ALLPCB
Overview
PV mounting structures are an important component of PV power plants, supporting the PV arrays. The choice of support directly affects module operational safety, damage rates, and project investment returns.
When selecting PV supports, different materials should be chosen according to application conditions. Based on the material of the main load-bearing members, supports can be classified into aluminum alloy supports, steel supports, and non-metal supports (flexible supports). Non-metal supports are used less frequently, while aluminum alloy and steel supports each have their own characteristics.
Non-metal supports, or flexible supports, use prestressed cable structures to address installation challenges in locations where traditional supports cannot be installed due to span or height limitations, such as wastewater treatment plants, complex mountainous terrain, low-load roofs, agro-photovoltaic sites, water-solar complementary installations, driving schools, and highway service areas. They can alleviate construction difficulty, severe shading, and lower generation found in valleys and hilly PV sites compared with flat areas (typically 10%–35% lower), and reduce the complexity and poor-quality structural issues found in some existing valley and hillside installations.
Non-metal supports offer broad adaptability, installation flexibility, effective safety, and economical reuse of land. A properly chosen support form can improve wind and snow load resistance. By leveraging the load-bearing characteristics of the support system, dimensions can be optimized to save material and reduce system cost.
The primary loads acting on PV module supports and foundations are: self-weight of the supports and modules (dead load), wind load, snow load, thermal load, and seismic load. Wind load is typically the controlling action, so foundation design must ensure stability under wind loads. Under wind action, foundations may be subject to uplift or fracture, and designs should prevent such failures under the design wind load.
Types and Characteristics of Foundations
Below are common foundation types for ground-mounted and flat-roof PV supports and their typical characteristics.
Ground-mounted PV foundations
Drilled cast-in-place piles: Drilling is relatively convenient, and the top elevation can be adjusted to suit terrain. Top elevation is easy to control, and the required concrete and rebar quantities and excavation volume are small. Construction is fast and causes limited damage to existing vegetation. It involves on-site concrete casting and is suitable for compacted fills, cohesive soils, silty soils, and sandy soils.
Steel helical foundations: Drilling is convenient and the top elevation can be adjusted for terrain. They are not affected by groundwater and can be installed in winter. Construction is fast, elevation adjustment is flexible, and environmental disturbance is minimal since there is no large-scale earthwork. They are suitable for deserts, grasslands, tidal flats, permafrost, and similar conditions. However, they use significant steel and are not suitable for highly corrosive soils or rock foundations.
Isolated footings: These foundations provide the strongest resistance to uplift and flood-related actions and perform well under wind loads. They require the largest volume of reinforced concrete and labor, involve substantial excavation and backfill, have long construction periods, and cause greater environmental disturbance. They are now rarely used in PV projects.
Reinforced concrete strip foundations: This foundation type is often used where ground bearing capacity is relatively low. It is suitable for relatively flat sites with low groundwater levels and where higher requirements on differential settlement apply, such as single-axis tracker supports.
Precast pile foundations: Precast prestressed concrete pipe piles with diameters around 300 mm or square piles with cross sections around 200 x 200 mm are driven into the ground. The top is reserved with a steel plate or bolts to connect to the upper support posts. Typical depths are less than 3 m. Construction is relatively simple and fast.
Drilled cast-in-place piles (soil requirements): This foundation type is lower in construction cost but has stricter soil requirements. It is suitable for silty soils with certain compaction or plastic to stiff silty clay, and not suitable for loose sandy layers. Very hard soils such as cobble or rubble may make drilling difficult.
Steel screw pile foundations: Installed by specialized machinery, these piles are screwed into the soil. Construction is fast, site leveling is unnecessary, and there is no major excavation or concrete work, which minimizes vegetation disturbance. The support height can be adjusted to the terrain, and helical piles can be reused.
Flat-roof PV support foundations
Cement ballast method: Concrete blocks are cast or placed on a cement roof. This is a common installation method; it provides stability while avoiding damage to the roof waterproofing.
Precast concrete ballast: Compared with casting in-place blocks, precast ballast saves time and reduces the need for cement-based embedded parts.
