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57-61 The Design of Solar Cell System

Author: Source: Datetime: 2016-12-24 14:09:57

Arrangement of PV arrays

Each solar cell can only produce about 0.5V DC voltage, much lower than the actual use of the required voltage. In order to meet the needs of practical applications, the need for solar modules in series components. The solar cell module contains a certain number of solar cells, which are connected by wires. Large photovoltaic power station components usually package 72 solar cells, the normal output working voltage is about 35V. When the application needs a higher voltage and current and a single component can not meet the requirements, multiple components can be string, parallel to form a square solar array to obtain the required voltage and current. Solar cell module string, parallel composition matrix is based on solar cell components and inverter performance parameters and in a 20 ~ 70 ℃ to check the temperature conditions to design. Such as the use of 280Wp crystalline silicon solar cell components, calculated by the 18 components in series suitable. The two component strings form a square matrix that can be mounted on a set of brackets. 102 sets of support, that is, a total of 204 components string, 1028.161kW power to form a MWp power generation unit. To build 20 1MWpd grid-connected PV power plants, it can be divided into 20 1MWp generating units, one set of box-type transformers in the middle of each power generation unit (see Figure 4-6) to reduce the inverter DC and AC cable length, While reducing losses, less land, etc. to improve efficiency.

types of solar cells

polysilicon

type of solar cell module

260

240

index

unit

data

unit

data

peak power

Wp

260

Wp

240

open circuit voltage Voc

V

60.5

V

37.2

short - circuit current Isc

A

5.53

A

8.37

operating Voltage Vmp

V

50

V

30.4

working current Imp

A

5.1

A

7.89

size

mm

1580x1069x40

mm

1650x992x40

quality

kg

24.5

kg

19.5

peak power temperature coefficient

%/K

-0.45

%/K

-0.43

temperature coefficient of open circuit voltage

%/K

-0.348

%/K

-0.32

short - circuit current temperature coefficient

%/K

0.031

%/K

0.043

12 years power decay

%

<10

%

<10

25 years power decay

%

<20

%

<20


Such as with 240Wp components, according to the performance parameters of the component and the inverter input voltage requirements, the optimal match, should be 20 components in series into a string; such as 260Wp components, should be 12 components in series into a string . 2) The series open-circuit voltage does not exceed the requirement of the maximum DC voltage of the inverter. 2) The maximum string-to-line voltage of the inverter does not exceed the MPPT range of the inverter.

In order to improve the efficiency of the array PV array combination of efficiency = WSDS = square matrix of effective power / nominal power of each component and the sum) must be rigorously screened for each component of the operating voltage, operating current: that is required component IV curve as consistent as possible to reduce Components in series, parallel to the power loss caused. In the PV array design, there are the following considerations.

① array tilt design, azimuth design, array spacing design, according to the overall technical requirements, geographical location, climate conditions, solar radiation resources, site conditions and other specific circumstances to carry out.

(2) try to ensure that the north and south to each column in the same axis, the solar cell components arranged neatly, standardized, beautiful, the best solar radiation, land use more compact and economical.

③ spacing between the two components must be set to ensure that the lowest elevation in the solar winter solstice date, all components are still more than 6h of sunshine time.

(3) solar cell phalanx tilt, azimuth determination

The optimal choice of square-pitch installation angle depends on many factors such as geographical location, annual solar radiation distribution, direct radiation and scattered radiation ratio, load power supply requirements and specific site conditions. The optimal installation angle of grid-connected photovoltaic power generation system can be determined by RETScreen professional system design software, which should be the inclination angle when the maximum annual power generation capacity of the system, that is, the arrangement of PV modules and the inclination of components, Edge and lower edge will have a relative height difference, the sun under the shadow of the components, in order to ensure the location of PV power plant winter solstice 9: 00 ~ 15: 00 PV modules received between the largest radiation, you must choose the best angle.

Solar array square azimuth is the square of the vertical and the positive angle of the south, east is set to negative, to the west is positive. It is determined from the site conditions set as far as possible south, because the azimuth is 0 ℃, the largest power generation.

(4) the calculation of the spacing of PV arrays

PV array layout to determine the general principles: the day of solstice 9: 00 ~ 15: 00 solar modules should not be blocked, PV square spacing should not be less than the minimum spacing.

In the northern hemisphere, the corresponding maximum sunshine radiation to receive the amount of the plane toward the front, square dip angle determined, it is necessary to pay attention to the north and south between the front and rear array to set aside a reasonable distance, so as to avoid shading occlusion. Before and after the interval: the winter solstice (one year in which objects in the sun the longest shadow of the day) 9:00 am ~ 3:00 pm set, north and south between the components without shading. Calculate the minimum spacing D of the PV modules installed before and after the installation, as shown in Figure 4-7.

The distance between each two columns must be guaranteed to be at the lowest solar day in the solar island. All components still have more than 6 hours of exposure time.


The Determination of the Inclination and Orientation of Solar Cell.

Depending on a number of factors, such as geographical location, annual solar radiation distribution, incoming radiation and aberration, negative-load power requirements, and specific site conditions, the phalanx installation inclination depends on many factors. The optimal installation angle of grid-connected PV system is determined by the optimized design of WKK's professional system design software, which should be the flicker of the system when the power generation is large for a whole year, ie, the arrangement of the photovoltaic elements and the inclination of the components The relative height difference between the upper and lower edges of the module will be generated • The shadow of the components will be generated in the sunlight. To ensure the location of the PV power plant, the radiation tt between the PV modules is maximum at 9:00 am to 5:00 pm. Choose to be good dumping Museum.

The azimuth of the square of the solar cell is the angle between the vertical surface of the square and the positive south, the east is negative and the west is positive. It is true that it is set as far as possible from the site conditions, since the azimuth angle is zero.

