Internationally, although Germany has completed hundreds of thousands of photovoltaic roof plans. Rich experience has been gained, but many problems have been found. Most photovoltaic buildings in Germany are designed by professional architects. The design is impeccable in terms of appearance, architectural function and light transmittance. However, these architects also ignore or do not understand the power generation characteristics of solar cells. For example, the orientation of solar cell array, occlusion and temperature rise.
(1) Orientation of solar cell array installation
When the solar cell array is combined with the building, sometimes it is not free to choose the direction of installation. The power generation of solar cell arrays with different orientations is different, so the power generation can not be calculated according to the conventional method. The basic estimation can be made according to the power generation towards the solar cell array in different directions.
Power generation of solar cell arrays installed in different directions:
① It is assumed that the power generation of the solar cell array installed at the South inclined latitude angle is 100;
② In other directions, the annual power generation decreases to varying degrees;
③ In different regions and under different solar radiation conditions, the degree of reduction is different.
(2) Shielding of solar cell array
The combination of solar cell array and buildings will inevitably be blocked sometimes. Shielding has a great impact on the power generation of crystalline silicon solar cells, but has a small impact on amorphous silicon solar cells. When a crystalline silicon solar cell module is covered by 1 / 10 of the area, the power loss will reach 50%; The amorphous silicon solar cell module is also shielded, and the power loss is only 10%.
If the solar cell is inevitably blocked, amorphous silicon solar cell should be selected as far as possible.
In order to reduce the influence of shadow, bypass diodes are often installed in the junction box of solar cell modules. If the installation of roof photovoltaic system will inevitably produce some shading shadows, it is best not to produce negative effects on multiple module strings. That way, shadows are generated on only one component string. Since the voltage of each component string is the same, it is also possible in some occasions, but it is not recommended.
(3) Temperature rise and ventilation of solar cell array
When the solar cell array is combined with the building, attention should also be paid to the ventilation design of the solar cell array to avoid the high temperature of the solar cell array, resulting in the reduction of power generation efficiency (when the junction temperature of the crystalline silicon solar cell module exceeds 25 ℃, the power loss is about 4% for every 1 ℃ increase). The temperature rise of solar cell array is related to the installation position and ventilation. The German solar energy society specially tests this situation. The measured temperature rise of solar cell array under different installation methods and different ventilation conditions is given below:
·As the facade wall material, there is no ventilation, the temperature rise is very high, and the power loss is 9%;
·As a roof building material, there is no ventilation, the temperature rise is very high, and the power loss is 5.4%;
·It is installed on the south facade, with poor ventilation, high temperature rise and power loss of 4.8%;
·It is installed on the inclined roof, with poor ventilation, high temperature rise and power loss of 3.6%;
·Installed on the inclined roof, with good ventilation, high temperature rise and power loss of 2.6%;
·Installed on flat roof, with good ventilation, high temperature rise and power loss of 2.1%· It is installed on the roof in ordinary way, with large ventilation gap and minimum temperature rise loss.
(4) Selection of solar cell module the combination of solar cell and building is different from being used alone as a power generation device. As a part of the building, in addition to power generation, other functions should be considered, such as indoor and outdoor isolation, rain proof, wind resistance, heat insulation, noise isolation, sun shading, beauty and as building materials for architectural designers to choose.
In order to combine with buildings and facilitate installation, solar cell modules can be made into solar cell tiles, or special brackets or guide rails can be made to install ordinary solar cell modules on them conveniently. In order to facilitate installation, solar cell modules combined with buildings are often made into frameless modules, and the junction box is generally installed on the side of the module rather than on the back like ordinary components .
Solar cell modules can also be combined with various glasses to make special glass curtain walls or skylights, such as thermal insulation glass modules, anti ultraviolet glass modules, sound insulation glass modules, laminated safety glass modules, anti-theft or bulletproof glass modules, fire-proof modules, etc.