JIMMIE wrote:

From the info I have gathered the life expectancy of a solar water
heate is comparable to a run of the mill non solar water heater. I
would think they should last just about forever. What goes out on
them?

Solar heaters are supposed to last longer than regular electric ones
because the heating element doesn't run as much and create really high
temperature spots that make the water boil and precipitate out the
minerals. But I think the main problem is still corrosion that
becomes really bad once the anode rod disappears, so replace it about
every six years. Some heaters have two anode rods.

If you don't like the $900 price of solar water tanks (probably why so
many old solar heating systems have been abandoned -- and why I've
been able to get solar collectors for free), you can use an ordinary
tank, almost unmodified in a 2-tank system (just disconnect the wires
to the heating elements and cover their ends with wire nuts). But
with a 1-tank system you have to disconnect the wires from the lower
heating element, use the drain opening as both the cold water inlet
and the output to the water pump (add a T for the drain valve), and
shorten the dip tube so it extends just 6" below the upper heating
element and use it as the return line from the solar collectors. IOW
cold water at the bottom, hot water out the top, and warm water in the
middle of the tank.