Why should I go for a Solar Water Heater? What do I save from it?

A 100 litre per day capacity system suitable for 3-4 people can save upto
1500 units of electricity in a year, depending on hot water used. It can
also save around 140 litres of diesel
in an establishment using oil fired
boiler besides reducing green house gas emissions in the atmosphere.
Higher capacity systems will save higher amount of electricity/fuel oil
besides reducing higher amount of GHG emissions.
Electricity is expensive
and is not available due to power cuts in many
areas when required for heating water. Solar Water Heater, since it stores
hot water in an insulated tank, provides water all the time when required.
Fuel oil is also ex
pensive and creates pollution.
Storing
the fuel oil for long
term use in commercial establishments is another problem.
The table below gives approximate likely electricity and money savings for
a
typical 100 liters per day
system
located in different
parts of the country.
Northern
Region
Eastern
Region
Southern
Region*
Western
Region*
Expected no. of days of use
of hot water
per year
20
0 days
200 days
300
days
250
days
Expected yearly electricity
saving
on full use of solar hot
water (units of electricity)
1000
1000
15
00
1250
Monetary savings at different prices of electricity, Rs/year
Rs. 4/kwh
4000
4000
6000
5000
Rs. 5/kwh
5000
5000
7500
6250
Rs. 6/kwh
6000
6000
9000
7500
* The use pattern and savings for southern region pertains to the typical
climate of Bangalore, while those for western region relate typically to
Pune climate.

What is Solar Water Heater?

Solar water heaters use the solar energy from the sun to generate heat (not electricity) which can then be used to heat water for showering, space heating, industrial processes or even solar cooling.
Solar energy is the primary energy source for our planet as it is responsible for providing energy for plant growth (photosythesis) and providing the warmth that makes our planet habitable.
While solar water heater devices have been around for over 100 years, the last 20 years have seen significant advances in absorber coating technologies, resulting in solar collectors that can reliably convert >50% of available sunlight for domestic hot water supply.  A solar water heater is one of the most effective ways of cutting a household's carbon footprint by reducing reliance on dirty fossil fuel usage. By offsetting the use of electricity, gas or heating oil, using solar water heaters can also provide financial savings by reducing energy costs.

Solar water heaters based on Evacuated Tube Collectors (ETC based SWH):

Here the 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.




                              Evacuated Tube Collector based Solar Water Heater


Solar water heating is now a mature technology. 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 & institutional establishments. Internationally the market for solar water heaters has expanded significantly during the last decade.  It is estimated that over 107 million sq.m. of collector area has so far been installed world wide for heating water.  In the country, the collector area so far installed for water heating is over 1.00 million sq.m. MNRE has plans to add another 1.00 million sq. m. in next two years.

General Specifications of Solar Water Heating System based on Evacuated Tube Collectors (ETC based SWH):

The Broad Specification of the Solar Water Heating Systems using ETC.

Number of Tubes in the ETC
For tubes with OD: 47 mm, ID: 34 mm and Length: 1500 mm	Minimum 7 numbers for each 50 LPD capacity of system.
For tubes with OD: 58 mm, ID: 47 mm and Length: 1800 mm.	Minimum 5 numbers for each 50 LPD capacity of system
Type of Coating (Selective Absorptive coating.	ALN-SS-Cu (Three Layer)
Tube bottom cap material / Thickness	H.D.PP. / 3 mm
Tube Seal	Silicon Rubber
Storage Tank (Inner tank, directly coupled with the tubes)
Fabricated using Argon arc or metal inert gas (MIG) welding Thickness when fabricated in SS 304 or 316 using Argon arc or metal inert gas (MIG) welding Thickness when fabricated using other type of welding Thickness when fabricated in GI (Internal coating: Epoxy paint stable up to 150ºC)	0.5 mm, minimum up to 300 LPD. 1.2 mm, minimum above 500 LPD. 0.8 mm, minimum up to 300 LPD. 1.5 mm, minimum above 500 LPD. 2.5 mm, minimum up to 500 LPD. 4.0 mm, minimum above 500 LPD.
Storage Tank (Outer cladding)
- Material - Thickness	Al/SS/FRP/GI coated sheets Suitable for handling the load
Storage Tank Insulation
- Material - Characteristic	PUF 55 mm thick / Rock wool 100 mm thick Night temperature drop should not be more than 5-6°C.
Stand / Frames	Should be either of non-corroding materials (viz. SS, Aluminum) or have corrosion resistant protective coating

