About the Foundation Quantity (BOQ)
Foundation quantity estimation calculates the volume of concrete, the number of anchor bolts, and the amount of reinforcing steel required for solar mounting structure foundations — used for civil cost estimation during project development and for material procurement during construction.
How to calculate it
- 1Foundation types: isolated pad (for individual structure columns), strip foundation (for continuous base plates), or driven pile (for soft soils).
- 2Isolated pad: Volume = L × W × D. Typical dimensions for a 5 kWp rooftop structure column: 400 mm × 400 mm × 600 mm deep = 0.096 m³.
- 3Number of foundations = number of structure columns. For a ground-mount row: typically 1 foundation every 1.5–2 m of row length.
- 4Reinforcing steel: typically 60–80 kg/m³ of concrete for lightly loaded foundations; 100–120 kg/m³ for wind-critical designs.
- 5Total material: concrete volume = Σ(all foundation volumes); steel = concrete volume × steel density factor.
Worked example
A 100 kWp ground-mount plant: 20 rows × 8 m long, 2 columns per row end = 80 foundation pads. Each pad: 450 × 450 × 700 mm = 0.142 m³. Total concrete: 80 × 0.142 = 11.4 m³. Steel at 80 kg/m³: 11.4 × 80 = 912 kg. Plus anchor bolts: 80 pads × 4 bolts each = 320 M12 anchor bolts. Estimated civil material cost: concrete ₹8,000/m³ (M20, site-mixed) × 11.4 = ₹91,200; steel ₹70/kg × 912 = ₹63,840.
What you can calculate
- Pedestal count
- Concrete m³
- Excavation m³
- IS 456:2000
Frequently asked questions
What type of foundation is best for ground-mounted solar in India?
For standard soil conditions (bearing capacity > 10 t/m²): isolated concrete pad foundations are the most common and cost-effective. For soft or expansive soils (black cotton soil in Maharashtra and Karnataka, or coastal sandy soils): driven galvanised steel piles (helical or straight) eliminate the need for excavation and concrete, are faster to install, and handle expansive soil movement better. Rocky sites may use directly anchored bolts into cut rock.
How does the design wind speed affect foundation size?
Foundation size is driven by uplift force (wind trying to lift the structure) and overturning moment. In high-wind-speed zones (Zone IV–V: Cyclone-prone Odisha, Andhra, Tamil Nadu coast with basic wind speed 44–55 m/s), foundation volumes can be 2–3× larger than in Zone II areas (central India, 33 m/s basic wind speed). Always verify the IS 875 Part 3 wind zone for the specific site, not just the district — coastal sites have higher wind speeds than inland sites in the same district.
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