Batteries: thermoelectric and photoelectric – Photoelectric – Panel or array
Reexamination Certificate
2002-05-30
2004-03-09
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Panel or array
C136S251000, C136S291000, C136S293000, C060S641800, C052S173300
Reexamination Certificate
active
06703555
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solar cell string having at least a part of an electric line thereof not housed in an insulating envelope, a solar cell array having the solar cell string, and a solar photovoltaic power system having the solar cell array.
2. Related Background Art
In recent years, awareness of ecological problems has been raised worldwide. Among others, the global warming resulting from CO
2
emission is seriously concerned about, and clean energy has been desired increasingly. In such a circumstance, a solar cell shows great promise to serve as a source of clean energy in terms of its safety and operability. The solar cell includes a photoelectric conversion layer for converting light into electricity, typical materials of which include single-crystalline silicon semiconductor, polycrystalline silicon semiconductor, amorphous silicon-based semiconductor, III-V compound semiconductor, II-VI compound semiconductor and I-III-VI2 compound semiconductor.
A solar photovoltaic power system including such a solar cell exists in a wide variety of scales from several watts to several thousands kilowatts. For example, a battery may be used to store energy generated by the solar cell, or a DC-AC converter may be used to supply output energy of the solar cell to a commercial system.
FIG. 1
is a block diagram of a typical solar photovoltaic power system disclosed in Japanese Patent Application Laid-Open No. 2000-207662. In this solar photovoltaic power system, four solar cell strings
104
to
107
are connected in parallel to constitute a solar cell array
101
, each of the solar cell strings being composed of a plurality of solar cell modules connected in series. An output of the solar cell array
101
is led to a power conditioner
102
having a controller for performing control of a maximum output and the like, and then supplied to a load
103
. The load
103
may be an electric power system, and such a system of flowing the power of the solar cell back to the electric power system is referred to as a utility connected system.
The solar photovoltaic power system is grounded through apparatus grounding or electric line grounding. The former apparatus grounding is generally carried out, and includes the grounding of a frame of the solar cell module and the grounding of a housing of the power conditioner. The latter electric line grounding varies from country to country. In Japan, the electric line of the solar cell array is typically insulated from the ground. On the contrary, in the United States, as described in the IEEE standard 1374-1998: “Guide for Terrestrial Photovoltaic Power System Safety” or the National Electrical Code Article (NEC) 690: “Solar Photovoltaic Systems”, the electric line of the solar cell array is generally grounded. In the above-described IEEE standard and NEC, it is described that the grounding of the electric line includes middle point grounding for connecting an electrical middle point of the electric line between the strings, positive-terminal grounding for connecting a positive-side electric line to the ground and negative-terminal grounding for connecting a negative-side electric line to the ground.
FIG. 2
shows an example of the solar photovoltaic power system having the negative-side electric line grounded. In
FIG. 2
, four solar cell strings
204
to
207
are connected in parallel to constitute a solar cell array
201
, each of the solar cell strings being composed of a plurality of solar cell modules connected in series. An output of the solar cell array
201
is led to a power conditioner
202
having a controller for performing control of a maximum output and the like, and then supplied to a load
203
. Similarly to the case of
FIG. 1
, the load
203
may be an electric power system. In addition, the electric line on the side of the negative terminal is connected to the ground via a grounding point
208
. Here, in the present application, this example is not identified as a prior art.
FIGS. 3A and 3B
show an example of a typical solar cell module used in the solar photovoltaic power system. In this drawing,
FIG. 3A
is a perspective view of a solar cell module
301
and
FIG. 3B
is a cross-sectional view taken along the line
3
B—
3
B of FIG.
3
A. As shown in
FIG. 3B
, the solar cell module
301
generally comprises a photovoltaic element
302
for converting received light into electricity, a front cover
303
made of glass, a translucent resin or the like disposed on the side of a light-receiving surface of the photovoltaic element, a back cover
304
made of glass, a resin, a metal or the like disposed on the side of a non-light-receiving surface of the photovoltaic element, an output cable
305
, a frame member
307
for reinforcing and fixing the solar cell module, and an adhesive
306
for bonding of the frame member.
One of the largest problems of the solar photovoltaic power system intended for electricity market is reduction of the power generation cost. In order to introduce the solar photovoltaic power system into the electricity market on a full scale, the cost reduction is essential, and it is needed to attain a cost comparing with the cost of conventional thermal power generation or nuclear power generation. However, as reported in an interim report (Jun., 11, 1998) from the Supply and Demand Party of the Advisory Committee for Resources and Energy of the Ministry of Economy, Trade and Industry, the energy cost of the solar photovoltaic power generation is 2.5 to 6 times than the electricity rate in Japan, and a radical cost reduction is needed for full-scale introduction thereof.
SUMMARY OF THE INVENTION
In view of such circumstances, particularly with a view to simplify an environmental resistant coating which significantly increases a cost of a solar cell module and an insulating coating of a member for interconnecting solar cells in series and parallel, an object of this invention is to significantly reduce power generation cost and to provide a solar cell string, a solar cell array and a solar photovoltaic power generation system with improved safety of an exposed electric line resulting from the simplification of the environmental resistant coating and the insulating coating.
In order to attain the object described above, the inventors have earnestly studied and obtained the following findings.
As shown in
FIGS. 3A and 3B
, besides a photovoltaic element which is an essential component for power generation, a conventional solar cell module requires many members including a front cover, a back cover, a frame member and the like. These members are necessary to protect the solar cell module against thermal stress, optical stress and mechanical stress in an outdoor environment and ensure electrical insulation thereof. The inventors has investigated a novel requirement of the solar cell module, which is intended to protect the photovoltaic element against the environmental stresses but not to ensure the electrical insulation so that a charging part thereof is partly exposed. As a result, a first finding has been obtained that the front cover and the back cover can be significantly reduced in thickness, and therefore, a significant cost reduction can be expected. Furthermore, by also excluding from the requirements the insulation performance for the interconnection member for interconnecting the solar cells in series and parallel, a significant cost reduction can be expected.
By excluding the electrical insulation as described above from the requirement, as expected as a matter of course, safety should be ensured because an insulation resistance between the solar cell array circuit and the ground is small, and the electric line for charging the solar cell array is exposed. Therefore, it is a major premise that such a system having such an exposed charging part is installed in a controlled area to which those other than an administrator are forbidden to enter. Furthermore, the inventors have investigated auxiliary means as an additional measure for safe
Itoyama Shigenori
Makita Hidehisa
Matsushita Masaaki
Mukai Takaaki
Takabayashi Akiharu
Canon Kabushiki Kaisha
Diamond Alan
Fitzpatrick ,Cella, Harper & Scinto
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