Data processing: measuring – calibrating – or testing – Calibration or correction system – Temperature
Reexamination Certificate
1998-06-04
2001-08-21
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Temperature
C702S065000, C702S063000, C320S101000, C323S906000
Reexamination Certificate
active
06278954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for estimating the generated energy of a solar cell and, more particularly, to a method and apparatus for estimating the generated energy of an amorphous silicon solar cell.
2. Description of Related Art
A solar cell is affected by a change in weather such as solar radiation or temperature because of its nature and therefore generates power unstably. For this reason, in order to estimate generated energy depending on the set state of a solar cell, a simulation is conducted using solar radiation or temperature data. Especially in recent years, solar cells for general housing purposes have become popular. To design the necessary number of solar cell modules, generated energy at the site where the solar cells are set must be estimated.
A method of estimating generated energy is disclosed in “Guidebook for Design of Photovoltaic Power Generation System” (The OHM-Sha, Ltd.).
The basic formula for simulation of generated energy of a photovoltaic power generation system is obtained in the following way. Using a mean tilt solar radiation I
s1
, an overall correction coefficient K and rated power R1 of a solar cell are input. The generated energy of the photovoltaic power generation system is calculated using equation (1):
P2=I
s1
·K·R1 (1)
The overall correction coefficient K is rewritten using a temperature correction coefficient D1′, a dust reduction correction coefficient D2, a power transmission loss correction coefficient D3, and an inverter correction coefficient D4:
K=D1′·D2·D3·D4 (2)
The temperature correction coefficient D1′ in equation (2) is given by:
D1′=1+&agr;
pmax
(Tcm−Ts) (3)
where
&agr;
pmax
: −0.0037 (single-crystal solar cell)
−0.0044 (polycrystalline solar cell)
−0.0020 (amorphous silicon solar cell)
Tcm: mean monthly ambient temperature A1+15° C.
Ts: solar cell temperature under standard conditions=25° C.
The power transmission loss correction coefficient D3 is given by equation (4) using an array unbalance loss E1, a wiring loss E2, and a diode loss E3:
D3=1−(E1+E2+E3) (4)
Assume that the above basic formula for calculating each monthly generated energy of the photovoltaic power generation system is used to estimate generated energy in a given area. As the mean monthly ambient temperature in that area increases, the temperature correction coefficient D1′ is corrected in the negative direction. For this reason, when an amorphous silicon solar cell is used, the generated energy is estimated to be smaller than the actually generated energy. Conversely, the temperature correction coefficient D1′ is corrected in the positive direction as the mean ambient temperature decreases. For this reason, when an amorphous silicon solar cell is used, the generated energy is estimated to be larger than the actual power. In the present invention, “amorphous silicon” includes “micro-crystallized silicon”.
FIG. 2
is a graph showing generated energy estimated by the above method (solid line
11
) and actually generated energy (broken line
12
) for each month. A solid line
13
indicates the mean monthly ambient temperature. In a season when the mean monthly ambient temperature is particularly high or low, the difference between the estimated generated energy and the actually generated energy becomes large.
As is known, the amorphous silicon solar cell exhibits an optical degradation phenomenon due to its nature: the initial performance immediately degrades after the manufacture due to long-time outdoor exposure and finally stabilizes. The optical degradation in performance is a reversible phenomenon so annealing by heat allows recovery of the initial performance. This is called annealing recovery.
The solar cell generates power outdoors under a solar ray. The solar cell absorbs not only the solar ray necessary for power generation but also light components which do not contribute to power generation. The light energy which does not contribute to power generation is converted into heat and increases the temperature of the solar cell module. Actually, the temperature of the solar cell module during power generation is 20° C. to 30° C. in winter when the mean monthly ambient temperature is 2° C. to 3° C., and sometimes exceeds 60° C. in summer when the mean monthly ambient temperature is 25° C. to 26° C. For this reason, as the ambient temperature or module temperature increases, the amorphous silicon solar cell recovers its performance by the above-described annealing recovery and generates more power. That is, the nature is reverse to that of a crystalline solar cell.
When the above-described basic formula for generated energy is used to estimate generated energy of a photovoltaic power generation system using an amorphous silicon solar cell, the temperature correction coefficient D1′ is corrected in the negative direction as the mean monthly ambient temperature increases, and the generated energy is estimated to be small. As the mean monthly ambient temperature decreases, the temperature correction coefficient D1′ is corrected in the positive direction, and the generated energy is estimated to be large. This increases the difference between the estimated generated energy and the actually generated energy for each month.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power estimation apparatus and method of accurately estimating power to be generated by a solar cell or a photovoltaic power generation apparatus on the basis of its installation site.
In order to achieve the above object, according to an aspect of the present invention, there is provided a method of estimating generated energy of a solar cell comprising the steps of: obtaining a mean solar radiation and mean temperature at a solar cell installation site; calculating a correction coefficient on the basis of the mean ambient temperature; and estimating the generated energy from the obtained mean solar radiation and correction coefficient, and rated power of the solar cell, wherein the correction coefficient increases as the mean ambient temperature increases.
According to another aspect of the present invention, there is provided an apparatus for estimating generated energy of a solar cell comprising: obtaining means for obtaining a mean solar radiation and mean ambient temperature at a solar cell installation site; calculation means for calculating a correction coefficient on the basis of the mean ambient temperature; and estimation means for estimating the generated energy from the obtained mean solar radiation and correction coefficient, and rated power of the solar cell, wherein the correction coefficient increases as the mean ambient temperature increases.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
REFERENCES:
patent: 5688337 (1997-11-01), Mosher
patent: 5867011 (1999-02-01), Jo et al.
patent: 8-36433 (1996-02-01), None
Kleiss et al., “Temperature-Dependent Influence of a Si:H Cell Degradation on the Energy Delivered under Realistic Operating Conditions”, IEEE, Jan. 1993.*
Knaupp, “Power Rating of Photovoltaic Modules From Outdoor Measurements”, IEEE, Aug. 1991.*
Nann et al., “A Numerical Analysis of PV-Rating Methods”, IEEE, Aug. 1991.*
Hussein et al., “Maximum Photovoltaic Power Tracking: an Algorithm for rapidly Changing Atmospheric Conditions”, IEEE, Jan. 1995.*
Krauter et al., “Actual Optical and Thermal Performance of PV-Modules”, IEEE, Apr. 1994.*
Fukae et al., “Outdoor Performance of Triple Stacked a-Si Photovoltaic Module in Various Geographical Locations and Climates”, IEEE, Apr. 1996.*
B. Kroposki, “A Comparison of Photovoltaic Module Performance Evaluation Methodologies for En
Lim Chin Chou
Takehara Nobuyoshi
Tamechika Masanari
Assouad Patrick
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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