jumped to fluctuate around 7 meters per second during the last
4
hours. For this reason, the schedule was designed to provide a substantially
constant
energy output level of about 2,500 kW during the first 20 hour period, and a
substantially constant energy output level of about 5,000 kW during the last 4
hour
period.
Setting the delivery schedule to provide relatively few constant power output
level periods during each day enables the system to avoid surges and swings
that
could otherwise adversely affect the system. Had only the immediate use
stations been
used, like in a conventional windmill system, the amount of energy supplied to
the grid
would have followed the peaks and valleys of the wind speed curve, which had
severe
fluctuations and oscillations. In such case, a severe peak or spike of energy
would
have been delivered to the grid at about 3 p.m., along with other fluctuations
and
oscillations, placing additional stress and strain on the power system. By
using the
present invention, on the other hand, it can be seen that the amount of power
delivered
to the grid was very predictable and constant over an extended period of time.
It can also be seen from Figure 6 that the cost of supplying power using the
first
schedule was $.033/kW-Hr, while the cost of the power using the second
schedule was
$0.051/kW-Hr. This is due to the inefficiencies associated with having to
obtain a
greater percentage of the energy from storage than from the immediate use
stations.
For this reason, what this shows it that it is usually desirable to use the
schedule that
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relies for a greater percentage of the power on the immediate use stations
than on the
energy storage stations.
During the time that the system is in operation, in addition to selecting a
schedule that relies as much on energy from immediate use than from energy
storage,
it is also desirable to balance the energy that is in storage, by keeping a
balance
between the energy that is introduced into storage, with the energy that is
being
extracted from storage, so that at the end of each day, the amount of energy
in storage
is no less than it was at the end of the previous day. Moreover, as discussed
above,
another consideration is to always maintain at least 100 psig of pressure in
storage, so
that in case the wind conditions do not actually occur as predicted in the
forecasts,
there will be sufficient energy left over that could be relied upon at a later
time if
needed. At the same time, it is also desirable not to have more than a
predetermined
amount of pressure in storage, in which case pressure may have to be vented
and
wasted.
The energy processed through storage involves the following three scenarios,
which must be accounted for in the development of the delivery schedule:
First, the system must be designed to account for periods when the input level
into storage is equal to the output. That is, if the constant delivery power
output level
matches the rate at which power is being supplied from a combination of the
immediate
use and energy storage stations, then theoretically, the amount of energy in
storage will
remain substantially constant during these periods. Of course, this does not
take into
account certain inefficiencies, as well as waste heat from the compressor, and
any of
the heating devices discussed above. Nevertheless, it is clear that there will
be times
when the amount in storage will remain substantially constant. This can occur,
for
example, when no energy from storage is used, and all of the energy is
obtained from
the immediate use stations, to maintain the constant power output level.
Second, the system must be designed to account for periods when the input
level into storage is less than the output. During these periods, it can be
seen that a
greater percentage of energy will be extracted from storage, than will be
provided into
storage, to maintain a constant power output level, in which case the amount
of energy
in storage can be reduced over time. While this can go on temporarily for a
short
period of time, eventually, the delivery schedule would have to be adjusted so
that the
energy in storage will be re-stored, to maintain the level of energy in
storage in
substantial equilibrium. In other words, the delivery schedule must be adapted
to factor
in the potential for more energy being introduced back into storage later that
day, in
24
CA 02527597 2005-11-29
WO 2004/113720 PCT/US2004/018899
order for the amount of energy in storage at the end of each day to equal or
exceed the
amount in storage at the beginning of each day.
Third, the system must be designed to account for periods when the input level
into storage is more than the output. In this case, energy will be introduced
into storage
at a rate that is greater than that at which it is extracted. As discussed,
this is important
because of the second scenario, where the energy in storage can otherwise
become
reduced. In this case, the delivery schedule must be adapted to account for
the
possibility that during some periods a greater percentage of energy will be
introduced
into storage than would be extracted from storage, such that the amount of
energy in
storage can be increased over time. At the point that the pressure becomes too
high,
however, the pressure will have to be vented, and/or the compressors will have
to be
turned off.
