943 m2 flat plate collector system (660 kW) with a 10,000 litres solar hot water tank designed to deliver 50,000 litres of hot water per day
Flat plate collector
Year of Installation
Name of the system
Chelsea Textile Mills, Gurgaon, Haryana
Description of the company
M/s Chelsea Mills is a textile manufacturing company which was established in 1978.
Type of Industry
The plant is a garment manufacturing company producing apparel wear, majorly denims.
Location of the company and the solar plant
The SWHS is installed on the roof top of the plant buildings at Manesar, Haryana, located at the following address:
M/s. Chelsea Textiles Mills
Sector 5 industrial area,
Manesar, Gurgaon. www.chelseamills.com
Heat demanding processes
The plant requires hot water in the temperature range of 55OC to 80OC for washing of apparels in multiple washing machines. The heat demand is for around 15 hours a day for 365 days a year.
Conventional heat supply
Three boilers are producing steam. One boiler is producing hot water for the washing process, which is mixed with solar heater water.
Conventional fuel used
Diesel oil is used in the hot water boiler. The price of the diesel was Rs 31 per litre at the time of installation of the SWHS system in 2008 and increased to around Rs 52 per litre in 2015. The energy content of the diesel is about 10,800 kcal/kg.
Motivation to use solar thermal energy
The company is interested to use renewable energy sources to reduce fuel costs. Investments are made, if the payback time is less than 3 years.
Description of the solar thermal system
Type of solar plant
Non-pressurised flat plate collector (FPC) solar water heating system. The solar heated water is directly used in washing machines. The SWHS system is designed to deliver about 50,000 LPD hot water at 60 °C - 65°C.
Year of installation
The SWHS was commissioned in the year 2008.
Solar collector field
410 flat plate collectors with an total aperture area of 943 m2 are installed. The collectors are installed on the flat roof of the plant and oriented towards South.
A 10,000 litres hot water storage tank is installed for the SWHS. This tank delivers heat to a 50,000 litres hot water tank, which is connected with the process and heated by the hot water boiler. In addition, waste heat from a diesel generator (UPS) is stored as well.
Hydraulics scheme & operation of system
The collector circuit is separated from the hot water tank by a heat exchanger. A water tank, which is located above the collectors assures, that the non-pressurized collector circuit is filled with water. A minimum pressure is generated by a manual pump. R.O. water is used as heat transfer fluid.
The solar hot water tank is located on the roof, while the process water tank is located at the ground. The cold water from the process water tank is pumped to the solar hot water tank and the solar hot water is flowing by a pipe, connected on the top, back to the process water tank. The process water tank is heated by the hot water boiler and by waste heat from the UPS diesel gen.
It is assumed, that the factory requires 50,000 litre per day of 75°C hot water for washing and the cold water temperature is equal to the annual average ambient temperature of 25°C. The plant heat requirement particularly for washing is calculated below.
Daily energy demand for hot water heating:
Qdaily = 50 m3/day * (75°C – 25°C) * 1.16 kWh/(m3*K) = 2,900 kWh/day
The annual energy demand for hot water heating is:
Qannually = 350 days * 2,900 kWh/day = 1015 MWh/year
Solar radiation-on site
The site receives an average annual solar irradiation of 5.05 kWh/(m2*day), this means 1,843 kWh/(m2*year) on horizontal surface. On collectors with an inclination of 30° the irradiation is 1.13 * 1,843 kWh/(m2*year) = 2083 kWh/(m2*year).
Useful solar energy delivery
The solar radiation on the collector surface is 943 m2 * 2083 kWh/(m2*year) = 1964 MWh/year.
Assuming a system efficiency of about 20%, the useful solar energy is about 1964 MWh/year * 0.2 = 393 MWh/year, which corresponds to 1076 kWh/day.
The useful solar energy delivered by the SWHS per m2 of collector is: 1.1 kWh/m2.
Fuel saved by solar energy
Assumed, that the boiler has an efficiency of 70%, the energy content of diesel saved by the SWHS System is 393 MWh/year / 0.7 = 561 MWh/year. This corresponds to 561 MWh/year / 9.5 kWh/litre = 59,100 litre/year or 162 litre/day.
(Assumptions: The energy content of diesel is 9.5 kWh/litre; plant working for 365 days a year; Boiler efficiency of 70%).
The CO2 emissions saved by the SWHS are 59,100 litre/year * 2.68 kg CO2/litre = 158 to CO2/year
(The CO2 emissions of diesel are 2.68 kg CO2/litre)
The total cost of the system is Rs 46.03 Lakh.
Accordingly the investment cost per m2 of collector area is about Rs 4882/m2
The project proponent has availed the MNRE subsidy of 30% on the total investment cost. I.e. Rs 13.81 lakh.
Economics of the solar system
Based on a diesel price of Rs 52 per litre, around 59,100 litre/year * Rs 52/Litre = Rs 30.7 Lakh is saved per year. Simple payback time (without considering interest on debt) is therefore (Rs 46.03 Lakh - Rs 13.81 Lakh) / Rs 30.7 Lakh/year = 1.0 years.
Since the installation of the system, the solar water heating system is working properly and the plant has never faced any major O&M problems.
Statement of the owner
The system owner has expressed his satisfaction about the project plant operation and financial benefit of the SWHS System.