What are the types of foundations for ground-mounted photovoltaic supports?

Bored cast-in-place pile foundation:
The hole formation is relatively convenient, and the elevation of the foundation top can be adjusted according to the terrain. The top elevation is easy to control, with low consumption of concrete and steel reinforcement, minimal excavation, fast construction, and little damage to the original vegetation. However, on-site hole formation and concrete pouring are required. It is suitable for general fill soil, cohesive soil, silt, sandy soil, etc.

Steel spiral pile foundation:
Hole formation is convenient, and the top elevation can be adjusted according to the terrain. It is not affected by groundwater, can be constructed normally in winter conditions, and offers fast construction, flexible elevation adjustment, minimal damage to the natural environment, no earthwork excavation or backfilling, and little damage to the original vegetation. No site leveling is required. It is suitable for deserts, grasslands, tidal flats, Gobi desert, permafrost, etc. However, it requires a larger amount of steel and is not suitable for strongly corrosive ground or bedrock foundations.

Independent foundation:
It provides the strongest resistance to hydraulic loads and offers excellent flood and wind resistance. However, it requires the largest amount of reinforced concrete, significant labor, extensive earthwork excavation and backfilling, a long construction period, and causes substantial environmental damage. It is rarely used in photovoltaic projects nowadays.

Reinforced concrete strip foundation:
This type of foundation is mostly used in areas with poor ground bearing capacity, relatively flat terrain, and low groundwater levels. It is suitable for single-axis tracking photovoltaic supports that require high resistance to uneven settlement.

Precast pile foundation:
Pre-stressed concrete pipe piles with a diameter of approximately 300 mm or square piles with a cross-section of about 200 x 200 mm are driven into the soil. The top is reserved with steel plates or bolts to connect to the front and rear columns of the support structure. The depth is generally less than 3 meters, and construction is relatively simple and fast.

Bored cast-in-place pile foundation (repeated entry with additional details):
It has a lower cost but has higher requirements for soil layers. It is suitable for relatively compact silt or plastic to hard plastic silty clay. It is not suitable for loose sandy soil layers, and harder soils such as pebbles or gravel may present difficulties in hole formation.

Steel spiral pile foundation (repeated entry with additional details):
Specialized machinery is used to screw it into the soil. Construction is fast, requires no site leveling, involves no earthwork or concrete, maximizes protection of vegetation on site, allows adjustment of support height according to terrain, and the spiral piles can be reused.