Solar water heater tank failure

A few days ago I was showing someone my solar domestic water heating system and when I opened the utility closet I was confronted with a quarter inch of standing water.  Clearly my solar heated water tank had sprung a leak.

The tank is a Whirlpool 40 gallon electric water heater that had a warranty of six years and by replacing the anode rod I extended that out to nine years or so.  My system is designed so that I can change the position of three gate valves to isolate the solar tank and continue to use hot water from our tankless water heater.  I did a web search to try and find a direct replacement for this tank because of its unique properties of having additional ports on the side and eventually found one in a Lowe's store about 40 miles away.  Fortunately it barely fit in the back of my Chevy Volt and I was able to spend the following day removing the old tank and replacing it.

I am an experienced plumber and engineered this system myself (I have a background in photo processing engineering from the 1970s) so it was relatively easy - yet time-consuming - to swap out the tanks.

I was quite disappointed that the water leak alarm that I had installed at the bottom of the tank (at bottom right in the top photo) did not alert me to this issue.  Perhaps it had run its battery down while I had been out of the house for a day.  Or perhaps I could not hear it in the rest of the house considering that the water heater is in a utility closet in a corner of the basement.  As part of the replacement and upgrade I have installed a deep drip pan under the tank and will find a better/louder leak alarm.  Lessons learned!

The old tank will find its way to the landfill eventually next time I do a major dump run with the help of a neighbor's pickup truck.  It bothers me that water heater tanks have a planned obsolescence of 6 to 10 years, but at least they don't contain any toxic materials!