Introduction: Cheap and Easy Passive Solar Water Heater for Your Home. ($300)

Heat your water for free with a solar water heater.  This $300 DIY solar water heater system even includes an electric backup water heater for cloudy days.  It heats water to 135F (55C) on sunny days in a 80 gallon (310 liter) tank - and there are no moving parts - it relies in a thermosyphon to circulate the water.
This heater uses PVC instead of copper.  PVC has a much lower thermal conductivity than PVC does, however there are a few ways to over come this weakness.  

One way to I increased the efficiency was to use old florescent light bulbs as sleeves over the PVC pipe to act as a double glazing.  This helps insulate the PVC and increases the efficiency of the heater.  I also insulated the PVC connections to help shield them from the intense heat of sunlight. 

The other way I increased efficient was increasing the surface area.  Since PVC is cheap it did not cost much to run more pipes that would be exposed to the sun.

 I also installed an automatic electric backup heater for $30.  It is a bucket heater that turns on at 80 degrees and off at 110.  Click on the link above to see more about that.