Switch on geyser, the current springs to life
T. NANDAKUMAR
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Solar water heaters are increasingly gaining acceptance as a source of clean, cheap energy.
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— Photo: N. Balaji
Energy efficient: Solar energy is yet to be tapped to optimum level in our country.
Switch on the geyser in your house and the electricity meter immediately springs to life. How you wish you could do away with the power-hungry gadget that pushes up your electricity bill.
With power tariffs showing an upward trend all over the country, solar-water heaters are increasingly gaining acceptance as a source of clean, cheap energy. They are safer than electric geysers and reflect one’s commitment to preservation of the
environment.
A large number of houses and commercial buildings in the city today are equipped with solar-water heaters of different capacities to suit various requirements.
A typical domestic solar water heater consists of a hot-water storage tank and one or more “flat-plate” or “evacuated-tube” collectors.
The collectors are glazed on the sun-facing side to allow solar radiation to come in.
A black absorbing surface (absorber) inside the collectors absorbs solar radiation and transfers the energy to water flowing through it. Heated water is collected in the tank which is insulated to prevent heat loss.
Water circulation
Circulation of water from the tank through the collectors and back to the tank continues automatically owing to density difference between hot and cold water (thermosyphon effect).
A flat-plate collector consists of an insulated outer metallic box covered on the top with glass sheet. Inside, there are blackened metallic absorber (selectively coated) sheets with a built-in grid of metallic tubes to carry water.
The absorber absorbs the solar radiation and transfers the heat to the flowing water.
The evacuated tube collector is made of hermetically sealed double-layer borosilicate glass tubes that provide insulation. The outer wall of the inner tube is coated with an absorbent material.
According to K. Sajikumar, chief executive of Intdecor, a dealer of solar-water heater systems, evacuated tube collectors are preferred over flat-plate collectors because of higher thermal absorption.
The hot-water storage tank in domestic solar water heating systems is typically a double-walled tank. The space between the inner and the outer tanks is filled with insulation to prevent heat losses.
The inner tank is generally made of copper or stainless steel to ensure a long life. The outer tank can be made of stainless steel sheet, painted steel sheet or aluminium. A solar-water heater should be mounted on a rigid structure and fixed to the roof. The temperature of water in the storage tank of a solar-water heater is approximately 60 degrees Celsius to 80 degrees Celsius. A 100-litre system is considered optimum for a family of four adults.
Unobstructed light
The basic requirement of a solar system is availability of unobstructed sunlight for the whole day. The collectors of the system have to face the sun and hence should be oriented due south for maximum interception of sunlight.
As far as possible, the area should be flat, away from trees and shady areas and close to the bathrooms where hot water is to be supplied.
Typical solar water heaters made using quality materials last for 15 to 20 years depending on the general upkeep. Most manufacturers offer a three-year guarantee.
A 100-litre solar water heating unit costs about Rs. 18,000.
At the current power tariff, the investment can be recovered in three to five years through the saving on power bills, Mr. Sajikumar says.
The insulation of the storage tank ensures that the water remains hot without a significant drop in temperature for around 24 hours. Thus, water heated during a day should be available for use in the next morning, Mr. Sajikumar says.
Most domestic solar-water heating systems are designed to blend with the building exteriors. Solar-water heating units need little maintenance. Occasional leakages in plumbing can be easily repaired by common plumbers. The copper tubes in flat-plate collectors tend to deposit scales over a period of time. This may require de-scaling with acids. Broken glass may also need replacement. A major advantage of evacuated tube collectors is that it does not allow scales to accumulate.
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