When selecting photovoltaic mounting structures, it is essential to choose materials appropriate for the specific application conditions. Based on the materials used for their primary load-bearing components, these structures can be categorized into aluminum alloy mounts, steel mounts, and non-metallic mounts (flexible mounts). Among these, non-metallic mounts (flexible mounts) are less frequently utilized, while aluminum alloy and steel mounts each possess their own distinct characteristics.

Non-metallic supports (flexible supports) utilize a prestressed cable structure to resolve technical challenges—specifically those imposed by span and height constraints—that render traditional support structures unfeasible in settings such as wastewater treatment plants, mountainous terrain with complex topography, roofs with limited load-bearing capacity, integrated forestry-solar and hydro-solar projects, driving schools, and highway service areas. Furthermore, this technology effectively mitigates the inherent drawbacks of existing photovoltaic power stations situated in valleys and hilly regions—including significant construction difficulties, severe shading issues, low power generation yields (typically 10% to 35% lower than those in flat terrain), poor support structure quality, and structural complexity.

Overall, non-metallic mounts (flexible mounts)—characterized by their broad adaptability, operational flexibility, effective safety, and the economic efficiency of enabling perfect secondary land utilization—represent a revolutionary innovation in photovoltaic mounting systems.

An appropriately designed form of PV mounting structure can enhance the system's resistance to wind and snow loads. By effectively leveraging the load-bearing characteristics of the mounting system, its dimensional parameters can be further optimized to conserve materials and, consequently, further reduce the overall cost of the PV system.

The primary loads acting upon the foundations of photovoltaic module support structures include: the self-weight of the supports and PV modules (dead load), wind loads, snow loads, thermal loads, and seismic loads. Among these, wind loads are typically the governing factor; therefore, the foundation design must ensure the stability of the foundation under wind loading conditions. Under the influence of wind loads, foundations are susceptible to failure modes such as uplift or fracture; consequently, the design must guarantee that no such structural failure occurs when subjected to these forces.

So, what are the various types of foundations for ground-mounted and flat-roof photovoltaic mounting systems? And what are their respective characteristics?

Ground-Mounted PV Support Foundations

Drilled and Cast-in-Place Pile Foundations: The hole-forming process is relatively convenient, allowing the top elevation of the foundation to be adjusted according to the terrain; moreover, the top elevation is easily controlled. This method requires minimal quantities of concrete and reinforcing steel, involves limited excavation, facilitates rapid construction, and causes minimal disturbance to existing vegetation. However, it necessitates on-site hole formation and concrete pouring. This foundation type is suitable for use in general fill, cohesive soils, silts, sands, and similar soil conditions.

Steel Spiral Foundations: These foundations facilitate easy hole formation, allow for the adjustment of top-surface elevations to suit the terrain, and remain unaffected by groundwater. Construction proceeds as usual even under winter climatic conditions; the process is rapid, and elevation adjustments offer great flexibility. They cause minimal disruption to the natural environment—requiring no earthworks (cutting or filling) or site leveling—and inflict minimal damage to existing vegetation. These foundations are suitable for use in deserts, grasslands, tidal flats, arid regions, permafrost zones, and similar environments. However, they entail a relatively high consumption of steel and are not suitable for use in highly corrosive ground conditions or on rocky substrates.

Independent Foundations: These offer the strongest resistance to water loads, providing robust protection against both floods and wind. However, they require the largest volume of reinforced concrete, demand significant labor, involve extensive earthworks (excavation and backfilling), entail a lengthy construction period, and result in substantial environmental disruption. Consequently, they are now rarely utilized in photovoltaic projects.

Reinforced Concrete Strip Footings: This type of foundation is frequently employed in areas with poor subgrade bearing capacity. It is particularly suitable for sites that are relatively flat and characterized by low groundwater levels, and is commonly utilized for flat single-axis tracking photovoltaic mounting systems where strict requirements regarding differential settlement must be met.

Precast Pile Foundations: Precast piles—specifically prestressed concrete tubular piles with a diameter of approximately 300 mm, or square piles with a cross-section of approximately 200 mm by 200 mm—are driven into the ground. Steel plates or bolts are embedded at the pile tops to facilitate connections with the front and rear uprights of the superstructure support frame. The installation depth is typically less than 3 meters, making the construction process relatively simple and rapid.

Bored Cast-in-Place Pile Foundations: While offering lower construction costs, this method imposes stricter requirements on soil conditions. It is suitable for silt or silty clay strata exhibiting a certain degree of compaction (specifically in plastic to stiff-plastic states); however, it is unsuitable for loose sandy soils. Furthermore, in ground conditions characterized by hard pebbles or gravel, difficulties may arise in successfully forming the boreholes.

Steel Screw Pile Foundations: Installed by screwing them into the ground using specialized machinery. This method offers rapid construction speeds, requires no site leveling, and involves no earthworks or concrete usage, thereby maximizing the preservation of on-site vegetation. The height of the mounting brackets can be adjusted to accommodate varying terrain, and the screw piles are reusable.Flat-Roof PV Mounting Foundations

Concrete Ballast Method: Involves casting concrete blocks directly onto a concrete roof surface. This is a common installation method, prized for its stability and for the fact that it does not compromise the roof's waterproofing integrity.

Precast Concrete Ballast: Compared to casting concrete blocks on-site, this method is more time-efficient and eliminates the need for embedded concrete components.