The most efficient solar technology is a solar collection system. 

Heating of water via the sun is very simple and hot water heating is one of the most expensive things that a typical home does, only HVAC is more expensive.  You can build a solar collector using old sliding glass doors and used water heaters, plywood and black paint.  It is one of the only solar systems that is just about guaranteed to pay for itself.  If you build it yourself using collected materials (it can be built for almost nothing if not nothing) it pays for itself in short order.

Want simplier you can run a cold water pipe into your attic and snake it back and forth attaching it to the rafters.  Attics get very hot in the summer thus the water in the pipe is heated before entering the hot water heater.  Caution they can freeze in winter. 

Solar Water Heaters are very efficient and are nearly 80% subsidized by the US Government.

Hot Water heating is the most expensive, nothing is more NOT even hvac

Most people dont use AC all year but, they do heat water.

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