Why does the Bureau of Energy Efficiency (BEE) Surat report for a 60 kilowatt (kW) steam turbine pay back in 1.64 years when the 40 kW one takes 2.04?

BEE's Surat reports put a 40 kW turbine on 3 tonnes of steam an hour for rupees (Rs) 34.50 lakh and a 60 kW one on 4 tonnes for Rs 41.50 lakh. They make 302,400 and 453,600 kilowatt hours (kWh) a year, worth Rs 16.93 and 25.40 lakh, so payback is 2.04 and 1.64 years.

The two reports side by side

• 40 kW: steam in at 10.5 kilograms a square centimetre (kg/cm2), out at 3.5, 3 tonnes an hour. 40 kW x 90% load x 24 hours x 350 days = 302,400 kWh. At Rs 5.60 a kWh, Rs 16.93 lakh. Cost Rs 32.00 lakh for turbine and generator plus Rs 2.50 lakh for panel and cabling: Rs 34.50 lakh. Payback 34.50 / 16.93 = 2.04 years.
• 60 kW: steam in at 10.7 kg/cm2, out at 3.5, 4 tonnes an hour. 60 x 0.9 x 8,400 = 453,600 kWh, Rs 25.40 lakh. Cost Rs 39.00 lakh plus Rs 2.50 lakh: Rs 41.50 lakh. Payback 1.64 years as printed (41.50 / 25.40 is 1.63).
• Printed indicators, 40 kW against 60 kW: internal rate of return (IRR) 31.64% and 43.28%, net present value (NPV) Rs 27.26 and 52.12 lakh, debt service cover 2.07 and 2.59.
• Both say the turbine saves no fuel; it only cuts the power bought from the grid. Both have a 15 year life.

Why the 60 kW set looks better

Cost per kW is Rs 0.86 lakh for the 40 kW set and Rs 0.69 lakh for the 60 kW set. Power per tonne of steam is also higher: 40 kW on 3 tonnes an hour is 13.3 kW a tonne, 60 kW on 4 tonnes is 15 kW a tonne. The pressure drop is 7.0 kg/cm2 for one and 7.2 for the other, which does not explain a 12.5% gap on its own. Our reading: ask the maker for the guaranteed steam rate in kg per kWh at your own flow and pressure.

Printed figures that do not tie

• Both summary tables say 4 days of process downtime; both texts say one week.
• The 60 kW report names Samta Silk Mills in its Table 1.4 with 1,078 megawatt hours of power and a 6 tonne an hour boiler. The 40 kW report names the same mill with 1,944 megawatt hours and 3 tonnes an hour. The 60 kW Table 1.1 gives the 1,078 to another mill. Use the reports' method, not their mill names.
• The 60 kW sensitivity table shows a net present value of Rs 41.22 lakh for a 5% increase in generation, lower than the Rs 52.12 lakh base case, and Rs 47.27 lakh for a 5% decrease. The increase should give more, not less.
• The 40 kW report's typical unit needs 4 tonnes an hour of steam but the turbine takes 3. The 60 kW report passes all 4.

The carbon dioxide (CO2) figure

Both print the factor: 0.85 tonne of CO2 a megawatt hour, giving 257 and 385 tonnes. Both count the grid power saved and nothing for extra fuel: each says "There is no additional fuel required for generating electricity" and that the turbine has no effect on fuel savings. Our reading, not the reports': a turbine turns part of the steam's heat into power, so less heat reaches the process and the boiler may need to burn more to make it up.

The linked page works the 40 kW case: net about 41 to 49 tonnes a year at the financial year (FY) 2025-26 grid factor of 0.675 kg a kWh, after extra coal. The 60 kW set makes 1.5 times the kWh, so scaled by 1.5 the same method gives about 62 to 74 tonnes. That scaling is our arithmetic, not the report's, and the linked page's 41 to 49 tonnes depends on its assumed 90% generator efficiency and 75% boiler efficiency, which the reports do not give.

Before you buy

• Log the steam that really goes through the pressure reducing valve for a full week. The turbine earns only when steam passes.
• Price the extra coal or lignite at today's rate and take it off the saving.
• Check first whether the boiler can run at a lower pressure; that saves fuel with no turbine.

The 60 kW set, step by step

• Power: 60 kW x 90% x 24 x 350 = 453,600 kWh a year
• Money: 453,600 x Rs 5.60 = Rs 25.40 lakh
• Payback: Rs 41.50 lakh / Rs 25.40 lakh = 1.63 years, printed 1.64
• CO2 printed: 453.6 x 0.85 = 385.6 tonnes
• Grid CO2 alone at 0.675: 453,600 x 0.675 = 306.2 tonnes, before the extra fuel

Figures are the reports' own at the reports' prices. The 0.675 is the Central Electricity Authority (CEA) version 22.0 grid factor for FY 2025-26, an estimate of today's grid saving.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the coal bought and the power drawn before and after a turbine are on file. It cannot see steam flow through the valve; that comes from your boiler log.

• Steam turbine on a pressure reducing valve
• Old report CO2 versus today's grid factor
• Surat 3 and 4 tonne boiler reports compared
• Green loan readiness check

Sources: BEE, Detailed project report: energy conservation turbine (40 kW), Surat textile cluster (SAMEEEKSHA), BEE, Detailed project report: energy conservation turbine (60 kW), Surat textile cluster (SAMEEEKSHA), Central Electricity Authority (CEA), CO2 Baseline Database for the Indian Power Sector

Last reviewed 2026-11-05. Report figures are from BEE's Small and Medium Enterprises (SME) programme project reports, with grid power at Rs 5.60 a kWh. Check your tariff, your steam flow and a current quote before you rely on the payback.