Calculation of the Squareness of Photovoltaic Square.

PV square array S-like to determine the principle: the day of the winter solstice 9: 00 ~ 15: 00 solar modules should not be blocked.Voltage square spacing should not be less than the minimum spacing.

In the northern hemisphere, the plane corresponding to the maximum sunshine radiation is oriented toward the front. • After the square dip is determined • Note that a reasonable spacing between the north and south front and rear arrays is required to avoid shading. Before and after the interval: winter solstice (one year the object in the shadow of the sun the longest day of the day) 9:00 am ~ 3:00 pm set between the north and south components without shading occlusion Calculate the PV modules installed before and after the square Minimum spacing D.
 
The formula for the solar elevation angle:
The formula for the solar elevation angle:
The formula of solar azimuth: sinβ = cosδsinω / cosa
Where ∅ is the local latitude (positive in the northern hemisphere, negative in the southern hemisphere; & sun declination; the sun declination in the winter solstice 23.5 °; ω for the angle, the angle of 9:00 am 45 °
D = cosβ * L
 L = H / tana
A == arcsin (sinφsinδ + cosωcosδcosω)
The calculation formula is as follows: D = 0.707H / tan [arcsin (0.648cos∅ - 0.399sin∅)]
Where H is the height difference between the highest point of the PV array or the obstruction and the possible obscuring component of the back row.

Design of PV Square Support
Bracket design considerations parameters and reference standards:

GB 50009-2006 GB 50017-2003 "Design Code for Steel Structures";


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Angles conform to GB 9787-1988;
Steel in line with GB 9788-1988:
GB 50205 -2001 "steel structure of engineering acceptance"
GB 3098 "Mechanical properties of fasteners Bolts, screws and studs"
Wind load calculation formula: W = CwPAw,
Where w is the wind pressure load • N:
Cw a wind power factor:
P a design wind speed pressure, N / m2;
Aw a force area.
The design wind pressure P is calculated as follows: P = PoUhueus
Where P0 a reference wind pressure • N / m2
Uh a height correction factor:
          Ue-environment factor:
          US One figure correction factor.
Set the reference height 10 m. The reference air pressure can be calculated from the following formula

PO 1/2 1/2 pV02
Where P0 is the air density wind speed • N * S2 / m4:
V0 a design with the reference wind speed: m / s;
The air density and wind speed are different in winter and summer. From the safety considerations, take the larger winter values • 1.274 * S2 / M4
The maximum instantaneous wind speed at a height of 10 m above ground for 50 years was designed with the reference wind speed.
The wind pressure height correction factor Uh can be found in Table 4-2.
Table Correction coefficient of wind pressure deviation Uh

Distance from the ground/m   Ground roughness  category
A B C D
5 1.17 1 0.74 0.62
10 1.38 1 0.74 0.62
15 1.52 1. 14 0.74 0.62
20 1.63 1.25 0.84 0.62
30 1.8 1.42 1 0.62
40 1.92 1.56 1.13 0.73
50 2.03 1.67 1.25 0.84


Environmental correction factor Ue: open to the wind without blocking the area: 1.15; a small amount of shelter against the wind: 0.9; the wind has a larger occlusion 0.7
Figure 4-3 shows the body shape correction coefficient Us
From China's actual situation, can be divided into four pressure area.

 1. The maximum wind pressure area: including the southeast coast and island, wind pressure value of 70-80kgf / m2 or more (1kgf / m2 = 9.80665Pa).
2. The second wind pressure area: including the northeast, north, northwest, wind pressure value of 40-60kgf / m2.
3. Tthe larger wind pressure area, including the Qinghai-Tibet Plateau, the wind pressure value of 30-50kgf / m2
4. The minimum pressure area: including Yunnan, aristocracy, Sichuan and western Hunan, western Hubei, 20-30kgf / M2.

According to the above range, for the safe and reliable, the reference value of the wind pressure is generally optional 60kgf / m2, this value can also be substituted into the wind load calculation formula, material selection of square steel supports.


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Wind power factor Cw, the solar cell module can refer to the number shown in Table 4-4, while the skeleton and monomer materials can refer to Court 4-8 and Table 4-5 data。

Table 4-3 Wind load shape correction coefficient

Downwind Square angle Upwind
0.79 15" 0.94
0.87 30" 1. 18
1.06 45" 1. 43


Table 4-4 Wind Coefficient of Solar Module

Installation status coefficient Remarks
Downwind/Upwind
Ground installation type (single) Cw(Positive pressure) θ Cw(Positive pressure) "If the number of brackets is several, the wind force coefficient of the peripheral end is taken as the left value, the wind force coefficient of the central part is 1/2 of the left value,
The Cw of the angle θ not marked on the left is given by:
(Positive pressure) 0.65 + 0.009θ
(Negative pressure) 0.71 + 0.016θ
15°≤θ<45°"
0.79 15° 0.94
0.87 30° 1.18
1.06 45° 1.43
Roof installation type Cw(Positive pressure) θ Cw(Positive pressure) If there is a protruding part of a brick or the like at the roof spine, 1/2 of the left negative pressure value may be obtained by the following formula:
(Positive pressure) 0.95 +0.0170
(Negative pressure) 一0. 10 + 0.0770θ—0• 0026θ2
12 ° ≤ θ ≤ 27 °
0.75 12° 0.45
0.61 20° 0.4
0.49 27° 0.08

ufo

Figure 48 Wind force coefficient of the skeleton

(As shown in the figure for the structure of the beam and the structure of the column cross-section, as the wind pressure area. Take the relative structure of the vertical direction to see& TAG: Intelligent Floating Mercedes Revolution MAS Funding Synergies Developing Window Sponge Zinc 3-D Shingles Base Production