The primary factors in any photovoltaic (PV) system installation are the solar panels as they are the devices that transform solar energy into electricity.
Despite their importance, there are other secondary factors which also take a crucial part in PV designs; we are referring to the mounting systems.
Mounting systems secure the modules to the underlying material over a lifetime of potentially harsh outdoor conditions. Typically, the modules are securely fastened to the structure which, depending on the selection, could be of a bolted or foundation type or merely weighted down on the surface underneath (ballasted option).
Materials for the mounting structures also change depending on local climates, for example, if you are located on coastal jurisdictions then you may be limited to the use of aluminium alloy due to its lack of susceptibility to salt corrosion.
At the end of the day, no matter the mounting system that you choose, the main purpose of the structure is to withstand the weight of the array components, the upward, downward and lateral wind forces under local design considerations, the seismic forces in accordance to local codes and the weight of snow if applicable.
Moreover, mounting systems do not only act as providers of structural strength for the modules but they also deeply influence the total system costs and efficiency of the PV array.
The selection of one or another type of mounting structure will require higher or lower costs of materials, labour and installation, as there are more complex systems that require more expertise and therefore expenses.
Besides, the efficiency of arrays can be affected due to the selection of the mounting system, as for example, roof mounted options do not allow any modifications to the tilt and orientation of the array across the year. This could lead to less power output on the overall scheme (depending on the location).
On the other hand, ground mounted options allow modification of the tilt and orientation according to the season if desired, while single axis or dual axis systems can also be installed for tracking options.
Therefore, it is important to know the available options in the market to make the choice that better suits your needs and those of your solar system design.
In this article, we will explain each type of mounting structure and the overall procedure of installation of the two most common mounting systems.
Ground Mounted Systems
As you can imagine these structures are designed to be located on the ground, supported by metal frames (generally of aluminium, steel or aluminium alloy) and fastened to the ground in different possible ways that we will explain below.
The best thing about ground mounted systems is the wide available range of options to design your solar system according to soil conditions, costs, weight to be supported, tracking system selection and array configuration.
Now, let’s take a look at some of the available options in ground-mounted systems.
Cast / Ballasted Concrete
When soil conditions are not right for making any penetration to the ground (rock, for example) then the best choice is to opt for a ballasted footing mount structure in which pre-cast concrete blocks are anchored to an evenly graded surface.
The best thing about this option is that no excavation is needed and it is a really simple installation among ground mounted options, although, if the system is big it may require a structural engineer to make the calculations for the concrete blocks.
The ground-mounted option par excellence. This structure consists of excavating the ground to install steel vertical driven or helical piles - screwed deep below the surface - or concrete piers which are poured into dug holes with steel pipes suspended in the middle of the concrete foundation.
The key consideration to select the correct option is the type of soil, which determines not only the type of foundation but also the length of the piles.
As a rule of thumb, the stronger the ground, the shorter the piles need to be. For this option, the types of soil material that can be considered are crystalline bedrock (strongest), sedimentary rock, gravel, sand and clay (weakest).
The elegant and cost-effective solution of the mounting systems.
These structures do not require the execution of complex foundations or surface levelling (as for ballasted options), as a simple rigid steel pole with a deep concrete anchor, is more than enough to sustain the solar panels.
Size and diameter of the pole will depend on the soil type and the expected total weight to withstand (panels’ weight, snow, wind, etc.).
Simpler configurations can be applied with the Side-Pole Mounts (SPM). Mostly used for lighting purposes and small load feeding solutions, these SPM are made with stainless-steel module hardware and a tamper-resistant hardware kit for installations with low maintenance.
When considering the bigger option - Top Pole Mounts (TPM) - you will be counting on heavy steel mounting sleeves, elevation pivots and strongbacks coated with a durable outdoor paint, and if your installation site has severe environmental conditions, then you can opt for hot-dip galvanized steel.
These Pole Mount structures can carry from 1 to 18 solar modules, and allow you to change the tilt of the modules from 15° to 60°.
The preferred option for farms and other, wilder residential and industrial areas.
The concept is the same as Pole Mounts but instead of adding more panels on the vertical side, the idea is to add more panels on the horizontal axis by installing additional vertical steel supports.
Multi-Pole Mounts (MPM) allow you to install between two and four solar modules with the same tilt and orientation.
The great advantage of this system is the possibility of expansion of the PV array if it is needed in the future.
Let us examine now the typical procedure of installation of a foundation ground mounted system.
1. Engineering Design Process
In this phase, the installer must dimension the PV array according to the number of strings to be connected and how they will be connected in parallel, typical sets between one and three rows, generally used for residential purposes.
Then the installer must evaluate the soil type and, based on the vertical foundation pressure and the particular coefficient of friction of the soil, will determine whether or not it is possible to make a foundation in the site or not.
Once established, if the soil allows it to, then helical piles or concrete pier components are chosen along with the material and size of such piles.
Once the design phase is over, the next step is beginning the excavation, using specialised equipment that makes it possible to dig a hole with a circular shape, ideal for the concrete piers. Or a drill can be used to place helical piles.
3. Placing Of Piers And Vertical Pipes
Once the hole is dug, then the next step is to place the concrete columns in such a way that the hole is filled with wet concrete and the vertical pipes are placed in the centre of the circle. The installers must wait for all the concrete to dry.
When the vertical bases are placed, the next step is to add the rails and cross beams of the structure. These are defined according to the number of strings that will be placed.
5. Solar Modules
Once the rails are placed, solar panels are attached to the mounting structure using bolts and clamps.
