Batteries: thermoelectric and photoelectric – Applications – Space - satellite
Reexamination Certificate
2002-06-04
2004-04-20
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Applications
Space - satellite
C136S244000, C136S246000, C244S173300, C322S00200R, C342S354000, C342S352000
Reexamination Certificate
active
06723912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a space photovoltaic generation system wherein sunlight is converted into electric energy in space and the electric power is transmitted by microwave, etc., and is received at a power base for use as electric energy.
2. Description of the Related Art
Because of finitude of electric energy based on the fossil fuels of oil, coal, natural gas, etc., and adversely affecting the environment, attention is focused on sunlight as an energy source to replace the electric energy based on the fossil fuels. Ground photovoltaic generation, etc., exists as one mode of electric energy use based on sunlight, but it is hard to stably supply electric power because of the sunshine amount between day and night, the effect of weather, etc., and the efficiency is poor. On the other hand, atmospheric attenuation scarcely exists in space and the solar energy density in space even in the vicinity of the earth reaches five to 10 times that on the ground; the lure of solar energy use in space is large. Research and development on a space photovoltaic generation system wherein solar energy in space is converted into electric energy and the electric energy is transmitted by microwave, etc., and is received at a specific location is underway.
As an example of a related art of such a space photovoltaic generation system,
FIG. 9
is drawing to show the configuration of a space photovoltaic generation system in a related art in “U.S.DOE and NASA Reference System Report, “Satellite Power System: Concept Development and Evaluation Program”, DOE/ER-0023, 1978.” In
FIG. 9
, numeral
4
denotes a power generation satellite, numeral
5
denotes a photoelectric conversion unit formed of solar cell panels installed in the power generation satellite
4
, numeral
9
denotes a transmitting antenna mounted on the power generation satellite
4
, numeral
10
denotes a microwave radiated from the transmitting antenna
9
, numeral
11
denotes a power base, and numeral
12
denotes a receiving antenna placed in the power base
11
.
In the space photovoltaic generation system shown in
FIG. 9
, the photoelectric conversion unit
5
installed in the power generation satellite
4
performs photoelectric conversion of sunlight. The generated power energy is transmitted through the transmitting antenna
9
to the power base
11
as the microwave
10
and is received at the receiving antenna
12
in the power base
11
. In the example cited as the related art, the photoelectric conversion unit
5
installed in the power generation satellite
4
has a size of 5×10 km, the transmitting antenna
9
has a diameter of 1 km, and the receiving antenna
12
in the power base
11
has a size of 10×13 km. The power generation satellite
4
has a weight of 50000 tons. The total size of the solar cell panels forming the photoelectric conversion unit
5
is determined in response to the amount of electric power generated by the power generation satellite
4
, and the sizes of the transmitting antenna
9
and the receiving antenna
12
are determined in response to the receiving power efficiency.
Here, defining the value of normalizing electric power P
rx
arriving at the aperture area of the receiving antenna
12
having an aperture diameter D
rx
based on electric power P
tx
transmitted through the transmitting antenna
9
having an aperture diameter D
tx
as receiving power efficiency &eegr;
b
, if distance d between the transmitting antenna
9
and the receiving antenna
12
is sufficiently long so as to form a Fraunhofer region (region assumed to be electrically infinite distance) and the aperture distribution of the transmitting antenna
9
is uniform in both amplitude and phase, radiation field distribution E of the transmitting antenna
9
and the receiving power efficiency &eegr;
b
are represented by the following expressions:
E
=
J
1
(
Z
θ
)
Z
θ
(
1
)
η
b
=
P
rx
P
tx
=
∫
0
θ
|
E
|
2
Z
θ
ⅆ
Z
θ
∫
0
π
|
E
|
2
Z
θ
ⅆ
Z
θ
=
1
-
J
0
2
(
Z
θ
)
-
J
1
2
(
Z
θ
)
(
2
)
Z
θ
=
π
D
tx
λ
sin
(
θ
)
(
3
)
θ
=
tan
-
1
(
D
rx
2
d
)
(
4
)
where &lgr; is the wavelength of the microwave
10
and J
n
(x) is a Bessel function of the order n. From expression (2), it is seen that the aperture diameters of both the transmitting antenna
9
and the receiving antenna
12
need to be made large to enhance the receiving power efficiency &eegr;
b
. If the transmitting antenna
9
and the receiving antenna
12
differ in aperture shape or aperture distribution, the calculation expression of the receiving power efficiency &eegr;
b
also varies accordingly. However, if the aperture diameter of the transmitting antenna
9
or the receiving antenna
12
is made large, the receiving power efficiency &eegr;
b
is always enhanced.
If the distance d between the transmitting antenna
9
and the receiving antenna
12
is sufficiently large as compared with the aperture diameter D
rx
of the receiving antenna
12
, the following expression holds according to expressions (3) and (4):
Z
θ
≅
π
D
tx
D
rx
2
λ
d
(
5
)
From expression (5), if either of the aperture diameters of the transmitting antenna
9
and the receiving antenna
12
required for achieve one receiving power efficiency is determined, the aperture diameter of the other is also determined. To provide high receiving power efficiency, the aperture diameter of the transmitting antenna
9
or the receiving antenna
12
needs to be made large. FIGS.
10
(
a
) and
10
(
b
) show the characteristics of the radiation field distribution of the transmitting antenna
9
in the Fraunhofer region and receiving power efficiency if the wavelength &lgr; of the microwave
10
radiated from the transmitting antenna
9
is 52 mm (frequency 5.8 GHz). From the figures, it is seen that, for example, if the power generation satellite
4
is placed in stationary orbit above the ground of 36000 km and the aperture diameter of the transmitting antenna
9
is 1 km and the aperture distribution is uniform, the aperture diameter of the receiving antenna
12
needs to be about 7 km to provide receiving power efficiency 90%.
From expression (2), if the transmission frequency of the microwave
10
radiated from the transmitting antenna
9
is made high (the wavelength is shortened), the aperture diameter of the transmitting antenna
9
or the receiving antenna
12
can be lessened, but a problem of interfering with the frequency bands used with the already existing satellite communications, ground microwave communications, etc., is involved. To place the power base
4
on the ground, generally as the frequency becomes high, an atmospheric loss cannot be ignored and the receiving power efficiency is lowered. Thus, the frequency range used for the microwave
10
is limited. 2-GHz band (2.45 GHz) and 5-GHz band (5.8 GHz) are named as the frequencies assumed in the space photovoltaic generation system so far.
To increase the amount of electric power generated by the power generation satellite
4
, the area of the solar cell panels forming the photoelectric conversion unit
5
, a reflecting mirror for condensing sunlight, or the like needs to be increased.
By the way, the power generation satellite installing the solar cell panels and the transmitting antenna needs to be hoisted into predetermined orbit in space using a rocket or a shuttle. On the other hand, the dimensions and weight that can be carried in a rocket, etc., are limited and thus if the dimensions or weight of the solar cell panels and the transmitting antenna contained in the power generation satellite are large, it is physically difficult to hoist and develop them into space at a time.
Then, a method of launching the components of the power generation satellite more than once is possible. In this case,
Mikami Izumi
Mizuno Tomohiro
Naito Izuru
Sato Hiroyuki
Diamond Alan
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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