Why do the Bureau of Energy Efficiency Jodhpur lime motor reports pay back in 21 to 25 months in the summary but 2.1 to 2.6 years in the text?

Three Bureau of Energy Efficiency (BEE) Jodhpur lime reports swap a 7.5, 15 or 40 horse power (HP) motor for rupees (Rs) 0.48, 0.96 and 1.92 lakh. The summary tables print 25, 25 and 21 months, which fit the equipment line alone (my arithmetic). The text divides a higher cost and prints 2.5, 2.6 and 2.1 years.

The three reports side by side

• 7.5 HP elevator motor (the file is named 75hp): measured 2.5 kilowatts (kW) in Annexure 1 (the summary says 1.0 to 2.0 kW). Efficiency printed 85% old, 94% new. Saving printed 1.00 kW, Rs 19,000 a year. Table 4.1 total Rs 0.48 lakh. Summary payback 25 months, text 2.5 years.
• 15 HP hydrator motor: measured 4.0 kW (the summary says 4.0 to 7.0). 85% to 94%. Saving 1.65 kW, Rs 38,000. Table 4.1 total Rs 0.96 lakh. Summary 25 months, text 2.6 years.
• 40 HP pulveriser motor: measured 28.5, headed hp in Annexure 1 (the summary says 25 to 30 kW). 85% to 94%. Saving 4.0 kW, Rs 90,000. Table 4.1 total Rs 1.92 lakh. Summary 21 months, text 2.1 years.
• All three run 16 hours a day and say pet coke is about 80% of a lime plant's energy bill, with electricity the rest. The kiln itself is 15 tonnes a day of quicklime from 30 of limestone, burning 3 to 4 tonnes of pet coke a day.

Equipment only or total cost

The summary figures fit the equipment line alone (my arithmetic): Rs 0.8 lakh / 0.38 = 25 months, Rs 1.6 lakh / 0.90 = 21 months and Rs 0.4 lakh / 0.19 = 25 months. The reports do not say that is their method, and each summary text quotes the total investment (Rs 0.48, 1.0 and 1.9 lakh) next to the same payback months. Section 4.3.2 uses the project cost, quoted as Rs 1.0, 1.9 and 0.48 lakh, and prints 2.6, 2.1 and 2.5 years.

Table 4.1 adds erection and a miscellaneous line to the equipment: 0.8 + 0.08 + 0.08 = 0.96, 1.6 + 0.16 + 0.16 = 1.92, and 0.4 + 0.04 + 0.04 = 0.48. Divided by the saving, those totals give 30.3, 25.6 and 30.3 months. The total cost is the safer figure to plan on.

The saving looks large against the measured draw

For the 7.5 and 15 HP motors the printed saving is about 40% of the measured draw: 1.00 of 2.5 kW and 1.65 of 4.0 kW. For the 40 HP motor it is 4.0 of 28.5, about 14%.

A gain from 85% to 94% efficiency is worth 1 minus 0.85 / 0.94, about 9.6%, of the power drawn. At the measured draws that is about 0.24, 0.38 and 2.73 kW. That is my own reading; the reports do not show how their saving figures were reached, and I could not reproduce them from the measured draws and printed efficiencies. The text of each report also says an efficient motor is 4 to 5% more efficient, while the annexure uses 9 points.

Other printed figures that do not tie

• The 7.5 HP report prints an internal rate of return (IRR) of 10.9% in its summary and Table 4.2, and 10.0% in section 4.3.4.
• The 7.5 HP sensitivity table (Table 4.3) shows the same IRR and net present value (NPV) rows as the 15 HP report: IRR 8.4, 11 and 13.3%, NPV -0.03, 0.02 and 0.08 lakh. Its own Table 4.2 gives NPV 0.01.
• In the 15 HP report a 5% lower saving turns the NPV negative, to -0.03 lakh. The 40 HP report stays positive at 0.194.
• The annexure column for rated power is headed kW but holds the HP sizes 15, 7.5 and 40, with 13, 5.0 and 36 as the new motor.

Before you order

• Put a meter on the motor for a full shift. The saving rides on what it draws, and each summary gives a range, not one figure.
• Count your own hours. All three assume 16 a day, and no report prints the tariff or the days used.
• Ask for the guaranteed efficiency at your load, since a motor running well under its rating loses efficiency.

The 15 HP report three ways

• Summary: Rs 0.8 lakh / Rs 0.38 lakh = 2.1 years, printed as 25 months
• Table 4.1 total: 0.8 + 0.08 + 0.08 = Rs 0.96 lakh; 0.96 / 0.38 = 2.5 years, about 30 months. Text: Rs 1.0 lakh / 0.38 = 2.6 years
• My reading at the measured 4.0 kW: 4.0 x (1 minus 0.85 / 0.94) = about 0.38 kW, against 1.65 printed
• The report's own rate is Rs 38,000 / 1.65 = about Rs 23,000 for each kW saved. 0.38 kW x Rs 23,000 = about Rs 8,800 a year, and Rs 0.96 lakh / Rs 8,800 = about 11 years

First three lines use the report's own figures. The last two are an example of my own reading, and move if the 4.0 kW is not the typical draw.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so your monthly units are on file next to a report's yearly kWh. A bill covers the whole plant, so the motor's own draw still needs a meter. The green loan check shows what a lender asks for.

• Green loan readiness check
• Lime kiln insulation and pet coke
• Pet coke storage loss at a lime kiln
• Jodhpur lime kiln units and pet coke carbon

Sources: BEE, Detailed project report: energy efficient motor 7.5 HP elevator, Jodhpur limestone cluster (SAMEEEKSHA), BEE, Detailed project report: energy efficient motor 15 HP hydrator, Jodhpur limestone cluster (SAMEEEKSHA), BEE, Detailed project report: energy efficient motor 40 HP pulveriser, Jodhpur limestone cluster (SAMEEEKSHA)

Last reviewed 2026-11-05. Report figures are from BEE's Small and Medium Enterprises (SME) programme project reports of 2011; costs and savings are at the report year's prices. Check a current quote and your own motor load before you rely on the payback.