Aavin dairy, Tirunelveli, Tamil Nadu

General Information on the company using solar thermal energy

Description of the company

Aavin Dairy Plant at Tirunelveli is one of the 17 Milk Procurement Unions Plants across 30 districts in the State of Tamil Nadu. Aavin Dairy is networked with around 12000 Milk Producer’s Cooperative societies, with a daily milk production of the order of 25 to 30 lakh litres.

The plant has an installed capacity of 100,000 litres and 4 chilling centres. It processes milk at a daily average of around 69,000 litres, while the maximum being 85,000 lpd. It has produced around 207 MT of Ghee, 10,650 kgs of kova and has average milk sales of 47,500 lpd.

Type of Industry

Dairy Industry: Milk & milk-based products processing plant.

Location of the company and the solar plant

The system is installed at:
M/s The Tirunelveli District Cooperative Milk Producers' Union Ltd.,
Reddiarpatti Road,
Tirunelveli-627 007.
Key Contact: Mr. B.Durai Raju.
No: 0462 -2522127, 2552004, 2552557.

Heat demanding processes

Hot water is required for 4 to 6 hours a day in various unit operations. The main requirement being, can washing (at 45°C), cleaning of work areas, cleaning of processing tanks (at 60°C).

Steam generated from boiler is used in various unit operations of milk processing, which is fed through the boiler, wherein the hot water is sent for pre-heating of boiler feed water.

Conventional heat supply

A furnace oil based boiler of 2 TPH is commissioned in 2012 and is used to generate steam at 120°C at 4 to 10 kg/cm2 pressure.

Conventional fuel used

The furnace oil requirement which is used as conventional fuel, on an average is 180 lpd. The energy content of furnace oil 825,000 kcal/day or 959kWh/day.

Motivation to use solar thermal energy

Aavin Dairy plant has sought supplementary source of heat through SWHS to reduce the furnace oil usage due to increasing costs.

Technical Description of SWHS

Type of solar plant

The solar water heating system is Flat Plate Collector(FPC). The SWH based Industrial Solar Water Heating System has a capacity of 15000 LPD. The system is preheating the feed water used for steam generation.

Year of installation

The SWHS system was commissioned in 2012

Solar collector field

The SWHS System consists of 180FPC collectorsand has a collector area of 360m2.

Water storage

Collector arrays are connected to three different water storage tanks with a volume of 5000 litre each.


The system is a closed loop system.

Operation of the system

Cold water (secondary liquid) from the overhead tank enters in the solar hot water storage tank of 5000ltrs each capacity due to gravity. Distilled water (primary liquid) in the Heat Exchanger of SS tubes immersed inside the storage tank is circulated by circulation pumps from morning to evening with the differential temperature control between the collector array and heat exchanger. These pumps are connected to the differential temperature control panel which gets switched-on due to the temperature difference at the inlet and outlet of the manifolds.

The heat gained by primary liquid from the FPC is dissipated to the secondary liquid inside the storage tank. By the end of the day, the water(Secondary liquid) attains temperature of about 80-85°C. This water is sent to the boiler as the feed water.

Hydraulic scheme

Supplier/manufacturer of the solar system

The solar system was designed, delivered and commissioned by:

M/s Photon Energy Systems Limited
Unit 19, Mount View Enclave,
Road No. 12, Banjara Hills,
Hyderabad 500034
Key Contact: Mr. Shankar dev
Cell: +91-9000333759

Data recorded

The plant was initially maintaining the records however currently they are not maintaining any records.

Energy Yield

Heat demand

It is assumed, that the factory requires 15,000 litre per day at 80°C hot water and the cold water temperature is equal to the annual average ambient temperature of 25°C.

The daily energy demand for hot water heating can be calculated with:

Qdaily = 15m3/day * (80°C –25°C) * 1.16 kWh/(m3*K) = 957 kWh/day

The annual energy demand for hot water heating is:

Qannually = 365 days * 957 kWh/day = 350 MWh/year

(The temperature difference in °C is measured in K (=Kelvin))

Solar radiation-on site

The site receives an average annual solar radiation of 4.92 kWh/m2/day. This means 1771 kWh/m2/year on horizontal surface.

On collectors with an inclination of 30° the irradiation is about 0.99 * 1771 kWh/(m2*year) = 1753kWh/(m2*year).

Location: Longitude: 77.69E & Latitude: 8.74N

Source: NASA Surface meteorology and Meteonorm

Useful solar energy delivery

The solar radiation on the collector surface is 360m2* 1753 kWh/(m2*year) = 631MWh/year.

Assuming a system efficiency of about 20%, the useful solar energy is about 631MWh/year * 0.2 = 126MWh/year, which corresponds to 345kWh/day.

The useful solar energy delivered by the SWHS per m2 of collector is: 0.96 kWh/m2.

Fuel saved by solar energy

Assumed, that the boiler has an efficiency of 80%, the energy content of furnace oil saved by the SWHS is 126 MWh/year / 0.8 = 157 MWh/year.

This corresponds to 157 MWh/year / 10kWh/litre = 15700litre/year or 43 litre/day.

(Assumptions: The energy content of furnace oil is 10 kWh/litre; plant working for 365 days a year; Boiler efficiency of 80%).

Emissions saved

The CO2 emissions saved by the solar system are of about 42 ton CO2 per annum.(The CO2 emissions of furnace oil are 2.52 kg CO2/litre)

Economics of SWHS Plant

Investment costs

The project is commissioned with an overall investment of Rs.27 Lakhs.


MNRE subsidy is Rs.810,000(30% of the investment costs).

Economics of the solar system

Based on a furnace oil price of Rs 45 per litre(2012 prices), around 15,700 litre/year * Rs 45/Litre = Rs 7Lakh is saved per year.

Simple payback period is 2 years and 7 months with MNRE subsidy.


Operation experience

Operation of the system is good.

Statement of the owner

Owner is satisfied about the operation and savings of the Solar Water Heating System.

Statement of the supplier/manufacturer

Manufacturer also satisfied with the turnover and supply of Solar Heating System setup to industries. Supplier expects subsidies either from MNRE or State Government to medium and small scale industries, in order to enable other industries to come forward for setting up solar system in their premises.