The typical selections in average households are roof-mounted systems, which provide security to the system, fewer shading obstacles, roof protection and are generally more economical than ground mounted systems.
As a rule of thumb, when considering the design of a solar roof-mounted system the designer must be able to ensure that the roof remains waterproof, is fire resistance, structurally strong and also meets electrical safety requirements.
As you can see, there is more than just electrical norms involved.
Among these type of mounting structures, you may also opt for one of several choices, so let’s take a look at them.
The flat roof configuration offers stability and maneuverability in the selection of orientation and tilt, although it is generally the considered option for commercial roof mounted, it is also possible to implement it in the residential sector if the roof is flat.
This type of system involves the design of a ballasted concrete structure (just like in ground mount) that enables the modules to be placed at a specific tilt.
Solar panels can be fastened to the concrete base, saving costs of metal materials for the mounting structure.
If the system has a solar tracking design, then the base for the aluminium structure is fixed to the concrete while at the same time providing mobility for the solar panels.
Within the sloped roof option there are three main possibilities:
Rail-Less Mounting System
Consists of a set of bolts and screws which are directly used to fasten the solar panels to the sloped roof without the use of rails.
This option is the most economical option among sloped roof options, as it saves costs in materials for the racking system and at the same time offers maneuverability, because the solar panels can be placed either in landscape or portrait position without affecting the entire system (as long as tilt and orientation are the same).
This allows the advantage of using more space than with the case of railed systems which require long distances to place a string of panels
Railed Mounting System
This is the typical roof installation nowadays. Solar panels are attached to a single straight line of rails which are fastened to the rooftop through a set of roof-mounted assemblies, bolts and screws.
The same configuration is presented as in railed mounted systems, the only difference is that the use of rails is generally diminished by one because the rails contained in the middle of the array are used to support two rows of solar panels.
Roof-mounted installation varies depending on the option selected and on the brand of racking system that you choose, however, the same basic steps are applied in all systems.
The components and tools of a roof-rail installation do not change either; there are five basic components:
> Roof mount assembly (basic support of the rails to the roof)
> Rail joiners
> End clamps (comprised of male and female L brackets with a key lock that is attached to the rails, they are used to secure the panels at the start and end of the rows)
> Mid clamps (comprised of a T bracket and key locks, they are used between panels to fasten them to the rails).
Regarding tools, all you need is a drill, a T-bar Allen Key, a measuring tape and gloves - not forgetting the ladder to reach the roof.
Now, let’s take a look at the steps to install a railed roof-mounted system.
1. Plan The Layer Of The Solar Array
The first step is to establish the scheme of the solar array by marking the distances between panels and the disposition in the available space of the roof.
This step is crucial to making an easy and good installation, so take your time to do it.
2. Find Out The Requirements Of Local Authorities
Make sure that before installing your design and roof covers, all the requirements from local authorities regarding: National Construction Codes (related to moisture protection and roof penetrations); Fire Codes (minimum fire ratings for roof including the mounting system); Structural Code (uplift, downforce and seismic resistance) and Australian Electrical Standards (regarding grounding methods), are met in your design.
3. Find The Rafters
The starting point of your array should be placed on the strongest side of your roof, therefore try to place the first roof mount assembly on one rafter or truss.
4. Positioning Roof Mount Assembly
Once you have found the rafter, drill a hole into the roof, then position the roof mount assembly and secure it with long roof screws.
Remember to use the supplied gaskets to ensure a watertight seal and prevent corrosion.
5. Mounting The First Rail
Once you have placed the roof mount assembly, you must connect the rails to the roof mount assembles by inserting the roof mount key lock into the rail channels and fastening them down.
Adjust the rail to the desired distance between the rail and the roof.
6. Rail Joiners
Depending on the size of your roof and your PV system, you might need to join two or more rails.
Use the rail joiners to put together two sets of rails by inserting the rail joiner into the rail channel of both rails and securing them with cap screws.
7. Set The Rails
Once you have the whole length of the first rail, repeat the process to place the other rails.
8. Position The First Module
Place the first panel at the extreme end of the rails. Then, insert the key lock of the end clamp into the rail channel and adjust the male and female L brackets of the end clamp to suit the thickness of the panel. Finally, tighten the cap screw of the end clamp to lock the panel into position.
Repeat the process for the upper rail of the panel and your first module will be placed.
9. Position The Next Module
Once you have tightened the first panel, place the key lock of the mid clamps into the rail channel and position the clamp against the first module, repeat the step for the upper rail.
Then, place the second module against the mid clamps and fasten the cap screws on the mid clamps to secure the second panel in place.
10. Place The Additional Mid Clamps And Panels
Repeat all the process above to complete the installation of all the panels on the roof.
11. Electrical System
Make sure that the power optimizer or micro-inverter for each panel is secured on the back of the panels and that the wires are attached to the cable management system (this should be provided by the manufacturer).
With this overall scheme you have an idea of the installation procedure of a rail-mounted system.
We have examined the different types of PV mounting systems available in the market and their installation procedures as well.
Ground mounting systems have a wide variability of choices and are suitable for different customer needs: residential, commercial, industrial and the utility sector.
Roof-mounted options are available for residential, commercial and in some cases industrial installations.
To make the best decision on which mounting system to choose, consult with your solar installer and always remember to take into account these facts:
- Overall system costs with either one of them
- Need or not for a precise tracking system
- Roof condition
- Soil type
- Security constraints
- Shadow obstacles nearby
Balancing the results of these facts with the location of your PV array will give you an idea of which solar mounting system is best for you.
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