Dump load domestic water heater

What in the world am I talking about?  With the new solar panels, 4kw total instead of 1 kW, I have so much surplus power on sunny days that it dissipates if it isn't needed.  (Moments like this make me wish I were tied to the grid!).  So I decided to add a dump load water heater that could heat my domestic hot water, especially during the summer.


A little background:  during the cold months, an outdoor wood boiler heats the water that runs through the floors.  This also heats the domestic hot water by running through a heat exchanger attached to the LP water heater, which heats the domestic water when the outdoor boiler isn't heating water, like in the summer.  Since I have excess solar power, especially during the longer days of summer, diverting this to an electric water heater will cut down on my LP use during summer and hopefully spring and fall.  

Tri-Star Solar Controller

First I bought a 50 gallon electric water heater, and then I needed to buy a DC heating element to switch out on the electric water heater. The electric water heater has two elements, but this system will only be using one.  It is wired directly - bypassing the temperature sensing part of the water heater, so that it is always on when the controller is dumping power to it.   To divert the power, a Tri-Star 45 solar controller was added which is the diversion regulator.

The power system.

We created a bypass loop that cut out the portion of the loop that went outside to the boiler, so

Looped Water Heaters

just heating a small loop that encompasses both water heaters.  We needed to add its own circulating pump to circulate the water from the dump load water heater through the heat exchanger already installed on the domestic LP water heater, and installed shut off valves to the rest of the system.

We tried it on a sunny day in the spring. The first hurdle we had to overcome was the tank built up too much pressure, so either we had to put in an expansion tank, or open a valve and release that pressure into the rest of the heating loop (the tubing that goes out to the wood boiler).  After much trial and error, it all works!

This system heated the domestic hot water during most of the late spring, summer and early fall.  As with all off-grid living, there were some changes in lifestyles.  For instance, there is some hot water remaining in the morning hours, but it usually takes about three to four hours of energy to heat the water to 120° F.  This means showering in the later afternoon, early evening, and doing dishes or laundry in the afternoon.  There were only a few times that we did use the LP water heater, because we needed hot water right away. I'm anxious to see the LP bill next year!

The next thing- could it heat the house in late fall and early spring?  Are the days long enough?  Are there enough sunny days?