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Solar Water Heater (Developed by DPG Sansthan)

Making of cheap solar water heater

I’ve seen a few different designs for solar water heaters and I wanted to share my own. It is quite an efficient design since every square inch of collector surface is in direct thermal contact with the water being heated. You can easily modify the design to any size you like. I made mine 8ft long by 22″ wide so that it can fit between the rafters in my attic. Tests showed that system output averaged about 530 Watts, heating 20 litres of water from 24 degrees C (75 degrees F) to 47 degrees C (117 degrees F) in one hour.

Warning – Don’t drink the water
It is not my intent for this design to be used for heating drinking water. The plastics and glues used will leach into the water so it’s a bad idea to drink any water that has been inside the panel. If you want to use this design for heating drinking water you should make a heat exchanger. Run the water from the collector through a coil of copper pipe placed in a tank suitable for drinking water. This collector design is also not meant to withstand city water pressure, but if you use a heat exchanger and an appropriate tank (such as a commercial hot water tank) you can use a collector like this to heat drinking water at city water pressure.

The collector is made from Corrugated plastic sheet ( which is used for signs and packing) . It has multiple square channels running lengthwise from end to end. When I first saw this type of sheet I immediately thought, “Wow, this would make an excellent flat panel solar collector if only there was a way to pipe water through all those little channels.” Several weeks later, a method of doing so occurred to me. If a slot of the right width is cut lengthwise in some ABS pipe (so the cross section looks like a “C”) then this pipe can be fit over the end of the corrugated plastic. The seams can be sealed to make everything water tight. The sheet can be painted black and voila… you have a flat panel solar collector.Because the whole collector is made of plastic, it is important that the temperature doesn’t get too high or it will soften and possibly spring a leak. 80 degrees C is about the limit. In practice the maximum temperature is difficult to guarantee. Water may stop circulating, or may drain out completely for a number of reasons and the panel will overheat. Therefore this may not be a practical design for residential installation but it is an inexpensive, easily built experimental system that produces as much or more hot water than commercially available systems. Mine cost about Rs 15000/- in materials (about Rs 62.5 per square foot) and about 6 hours of construction time. 

Tools and Materials

  • Table Saw
  • Hand Saw
  • Drill press
  • Power drill
  • 3/4″ drill bit
  • 1″ hole saw
  • Exacto knife
  • Tape measure
  • Screw driver
  • Digital thermometer
  • Caulking gun for adhesive
  • Coarse round file

Materials for collector

  • 1 – sheet of Corrogated plastic sheet (4′x8′x4mm) cut to 22″x90″ – Rs 1500
  • 1 – 4′ of 1 1/4″ ABS tubing – Rs 65/- (Note: Do not use PVC as it softens at too low a temperature causing leaks.)
  • 4 – 1 1/4″ ABS caps – Rs 1000/-
  • 2 – threaded 1/2″ hose nipples – Rs 90.00
  • 1 – cartridge of silicone adhesive/sealant suitable for plastic – Rs 640/-
  • 1 – can of flat black spray paint – Rs 800.00

Materials for frame

  • 1 – 1/2″ sheet of plywood (4′x8′) cut to 24″x8′ – Rs 800.00/-
  • 1 – 3/4″ sheet of polystyrene (2′x8′) cut to 22″x87.5″ – Rs 750/-
  • 2 – 2×3 x 8′ – Rs 900.00 used
  • 1 – at least 4′x10′ of transparent plastic sheet – scrap
  • misc screws and staples

Materials for tank / water circulation

  • 1 – cooler (or other water tank, preferably insulated) – $40 but I already had one scrap
  • 1 – 15ft of 5/8″ garden hose – Rs 550/-
  • 2 – 1/2″ hose clamps – Rs 180/-
  • Total cost of materials = Rs 8000/-