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87-89 BIPV design points

Author: Source: Datetime: 2017-01-01 23:47:54

4.2.3 BIPV design points

Internationally, although Germany has completed hundreds of thousands of PV roof plan, gained rich experience, but also found many problems. Most of the German photovoltaic buildings are designed by professional architects, in appearance, architectural features and in light transmission and construction in harmony, the design seems impeccable. However, these architects have also ignored or do not understand the power characteristics of solar cells, such as the direction of the square of solar cells, block and temperature rise and other issues.
(1) the orientation of the solar array

Solar array and the combination of buildings, and sometimes can not freely choose to install the orientation. The solar cell arrays of different orientations produce different amounts of electricity and can not be calculated according to the conventional method. A basic estimate of the amount of electricity generated from different orientations of solar cells can be found in Figure 4-22.

Figure 4-22

Figure 4-22 shows the amount of electricity generated by the different arrays of solar cells facing each other.

1. Assuming that the installed capacity of the square solar cell array is 100 in the south-angled latitude angle;

2. the other generation has a different degree of reduction;

3. In different regions, different solar radiation conditions, the degree of reduction is different.

(2) solar cell phalanx of the block

Solar array and the combination of buildings, and sometimes will inevitably be blocked. The occlusion has a large influence on the power generation amount of the crystalline silicon solar cell and has little effect on the amorphous silicon solar cell. A block of crystalline silicon solar cell module is blocked 1/10 of the area, the power loss will reach 50% i:

Surface amorphous silicon solar modules are similarly blocked, with a power loss of only 10%, as shown in Figure 4-23.

Figure 4-23

Figure 4-23 Amorphous Silicon (a) and Crystalline Silicon (b) Power Loss When Blocked Solar Cell Module
If the solar cell will inevitably be blocked, should try to use amorphous silicon solar cells.
In order to reduce the shadow of the impact of solar cell components in the junction box are often equipped with bypass diodes. For the function of the bypass diode, please refer to Chapter 5, Section 5.2.
If rooftop PV systems are installed with unavoidable shadows, it is best not to create shadows on multiple component strings, as shown in Figure 4-24 (c). Figure 4_24 (a) and Figure 4_24 (c), because the string voltage of the same component, in some cases is possible, but not worth recommending. As shown in Fig. 4_24 (b), the power balance of each component string is the worst, and the grid-connected inverter can not be in the best working condition, which will lead to a large reduction of power generation. This situation should be avoided as far as possible.
(3) the square of the solar cell temperature and ventilation
Solar cells and buildings should also pay attention to solar array square ventilation design • to avoid the solar cell array temperature is too high, resulting in lower power efficiency (crystalline silicon solar module junction temperature exceeds 25 ℃, the rise of 1 ℃ power loss of about 4% .The solar cell phalanx temperature rise and the installation location and ventilation .De solar energy society on this situation specifically tested, the following are given different installation and different ventilation conditions, the solar cell phalanx Measured temperature rise situation:
• As an upright wall material, there is no ventilation, the temperature rises and the power loss is 9%.
• As a roofing material, there is no ventilation, the temperature rise is very high, power loss of 5.4%;
• Installed in the south elevation, poor ventilation, high temperature rise, 4.8% power loss;
• Installed on sloping roofs with poor ventilation, high temperature rise, 3.6% power loss;
• Installed on a sloped roof, with good ventilation, high temperature rise, 2.6% power loss;
• Equipped with flat roof, good ventilation, high temperature rise, 2.1% power loss;
• Common installation on the roof, there is a large ventilation gap, the smallest temperature loss.

Figure 4-24 An example of a shadow produced by a solar array(A) One component of each system is shadowed;

Figure 4-24 An example of a shadow produced by a solar array(B) One and two components of the two systems are shadowed;

Figure 4-24 An example of a shadow produced by a solar array(C) 3 shadows on one system; 

Figure 4-24 An example of a shadow produced by a solar arrayComponents without shadows;A shadow-generated component;

(4) the choice of solar cell components
In addition to generating electricity, but also consider other functions, such as indoor and outdoor isolation, rain, wind, heat insulation, noise, shade, beautiful, but also consider the use of solar cells and solar energy, And as a building material for the architectural designer selection.

In order to facilitate integration with the building and installation, the solar cell module can be made into a solar cell tile, can also be made special bracket or rail, easy to install the ordinary solar cell components, in order to facilitate the installation, combined with building solar modules (Figure 4-25), and the junction box is usually mounted on the side of the module rather than on the back (Figure 4-26) as in a normal assembly.

(Figure 4-25

Solar modules can also be combined with a variety of different glass to create a special glass curtain wall or skylight, such as insulation glass components, anti-UV glass components, acoustic glass components, laminated safety glass components and anti-theft or bulletproof glass components, fire components etc.

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