How to Size a Solar Submersible Pump for a Borehole in Nigeria

How to Size a Solar Submersible Pump for a Borehole in Nigeria

Sizing a solar submersible pump for a borehole in Nigeria is not complicated when you follow the right steps. The problem is that most installers skip the calculations entirely and use guesswork. That guesswork leads to pumps that cannot deliver enough water, panels that cannot run the motor, or motors that burn out within the first dry season.

This guide gives you the exact four-step sizing method used by professional solar engineers. By the end, you will know your Total Dynamic Head, your required flow rate, how to read a pump performance curve, and exactly how many panels you need. Every number in this guide is based on real Nigerian borehole conditions.

This post is part of the Eneronix Solar Water Pumping series. If you are new to solar pump systems, start with the pillar guide: Solar Water Pump System in Nigeria: How It Works, What It Costs, and How to Size One.

Why Sizing Matters More Than the Brand You Buy

The most expensive solar pump in the world will fail if it is wrongly sized for your borehole. Correct sizing determines three things:

1. Whether your pump can physically lift water from your borehole depth to your storage tank
2. Whether your solar panels can generate enough power to run the motor every day, including harmattan season
3. Whether your pump will survive for 8 to 15 years or burn out within 18 months

A pump that is undersized for your Total Dynamic Head will run constantly, never fully filling the tank, and eventually burn out the motor. A pump that is oversized for your solar array will fail to start on mornings with low solar irradiance. Both scenarios are entirely preventable with the right calculations.

Before you size a pump, you need to understand your energy demand. See the Eneronix guide on How to Do a Proper Load Audit Before Sizing an Off-Grid System for the same analytical thinking applied to water demand.

The Four-Step Sizing Method

Professional solar pump sizing follows four steps in this exact order. Do not skip any of them.

1. Calculate your Total Dynamic Head (TDH)
2. Calculate your required flow rate
3. Select the pump using a performance curve
4. Size the solar array to match the pump

Each step feeds into the next. Getting step one wrong will make every other calculation useless.

Step 1: Calculate Your Total Dynamic Head (TDH)

Total Dynamic Head is the single most important number in solar pump sizing. It represents the total resistance your pump must overcome to move water from the bottom of the borehole to the top of your storage tank.

TDH is measured in metres and it includes three components:

1. Static water level: how deep the water sits below the surface in your borehole
2. Vertical lift: the height from ground level to the outlet of your overhead storage tank
3. Friction losses: pressure lost to pipe length, diameter, bends, and fittings

TDH Formula: TDH = Pump Setting Depth + Vertical Lift to Tank + Friction Losses

How to Determine Your Pump Setting Depth

The pump setting depth is NOT the same as your static water level. It is the depth at which you physically hang the pump inside the borehole casing.

The pump must always sit below the static water level to ensure it is submerged. But the static water level is a moving target. During dry season in Nigeria, especially in North-Central and North-West states, water tables can drop by 5 to 15 metres below their wet-season level.

The correct formula for pump setting depth is:

Pump Setting Depth = Static Water Level + 15 metre safety margin (minimum)

That 15 metre margin accounts for dry season water table drop and ensures the pump stays submerged all year. In northern states like Kano, Sokoto, and Borno where dry season drops are more severe, use a 20 metre margin.

Dry-run protection is the most critical safety feature in any Nigerian borehole installation. Read more about why in the main solar water pump system guide which covers the five most common pump failure modes in Nigeria.

Worked Example: TDH Calculation for an Abuja Borehole

Parameter	Value	Notes
Static water level	50 m below surface	From driller’s report
Pump setting depth	65 m (50 + 15 margin)	Accounts for dry season drop
Overhead tank height	4 m above ground	Elevated tank for gravity supply
Pipe friction losses	4 m (estimated)	80 m of 1.25-inch HDPE pipe
TOTAL DYNAMIC HEAD	73 m	65 + 4 + 4

This means you need a pump rated for at least 73 metres of head. Always buy a pump with a head rating 10 to 15 per cent above your TDH, never exactly at it.

