What does a soft starter with energy saver save on a dairy ammonia compressor?
Six per cent of the compressor motor's draw, in Bureau of Energy Efficiency (BEE)'s Gujarat dairy reports: 11,520 kWh a year on a 30 kW motor and 25,012 kWh on a 75 kW one. Payback is 2.1 and 1.67 years at 2010 prices. The 30 kW report shows 21.7 kW in its text but sums on 26.7 kW.
Why a compressor motor wastes power
A reciprocating ammonia compressor loads and unloads cylinders as demand moves, so the motor often runs well below full load, down to about 25% at times. BEE's auditors logged this on site. Refrigeration is at least 30% of the energy a dairy cluster plant uses. A soft starter with an energy saver replaces the star-delta starter, lowers the voltage at part load and eases the start, which also cuts the starting current. The reports claim 6%.
The two cases side by side
- 30 kW motor, measured 26.7 kW: saving 11,520 kWh, cost Rs 1.44 lakh, payback 2.10 years.
- 75 kW motor, measured 57.9 kW: saving 25,012 kWh, cost Rs 2.45 lakh, payback 1.67 years.
- Both assume 20 hours a day for 360 days, so 7,200 hours.
A slip in the 30 kW report
Its text says the compressor draws 21.7 kW, which is 156,240 kWh a year. Its annexure, which the saving is built on, says 26.7 kW. Six per cent of 26.7 kW is the 11,520 kWh. If your motor draws the lower figure, the saving is smaller, so log your own motor before you accept either. The 75 kW report also counts 2 motors and prices the starter at Rs 2.45 lakh, yet its saving covers one 57.9 kW compressor, so its payback is unclear.
Other changes the report lists
- The capacitor between the motor and the starter moves out of the circuit.
- No civil work beyond minor grouting for the new frame.
- Maximum demand and mechanical wear should both fall, but the report does not put a number on either.
The sums
- 30 kW: 26.7 kW x 6% = 1.6 kW (rounded). 1.6 x 20 x 360 = 11,520 kWh. At Rs 5.96 a kWh = Rs 68,659. Payback 1.44 lakh / 68,659 = 2.10 years
- 75 kW: 57.9 kW x 6% x 7,200 hours = 25,013 kWh (the report shows 25,012). At Rs 5.86 = Rs 1.466 lakh. Payback 2.45 / 1.466 = 1.67 years
- CO2 at 0.675 kg a kWh (Central Electricity Authority (CEA), financial year (FY) 2025-26): 11,520 x 0.675 = 7.8 tonnes (t) and 25,012 x 0.675 = 16.9 t (the 75 kW report states 21.3 t, also about 0.85 kg a kWh)
- The 30 kW report states 9.79 t, which is 0.85 kg a kWh
Report figures at the report's tariffs. The 75 kW sum covers one 57.9 kW compressor.
What Senseible does here
Senseible reads electricity bills into monthly kWh and carbon dioxide equivalent (CO2e) at the grid factor for the bill's financial year, so a saving shows in later bills. A bill covers the whole plant, so a single compressor's saving is small beside it; log the motor's own kW as well.
- Green loan readiness check
- Efficient motors on the same compressors
- Gujarat chilling centres: energy and carbon
- Ice bank thermal storage
Sources: BEE, Detailed project reports: soft starter with energy saver for motor 30 kW and 75 kW, Gujarat dairy cluster (2010, SAMEEEKSHA), BEE, Detailed project report: soft starter for motor 75 kW, Gujarat dairy cluster (2010, SAMEEEKSHA), CEA CO2 Baseline Database, version 22.0
Last reviewed 2026-11-04. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's prices and a current quote before you rely on the payback. Re-check the grid factor when CEA publishes a new edition.