The first chart in Figure 7a shows the two constant power output periods (one
lasting 20 hours and the other lasting 4 hours) being compared to the amount
of energy
that is being supplied into storage, which is shown by the up and down curve.
It can be
seen that there are severe differences between these curves, which represent
the
second and third scenarios discussed above, i.e., periods where input exceeds
output,
or output exceeds input. As shown in the second chart of Figure 7a, there are
changes
in the "wind stored" curve, which occur by virtue of the energy level in
storage being
increased at times, and reduced at times, depending on which of the above
scenarios
apply at any moment in time. This chart shows that less than 1,000 kW of net
power
was supplied into storage at any given time based on 87% of the power being
supplied
directly to the grid, and 13% of the power being processed through storage.
The
curvature of the "wind stored" line also shows that the amount of energy being
supplied
into storage can fluctuate over time.
Figure 7b shows the net energy accumulated into storage during the day, again,
based on the occurrence of the three scenarios discussed above. It can be seen
from
the top chart in Figure 7b that the accumulated energy in storage fluctuates
over the
course of the day, which is necessary for the power output levels to remain
constant. It
can also be seen in the bottom chart that the pressure level (shown by the top
curve) in
storage drops to almost 100 psig at about 1:00 p.m. and then again between
6:00 and
8:00 p.m., which is a result of a combination of the three scenarios discussed
above,
where net energy being extracted may exceed the net energy being supplied. It
can
also be seen that the delivery schedules have been plotted successfully to
ensure that
the pressure never goes below 100 psig, and that an equal amount or more
energy is in
CA 02527597 2005-11-29
WO 2004/113720 PCT/US2004/018899
storage at tffe""'°erid~of"the d'ay than at the beginning of the day.
The pressure also never
exceeds 600 psig.
In actual practice, since these delivery schedules will be based on projected
wind speed forecasts, the actual planning of the schedules will have to
reflect a fairly
conservative approach, to account for the possibility that the actual wind
conditions may
not be as anticipated. If the schedules are not conservative, it may be
possible that the
pressures could fall below 100 psig or run out altogether, in which case there
will not be
enough pressure in storage to supply power to the grid. If energy in storage
does run
out, the system will fail to be able to provide a constant power output level
during those
times, i.e., wind speed fluctuations will continue to cause fluctuations in
the delivery of
power output, since there will be no energy in storage to offset and smooth
the wind
speed and power generation fluctuations from the immediate use stations. In
such
case, the delivery schedule will have to be adjusted to make up for the loss
of power in
storage during the previous periods, which the present invention contemplates
may be
necessary at times. On the other hand, if the schedules are too conservative,
pressure
in storage may have to be vented, in which case energy may be wasted.
Figures 8a and 8b, and 9a and 9b, show similar charts for the 24 hour periods
on
November 5 and 6, 1996, respectively.
Figure 8a shows a delivery schedule that has been developed for the 24-hour
period on November 5, 1996, based on the wind history that occurred on that
day. This
chart represents a delivery schedule where 60% of the total wind generated
power is
delivered to the grid directly from the immediate use stations, and 40% of the
power is
processed through storage. Because the wind speed curve on this day varied
significantly, this delivery schedule was developed to provide seven different
constant
power output periods, not two or three.
The first constant level period (from midnight to 3:00 a.m.) provides very
little if
any power to the grid. This is mainly due to the fact that there was little or
no wind
during that time.
The second constant level period from 3:00 a.m. to 9:00 a.m. provides about
4,000 kW, which is due to a slight increase in wind speed beginning at about
4:00 a.m.
The third constant level period extends only from 9:00 a.m. to 10:00 a.m. due
to the
sharp increase in wind speed that begins at about 8:00 a.m. This period is
short
because the increase in wind speed is so dramatic that the output had to be
increased
to 10,000 kW to efficiently use the energy being supplied and generated.