How to Estimate Pipe Friction Losses

Friction losses increase with longer pipe runs, smaller pipe diameter, and more bends. For most Nigerian residential borehole installations, friction losses fall between 3 and 8 metres. Use these rules of thumb:

Pipe Diameter (HDPE)	Pipe Run Length	Approx. Friction Loss
1 inch (25 mm)	Up to 50 m	5 to 8 m
1.25 inch (32 mm)	Up to 80 m	3 to 5 m
1.5 inch (40 mm)	Up to 120 m	2 to 4 m
2 inch (50 mm)	Up to 150 m	1 to 3 m

The same resistance principles that apply to pipe friction apply to drop cable voltage drop. See the Eneronix guide on DC Cable Sizing for Off-Grid Solar Systems for the calculation framework.

Step 2: Calculate Your Required Flow Rate

Flow rate tells you how many litres of water the pump must deliver per hour to meet your daily demand within the available sunlight window.

Flow Rate Formula: Required Flow Rate (L/hr) = Daily Demand (litres) divided by Peak Sun Hours

Daily Demand Benchmarks for Nigeria

Application	Demand Per Unit	Notes
Household (basic use)	50 litres per person per day	WHO minimum standard
Household (garden + livestock)	80 to 100 litres per person	Higher usage household
Small school	5 to 10 litres per pupil per day	Depends on cooking facilities
Cattle or livestock watering	50 to 100 litres per animal per day	Depends on animal type
Drip irrigation (per hectare)	2,000 to 4,000 litres per day	Depends on crop and climate

The WHO and UNICEF joint monitoring report on rural water demand provides the baseline figures used above. See: WHO/UNICEF Rural Water Demand Guidelines.

Peak Sun Hours by Nigerian Region

Peak sun hours are the number of hours per day during which solar irradiance averages 1,000 W/m2. This is what determines how long your pump runs at full rated output. It is not the same as daylight hours.

Region	States	Avg Peak Sun Hours	Harmattan Adjusted
South-South	Rivers, Delta, Bayelsa, Akwa Ibom	4.5 to 5.0 hrs	3.5 to 4.0 hrs
South-West	Lagos, Ogun, Oyo, Osun	5.0 to 5.5 hrs	3.8 to 4.5 hrs
South-East	Anambra, Enugu, Imo, Abia	5.0 to 5.5 hrs	3.8 to 4.5 hrs
North-Central	Abuja, Kogi, Niger, Plateau	5.5 to 6.0 hrs	4.0 to 4.8 hrs
North-West	Kano, Sokoto, Kaduna	6.0 to 6.5 hrs	4.2 to 5.0 hrs
North-East	Borno, Adamawa, Bauchi	6.0 to 6.8 hrs	4.2 to 5.2 hrs

For verified solar irradiance data by Nigerian state, refer to the Rural Electrification Agency (REA) Nigeria Solar Resource Map. This data is used by engineers for professional system design.

Worked Example: Flow Rate for a Family of 8 in Abuja

Parameter	Value
Daily demand	8 people x 50 L = 400 litres
Peak sun hours (Abuja, conservative)	5.5 hours
Minimum flow rate needed	400 / 5.5 = 73 L/hr
Recommended pump selection	At least 90 L/hr at your TDH (25% buffer)

Always build a 20 to 25 per cent buffer into your flow rate selection. This accounts for cloudy mornings, system inefficiency losses, and future demand growth.

Step 3: Select the Right Pump Using the Performance Curve

This is the step that most buyers completely skip. It is also the step that causes the most pump failures in Nigeria.

Every pump has a performance curve published by the manufacturer. The curve shows how the pump’s flow rate changes as head increases. A pump rated for 200 L/hr might only deliver 85 L/hr at 70 metres of head. If you only looked at the maximum flow rate on the label, you would install a pump that cannot fill your tank.

