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Solar Water Heater |
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Solar Lighting |
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RO Water Purifier |
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Nano Water Purifier |
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Automatic Water level Controller |
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| Product Overview | Features | Technical Specifications | FAQs | ||||||||||||||||||||||||||||||||||||||||||||||||||
 Frequently Asked Questions - Solar Water Heater |
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Why should one go for solar water heating? Because--Solar water heaters save electricity and thus money; electricity is becoming more and more expensive; they could even turnout to be more reliable than electric power supply (at least in many parts of our country); they are clean and green and thus reflect one's commitment for preservation of environment; they are safer than electric geysers as they are located on the roof; and, if well designed, may even look good on the house top. Back to Top Do they really work? Of course they do. After all, more than 50,000 domestic systems are being installed every year all over the country. Back to Top Is their working difficult to understand for a layperson/ How do they work? The working of solar water heaters is very simple to understand. Two common phenomena observed in everyday life are the key functioning of solar water heaters. These are first, a black surface heats up when left in the sun, by absorption of solar radiation and second, the inside of a car becomes very hot, if it is left in the sun with windows closed. A car becomes hot in sun because solar radiation can pass through the glass windows but cannot come out. It is trapped inside and thus heats up the car. The heat trapping principle is the famous Green House Effect. The good absorption property of black surfaces is used to improve solar energy absorption in a solar heater. These two phenomena are utilized in flat plate collectors of commonly available solar water heaters. A typical domestic solar water heater consists of a hot water storage tank and one or more flat plate collectors. The collectors are glazed on the sun facing side to allow solar radiation to come in. A black absorbing surface (absorber) inside the flat plate 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. Circulation of water from the tank through the collectors and back to the tank continue automatically due to density difference between hot and cold water (thermosyphon effect). Back to Top What is a flat plate collector? It is the heart of a solar water heating system. It consists of an absorber plate which is coated on its sun facing surface with an absorbent coating, also called selective coating. The absorber consists of a grid of metallic tubes and sheets. Water flows through the tubes. Sheet absorbs the solar radiation falling on it and transfers it water. The absorber plate is placed in a open box to protect it from weather. The space between back and sides of the absorber and the box is filled with insulation reduce heat losses. The front of the box is covered with a high transmittance glass plate. Flat plate collectors are specified on the basis of their area and are of commonly 1x2 m size. Back to Top Are there any other types of collectors? Flat plate collectors are the most common type used in the domestic solar water heating systems, specially in India, in view of their cost economics. Evacuated tube collectors have also been proposed for domestic solar water heating systems, but are not commonly available. Concentrating collectors are likely to be more useful for higher temperature applications such as power generation and industrial use. Back to Top What should one look for in a good Flat Plate Collector? Bureau of Indian standards has laid down specifications of flat plate collectors for use in solar water heating systems and thus the IS mark is an assurance on use of proper materials. The important characteristics are, the materials of construction of the absorber plate, the type of absorbent coating on it, the quality of the glass plate used, the material of the box, the insulation thickness etc,. Back to Top What are the desirable characteristics of hot water storage tank? 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 long life. The outer tank could be made of stainless steel sheet, painted steel sheet or aluminum. Electrical heating elements controlled by thermostats can be provided as an option in the tank itself to take care of those days when sun is not there or demand of water has gone up. The capacity of the tank should be in proportion to the collector area used in the system. A commonly used thumb rule is to provide 50 liters of storage for every sq. m of collector area. to large or to small tanks are both detrimental to efficiency. Back to Top How does one identify a good solar water heater? How big a system should one purchase? The fundamental rule is that it is better to buy a system smaller than your requirement and use back up when you fall short of hot water, rather than buy a system much bigger than your requirement (because you can afford it). This will lead to inefficiencies and may even cause operational problems. The best is to make an actual estimate of daily demand of hot water by measurements on the main use points. Do remember that the solar system is capable of heating only an approximately fixed quantity of water and is designed for typical sunny days. Thus in this characteristic it is unlike an electric geyser which can supply widely varying quantities of hot water in a day. Also remember that the temperature of water in the solar system is determined by the combination