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The vast majority of household and industrial and commercial photovoltaics install photovoltaic modules on the roof, which can not only help owners save electricity costs, but also optimize the roof Use of space to cool the roof.
This article will discuss some of the most important things to know about installing a PV plant on a flat roof.
Key 1. Which installation form to use
The methods of installing photovoltaic modules on different roofs are also different. Common installation methods include additional type, ballast type and pile foundation type.
If the roof is of the color steel tile type, the additional type is generally considered, and the components are directly tiled on the color steel tile. Especially, the general color steel tile roof has no parapet, and the tiled type has the best windproof effect. It is the safest; in addition, the color steel tile roof also has a certain inclination angle, although it may not be the best inclination angle corresponding to photovoltaic power generation, but the transformation cost brought by increasing the inclination angle also needs to be considered comprehensively.
For cement roofs, it is usually flat, and the common installation methods are ballast type and concrete foundation pile type, as shown in the above picture.
Many times, building owners are not allowed to drill holes in concrete flat roofs, 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 why ballast type or concrete foundation installations are chosen.
Ballast type has no anchor connection with the roof, so the side can be considered for windproof treatment, especially for the cement roof without parapet. The main purpose of the
concrete base is to ensure that the support system remains intact even during stormy seasons. It guarantees a good installation without causing leaks in the roof and also increases the efficiency of the solar cell module and reduces the sun shade from the parapet.
Key 2 , Flat roof does not mean tile installation
Install PV modules in a tiled way on a flat roof,It seems to be the most natural way, not only the installation volume/area can be maximized, but also it is possible to use photovoltaics as a roof to increase the space area.
But in fact, installing PV on a flat roof does not mean that you should also set its inclination to 0 degrees, we need to consider many factors, and flat installation should be avoided, including:
l Tiled modules are easy to accumulate
l Cleaning is more inconvenient, and the accumulated water is not easy to flow out;
l Compared with inclined installation, the power generation will be reduced;
l ROI will be longer;
l ash deposits may not be removed by natural rainfall;
There will be significant The 11.2kWp solar energy system is simulated and the inclination 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 13,480.3kWh, and at a 5 degree inclination angle, the annual power generation of the system reaches 14,066.9kWh. In fact, when the inclination angle is 10 degrees, the annual power generation of the system reaches 14,520kWh.
It can be seen from the results that for every 5 degrees increase, the system increases the power generation by 500kWh per year (after 15 degrees, the increase will be significantly reduced, and it will be lower after exceeding the optimal inclination angle). Moreover, the above simulations have not considered the loss of power generation due to fouling during installation at low inclination angles.
suggest that if you are unwilling to use the best inclination for installation, the installation inclination should be as high as possible. If it must be tiled, it is recommended to design the inclination angle between 5-10 degrees.For flat roofs, an angle of 5-10 degrees is flat enough, while for color steel tile roofs, an angle of more than 3 degrees is generally left. Compared with the additional cost of increasing the inclination angle, let it be , Going with the slope is also a good choice.
Key 3. Wind speed must be considered for flat roof installation
During the design stage of solar energy systems, the maximum possible local wind speed must be considered, especially in areas with wind speeds exceeding 180 kilometers per hour.
It is not a once in five years, a once in ten years, the life of a photovoltaic system is 25 years, and it must be considered once in 50 years!
The typhoon that occurred in Nantong, Jiangsu at the end of April 2021 is enough to explain everything. With the improvement of construction quality, for the buildings in the Nantong area, almost no one will think too much about what happened 30 years ago. The typhoon disaster, after all, the typhoon in the Nantong area can also have a little impact on the previous square, thatched hut, and greenhouse.
But at the end of April this year, the strong wind that occurred in Nantong blew the solar photovoltaics and solar water heaters on the roof to the ground, killing more than a dozen people during the typhoon. It is no exaggeration to encounter it once in 50 years.
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 block the wind, the wind protection is not considered between the arrays, and the instantaneous wind speed caused by the airflow in the local area will be far away. exceeds the actual wind speed.
At this time, the selection of brackets, structural design, ballast or concrete foundation strength design must rely on the recommendations of professional institutions, even the tiling of color steel tile roofs, there must be scientific analysis.
