Build a simple solar water heater

 Reposted from I Will Try.org - great name!
http://www.iwilltry.org/b/projects/build-a-simple-solar-water-heater/

Introduction

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.

Aside: I’m in the middle of re-roofing my house and plan to build in a transparent section of roof in one area. Then I can experiment with different solar collector designs like this one and install and remove them easily from inside my attic instead of having to go out on my roof. It will make the plumbing easier too. The drawback is that if a collector springs a leak, it will leak into my home instead of into my gutter. See Build a solar attic for details.

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.

Concept

The collector is made from Coroplast (see http://www.coroplast.com) which is a corrugated plastic sheet, commonly used for making signs. 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 (176 degrees F) is about the limit. Don’t think it can get that hot? Think again. 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 $60 in materials (about $4.00 per square foot) and about 6 hours of construction time.

...more (with excellent photos and instructions:

http://www.iwilltry.org/b/projects/build-a-simple-solar-water-heater/