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对于屋顶平铺光伏，优化设计后仍然可以获得最佳发电能力，这可以通过不同的方式来完成。
Which installation method is used for 01
The method of installing photovoltaic modules on different roofs also varies, and common installation methods include additional, ballast, and pile foundation types.
If the roof belongs to the color
steel tile type, the additional type is generally considered, and the components are directly laid on the color steel tile. In particular, the general color steel tile roof has no Parapet, and the flat type is the best and safest for wind protection;
In addition, the color steel tile roof also has a certain inclination angle. Although it may not be the optimal inclination angle for photovoltaic power generation, the renovation cost brought about by increasing the inclination angle also needs to
be comprehensively considered.
For cement roofs, they are usually flat, and the common installation methods are ballast type and concrete foundation pile foundation type, as shown in the figure.
In many cases, building owners are not allowed to drill holes on the concrete
Flat roof. On the one hand, they are worried about the strength of the old building or do not want to change the waterproof performance of the roof. This is the reason for choosing ballast type or concrete foundation installation.
Since the
ballast type is not anchored to the roof, wind proof treatment can be considered for the side, especially for the cement roof without Parapet.
The main purpose of the concrete foundation is to ensure that the support system remains intact even
during stormy seasons. It ensures good installation without causing water leakage on the roof, improves the efficiency of solar cell modules, and reduces the Parapet's blocking of sunlight
02 Flat roof does not mean flat installation
It
seems to be the most natural way to install photovoltaic modules on Flat roof in the way of tiling. Not only can the installation amount/area be maximized, but also it is possible to use photovoltaic as a roof ceiling to increase the space area.
However, the fact that photovoltaic is installed on a Flat roof does not mean that you should also set its inclination to 0 degrees. We need to consider many factors, including:
Tiled components are prone to dust accumulation, which may result
in a 10% or even 30% loss of power generation;
Cleaning is more inconvenient, and accumulated water is not easy to flow out;
Compared to inclined installation, the power generation will be reduced;
The investment return period will
be longer;
It may not be possible to rely on natural rainfall to remove accumulated ash;
There will be obvious differences between the power generation of tilted and flat Photovoltaic system. Through the simulation of an 11.2kWp solar
system, the tilt angles are 10 degrees, 5 degrees and 0 degrees respectively.
The simulation results show that if the inclination angle is 0 degrees, the annual power generation of the 11.2kWp system is about 13480.3kWh, while at a 5 degree
inclination angle, the annual power generation of the system reaches 14066.9kWh. In fact, when the inclination angle is 10 degrees, the annual power generation of the system reaches 14520kWh.
From the results, it can be seen that for every 5
degree increase, the system generates an annual increase of 500kWh of electricity (after 15 degrees, the increase will significantly decrease, but after exceeding the optimal inclination angle, it will actually be lower). Moreover, the above simulation
has not yet taken into account the power generation loss caused by ash accumulation during low inclination installation.
If you are not willing to use the optimal inclination angle for installation, the installation inclination angle should
be as high as possible. If it is necessary to lay flat, it is recommended to also design the inclination angle between 5 and 10 degrees. For Flat roof, 5-
03 Wind speed must be considered for installation of Flat roof
In the design phase
of solar systems, it is necessary to consider the maximum wind speed that may occur locally, especially in areas with wind speeds exceeding 180 kilometers per hour.
Not once every five years, once every ten years. The lifespan of the photovoltaic
system is 25 years, and a once every 50 years must be considered!
The typhoon that occurred in Nantong, Jiangsu at the end of April 2021 is a testament to everything. With the improvement of building quality, almost no one would think too much
about the frequent typhoon disasters that occurred thirty years ago for buildings in the Nantong area. After all, typhoons in the Nantong area can also have some impact on the square, thatched houses, and greenhouses of the past.
But the strong
wind that occurred in Nantong vividly blew the solar photovoltaic and solar water heaters on the roof to the ground, causing more than ten deaths during the typhoon, which is no exaggeration.
The ordinary Flat roof solar power generation system can withstand the wind speed of 160 km/h (Level 13 typhoon), but if there is no Parapet to wind, and wind protection is not considered between arrays, the instantaneous wind speed caused
by airflow in local areas will far exceed the actual wind speed.
At this point, the selection of brackets, structural design, ballast or concrete foundation strength design must rely on the advice of professional institutions, even for the flat
laying of colored steel tile roofs, there must be scientific analysis.
04 Water leakage risk of Flat roof installation
Ponding is common on Flat roof. Due to the flat roof, there is no place for water to go, or the drainage slows down,
and the time spent on the roof will be longer. Therefore, any gaps or holes in the roof will become a place for stagnant water to stay.
At this time, for the Flat roof with photovoltaic system installed, the waterproof layer may be damaged during
the installation of support and concrete pile foundation, which becomes the biggest risk of water leakage for Flat roof photovoltaic.
If it is a colored steel tile roof, using fixtures for installation is better than drilling holes on the colored
steel tile; If colored steel tiles are not suitable for connecting with fixtures, using structural adhesive bonding is also an option.
05 Mechanical units on Flat roof need to be considered
One of the challenges of designing and installing
photovoltaic on the cement Flat roof is the various mechanical devices on the roof of the existing building, such as outdoor air conditioning units, drainage pipes, Whole-house fan, ventilation facilities, water tanks, railings, roof structures, HVAC
systems and water pipes.
These existing equipment not only affect the layout of roof photovoltaic, affect the spacing and arrangement of tie brackets, but also may have a shadow on the Photovoltaic system, or affect future operation and maintenance.
Some designers
may consider installing photovoltaics above these facilities to provide shelter from wind and rain, but another issue that arises is the height design requirements and wind protection requirements, as well as the difficulty of operation and maintenance.
For rooftop facilities, design can only be carried out according to local conditions, but this is an issue that cannot be avoided by rooftop photovoltaics and must be taken seriously.
06 Additional issuance of roof tile components
Generally,
there is no absolute 0 degree flat installation, but low inclination is indeed an unavoidable problem, even for cement roofs.
For rooftop tiled photovoltaics, optimized design can still achieve optimal power generation capacity, which can be
achieved through different methods.
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