QDTB® Transformer

Solar Water Pumping Calculator

Enter head and daily water volume to size the pump, PV array and buffer tank. Water storage replaces the battery — the core of direct PV pumping — with a no-battery vs battery comparison.

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How solar pumping is sized

The pump lifts the daily volume during peak-sun hours. Hydraulic power is P = ρ·g·Q·H; PV capacity = pump power ÷ (inverter efficiency × mismatch) × 1.2 safety margin. Over-pumping into a buffer tank stores energy as water, eliminating the battery.

Worked Example — Solar Water Pumping

Example 1 — 100 m³/day Solar Water Pumping (30 m head, no battery)
Solar water pumping · 100 m³/day
3.5 kWp PV
head 30 m · pump 2.5 kW · 5.5 peak-sun-hours
Buffer tank
150 m³
Daily supply
100 m³/day
Est. BOM (FOB)
POA
📦 Bill of Materials
EquipmentModelSpecQty
Solar PV modules6 × 550 Wpmono PERC · 3.5 kWp DC (safety margin 1.2)1
Solar pump inverter (MPPT VFD)2.5 kWdedicated water-pump VFD · wide MPPT · dry-run protection1
Submersible pump2.5 kWborehole submersible · head 30 m · source: well1
PV mounting structure3.5 kWpground / pole mount1
Buffer water tank150 m³elevated / ground storage · water storage replaces battery (100 m³/day × 1.5)1
Piping & fittings50 msuction + discharge pipe · valves · foot valve1
Summary
Estimated total (FOB Qingdao, EXW) — priced equipmentPOA
💧 No-battery vs battery comparison
OptionEnergy storageIndicative costMaintenance
No battery (推荐)150 m³ water tank (蓄水=蓄能)POA (tank + civil)near-zero
With battery37 kWh LFP (night pumping)POA5–10 yr replacement
📐 System diagram
PV array3.5 kWp DCPump inverterMPPT VFD - 2.48 kWPump30 m headWater tank100 m3/day - buffer 150 m3
LEGENDDC breakerSPD (surge protection)kWhFlow / level sensor
📏 Standard basis
TopicStandard
PV water pumpingIEC 62253 — photovoltaic pumping systems (design qualification)
Solar water pumpingGB/T 37552 — solar photovoltaic pumping systems
Water supplyGB/T 50801 — code for design of water supply & drainage
🧮 How it was calculated
1. Flow during sun hours = 100 m³ ÷ (5.5 h × 3600 s) = 0.00505 m³/s
2. Hydraulic power = 9.81 × 0.00505 × 30 = 1.49 kW
3. Pump shaft power = 1.49 ÷ η_pump 0.60 = 2.48 kW
4. PV capacity = 2.48 ÷ (0.95 × 0.90) × 1.2 = 3.5 kWp
5. Buffer tank = 100 m³/day × 1.5 = 150 m³ (water storage replaces battery — 蓄水=蓄能)
6. No-battery design stores energy as water; optional battery (37 kWh) only needed for night/overcast pumping.
📋 Design notes
Water storage = energy storage: The core of direct PV pumping is to over-pump during sunshine into an elevated/ground tank, so the water itself is the "battery". This eliminates battery CAPEX, replacement and round-trip losses — the key advantage over battery-buffered pumping.
No-battery vs battery: No-battery: 150 m³ tank (~1.5 days) supplies water overnight and through 1–2 cloudy days. Battery option (≈37 kWh) would run the pump at night instead, but costs more and adds maintenance — recommended only when a tank is impractical or land is scarce.
Pricing basis: PV modules, pump inverter and mounting are priced from the catalogue. Submersible pump, buffer tank and piping are quoted per project (POA) — pump price depends strongly on head, casing material and depth.
Daily supply: The system is sized to deliver 100 m³/day at 5.5 peak-sun-hours. On shorter or cloudier days, output falls proportionally — the 1.2× PV safety margin and 1.5× tank buffer absorb typical variability.
Design review: This is a preliminary sizing. Verify borehole yield, static/dynamic water level, total dynamic head (incl. pipe friction) and sand content before selecting the pump.

How it was calculated

Core formulas

Flow Q = daily volume ÷ (sun hours × 3600). Hydraulic power = 9.81 × Q × head. Pump power = hydraulic power ÷ η_pump. PV = pump power ÷ (0.95 × 0.90) × 1.2.

Applicable standards

IEC 62253 (PV pumping systems), GB/T 37552 (solar PV pumping), GB/T 50801 (water supply design).

Frequently asked questions

Why does water storage replace the battery?

Direct PV pumping over-pumps into an elevated/ground tank during sunshine, so the water itself is the energy store. This removes battery CAPEX, replacement and round-trip losses — water storage is the key advantage of this approach.

When would I add a battery?

Only when a tank is impractical or land is scarce, to run the pump at night or through long overcast spells. The calculator shows the no-battery and battery options side by side.

How is PV capacity derived?

From the pump shaft power divided by inverter efficiency (0.95) and a mismatch factor (0.90), then ×1.2 safety margin to absorb irradiation variability.

What drives pump selection?

Head, daily volume and water source (well/river/reservoir) — deeper wells need multi-stage borehole pumps and more head. The pump and piping are quoted per project.

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Results are engineering estimates for reference. Final design must be confirmed by a licensed local engineer against site conditions and applicable codes. Prices are FOB Qingdao (EXW) and do not include freight, duty or installation.

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