The performance curve, not the label, is what tells you if a pump is right for your borehole. Always cross-reference the curve at your specific TDH.

How to Read a Pump Performance Curve

On a pump performance curve, the X-axis shows flow rate in litres per hour (or m3/hr). The Y-axis shows head in metres. The curve itself shows the relationship between the two for that specific pump.

To use it for your sizing:

1. Find your TDH on the Y-axis
2. Draw a horizontal line across to the curve
3. Drop a vertical line down to the X-axis
4. That intersection is your pump’s actual flow rate at your borehole depth

If that flow rate is equal to or greater than your required flow rate from Step 2, the pump is correctly sized. If it is lower, you need a pump with a higher-head curve.

Grundfos publishes free, detailed performance curve data for the SP and SQFlex series at: product.grundfos.com. This is the professional tool for pump selection in Nigeria.

Pump Selection Criteria for Nigerian Boreholes

Specification	What to Look For	Why It Matters in Nigeria
Motor type	Brushless DC or AC induction only	Brushed DC motors wear rapidly in sandy Nigerian groundwater
IP rating	IP68 minimum	Full submersion rating required for permanent borehole use
Body material	HDPE or stainless steel	Corrosion-resistant in acidic southern Nigerian groundwater
Impellers	Stainless steel for sandy boreholes	Plastic impellers fail rapidly in abrasive sandy water
Motor cooling	Water-cooled (all submersibles)	Confirms motor needs water flow to stay cool – dry-run kills it
Head rating	At least 10-15% above your TDH	Leaves performance margin and allows for future depth changes

Pump Brands Available in Nigeria (2026)

Brand	Series	Best Use Case	Support in Nigeria
Grundfos	SP / SQFlex	Deep boreholes 40-120 m	Lagos, Abuja, PH dealers
Lorentz	PS2 / PS+	Solar-direct DC pump systems	Authorised Lagos/Abuja dealers
DAB / Pedrollo	Multi-range	AC pump with VFD setup	Alaba Market and city dealers
Leo Pumps	Multi-range	Budget household boreholes	Widely available nationwide
Generic OEM (CN)	Various	Short-term budget use only	Very limited warranty/parts

Step 4: Size the Solar Array to Power the Pump

Once you know your pump’s motor wattage, sizing the solar array follows two fixed rules. Both rules must be applied. Using only one of them is a common installer mistake.

Rule 1: Size the Array at 1.5 Times the Motor Wattage

Pumps draw significantly more current at startup than during steady running. This is called the Locked Rotor Current (LRC). If the solar array is only sized for running power, the pump will fail to start on low-sun mornings when the array is not producing peak output.

Array Minimum (before harmattan) = Motor Rated Wattage x 1.5

Rule 2: Add a 30 Per Cent Harmattan Buffer

Between December and February, harmattan dust from the Sahara coats solar panels across northern and central Nigeria. Panel output can drop by 25 to 40 per cent. If you sized the array for clean-panel performance, your pump will be severely underpowered for three months every year.

Final Array Size = (Motor Wattage x 1.5) x 1.30

Worked Examples: Array Sizing by Pump Size

Pump Motor	Base Array (x1.5)	With Harmattan Buffer (x1.30)	Practical Panel Configuration
0.5 HP (375W)	563W	732W	2 x 400W panels = 800W
0.75 HP (560W)	840W	1,092W	3 x 400W panels = 1,200W
1 HP (750W)	1,125W	1,462W	4 x 400W panels = 1,600W
1.5 HP (1,100W)	1,650W	2,145W	6 x 400W panels = 2,400W
2 HP (1,500W)	2,250W	2,925W	8 x 400W panels = 3,200W
3 HP (2,200W)	3,300W	4,290W	11 x 400W panels = 4,400W

For the complete technical framework on solar array sizing, including tilt angle optimisation for Nigerian states, read: Solar Array Sizing for Off-Grid Lithium Battery Systems. The same engineering principles apply to pump arrays.