Measurements of collector area:

Flat Plate Collector: Gross area of solar collector is defined as the total area on which solar radiation is falling (taking into account the gap, if any, between the tubes, and also the frame etc.). It shall be calculated by multiplying width and length of the collector measured from outer edge to the outer edge.
Evacuated Tube Collector: For the solar water heating models using all-glass ETCs, length should be measured from bottom side of the storage tank to the outer edge of bottom tube holder while width should be taken as equal to the length of the bottom tube holder. The measurement accuracy of the gross area should be ± 0.1 %. The volume of the storage tank should be measured to an accuracy of ± 1%.

Solar water heaters based on Flat plate Collectors (FPC based SWH):

Here 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.

                                                                                                                           
              Flat Plate Solar Collectors is the earlier technology used in Solar Water Heating Systems; however they are still today the most efficient & reliable for Solar Water Heating Systems. Under soft water conditions they have a life of 20 years & more.. Our ATASH Flat Plate Collectors have been carrying the prestigious ISI Mark, since the last 12 years & our manufacturing for the same has been since the last 21 years.

General Specifications of Solar Water Heating System based on Flat plate Collectors (FPC based SWH):

Detailed specifications of various components of Solar Water Heating System are given below:

1. FLAT PLATE COLLECTOR

   As per BIS specifications and ISI certificate with area of 2 M² with selectively coated Cu-Cu absorber. Minimum one number flat plat collector with 2 M² areas for each 125 LPD capacity of system.

   1. ABSORBER

      1. Material : Copper sheet and Copper Tube
      2. Thickness of the sheet : 38 SWG (0.15MM)
      3. Risers: Diameter  : 12.7 mm O.D.(+ 0.5 mm) Thickness    : 24 SWG (0.56 mm) (as per IS 2502)
         Nos.  : 8 or 9 nos.
         
      4. Header:Diameter                     : 25.4 mm O.D. (0.71mm + 0.5mm) Thickness                    : 22 SWG (0.8 mm)
         Projection outside       : 40 mm (+0.5mm) including the collector box and the flanges
         
      5. Space between Riser Tubes: Maximum 12 cms from center to center of the risers. The free edges at the sides not to exceed 6 cm from the center of the extreme and riser tube. For independent fin or joints in the sheet an overlap of minimum 2 mm.
      6. Bonding between Riser & Sheet: Welding may be of continuous nature inter-arc-spot welding type with the product of number of spots per fin & area of spots exceeding the product length of the fin & twice the thickness of the fin for each fin (continuous welding). The brazing & soldering with minimum 40% tin solder or suitable brazing material. Brazing of soldering continuous with 10% of the total length of each fin & any continuous non-soldering area not exceeding 25mm at any stretch (Brazing/Soldering).
         
      7. Effective area of Absorber : 2 M² (± 0.1 M²) including the projected area of header
      8. Header-Riser joints: The assembly of risers with the header should ensure not more than 5mm tube protrusion inside the header. The riser should be brazed with suitable brazing alloys with or without the use of flux. Any flux used in soldering/brazing shall be mechanically remove & neutralized with the solution of sodium carbonate to avoid corrosion problems in future.
      9. Absorber Coating.

         i. Absorbivity	92 %
         ii. Emissivity	2.5%
         iii. Coating Stability	up to 300 ºC

         Deterioration in these values should not be greater than 5% in a year.
         The absorber panel should be degreased & suitable primer with proper adhesion & compatibility with base material should be used prior to the application of points.
         
