Roof Ridge Solar Heater

I like that this is so no-big-deal designwise.

From Treehugger:
Sometimes the most impressive products at Greenbuild are the most innocuous and boring looking things; last year I thought the best of show was Agriboard, a SIP made from straw. This year I spent some time trying to figure out this ridge vent for a standard shingled roof with tubes running through it, thinking that there wasn't much surface area on it and it isn't going to do much. Then I realized that all of the heat in an attic runs through the ridge vent and this thing turns your entire roof into a solar collector.

As much as 25% of the energy consumed in a house goes to making hot water, and as we have shown before, it costs a tenth as much to generate a watt of power from the sun to heat water as it does to make electricity, so it makes a lot of sense to do this first. The Greenward solar ridge vent may tilt the economics even more, since you already own about 90% of the system- the roof of the house.

As the sun beats down on those dark grey shingles, the heat rises and flows out through the ridge vent around PEX plastic tubes, heating an ethylene glycol and water mixture that is pumped down to a heat exchanger, preheating the water before it gets to the water heater. The existing hot water heater only fires up when needed.