Application of Ground Screws in Ground Mounted Photovoltaic Racking Systems

At present, the foundation of photovoltaic mounts in ground power stations is basically reinforced concrete piles foundation, and ground screw foundation is seldom used. However, when encountering special conditions of construction, such as: when the groundwater level of the site is low, the depth of the stabilizing layer is large, the construction in winter, the terrain is undulating, or the ecological restoration of the site requires a high degree of, the foundation of the photovoltaic bracket can be used as a ground screw pile.

Types of Ground Screws

Ground screw is a kind of shaped pile with complex geometrical surface, which consists of a central steel shaft connected with a number of spiral blades. According to the form of blade arrangement is generally divided into layered blade type ground screws and continuous blade type ground screws.

Advantages of Ground Screws

For the disadvantages of the traditional reinforced concrete grouted pile foundation for PV mounting which requires earth excavation, destroys the environment, has a long construction period, requires high site conditions and is difficult to remove, helical piles have the following advantages:

(1) The construction is fast and economical. Ground screws are generally constructed using special machinery (as shown below), a ground screw can be completed in a few minutes, and the pile foundation can be used immediately after construction, without concrete construction and maintenance problems, saving the wage consumption of individual foundation personnel. The construction equipment is highly mobile, quick and inexpensive to move in and out, and can reach any difficult terrain or work in confined spaces.

(2) Convenient quality control. Ground screws are all produced in the factory, avoiding the uneven quality of foundation workmanship in reinforced concrete piles construction due to different skill levels of construction personnel.

(3)Environment friendly and good recyclability. There is no need for earth development in the construction of steel piles, direct screwing, also basically no vibration and noise, the ecological damage is minimized. Steel piles can be reversed and pulled out after use without leaving any underground obstacles and the site can be recovered.

(4) Installation of photovoltaic racking is highly adjustable. At present, the ground power station is basically mountainous photovoltaic, the terrain is mostly uneven area, in order to ensure that the photovoltaic module into the best tilt angle, the requirements of the bracket is easy to install and adjustable, because the ground screws using bolts and brackets directly connected, adjustable relative to the concrete pre-embedded bolts foundation is larger, reduce the difficulty of installing photovoltaic brackets.

Ground Screw Connection

Ground screws are mainly through the bolt, flange and other types, can easily realize the connection with the upper various types of photovoltaic bracket, and can be telescopic adjustment of column height. The flange of the ground screw is made of steel plate of a certain thickness, welded with the center steel shaft as a whole. The connection flange is reserved with bolt holes, which is easy to connect with the power head of the installation machinery during installation and also easy to connect with the upper support. Some piles do not have flanges, but have bolt holes reserved in the upper part, so that the bolts can be used to connect with the power head through the bolt holes during installation, and can also be used to connect with the upper support after installation.

Structural reliability of ground screws

The reliability of the structure refers to the safety, applicability and durability of the structure, the following is a small introduction to the structural reliability of ground screws from these three aspects.

(1) the safety of ground screws

That is, the ground screws of the bearing capacity of the problem, does not occur damage that is safe. According to the relevant literature, the change of ground screw blade pitch ratio (blade pitch/blade diameter) is an important factor that affects the ultimate pullout and compressive bearing capacity of steel pile. And the pile length of ground screw is the same as the length of reinforced concrete grouted pile, which is generally about 2m.

(2) Suitability of ground screws

That is to say, it refers to the deformation and crack problem of ground screws. Due to the high strength of the ground screw itself, and the photovoltaic mounting system on the ground screw load role is not particularly large, the ground screw generally does not appear too large deformation and cracks.

(3) ground screw durability

Durability mainly refers to the ground screw corrosion problems, the current photovoltaic power station in the metal components of corrosion, generally use hot-dip galvanizing anti-corrosion measures.