      10. LEAKAGE TESTING OF RISER – HEADER ASSEMBLY: It should be treated for leakage & strength at a minimum hydraulic/pneumatic pressure of 5 kg/cm².
          

   2. FLAT PLATE COLLECTOR BOX:

      1. Overall dimensions of the box :
         1. Length       : 186 cm (±1 cm) /212 cm (±1 cm)
         2. Breadth     : 124 cm (±1 cm) / 104 cm (±1 cm)
         3. Height       : 10 cm (±1 cm)

      2. Collector box materials: Aluminum

         • 22 SWG Aluminum sheet for the bottom
         • Aluminum extruded sections of size of 100mm x 25 mm channel sections with thickness 1.6 mm for the sides.
         • 16 SWG Aluminum angle (dim.25mm x 25mm) for retaining collector glazing.

      3. Fabrication of the Box:

         Side channels should be welded by inert-arc gas welding or gas brazing to ensure leak proof continuity of the joints of the box.
         

      4. Attachment of Bottom Sheet:

         By riveting spot welding or with S.S. Screws & caulking of the joints with sealing paste of zinc oxide based or rubber based or silicon rubber based or epoxy based sealing compounds.  Caulking may be done on the inside joints or inside as well as outside joints to ensure leak proof joints.
         

   3. Collector Support Frame:

      1. The structure should be in a position to withstand a wind velocity of 100 Kms. / hr. A typical way do this is that it should be made with angle iron stronger than 35 mm x 35mm x 3mm and should have vertical support at top & bottom edge of the inclined plane of the collector at a distance of 2.5m or less.  The vertical support should be firmly grouted to the roof in the ground in case of ground mounted system.  The grouting blocks should be of minimum equal to 25 cm x 25 cm x 15 cm and finished properly.  In case the grouting is carried out on a roof already water proofed with asphalt the back support of the collectors may be angled to the parapet or the size of the grouting block should be increased to provide for a dead weight anchoring of 75 kg per leg of the vertical support.
      2. Painting of the Support Frame: Proper cleaning & degreasing of the surface should be done before painting. Two coats of zinc chromate, red oxide primer should be applied followed by one coat of enamel paint of suitable colour.
         

2. HOT WATER STORAGE TANK (Material of construction):

   
   

   Sr. No.	SWHS capacity in LPD	Cu (thickness in mm)	S.S. (thickness in mm)	MS coated with anti-corrosive treatment and epoxy paint stable up to 150ºC (thickness in mm)
   01	250 to 300	0.9 to 1.0 mm.	1.0 to 1.2 mm.	4.0 mm
   02	500 to 1000	1.2 mm	1.5 to 1.6	4.0 mm
   03	Above 1000	-	-	4.00 mm

   Jacketed Tank for Hot Water Storage (Material of construction):

   
   

   Sr. No.	SWHS capacity in LPD	Cu (thickness in mm)		S.S. (thickness in mm)		MS coated with anti-corrosive treatment and epoxy paint stable up to 150ºC (thickness in mm)
   		Tank	Jacketing	Tank	Jacketing	Tank	Jacketing
   01	250 to 300	0.9 to 1.0	0.6	1.0 to 1.2	0.8	4.0	2.0
   02	500 to 1000	1.2	0.6	1.5 to 1.6	0.8	4.0	2.0
   03	Above 1000	-	-	-	-	4.0	2.0

   1. Insulation of Tank:

      Specification of the insulation to withstand 100 ºC should be as given below:
      
      

      Sr. No.	SWHS capacity in LPD	PUF Insulation	Glass wool / Rock wool
      01	250 to 500	55 mm	100 mm
      02	500 & above	-	100 mm

   2. Cladding of Hot Water Storage Tank:

      Aluminum sheet of 24 SWG should be used as a cladding material for system capacity 250 LPD to 2500 LPD system.  For 3000 LPD to 3500 LPD system 28 SWG GI sheet with Powder Coating should be used. Chicken mesh should be used for securing the glass wool insulation to the tank outer surface.
      Safety valve at the hot water storage tank should be provided for system above 500 LPD.