How many solar panels do I need for a borehole?

Confused by solar panel calculations for your borehole?
Guessing can lead to system failure or wasted money.
Understanding the key factors ensures a reliable water supply.

The number of panels depends on the pump's power (in watts), your location's peak sun hours, and the total work required (head and flow).
For instance, a 750W pump might need three 330W panels in a location with good sunlight to ensure sufficient power.

Determining the right number of solar panels is not a simple guess.
It is a calculation based on several critical factors.
Getting it wrong can leave you with an underpowered system that fails when you need it most, or an oversized one that costs more than necessary.
This guide will walk you through the essential steps to accurately determine how many solar panels your borehole pump requires.
You will learn to size your system correctly for a reliable and cost-effective water solution.

The Most Important Factor: Your Pump's Power Consumption

Don't know your pump's power rating?
Choosing panels without this information is a shot in the dark.
This number is the foundation of your entire solar array calculation.

First, find the pump's power rating in watts (W) on its specification sheet or motor label.
This figure tells you the direct energy demand the pump has to operate.
A higher wattage pump will always require more solar panels.

Before you can even think about solar panels, you must know the energy demand of the device you want to power.
In this case, that device is your borehole pump.
The pump's power consumption, measured in watts, is the single most important piece of information for sizing your solar array.
It represents the amount of electrical power the pump needs to do its job.
This value is the starting point for all subsequent calculations.
Without it, you are simply guessing.

Why Pump Wattage is the Starting Point

The wattage of a pump motor dictates the minimum power output required from your solar array.
For example, a pump with a 500-watt motor needs at least 500 watts of solar panel output under ideal, real-world conditions to run effectively.
In practice, it is recommended to "oversize" the solar array by about 25-30%.
This oversizing ensures the pump receives enough power during less-than-perfect sunlight conditions, such as on slightly overcast days or early in the morning.
For a 500W pump, this would mean aiming for a solar array of around 625W to 650W.
This extra capacity provides a crucial buffer, improving system reliability and extending the daily pumping time.

How Pump Type Affects Power Needs

The type of pump you choose for your borehole directly influences its power consumption.
Different pump designs are optimized for different tasks, and their efficiency varies based on the application.

• Solar Screw Pumps: These are designed for high-head, low-flow applications. They are excellent for deep wells but consume power efficiently because they are moving a smaller volume of water.
• Solar Plastic Impeller Pumps: These are built for high-flow, medium-head situations. They are great for irrigation but may require more power to move large volumes of water.
• Solar Stainless Steel Impeller Pumps: These offer a balance of high flow and medium-to-high head, with a focus on durability. Their power consumption depends on the specific demands of the corrosive environment or deep well they are used in.

The Critical Role of a High-Efficiency Motor

The motor is the heart of the pump, converting electrical energy into mechanical force.
Modern solar pumps use high-efficiency Brushless DC (BLDC) permanent magnet motors.
These motors can achieve efficiencies of over 90%.
This means less energy is wasted as heat, and more of the solar power is used to pump water.
A pump with a high-efficiency BLDC motor will require fewer solar panels to perform the same amount of work as a pump with an older, less efficient motor.
This directly translates to lower upfront costs for your solar array.

Calculating Your Water Needs: Head and Flow Rate

Is your borehole deep or your storage tank far away?
Ignoring the total workload on your pump leads to an underpowered system.
Calculate your "head" and flow to size your panels correctly.

A pump's workload is defined by its Total Dynamic Head (TDH) and required flow rate.
A deeper well or a higher demand for water volume increases the pump's power consumption, thus requiring more solar panels to operate.

A pump's power rating tells you what it can consume, but the actual power it does consume is determined by the work it has to do.
This work is defined by two key variables: how high it has to lift the water and how much water it has to move.
Miscalculating this workload is a common reason for system failure.
If the pump has to work harder than you planned for, it will draw more power.
If your solar array cannot supply that extra power, the pump will underperform or fail to run at all.
Accurately determining your head and flow requirements is a non-negotiable step in designing a reliable solar pumping system.

Understanding Total Dynamic Head (TDH)

Total Dynamic Head (TDH) is the most accurate measure of the total vertical pressure the pump must overcome.
It is not just the depth of your well.
It is calculated by adding two components:

1. Static Head: This is the total vertical distance the water needs to be lifted. It is measured from the water level in the borehole (not the ground level) to the highest point of the outlet pipe (e.g., the inlet of a storage tank).
2. Friction Head (Friction Loss): As water moves through pipes, elbows, and valves, it encounters friction. This friction creates back pressure, which the pump must also overcome. This "friction head" increases with the length of the pipe, the narrowness of the pipe's diameter, and the speed of the water flow.

A long horizontal pipe run can add significant friction head, making the pump work as if it were lifting the water several extra meters vertically.

How Flow Rate Demands Power

Flow rate is the volume of water you need the pump to deliver in a given period, often measured in liters per minute (LPM) or cubic meters per hour (m³/h).
A higher flow rate means the pump motor must spin faster or work harder, which consumes more energy.
You must first determine your daily water requirement.
For example, if you need 10,000 liters of water per day and you have 5 peak sun hours, you need a pump system capable of delivering at least 2,000 liters per hour.
Your solar array must be large enough to power the pump to meet this required flow rate at your calculated TDH.

Sizing Your Solar Array: The Final Calculation

Think you can just match panel wattage to pump wattage?
Ignoring your location's sunlight and system losses will leave you short on power.
Properly sizing the array ensures your pump runs when you need it.

To size your array, divide the pump's wattage by the panel's wattage, then factor in your location's peak sun hours and a 1.3 efficiency buffer.
This ensures sufficient power even on less-than-perfect days.

