Energy Cost of Pumping Calculator

About the Energy Cost of Pumping Calculator

Pumping water is the single largest energy expense on most irrigated farms. The cost depends on the volume of water pumped (GPM), the height it must be lifted (total dynamic head), the efficiency of the pump and motor, and the cost of electricity or fuel.

The water horsepower (WHP) required to lift water is derived from the basic hydraulic formula: WHP = GPM × TDH / 3960. Converting horsepower to kilowatts, then multiplying by run hours and the electricity rate, gives you the operating energy cost per irrigation event, per season, or per acre-inch.

This page converts hydraulic load into monthly or seasonal pumping cost so rate plans and efficiency upgrades can be compared on dollars, not intuition.

When This Page Helps

Pumping energy decisions should start with cost per acre-inch or per season, not just motor size. This page gives that budget view.

How to Use the Inputs

1. Enter the pump flow rate in gallons per minute (GPM).
2. Enter the total dynamic head (TDH) in feet.
3. Enter the pump efficiency as a percentage.
4. Enter the motor efficiency as a percentage.
5. Enter the number of hours the pump runs.
6. Enter the electricity rate in dollars per kWh.
7. Read the total energy cost.

Example Calculation

Tips & Best Practices

• Annual pump tests detect efficiency losses before they become costly.
• Variable-frequency drives (VFDs) save 10–25% on systems with variable demand.
• Off-peak electricity rates can cut pumping cost by 20–40%.
• Pump efficiency declines with wear; a drop from 80% to 65% raises cost 23%.
• Convert diesel cost to $/kWh-equivalent for fair comparison: 1 gal diesel ≈ 12–14 kWh.
• Meter your pump separately for accurate cost tracking.

The Pump Performance Curve

Every pump has a performance curve relating flow (GPM), head (ft), efficiency (%), and power (HP). Operating away from the best efficiency point (BEP) wastes energy. Selecting a pump whose BEP matches your system's GPM and TDH requirements is the single most important design decision.

Pump Testing

An annual pump test measures flow, pressure, and power draw to calculate actual efficiency. Many states offer pump testing programs through extension services or natural resources districts. A $200 test can reveal $2,000+ in annual energy waste.

Variable-Frequency Drives

VFDs adjust motor speed to match actual flow demand. When the pivot is in a low-demand area or during low-ET periods, the VFD slows the pump, saving energy. Typical ROI for VFDs on irrigation pumps is 2–4 years.

Frequently Asked Questions

• What is total dynamic head?

  TDH is the total pressure the pump must overcome: pumping lift (static head) plus friction loss in pipes and fittings plus the operating pressure at the system outlet. It is measured in feet of head.

• What is a typical pump efficiency?

  New well-matched pumps operate at 70–82% efficiency. Older or mismatched pumps may fall to 50–65%. Turbine pumps tend to have higher efficiency than centrifugal pumps.

• How do I account for demand charges?

  Many utilities charge a monthly demand fee based on peak kW draw. Add monthly demand charges to the kWh-based energy cost for a complete picture of pumping expense.

• Should I upgrade my pump?

  If your pump test shows efficiency below 60–65%, considering a pump bowl replacement or upgrade. The energy savings can pay back the investment in 2–4 years.

• How do I convert from diesel to electric cost?

  One gallon of diesel produces approximately 12–14 kWh of useful work in a pump engine. At $3.50/gal diesel and $0.10/kWh electric, diesel costs about $0.27/kWh equivalent — nearly 3× electric.

• What GPM do typical center pivots require?

  A quarter-section pivot applying 1 in per revolution in 3 days needs about 700–900 GPM. Smaller pivots or longer rotations need less.