Solar Tube Well vs Diesel - Monthly Savings Math and Payback Analysis

Key Takeaways

• OGRA's ex-depot price for high-speed diesel was Rs 398.07 per litre on 28 October 2026, up from Rs 389.27 on 20 October and Rs 360.06 on 21 July. Pumps pay more because ex-depot excludes secondary freight.
• Fuel burn is a large unknown. A 2003 IWMI survey reported 1.5-2.5 litres per hour for Chinese pump and slow-speed diesel sets and 3.5-5.0 for tractor-operated tube wells. An Indian engine maker's undated catalogue works out to about 3.5 litres per hour for a 15 hp engine if its fuel figure applies at rated output (our arithmetic).
• The same 2003 IWMI paper found diesel tube wells in its Punjab survey ran 6 hours a day on 120 days a year, about 60 hours a month. A Punjab planning study assumed 1,600 hours a year, about 133 hours a month. Both are old and neither is a 2026 average.
• On fuel alone, a 15 HP solar system pays back in 7.9 to 41.9 months across those inputs and five retail prices from three sellers. The shortest figures use Alpha Solar's prices, which do not list a pump. More pumping hours shorten payback.
• The two panel datasheets we read give a 25-year (LONGi) and a 30-year (JinkoSolar) linear power warranty. A warranty is not a lifespan.

Introduction

Solar tube wells are usually sold on the fuel they replace. Whether that sale is a good one depends on three numbers that farms rarely measure: how many litres the engine burns, how many hours it runs, and what a litre costs. This guide takes each from a published source, shows the sum, and says where the sources run out.

What does diesel cost per litre in Pakistan?

OGRA, the oil regulator, publishes the maximum ex-depot price of high-speed diesel (HSD) in its price publications. It excludes secondary freight, the cost of moving fuel from the depot to the pump, so a pump in a town charges more.

The price moves from day to day. OGRA's page lists a price publication for most working days, and its sheet says the full impact of a change in the daily international price is passed on in seven working days. Use the figure for the day you read this, not the one in the table.

How much diesel does a tube-well engine burn?

No source we found gives litres per hour for a 15 hp engine at irrigation load in Pakistan. These are the nearest figures, and they disagree.

The catalogue arithmetic is hp times grams per hp-hour, divided by 838 grams per litre, the typical density on an Attock Refinery diesel data sheet: 15 × 195 ÷ 838 is about 3.5. Oklahoma State University's extension service takes a different route. It expects an irrigation diesel engine to develop about 16.49 HP-hr per US gallon and says to deduct 20 percent from advertised horsepower for continuous load. For a 15 hp engine that is about 12 hp, or about 2.75 litres an hour (our arithmetic).

So the sources put a pump engine anywhere from 1.5 to 3.5 litres an hour, and a tractor-driven set higher. They do not tell you where your engine sits. Measure yours with a graduated container over a full pumping hour.

How many hours a year does a diesel tube well run?

The 2003 IWMI paper's Punjab survey of diesel tube wells gives an average of 6 hours a day on 120 days a year, about 60 hours a month. The 2015 Punjab model assumes 1,600 hours a year, about 133 hours a month. Both are old and neither is a 2026 average. Your own hours decide the result.

What is the monthly fuel bill?

Hours times litres per hour times the price per litre. This table uses OGRA's ex-depot price of Rs 398.07 on 28 October 2026, so a pump price will be higher. It is a worked example, not a measurement.

At 3.5 litres per hour the cost per running hour is Rs 1,393.

What do solar tube wells cost?

Retail prices for a 15 HP system differ by seller and by what they include.

One lakh is 100,000 rupees. These are retailer prices, not quotes, and the pages do not explain the wide spread between them.

How long does the investment take to pay back?

Dividing a system price by the monthly fuel bill gives a simple fuel-only payback in months. It ignores engine repairs and lubricants, water delivered, borewell condition and changes in solar output. Rs 1,250,000 and Rs 1,690,000 are Alpha Solar's 15 HP prices, which do not list a pump. Rs 1,900,000 is the top of Pakistan Solar Traders' range for a complete system. Rs 2,200,000 and Rs 3,000,000 are the ends of Solar Citizen's 22 to 30 lakh range, which includes the pump and installation.

Published paybacks disagree, and none comes from a measured Pakistani 10-15 HP comparison with stated assumptions:

• Pakistan Solar Traders, a seller: most systems pay for themselves within 1.5 to 3 years.
• Solar Citizen, a seller: 4-6 years for a 10 HP system at roughly 18 lakh with 3-4.5 lakh in annual diesel savings.
• A 2023 peer-reviewed review in Water: a solar irrigation payback of 3 to 5 years, with no assumptions in the passage we read.
• A Dawn opinion column of 12 April 2026: two to three years, with no assumptions given.

What does payback depend on?

• Hours. A Nepal study of a small 1.5 HP solar pump against a 5 HP diesel set found solar needed at least 700 hours a year to compete. That is a different country and pump size, but it shows the direction: a pump that runs few hours recovers little.
• Depth. IWMI's 2021 report says that for depths greater than 100 feet the cost of solar tube wells increases significantly and becomes uneconomical.
• Sunlight hours. The same report notes that solar pumps can only operate during sunlight hours.
• Fuel. The sums above scale directly with the diesel price. A cheaper litre lengthens payback.
• Non-fuel diesel costs. Lubricant changes, repairs and engine replacement are real, but the sources we found price them only for 2003 and 2013, so the tables above leave them out.

How long do solar panels last?

Datasheets state warranties, not lifespans. JinkoSolar's JKM580-605N panel carries a 12-year product warranty and a 30-year linear power warranty, with 1 percent first-year degradation and 0.40 percent a year after, ending at 87.4% at year 30. LONGi's LR5-72HTHF carries a 15-year warranty for materials and processing and a 25-year warranty for extra linear power output, with 0.40% a year from year 2 to 25. Neither datasheet says panels stop working when the warranty ends.

Summary and Recommendations

• Measure your engine's litres per hour and your annual pumping hours before any quote. With retail system prices spread two- to three-fold, litres per hour, hours and system price all move payback.
• Use the day's OGRA price, then add the secondary freight your pump charges.
• Compare solar quotes by what they include: pump, installation, borewell work and structure.
• Check the well depth. IWMI's 2021 report says solar tube wells deeper than 100 feet become uneconomical.
• Related guides: drip irrigation and solar combo economics and the solar pump VFD selection guide.

Correction, 28 October 2026: earlier versions of this guide used a diesel price, a fuel-burn figure, pumping hours, a system price, a payback and a 10-year saving that could not be traced to any source, and two of its own monthly fuel costs disagreed. They have been replaced.