Solar Water Heating

Solar Thermal Energy

India is blessed with abundant Solar Energy which comes to us free of cost. The solar radiation in form of heat that falls on the surface of the earth can be used for water heating, space heating and space cooling and process heat generation.

One of the popular devices that harness the solar energy is solar hot water system (SHWS). The SHW systems are economical, pollution free and easy for operation in our country with high solar insolation (Incident Solar Radiation). Wide spread utilization of solar water heaters can reduce a significant portion of the conventional energy being used for heating water in homes, factories and other commercial and institutional establishments.

A solar water heater consists of a collector to collect solar heat and an insulated storage tank to store hot water. During the day time, water in solar collectors gets heated which is either pumped or flown automatically on thermosyphon principle to the storage tank. Hot water then stored in the tank is ready for use. Based on the collector system, solar water heaters can be of two types.

• Flat Plate Collectors (FPC) based Solar Water Heaters
• Evacuated Tube Collectors (ETC) based Solar Water Heaters
  

Flat Plate Collectors (FPC) based Solar Water Heater

The solar radiation is absorbed by Flat Plate Collectors which consist of an insulated outer metallic box covered on the top with glass sheet. Inside there are blackened metallic absorber (selectively coated) sheets with built in channels or riser tubes to carry water. The absorber absorbs the solar radiation and transfers the heat to the flowing water.

Evacuated Tube Collectors (ETC) based Solar Water Heaters

Evacuated Tube Collector is made of double layer borosilicate glass tubes evacuated for providing insulation. The outer wall of the inner tube is coated with selective absorbing material. This helps absorption of solar radiation and transfers the heat to the water which flows through the inner tube.

Features of Solar Water Heating System

• 60 – 80 degree C temperature can be attained depending on solar radiation, weather conditions and solar collector system efficiency
• Hot water generation - Maximum on clear sunny days, Moderate on partially cloudy days , may not be adequate but not on rainy or heavyly overcast day
• Can be installed on roof-tops, building terrace and open ground where there is no shading
• Solar Collectors to be oriented towards South and over-head tank above SWH system
• Water Quality to be tested by the buyer for total dissolved salt and chlorine
• Hot water tanks suitable for soft or hard water has to be selected

Cost of Solar Water Heaters

The Cost of solar water heater depends on size and type of system installed. The total cost involves the,

1. Solar water heating system with solar collector, hot water tank and other installation accessories.
2. Cold water tank & its stand if the overhead tank is not already installed
3. Internal plumbing inside the house for hot water piping for all the bathrooms/kitchen/wash area
4. Cost of transportation of the system to the site and installation

The cost does not increase linearly with increase in capacity; rather it comes down proportionately as we go for higher capacity systems. Although, the initial investment for a solar water heater is high compared to available conventional alternatives, it is a practical investment for your home.

Environmental benefits

A 100l SWH can prevent emission of 1.5 tonnes of carbondioxide per year.

Service Life : 15-20 years

Payback Period and Financial Savings

• A Family of 4 taking shower in 2 different bathrooms
• Recommended size - 200 L/day Solar Water Heater
• Average Payback Period : 3 - 4 years