The vast majority of residential and commercial/industrial PV is installed with PV modules on the roof, which not only helps homeowners save money on their electricity bills, but also optimizes the use of roof space and cools the roof.
In this article, we will discuss a few of the most important things you must know about installing solar panels on a flat roof.
01 Which form of installation to use
Different roofs have different methods of installing PV modules. Common installation methods include attached, ballasted and piled types.
If the roof belongs to the color steel tile type, generally consider the additional type, directly lay the module flat on the color steel tile, especially the general color steel tile roof are no wall, the use of flat type wind effect is the best, the most secure; in addition to the color steel tile roof also has a certain inclination, although it may not be photovoltaic power generation corresponds to the optimal inclination, but increase the inclination angle brought about by the transformation costs are also need to be comprehensively considered. For concrete roofs, which are usually purely flat, common installation methods are ballasted and concrete foundation pile base type, as shown in the figure above. Many times, building owners will not allow drilling on a flat concrete roof, either because they are concerned about the strength of the old building or because they don't want to change the waterproofing of the roof. This is the reason for choosing either the ballasted type or the concrete foundation installation. The ballasted type can be considered windproof on the side since it does not make an anchor connection to the roof, especially for concrete roofs without a wall. The main purpose of the concrete base is to ensure that the bracket system remains intact even during the storm season. It ensures a good installation without causing the roof to leak, and also improves the efficiency of the solar modules and reduces the shading of the sunlight by the wall.
02 Flat roofs don't mean flat installation
Installing PV modules on a flat roof using a tiling method seems to be the most taken-for-granted way, not only can the installation volume/area be maximized, but there is also the possibility that the PV can be used as a roof canopy, increasing the space area. But in fact, installing PV on a flat roof doesn't mean you should also set its tilt to 0 degrees. We need to consider many factors that should be avoided with a flat installation, including: l Flat modules are prone to dust buildup, which may result in a loss of power generation of 10% or even 30%; l Cleaning is more inconvenient, and the accumulated water is not easy to come out; l Compared with a tilted installation, the amount of power generation will be reduced; l The payback period will be much longer; l It may be It may not be possible to remove accumulated ash by natural rainfall; There will be a significant difference in power generation between a tilted installation and a purely flat PV array. If you do not wish to install using the optimum tilt angle, the installation tilt angle should be as high as possible.
03 Wind speed must be taken into account for flat roof installations
During the design phase of a solar system, the maximum possible local wind speed must be taken into account, especially in areas with wind speeds of more than 180 kilometers per hour. If there is no wall to block the wind, the array is not considered between the wind, the local area due to airflow and the instantaneous wind speed will far exceed the actual wind speed. At this time for the bracket selection, structural design, ballast or concrete foundation strength design must rely on the recommendations of professional organizations, even if it is a color steel tile roof flat, there must be a scientific analysis.
04 Leakage risk in flat roof installations
Standing water is common on flat roofs. Since the roof is flat, there is nowhere for the water to go, or the drainage becomes slower and stays on the roof for a side-long period of time, so any gaps or holes in the roof can become a place for water to stay. At this point, the flat roof with photovoltaic system installed becomes the biggest water leakage risk of flat roof photovoltaic due to the waterproof layer damage that may be caused by the installation of the bracket and the installation of the concrete pile foundation. In the case of color steel tile roofs, it is better to use jig mounting than to punch holes in the color steel tiles; if the color steel tiles are not suitable for jig attachment, bonding with structural adhesive is also an option, and if holes must be punched, you need to make sure that all of the holes are correctly sealed to waterproof the roof.
05 Mechanical units on flat roofs need to be considered
One of the challenges of designing and installing PV on concrete flat roofs is the various types of mechanical units on the roofs of existing buildings, such as outdoor air conditioning units, drains, exhaust fans, ventilators, water tanks, railings, roof structures, HVAC systems and plumbing, to name a few. These pre-existing devices not only affect the layout of the rooftop PV and the spacing and alignment of the tethering brackets, but may also create shadow shading of the PV array or affect future operations and maintenance. Some designers will consider installing PV above these facilities to shield them from the wind and rain, but this brings another problem in terms of height design requirements and wind protection requirements, as well as difficulties in operation and maintenance.