26
CA 02527597 2005-11-29
WO 2004/113720 PCT/US2004/018899
T~ie~'fourth co'iisfant~level period extends from 10:00 a.m. to 1:UU p.m., at
a ~eve~
of about 24,000 kW, which reflects the increasing wind speeds during that
time. ,
Because the wind speed continues to increase after 1:00 p.m., and continues to
blow at
very high levels, the fifth constant level period is set at 35,000 kW and
extends for nine
hours from 1:00 p.m. to 10:00 p.m. This is the period during which the power
levels are
constant for the longest period during the day, wherein the output levels and
therefore
delivery of power to the grid are predictable and stable.
What happens at the end of the day, towards midnight, however, is that the
wind
speeds begin to drop off dramatically. Accordingly, the final two hours of the
day are
broken up into two more constant power level periods, beginning with a level
of about
32,000 kW from 10:00 p.m. to 11:00 p.m., and then dropping significantly to
about
10,000 kW from 11:00 p.m. to midnight. While it is certainly more advantageous
to
create fewer constant level periods during each day, when considering the
severe
fluctuations and oscillations that have occurred during the day, it can be
seen that the
system was required to be adjusted more frequently to provide the degree of
predictability and stability that would be needed to provide the advantages
discussed
above. By using the present invention, the amount of power delivered to the
grid was
made more predictable and constant for fixed periods during the day, even
though
there were more of those periods on this day than on November 1.
The second chart in Figure 8a shows the net energy being supplied into storage
during the day (shown by the grey line). This is based on having 40% of the
power
from the windmill stations being introduced into storage, while at the same
time, a
certain amount of energy being extracted from storage at a rate necessary to
maintain
the overall power output levels relatively constant. Again, the amount stored
is based
on the accumulation of various conditions existing throughout the day,
including the
occurrence of the three scenarios discussed above.
It can be seen from the second chart in Figure 8a that the supply of energy
into
storage fluctuates over the course of the day, from a relatively small amount
in the
morning, to a relatively large amount in the afternoon. Although a greater
amount of
power is delivered to the grid during the afternoon hours, the immediate use
stations
generate the bulk of that power. Accordingly, it can be seen that a
significant amount of
energy is being supplied into storage during the afternoon hours, even though
a
significant amount of power, i.e., 35,000 kW, is delivered to the grid at the
same time.
The top chart in Figure 8b shows the accumulation of energy in storage during
that day, which increases substantially over time. This is due to the
significant amount
27
CA 02527597 2005-11-29
WO 2004/113720 PCT/US2004/018899
df''eh~rgy-tY~at"is' being"'iiitroduced into storage, as shown in the bottom
chart of rigure
8a. The top chart of Figure 8b shows the curve going from about 10,000 kW-hr
to
about 70,000 kW-hr over the course of the 24 hour period.
The bottom chart shows that there are contributions being made to the total
energy by virtue of the temperature and pressure levels increasing in storage
as well. It
also shows severe fluctuations in the amount of pressure in storage, which is
one of the
reasons that seven different constant output level periods had to be scheduled
on that
day, to ensure that the pressure never exceeded 600 psig, and never went below
100
psig, although it can be seen that an excessive buildup of pressure in storage
that
exceeded 600 psig nevertheless occurred at about 1:00 p.m.
Figure 9a shows a delivery schedule that has been developed for the 24-hour
period on November 6, 1996, based,on the wind history that occurred on that
day. This
chart represents a delivery schedule where 50% of the total wind generated
power is
delivered to the grid directly from the immediate use stations, and 50% of the
power is
processed through storage. Because the wind speed curve on this day varied
significantly, this delivery schedule was developed to provide six different
constant
power output periods, which, as discussed below, was necessary to maintain the
pressure in storage between 100 psig and 600 psig.
On this day, the amount of power remaining in storage from the previous day
was relatively high, as discussed above, and the wind speeds were relatively
high
during the early morning hours, and continued to be high throughout the
morning and
into early afternoon, when it began to drop off slightly. Accordingly, the
delivery
schedule shows a significant amount of power being delivered to the grid
during the late
morning and early afternoon hours, with several incrementally increasing
constant
power output periods extending from midnight the night before until about 2:00
p.m.
For example, three constant level periods were implemented, including one from
midnight until 3:00 a.m., wherein the energy delivered was about 14,000 kW. In
the
other two periods, one extended from 3:00 a.m. to 6:00 a.m., with about 27,000
kW of
energy being delivered, and another extended from 6:00 a.m. to 2:00 a.m., with
about
36,000 kW of energy being delivered during that period.