Series vs Parallel Panel Wiring for Pump Systems

How you wire the panels affects the voltage and current delivered to the pump controller. The controller’s input voltage window determines the correct wiring configuration.

1. Series wiring: voltage adds up, current stays the same. Used when the controller needs higher input voltage.
2. Parallel wiring: current adds up, voltage stays the same. Used when the controller needs higher current at lower voltage.
3. Series-parallel: the most common configuration for arrays of 4 or more panels.

See the full wiring guide with worked examples at: Series vs Parallel vs Series-Parallel Solar Array Wiring before connecting your pump array.

Complete Sizing Example: 3-Bedroom Home in Kano

Here is a full sizing walkthrough for a home in Kano, representing a North-West Nigeria borehole scenario with a deep water table.

Given Information

1. Household size: 6 people
2. Static water level: 80 m below surface
3. Overhead tank height: 5 m above ground
4. Pipe run from pump to tank: 100 m of 1.25-inch HDPE
5. Peak sun hours (Kano, conservative with harmattan): 4.5 hours

Step 1: TDH Calculation

Component	Value
Static water level	80 m
Safety margin for dry season	+20 m (North-West: larger margin)
Pump setting depth	100 m
Overhead tank lift	+5 m
Friction losses (100 m of 1.25″ pipe)	+5 m
TOTAL DYNAMIC HEAD	110 m

Step 2: Flow Rate Calculation

Parameter	Value
Daily demand	6 x 50 = 300 litres
Peak sun hours (with buffer)	4.5 hours
Minimum flow rate	300 / 4.5 = 67 L/hr
Recommended selection (25% buffer)	At least 85 L/hr at 110 m TDH

Step 3: Pump Selection

For 110 m TDH and 85 L/hr minimum flow, the correct choice is a pump rated for 120 to 150 m maximum head. From the Grundfos SP or Lorentz PS2 range, check the performance curve at 110 m. Motor size will typically fall in the 1 to 1.5 HP range for this application.

For this example, assume a 1 HP (750W) AC motor via VFD is selected, confirmed from the pump curve to deliver 95 L/hr at 110 m TDH.

Step 4: Solar Array Sizing

Calculation	Result
Motor rated power	750W
Array minimum (x1.5 for startup)	750 x 1.5 = 1,125W
With harmattan buffer (x1.30)	1,125 x 1.30 = 1,462W
Panel configuration selected	4 x 400W monocrystalline = 1,600W
Controller type needed	AC VFD rated for 1,600W input, 750W AC motor output

Final system for this Kano installation: 4 x 400W panels, AC VFD controller, 1HP AC submersible pump at 100m depth, 1.25-inch HDPE drop pipe, float switch, dry-run protection enabled.

Drop Cable Sizing: The Component Most Installers Get Wrong

The drop cable carries electricity from the surface controller down to the submerged motor. If the cable is undersized, voltage drop occurs. The motor receives less voltage than it is rated for, draws higher current to compensate, overheats, and burns out.

This is the second most common cause of early pump failure in Nigeria, after dry-run damage.

Pump Depth	Cable Cross-Section	Voltage Drop Limit	Notes
Up to 30 m	2.5 mm2 copper	Under 3%	Minimum acceptable for any installation
30 m to 50 m	4 mm2 copper	Under 3%	Standard for most Lagos/SW installations
50 m to 80 m	6 mm2 copper	Under 3%	Required for most North-Central installations
80 m to 120 m	10 mm2 copper	Under 3%	Required for deep northern Nigeria boreholes
Over 120 m	16 mm2 copper	Under 3%	Specialist installation, verify with engineer

The voltage drop calculation methodology for pump cables is identical to the two-constraint framework described in: DC Cable Sizing for Off-Grid Solar Systems. Apply the same maximum 3% voltage drop limit to your drop cable.