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Key 4. Leakage risk of flat roof installation
Water accumulation is common on flat roofs.Since the roof is flat, the water has nowhere to go, or the drainage becomes slower, and the time it stays on the roof will be longer. Therefore, any gaps and holes in the roof will become a place for water accumulation.
At this time, the flat roof with photovoltaic system installed will become the biggest water leakage risk of flat roof photovoltaic due to the damage to the waterproof layer that may be caused when the bracket is installed and the concrete pile foundation is installed.
If it is a color steel tile roof, it is better to use a fixture to install it than to punch holes on the color steel tile; if the color steel tile is not suitable for connecting with a fixture, using structural adhesive bonding is also an option, Zhejiang Lexus organic Silicon has a solution; if holes must be punched, make sure all holes are properly sealed against water.
Key 5. Mechanical units on flat roofs need to be considered
One of the challenges of designing and installing PV on a concrete flat roof is the various mechanical units on the roof of an existing building, such as outdoor air conditioning units, drainage pipes , exhaust fans, ventilation, water tanks, railings, roof structures, HVAC systems and plumbing, etc.
These existing devices not only affect the layout of rooftop photovoltaics, but also affect the spacing and arrangement of the brackets, and may also shade the photovoltaic array, or affect future operation and maintenance.
Some designers will consider installing photovoltaics above these facilities to shield the facilities from wind and rain, but another problem brought about by this is the height design requirements and wind protection requirements, as well as the difficulty of operation and maintenance.
Rooftop facilities can only be designed according to local conditions, but this is an unavoidable issue for rooftop photovoltaics and must be paid attention to.
Key 6. Additional issuance of roof tiling components
Generally, there is no absolute 0-degree tiling installation, but low inclination is indeed an unavoidable problem, even cement roofs will have such a demand.
The roof of Wuxi Tianpeng Food City is a typical application of installing photovoltaic greenhouses on cement roofs:
For roof tile photovoltaics,The optimal power generation capacity can still be obtained after the optimized design, which can be done in different ways.
Method 1: In the case of tiling, make a certain inclination angle as much as possible, not necessarily the best inclination angle, especially when the inclination angle is greater than 15 degrees, the windproof problem of the roof needs to be carefully considered (the larger the inclination angle, the more the greater the influence of wind). Usually 5-10 degrees is enough. At the same time face the best orientation.
Method 2: For approximately tiled components with very low inclination angles, leave a gap between the upper and lower rows of components so that water on the component surface can flow out of the component surface instead of accumulating on the next component.
This is an additional requirement for a photovoltaic array designed as a ceiling, because the ceiling is to block the rain, and it can be realized by adding a drainage groove between the modules (this solution is currently very common in photovoltaic applications in sun rooms, Industrial and commercial roofs can be used as a reference).
The surface of the module in the picture of Wuxi Tianpeng Food City has obvious traces of mud belt on the lower border, which is the result that the muddy water on the surface of the module cannot be drained out of the surface of the module in time.
Method 3: For low-inclination roof photovoltaic modules, install a product called an automatic drainage desilter to completely eliminate water and ash accumulation on the surface of photovoltaic modules with an inclination of 3-15 degrees.
Because it is a roof and ceiling application, it is inconvenient to climb up for operation and maintenance in the later stage. The selection of the drainage and desilter should take into account the later operation and maintenance. It will need to be replaced; it is also necessary to consider the problem of foreign metal corrosion between the material and the aluminum frame of the component, and to choose a material that does not affect the surface resistance of the aluminum frame to avoid the risk of PID of the component.
【Conclusion】
In conclusion, the above six most important things to consider when installing solar panels on a flat roof.
The rise in module prices in 2021 will make it difficult for ground-based power plants to achieve grid parity. The profitability of the industrial and commercial rooftop photovoltaic power station market on the electricity price will be the most important battlefield for photovoltaics in 2021. Knowing the 6 things most relevant to flat roof PV systems, your ROI can avoid mistakes and achieve the highest ROI.
Content source: Global PV
Disclaimer: The above content is reproduced from PV Box, and the content does not represent the position of this platform. National Energy Information Platform Tel: 010-65367702, Email: hz@people-energy.com.cn, Address: People's Daily
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