When the wind speeds began to drop off, however, the amount of power
scheduled to be delivered also dropped off. Three additional constant level
periods
were experienced, including one from 2:00 p.m. until 3:00 p.m., where the
energy
delivered was about 18,000 kW, one from 3:00 p.m. to 4:00 p.m., with about
13,000 kW
of energy being delivered, and the last from 4:00 p.m. to midnight, with about
10,000
28
CA 02527597 2005-11-29
WO 2004/113720 PCT/US2004/018899
kYIU 'of energy being beliverea. During this day, while the schedule called
for six
constant output level periods, two of the periods lasted for 8 hours each,
which
provided an extended period of 16 hours during which output levels were
constant for
an extended period of time.
The second chart in Figure 9a shows the net energy being supplied into storage
during the day (shown by the grey line), which is based on having 50% of the
power
from the windmill stations introduced into storage. It can be seen that the
supply of
energy into storage fluctuates over the course of the day, starting with a
relatively high
level of energy being supplied during the morning hours when the wind speeds
were
high, to a relatively low level of energy being supplied into storage during
the afternoon
and evening hours when the wind speeds began to dissipate. In this case, the
bulk of
the power delivered to the grid during the morning hours was generated by the
immediate use stations, but a substantial amount of power was also being
delivered
through storage, as the difference between the two curves show in the top
chart in
Figure 9a.
The top chart in Figure 9b shows the accumulation of energy in storage during
the day, wherein the amount increases steadily over time. This is due to the
significant
amount of energy being introduced into storage, as shown in the bottom chart
of Figure
9a, particularly during the morning hours. The top chart of Figure 9b shows
the curve
going from about 0 kW-hr to about 90,000 kW-hr over the course of the 24 hour
period.
The bottom chart shows that there are contributions being made to the total
energy
from the temperature and pressure increases, which fluctuated substantially,
in storage
as well.
As can be seen in the bottom charts on Figures 8a and 9a, the pressure curve
fluctuated considerably during the two day period between November 5 and 6,
1996.
These pressure curves are significant because they show how important it is to
change
the level of the constant level output periods occasionally to ensure that the
pressures
do not go below 100 psig, nor above 600 psig. As can be seen, the curve on
several
occasions, on November 6, went above the 600 psig level. In some
circumstances,
such as when temperature levels are above 70 degrees F., it may be permissible
to
increase the pressure to 800 psig, although the system would have to be
designed with
the appropriate storage facilities to ensure that higher pressures can be
handled by the
system.
Figure 10 shows how the delivery schedule was carried out using a
predetermined number of immediate use, energy storage and hybrid stations on
any
29
CA 02527597 2005-11-29
WO 2004/113720 PCT/US2004/018899
green day during the period. Can each day, all of the windmill stations were
operational,
but the ratio between the types of stations that were used at any given moment
was
adjusted based on how many hybrid stations were set to immediate use and
energy
storage. For example, on November 1, the total ratio used included 43
immediate use
windmills (including 24 immediate use stations and 19 hybrid stations
converted to
immediate use) and 6 energy storage stations. This accounted for the 87% to
13%
ratio discussed above.
On November 5, the ratio included 30 immediate use windmills (including 24
immediate use stations and 6 hybrid stations converted to immediate use) and
19
energy storage windmills (including 6 energy storage stations and 13 hybrid
stations
converted to energy storage). This accounted for the 60% to 40% ratio
discussed
above.
On November 6, the ratio included 25 immediate use windmills (including 24
immediate use stations and 1 hybrid station converted to immediate use) and 24
energy
storage windmills (including 6 energy storage stations and 18 hybrid stations
converted
to energy storage). This accounted for the 50% to 50% ratio discussed above.
The chart also shows that the number of storage tanks required at any given
moment will depend on the number of energy storage stations that are
operational.
Also, the chart shows that over the course of a 20 year period, the cost of
the energy
generated by these three different delivery schedules remains relatively
constant, i.e.,
about $0.033 kW-hr.
