Solar Water Heating Systems


Solar water heating system (SWHS) is a device which supplies hot water at 60°C to 80°C using only solar thermal energy without any other fuel. It has three main components, namely,

  1. Solar Collector
  2. Insulated hot water storage tank and
  3. Cold water tank with required insulated hot water pipelines and accessories.

In the case of smaller systems ( 100 – 2000 litres per day ), the hot water reaches the user end, by natural (thermo – siphon) circulation for which the storage tank is located above the collectors. In higher capacity systems, a pump may be used for forced circulation of water.

Working Principle

In a typical solar water heater, water is heated by the solar thermal energy absorbed by the collectors. The hot water with lower density moves upwards and cold water with higher density moves down from the tank due to gravity head. A bank of collectors can be arranged in a series – parallel combination to get higher quantity of hot water. A typical 100 litres insulated tank with a 2 m2 collector area, will supply water at a temperature of 60 – 80°C.

Hot Water Storage Tank

The tanks are generally made of stainless steel to avoid corrosion and are insulated to reduce heat losses. They are also fitted with electrical heater as a backup during monsoon days. The tanks may also be made of G.I. sheets or aluminium.

Cold Water Tank & Pipelines

Cold water comes from the over head tank.  Hot water from the system is transferred to various utility points through to insulated pipelines. A heat exchanger may be provided when the water is hard.


Domestic: Bathing, Coffee / Tea preparation, Dishwashing etc.

Industrial: Pre-heating of boiler feed water, cooking / dishwashing in industrial canteens. washing of milk canes in dairies, sterilisation of surgical instruments etc.

Economics (Tentative)

  • A 100 lpd domestic solar water heating system (SWHS) can cater to a family of 5 persons and costs about Rs.20000.
  • It saves about 1500 units of electricity per annum equivalent to about Rs.5000/- per year.
  • The payback period would be about 3 years against the life of 15 years and above for the system.
  • A 1000 lpd industrial system would cost about Rs.2.0 lakhs and would have a payback period of 2 years.


  • Soft loan @ 2 % to domestic users 3% to institutions users not availing accelerated depreciation and 5% to industrial / commercial users availing depreciation is available through IREDA  and public / private sector banks etc.
  • Capital subsidy equivalent to upfront interest subsidy @ Rs.3300/- per sq.m. of collector area will be available for flat plate collectors and Rs 3000 for evacuated  tube collectors
  • 100% subsidy for Govt. run institutions such as hospitals, hostels etc.

Mandatory Provision

Govt. of Tamil Nadu has issued amendments to the Building Rules making the use of solar water heating systems mandatory for certain type of new buildings as per two Government orders:

  • G.O. Ms. No. 112 Municipal Administration and Water Supply (MA1) Dept. dt. 16.08.02 covers all the districts and municipal corporations.
  • G.O. MS. No. 277 Housing and Urban Development (UD 1) Dept. dt. 14.11.02 covers Chennai metropolitan areas.

Categories of the building covered are –

Chennai Metropolitan Area

  1. Nursing Homes/Hospitals
  2. Hotels & Lodges Floor area exceeding 500 sq.m
  3. Kalyanamandapams
  4. Hostels having more than 50 rooms

All Districts & Municipal Corporations

  1. Hospitals and Nursing Homes
  2. Hotels, Lodges and guest houses
  3. Schools, Colleges, Training Centres and Hostels.
  4. Barracks of armed forces / para-military forces and police
  5. Individual residential buildings with more than 150 sq.m. plinth area
  6. Functional buildings of railway stations, airports etc.
  7. Community centres, Kalyanamandapams etc.

A large number of solar water heaters have also been installed in private sector mainly hotels, hospitals etc. without subsidy.

The total collector area of all the solar water heaters installed is about 1 lakh sq. m. which is equivalent to 100 MW of power which would otherwise require an investment of Rs 400 crores besides operating cost. The emission mitigation is about 7.7 lakh tonnes of CO2 per annum.

Testing facility

MNRE has established a full-fledged testing facility at  Solar Energy Center, Gurgaon. In addition, Madurai- Kamarajar University also has a center for testing of solar water heating systems. University also conducts training and awareness programmes and offers consultancy services.

For availing the benefit of interest subsidy schemes of MNRE, the solar collectors used should have either BIS certificate or should be procured from MNRE certified manufacturers.

MNRE has accorded sanction for the installation of Solar Water Heating Systems for 25000 sq.m

Application from Various Beneficiaries such as Domestic/ Industries / Commercial establishment/ Institution are invited.

Systems installed as on 31-10-2011  under subsidy schemes:


Collector area
sq. m




Non profit Institutions



Govt. Institutions







View the list of manufacturers approved by MNRE

Install solar on house – save upto Rs.14,700 per year

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