of collector area and the tank capacity. Typically it would be 60 to 70°C, which is much hotter than the bathing water temperature (around 40°C). Estimation of your demand can also be made with the help of the table given below. As a typical example on sizing of solar systems, it may be mentioned that a 100 liters system is considered generally optimum for family of 4 adult members. Back to Top How much would a solar water heater cost? The total cost of a solar water heating system is dependent upon many things. These include, the capacity, the kind of back-up used, the materials used for the inner and outer tanks, the length of distribution piping required to take hot water to the bathrooms, and not insignificantly, the brand value. Typically, for an Indian make system with a single BIS approved flat plate collector of 2 sq. m area, the current market costs are reported to be in the range of Rs. 15,000-20,000, excluding the distribution piping. However this range is indicative, and could vary from manufacturer to manufacturer. Back to Top What are the site requirements for installation of a solar water heating system? Can the system be installed somewhere other than on the roof? The system can also be installed on a bracket on a south facing wall, close to the bathrooms. However, the installation is difficult and leads to extra cost. The fixing of the system to the bracket should be proper. Access to the system for repairs should also be ensured. Cost of hot water distribution piping could be reduced in such installations as the system will be close to the use point. Back to Top How can the system be installed in multistoried buildings? What would happen if water supply is irregular? A regular cold water supply, at a height of around 2.5 m is necessary for functioning of the solar system. In case cold water is not available continuously, a separate cold water tank may have to be installed, at least equal in capacity to the capacity of the solar system. In case cold water supply is interrupted during the day, the heating of water by the solar system may not be affected significantly, although hot water cannot be drawn for use till the water supply is restored. Back to Top What would happen on cloudy days? The heating of water by the solar system will obviously be affected. If it is so cloudy that energy received from the sun is almost zero, the output of solar collectors also will be nil. On partially cloudy days some output can be expected. But, the system can be designed with a suitable electrical back up heater to take care of hot water demand on cloudy days. Back to Top How much electricity and money can be saved?
What is the expected life of a solar water heater? Typical solar water heaters made using materials as per BIS specifications could last for 15 -20 years depending upon the general upkeep, etc. Back to Top Is any electricity required for operation of the solar water heater? Domestic solar water heaters work on the principle of thermosyphonic action in which water circulates through the system by virtue of density difference between hot and cold streams. No electricity is required for circulation of water or for any other operation in such systems. However, in case a back up heater is provided to take care of hot water requirement during cloudy days, electricity will be required. Back to Top How long will the water heated by solar energy remain hot in the tank? Will one get hot water in early morning when sun is not there? Hot water produced by the solar system during the day is stored in an insulated storage tank. The insulation of the tank is such that water should remain hot without significant drop in temperature for around 24 hrs. Thus water heated during the previous day should be available for use in the next morning. Back to Top Are there any financial incentives from the government on these systems? Will the solar system match with the building exteriors? Though aesthetics are a matter of individual preference, most domestic solar water heating systems can be either designed to blend with the building exteriors or can be designed so that they are hidden from view. If systems are well installed and maintained, they might even add to the aesthetics. Back to Top What are the operational requirements? Domestic solar systems do not require any special operational skills. However, if following are observed, the efficiency of the systems will be maintained at a high level: Ø Try to consume most of the heated water at one time to either in the morning or in the evening. Frequent on and off of the hot water tap would lead to reduced electricity savings. Ø If an electrical back up is provided in the tank, set the thermostat at the lowest acceptable temperature. Ø In the north Indian climate, hot water may not be used for bathing in summers. If the system is to be put totally out of use, it should be drained of water and the collector should be covered. Alternatively, if the hot water requirement remains in summers also, though at a reduced level, cover the collector partially. Ø Dust deposition on the collector would reduce its efficiency. Try to get it cleaned at least once in a week. Back to Top What are the Maintenance Requirements? Domestic solar water heating system do not need significant maintenance requirements. Occasional leakages in the plumbing could be easily repaired by common plumbers. In case quality of water is hard, scale deposition in the collectors may result over the years. This may require decaling with acids for which it is best to contact the suppliers. Broken glass may also have to be replaced by the suppliers. If outside exposed surfaces are painted, the paint may have to be redone every 2-3 years to prevent corrosion of the surfaces. Back to Top |
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