Solar Hot Water

There is no other renewable energy technology that is more appropriate than solar (lo-temp) thermal, commonly called solar hot water (SHW) systems. Residential households use about 2000KWH a year or $350/year in a typical utility bill. This energy bill can easily be eliminated with a solar hot water heater.  Unless the location receives no sunlight for substantial periods of time, it's feasible everywhere.  One of the BIG advantages of solar hot water is that only partial sunlight is required to make hot water, and one of the typical issues with SHW is that you get TOO much hot water - a very nice problem to have! 

SHW systems are typically between 60-80% efficient in converting solar radiation (insolation) to useful (BTU) heat.  The highest efficiency in large commercial power plants is 34% from a solar hi-temp thermal Stirling engine type.


Wikipedia has an EXCELLENT summary of solar hot water systems for residential usage.

 There are two major types of solar HW systems:  Direct or Indirect.  Passive or Active.  So you can have an indirect active system (most common) or a direct passive system such as a thermosiphon.

I recommend Direct semi-active systems = Drainback with a PV powered variable DC pump.  Here's a simple illustration:

 

In a drainback system, the water drains out of the collector when there's no hot water - thereby preventing freezing.

I can highly recommend this book by Tom Lane.  You can obtain it from the Builders Booksource here.