Storage Tank Sizing: Often Overlooked, Always Critical

The storage tank is what allows a solar pump to provide 24-hour water supply. The pump fills it during the day; the tank supplies water at night and on cloudy mornings.

Size your tank for at least 2 full days of demand. This provides a buffer for cloudy days and low-sun periods without leaving your household without water.

Tank Sizing Rule: Tank Capacity = Daily Demand x 2.5 (minimum)

Application	Daily Demand	Minimum Tank Size	Recommended Tank
Family of 4	200 litres	500 litres	1,000 litres (overhead)
Family of 8	400 litres	1,000 litres	2,000 litres (overhead)
Family of 12	600 litres	1,500 litres	2,500 to 3,000 litres
Small school (100 pupils)	1,000 litres	2,500 litres	5,000 litres
Small farm (drip irrigation)	3,000 litres	7,500 litres	10,000 litres

Always install a float switch at the tank. When the tank is full, the float switch signals the controller to stop the pump. Without this, the pump runs dry when the tank overflows, or runs continuously wasting energy and wearing the motor.

Borehole Depth by Nigerian Region: Reference Table

Your borehole depth is the starting point for every calculation in this guide. If you do not have a driller’s report, use this regional reference table to estimate. Then verify with the actual driller before purchasing your pump.

Zone	States	Static Water Level	Typical Pump Setting Depth	Min Array
SS	Rivers, Delta, Bayelsa, Akwa Ibom, Edo, Cross River	5 to 20 m	20 to 40 m	800W
SW	Lagos, Ogun, Oyo, Osun, Ekiti, Ondo	15 to 40 m	35 to 60 m	1,200W
SE	Anambra, Enugu, Imo, Abia, Ebonyi	20 to 45 m	40 to 65 m	1,200W
NC	Abuja, Kogi, Niger, Kwara, Plateau, Benue, Nassarawa	30 to 60 m	50 to 80 m	1,600W
NW	Kano, Sokoto, Kaduna, Kebbi, Zamfara, Katsina, Jigawa	40 to 90 m	70 to 110 m	2,000W
NE	Borno, Adamawa, Bauchi, Gombe, Taraba, Yobe	50 to 120 m	80 to 130 m	2,400W

A Lagos borehole at 40 m TDH needs roughly half the panel wattage and a much smaller pump motor than a Kano borehole at 100 m TDH. This is why installers who quote without knowing your borehole depth are not sizing your system. They are guessing.

For more context on how panel output varies by Nigerian state and how to account for harmattan losses in your array, see: How to Clean Solar Panels in Nigeria (Harmattan Dust & 40% Output Loss Explained).

Common Sizing Mistakes and How to Avoid Them

Mistake	What Goes Wrong	How to Avoid It
Using static water level as pump setting depth	Pump runs dry during dry season, burns out motor	Always add a 15 to 20 m safety margin below static level
Ignoring friction losses in TDH	Pump underperforms, cannot fill tank	Calculate friction for your specific pipe diameter and run length
Reading max flow rate from label only	Pump delivers far less water than expected at your actual depth	Always check the pump performance curve at your TDH
Sizing array only for running current	Pump fails to start on low-sun mornings	Size array at 1.5x motor wattage, then add 30% harmattan buffer
Undersizing the drop cable	Motor overheats from voltage drop, fails early	Size cable for under 3% voltage drop at your pump depth
No float switch on tank	Pump runs continuously, motor overheats, tank overflows	Always install a float switch at the storage tank
No dry-run protection	Borehole water table drops, pump runs dry and burns out	Buy a controller with built-in under-current dry-run detection

For the complete list of off-grid solar system mistakes that also apply to pump installations, see: Top 10 Costly Off-Grid Solar Mistakes (And How to Avoid Them).

