Solar Water Heating System
Internationally, solar water heating has been identified as one of the most promising decentralized solar applications, having significant potential to reduce electricity consumption and consequent emissions reduction. It is being increasingly recognized as an application that can help urban areas and industries in reducing their dependence on grid and reducing diesel/gas consumption.
A solar water heater consists of a collector to collect solar energy and an insulated storage tank to store hot water. The solar energy incident on the absorber panel coated with selected coating transfers the heat to the riser pipes underneath the absorber panel.
The water passing through the riser gets heated up and is delivered the storage tank. The re-circulation of the same water through absorber panel in the collector raises the temperature to 80 C (Maximum) in a good sunny day.
The total system with solar collector, storage tank and pipelines is called solar hot water system. Broadly, the solar water heating systems are of two categories. They are: closed loop system and open loop system.
In the first one, heat exchangers are installed to protect the system from hard water obtained from borewells or from freezing temperatures in the cold regions.
In the other type, either thermosyphon or forced circulation system, the water in the system is open to the atmosphere at one point or other. The thermosyphon systems are simple and relatively inexpensive. They are suitable for domestic and small institutional systems, provided the water is treated and potable in quality. The forced circulation systems employ electrical pumps to circulate the water through collectors and storage tanks.
The choice of system depends on heat requirement, weather conditions, heat
transfer fluid quality, space availability, annual solar radiation, etc. The SHW systems are economical, pollution free and easy for operation in warm countries like ours.
Based on the collector system, solar water heaters can be of two types.
1) Flate Plate Collector (FPC) type Solar Water Heating Systems: -
In FPC, the fins are made of copper tubes with selective Nickel Chrome plating to which the copper tubes are ultrasonically welded. These fins are covered with toughened glass in an insulated box with Aluminium frame. In this type of system the water temperature goes upto 60 to 65 C.
2) Evacuated Tube Collector (ETC) type Solar Water Heating Systems: -
Evacuated tubes are the absorber of the solar water heater. They absorb solar energy converting it into heat for use in water heating. Each evacuated tube consists of two glass tubes made from borosilicate glass. The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating (Al-N/Al), which features excellent solar radiation absorption and minimal reflection properties. In this type of system the water temperature goes upto 85 C.
Normally, for storing water overnight or on cloudy days, a storage tank is needed. A very simple way of doing this, making use of gravity i.e. the thermosyphon system. The principle of the thermosyphon system is that cold water has a higher specific density than warm water, and so being heavier will sink down. Therefore, the collector is always mounted below the water storage tank, so that cold water from the tank reaches the collector via a descending water pipe. If the collector heats up the water, the water rises again and reaches the tank through an ascending water pipe at the upper end of the collector.
Thermosyphon systems operate very economically as domestic water heating systems, and the principle is simple.
In contrast to thermosyphon systems, an electrical pump can be used to move water through the system by forced circulation. Collector and storage tank can then be installed independently, and no height difference between tank and collector is necessary. This type of system is basically used for commercial & industrial applications.
Fuel Savings -
A 100 litres capacity SWH can replace an electric geyser for residential use and saves 1500 units of electricity annually.
Avoided uitility cost on generation -
The use of 1000 SWHs of 100 litres capacity each can contribute to a peak load shaving of 1 MW.
Environmental benefits -
A SWH of 100 litres capacity can prevent emission of 1.5 tonnes of carbon dioxide per year.
Central Financial Assistance -
No capital subsidy is available for Solar Water Heating System as per MNRE, GoI letter no.30/31/2012-13/NSM dated on 19th September 2014.
Status / Achievement of our Program -
MEDA has received two consecutive awards for maximum installation in the State for the year 2011-12 & 2012-13.