Once you know your pump's power requirement and your daily water needs, you can perform the final calculation to determine the number of solar panels.
This step involves bringing together the pump's wattage, the wattage of your chosen solar panels, and a crucial environmental factor: the amount of sunlight your location receives.
It also requires adding a safety margin to account for real-world inefficiencies.
This final calculation will move you from a rough estimate to a concrete number of panels.

The Simple Formula for Sizing

At its most basic, the calculation is straightforward.
You divide the pump's power requirement by the wattage of a single solar panel.

Number of Panels = Total Pump Power (Watts) / Single Panel Power (Watts)

For example, if you have a 750W pump and you plan to use 330W panels:
750W / 330W = 2.27
In this case, you would round up to 3 panels.
This gives you a total array power of 3 x 330W = 990W.
This initial calculation provides a good starting point and already includes a healthy buffer (990W is 32% more than the required 750W).

Adjusting for Peak Sun Hours and Inefficiencies

For a more precise calculation, you must consider Peak Sun Hours and system inefficiencies.

• Peak Sun Hours: This is not the total number of daylight hours. It is the number of hours per day when the sun's intensity is at its peak (1000 W/m²). This value varies greatly by location and season. A system in Arizona might get 6-7 peak sun hours, while one in Germany might only get 3-4. Fewer peak sun hours mean you need a larger solar array to pump the same amount of water in a shorter time.
• System Inefficiencies (Derating Factor): Real-world solar arrays do not operate at 100% of their rated power. Power is lost due to factors like dust on the panels, high temperatures (panels are less efficient when hot), wire resistance, and controller inefficiencies. A common practice is to use a derating factor of 1.3 to 1.4 to account for these losses.

A More Advanced Calculation

Let's refine the example.
You need to produce 750W of power for your pump.
You account for system losses by multiplying this by a 1.3 derating factor.
Required Array Power = 750 W * 1.3 = 975 W
Now, you divide this by the power of your chosen panels.
Number of Panels = 975 W / 330 W = 2.95
Again, you round up to 3 panels.
This more detailed calculation confirms that 3 panels, providing a total of 990W, is the correct choice for this 750W pump, ensuring it has ample power to run reliably.

Overcoming Limitations: The AC/DC Hybrid Solution

Worried about having no water on cloudy days or at night?
A purely solar-powered system is dependent on sunshine, creating inconsistency.
An AC/DC hybrid solar pump system ensures you have water 24 hours a day.

A hybrid system with an AC/DC controller provides a worry-free water supply.
It automatically uses solar power when available and seamlessly switches to a grid or generator backup when sunlight is insufficient, maximizing energy savings.

One of the most significant challenges of a purely solar-powered system is its reliance on the sun.
This dependency means no water at night and reduced performance on overcast days, which is not acceptable for critical applications like household water supply or livestock watering.
Additionally, the high upfront cost of a large solar array, sized to meet peak demand even in poor weather, can be a major barrier.
The AC/DC hybrid solar pump system is an elegant technological solution that overcomes both of these fundamental disadvantages.
It offers reliability without compromising the economic benefits of solar.

The Power of Dual-Input Technology

A hybrid system is centered around an intelligent AC/DC controller.
This controller is engineered with two separate power inputs, allowing it to be connected to both your solar panels (DC power) and an alternate power source, such as the utility grid or a backup generator (AC power), simultaneously.
The controller's built-in software continuously monitors the power available from the solar panels and manages the power sources automatically to ensure the pump never stops.

How the System Ensures 24/7 Water

The controller's logic is designed to prioritize free solar energy, only using the backup source when absolutely necessary.

1. Full Sun Operation: During bright, sunny conditions, the controller powers the pump entirely from the solar panels. The AC input is on standby, consuming no power.
2. Hybrid Function in Low Light: On cloudy days or when sunlight is weak, the controller activates its hybrid mode. It draws as much power as it can from the solar panels and intelligently supplements the shortfall with a small amount of AC power to keep the pump running at the desired speed.
3. Automatic AC Switchover: At night or during heavy storms when there is no solar input, the controller seamlessly switches to 100% AC power.

This automated management guarantees an uninterrupted water supply around the clock.
It provides the cost savings of solar with the dependability of the grid.
For users, this means you can often install a smaller, less expensive solar array, knowing that you have a reliable backup to handle any periods of low solar generation.

Conclusion

Calculating the right number of solar panels depends on pump wattage, head, flow, and sunlight.
Proper sizing and high-efficiency components ensure reliability, while a hybrid system guarantees a 24/7 water supply.

FAQs

How many solar panels do I need for a 1hp pump?

A 1HP pump is about 746 watts.
You'll likely need a solar array of 1000-1200 watts, which would be three or four 330W panels, to ensure reliable performance.

Can I add more solar panels later?

Yes, you can add more panels to a system.
However, you must ensure they are compatible with your existing panels and that your controller can handle the increased voltage and amperage.

What is the difference between connecting panels in series vs. parallel?

Connecting in series increases voltage, which is good for long wire runs.
Connecting in parallel increases amperage, which is useful for meeting the pump motor's current requirements.

Do I need a battery for my solar borehole pump?

No, most modern systems are direct-drive and do not need batteries.
The pump operates when the sun shines, and water is typically stored in a tank.

How much does it cost to set up a solar water pump?

The cost varies greatly, from under a thousand to many thousands of dollars.
It depends on the pump's size, well depth, solar array size, and installation complexity.

How deep can a solar pump go?

Specialized solar pumps, like screw pumps, can lift water from depths exceeding 200 meters (over 650 feet).
Centrifugal pumps are better for shallower wells with higher flow needs.

What maintenance does a solar pump system require?

Maintenance is minimal.
You will need to clean the solar panels periodically.
The brushless motor is maintenance-free, and the pump end may require occasional checks depending on water quality.