Summary: The Solar Submersible Pump Sizing Checklist

Before you buy any pump for a Nigerian borehole, confirm you have completed each of these:

1. Get your borehole driller’s report with the static water level
2. Add a 15 to 20 m safety margin below static level to get pump setting depth
3. Calculate vertical lift to tank and pipe friction to get your TDH
4. Calculate daily water demand and divide by peak sun hours to get required flow rate
5. Check the pump performance curve at your TDH, not just the label flow rating
6. Confirm motor wattage and multiply by 1.5, then by 1.30, to get your array size
7. Size your drop cable for under 3% voltage drop at your pump depth
8. Size your storage tank for at least 2.5 days of demand
9. Install a float switch at the tank and dry-run protection at the controller

For help selecting the right controller for your pump, including VFD selection for AC pump systems, see the Eneronix guide: How to Select an Off-Grid Inverter. The controller sizing principles are directly applicable.

Frequently Asked Questions

Q1: What is a good TDH for a solar pump in Nigeria?

A good TDH depends entirely on your borehole depth and tank height. In South-South Nigeria, TDH values of 30 to 50 m are common. In North-West Nigeria, values of 90 to 130 m are typical. There is no single right answer. Always calculate TDH for your specific borehole before selecting a pump.

Q2: Can I size a solar pump without the driller’s report?

You can estimate using the regional depth table in this guide, but you should not buy a pump based on estimates alone. Static water levels vary significantly even within the same city. A wrong assumption can lead to a pump that is either too weak for your depth or set too shallow to survive dry season. Get the driller’s report first.

Q3: What happens if I undersize the solar array for my pump?

An undersized array will cause the pump to fail to start on mornings with low solar irradiance. When the pump tries to start with insufficient power, it draws the full Locked Rotor Current but the motor cannot overcome the static head. The motor stalls, draws excessive current, overheats, and burns out. This is why the 1.5x multiplier for array sizing is non-negotiable.

Q4: How do I know if a pump I am buying has the right performance curve for my borehole?

Ask the supplier for the pump performance curve document, or download it from the manufacturer’s website. For Grundfos, curves are available at product.grundfos.com. For Lorentz, at lorentz.de. Find your TDH on the Y-axis, trace across to the curve, and read the corresponding flow rate on the X-axis. If that flow rate meets your Step 2 requirement, the pump is correctly matched.

Q5: Do I need a VFD or a DC pump controller?

If you are using a standard AC submersible pump (recommended in Nigeria for spare parts availability), you need a VFD. If you are using a brushless DC pump from Grundfos SQFlex or Lorentz PS2 range, you need a solar pump MPPT controller specific to that pump. Never use a standard battery MPPT charge controller for a pump. They are designed for different loads and will not protect or regulate the pump motor correctly.

Q6: How deep can a solar pump lift water in Nigeria?

Most quality solar submersible pumps available in Nigeria handle Total Dynamic Head values of 30 to 120 m. For very deep boreholes in Kano, Sokoto, or Borno where depths exceed 100 m, you need a high-head pump with a solar array of at least 2,000W. Confirm with the pump’s performance curve that your required flow rate is achievable at your specific TDH.

Q7: What size tank do I need for a solar pump system?

Size your storage tank for at least 2.5 times your daily demand. This provides water supply through a full cloudy day and a full night without pumping. For a family of 8 consuming 400 litres per day, a minimum 1,000-litre tank is needed, and a 2,000-litre tank is strongly recommended for reliability.

Q8: How often should I maintain a solar submersible pump in Nigeria?

The pump itself requires very little maintenance if it is correctly sized and protected. Focus on the accessible parts: clean solar panels at least once a week during harmattan season, check cable connections quarterly, inspect the float switch and controller settings every six months, and test dry-run protection annually. Do not pull the pump from the borehole for inspection unless you have a documented fault. Every pull is a risk of pipe damage or contamination.