# Does a solar water heater pay back in a petcoke-fired textile processing unit?

Canonical: https://senseible.earth/answers/textile-solar-water-heater-long-payback

Not quickly. BEE's Pali report puts a 3,000 litre a day solar water heater at Rs 4.5 lakh against 10.98 t of pet coke saved, worth Rs 0.82 lakh: about 5.5 years at 2010 coke prices. CO2 falls about 35 t a year, not the 11 t the report states.

## Why the case is weak

Hot water for jiggers, mercerising and washing is made by injecting steam from a coke boiler, and coke at Rs 7,500 a tonne is cheap heat. Pali gets only about 15 cloudy days a year, so sunshine is not the problem; the price of what it replaces is.

## The arithmetic

- 3,000 litres a day heated from 35 C to 95 C: 180,000 kcal a day, 63 million kcal over 350 days.
- Boiler and pipes at 70%: 90 million kcal of coke heat / 8,200 = 10,976 kg.
- At Rs 7,500 a tonne: Rs 82,317 a year.
- Rs 4.5 lakh / Rs 0.82 lakh = 5.5 years. The report's own IRR is 10.35% and NPV Rs 0.05 lakh: barely positive.

## What would change the answer

- Coke price: payback falls in step with it. For 3 years, coke must cost about Rs 13,700 a tonne.
- Outlet temperature: if the heater gives 75 C instead of 95 C, the saving falls by a third. Ask for a guaranteed outlet temperature.
- Cheaper steps first: in the same cluster, jigger temperature control and condensate recovery each pay back within a year.

## The report's CO2 figure is wrong

It states 11 t a year for 10.98 t of coke, about 1 t of CO2 per tonne. At the IPCC default for pet coke the saving is about 34.8 t.

## One 3,000 litre system, one year

- Heat: 3,000 x (95 minus 35) x 350 = 63 million kcal
- Coke: 63 million / 0.70 / 8,200 = 10.98 t
- Money: 10.98 x Rs 7,500 = Rs 0.82 lakh; payback 5.5 years
- CO2: 10.98 x 3.17 = 34.8 t

Pet coke at the IPCC 2006 default, 3.17 t CO2 a tonne (32.5 GJ a tonne x 97.5 kg CO2 per GJ). An estimate; a lab analysis of your own coke is better.

## What Senseible does here

Senseible reads pet coke invoices into monthly tonnes, each linked to its bill, so you can see what a solar heater would really displace before you buy one. It has no pet coke factor; use the 3.17 above.

- [Green loan readiness check](https://senseible.earth/green-loan-check)
- [Solar water heater CO2 savings](https://senseible.earth/answers/solar-water-heater-factory-co2-savings)
- [Jigger auto temperature control](https://senseible.earth/answers/jigger-dyeing-auto-temperature-controller)
- [Jet dyeing condensate recovery](https://senseible.earth/answers/jet-dyeing-condensate-recovery-petcoke-saving)
- [Pet coke emission factor in India](https://senseible.earth/answers/petcoke-emission-factor-india)

Sources: [BEE, Detailed project report: solar water heater, Pali textile cluster (2010, SAMEEEKSHA)](https://sameeeksha.org/pdf/dpr/PAL_TXT11.pdf), [IPCC 2006 Guidelines, Volume 2 Energy, Tables 1.2 and 2.3](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-11-01. Report figures are from a BEE SME programme project report; costs and paybacks are at the report year's prices. Check today's fuel and power prices and a current quote before you rely on the payback.