Solar Water Heaters

Working principle: When sun rays strike the collector glass cover, three things happen. A small portion of the energy is observed by the cover itself, sun is reflected and the remaining portion is transmitted through glazing to reach the absorber and transformed into heat which is conducted to the water flowing in riser tubes attached to the absorber plate. The water circulates to the storage tank and continues to recirculation to the evening.  The circulation takes place either through the natural process (thermo-siphon) /forced of conversion (hot water rises the top and cold water flows into replace it from the bottom). The tank is well insulated to prevent loss of heat by radiation to the atmosphere temperature of the water rises from 25 degrees centrigrade to 70 degrees centigrade in a day.

Solar Water Heaters are Basically Two Types

Based on Flow of Water

Thermo-siphon system: This is a method of passive heat exchange based on natural convection which circulates liquid without the necessity of a mechanical pump. This circulation can either be open-loop, as when liquid in a holding tank is passed in one direction via a heated transfer tube mounted at the bottom of the tank to a distribution point – even one mounted above the originating tank – or it can be a vertical closed-loop circuit with return to the original vessel. Its intended purpose is to simplify the pumping of liquid and/or heat transfer, by avoiding the cost and complexity of a conventional liquid pump. This system is simple, relatively inexpensive and require little maintenance due to absence of moving parts. Flat plate Thermo-siphon systems are however not suitable in freezing climates because water remains in the collectors always and may freeze on very cold days resulting in the bursting of the pipes. These types of systems are suitable for domestic applications with relatively small requirements.

Force flow system: This system is for commercial use and utilized a pump to circulate water with the help of mechanical. Pump.

Based on Type of Solar Collectors

Flat Plate Collector system (FPC): In this system the solar radiation is absorbed by the flat plate which consists of an insulated outlet metallic box covered on the top with a glass sheet.  Inside there are blackened metallic absorber (selectively coated) sheets with built in channels or riser tubes to carry water.  The absorber absorbes solar radiation and transfers the heat to the flowing water.

Technical Specifications

Overall dimensions 2132 x 1045 x 95mm
Effective absorbed area 2 +/0.1 M SQ.
Glazing material  and thickness 85% and 4 mm thick
Absorbed material and thickness Copper: 0.214 thickness
Absorber coating Block chrome and selective
Absorber absorptive and emissivity >0.96
Expected efficiency 65%
Riser material and size Copper tube 12.50mm; OD 0.56T
Header material and size Copper tube 25.40 mm; OD 0.71T
Method of bonding with absorber Cu-cu eutectic alloy brazing
Ceiling of collector panel Neoprene/EPDM rubber gasket with sealant
Bottom insulation material and thickness Pre laminated resin bonded rock wool – 48 Kg/M Cu density – thickness 50mm bottom, 25 mm sides
Collector stand materials MS angles with epoxy painting as per IS 226 size, 40 x 40 x 6 mm.  Vent valves, Gun metal chrome plated suitable, end connections for connecting two collectors brass flange 65 OD 3mm thickness (according to system capacity), ½ inch  expansion bolts will be anchored for collectors. 
Collector housing Extruded aluminium section 1.6mm thickness of suitable shape on sides and 0.7mm thickness Al. sheet at the back shall be used for the collector box.  The box should be mount on a MS stand. Contact between different metals shall be insulated by neoprene rubber packing washers.

Evacuated Glass Tube Collector (ETC)

In this system solar collector is made of double layer borosilicate glass tubes evacuated for providing insulation. The outlet 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.

Technical Specifications

Output water temperature 65 t0 70 degrees
Length of tube 1500 mm, 1800 mm
Tube outer diameter 47 mm, 57 mm
Inner tube diameter 37 mm, 47 mm with selective absorption coatng

Number of tubes

Sl.No. Capacity in LPD 1500mm, 37mm & outer 47mm dia 1800mm, 47mm & outer 57mm dia
1 100 15 -
2 150 22 -
3 200 30 -
4 500 60 -
5 500 70 -
Storage tank volume 100 litres tank
Storage tank material SS 304 – Stainless steel inner
Support structure Black power coated – mild steel
Electric backup 2 Kw
Insulation Poly Urethane foam
Reflector material Al