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Solar pumping — complete sizing guide
A solar pump project in SolarDim Pro differs from a residential project. There are usually no batteries — the water tank plays that role — and pump power must be available instantly during sunshine hours. SolarDim Pro offers 3 configurations depending on your need.
| Configuration | When to use | Typical use | Cost |
|---|---|---|---|
| Config 1 — PV direct | Pumping ≤ peak sun hours | Village, irrigation, livestock | Low |
| Config 2 — PV + batteries | Pumping > peak sun hours | Critical water, hospital | High |
| Config 4 — PV + grid | Eneo/grid available | Urban area, bill savings | Medium |
Config 3 (pump integrated into house system) does NOT use the pump wizard. Simply add the pump as an appliance in a space of the standard wizard with its usage profile (day or continuous).
The pump wizard has 4 steps: (1) Site and flow — daily volume, pumping hours, tank. (2) Hydraulic data — TDH, source type, water quality. (3) Configuration and efficiencies. (4) Results calculated by Python (solardim-calc).
Q [m³/s] = Daily_volume [m³/day] ÷ (pumping_hours × 3600)MANDATORY CONVERSION — never use m³/day directly in P = ρgQH
Classic error: using 50 m³/day directly in the formula instead of flow rate in m³/s. Gives a result 5 to 20× too large. SolarDim Pro handles this conversion automatically.
P_hydraulic [W] = ρ × g × Q [m³/s] × TDH [m]ρ = 1000 kg/m³ (freshwater) · g = 9.81 m/s² · TDH = static head + friction losses
P_motor [W] = P_hydraulic ÷ (η_pump × η_motor)η_pump default 0.65 (submersible) or 0.70 (surface) · η_motor default 0.90
kWp = (P_motor × pumping_hours ÷ η_system) ÷ (PSH × derating)η_system ≈ 0.80 (cables + controller) · derating ≈ 0.90 (heat + mismatch)
50 m³
Daily volume
5h pumping · TDH 45m
10 m³/h
Required flow
0.00278 m³/s
1.23 kW
Hydraulic power
2.09 kW
Motor power (η=63%)
2.9 kWp
PV array
PSH 4.5h
Measure TDH in dry season
Static head must be measured at the lowest water level (dry season, after several hours of pumping). An error here undersizes the entire installation.
Check pipe flow velocity
SolarDim Pro automatically calculates flow velocity. A warning appears if it exceeds 2.5 m/s — beyond that, the pipe will erode rapidly.
Adjust efficiencies from the pump datasheet
Defaults (η_p=0.65, η_m=0.90) are conservative. If Grundfos SP datasheet shows η=0.72, enter 0.72 — you'll reduce the PV array by 10–15%.
Config 2: batteries for night hours only
Batteries are sized only for off-sun pumping hours, not total daily volume. The PV array must also cover recharging — it is therefore larger than Config 1.
| Parameter | Default | Range | Adjustable |
|---|---|---|---|
| Water ρ | 1000 kg/m³ | Fixed | No — physical constant |
| g | 9.81 m/s² | Fixed | No — physical constant |
| η pump | 0.65 | 0.30–0.90 | Yes · Step 3 |
| η motor | 0.90 | 0.70–0.97 | Yes · Step 3 |
| η system | 0.80 | 0.60–0.95 | Yes · Step 3 |
| PV derating | 0.90 | 0.75–0.98 | Yes · Step 3 |
| Battery DoD | 0.80 (LiFePO4) | 0.50 (Gel/AGM) | Yes · auto by tech |
If desired pumping hours exceed peak sun hours (PSH), SolarDim Pro automatically suggests Config 2 (batteries) or Config 4 (grid). A large water tank with Config 1 is often 2–3× cheaper than batteries for the same result.
Common mistakes
- Using m³/day directly in the hydraulic power formula instead of m³/s
- Measuring TDH in the rainy season instead of dry season (lowest water level)
- Sizing Config 2 batteries on total volume instead of off-sun-hours only