In planning my off grid existence, I quickly realized that water heating was going to be a large challenge. The house came with two 50gal electric water heaters. One seemed to be solely dedicated to the kitchen sink and dishwasher with the other doing everything else.
Running one was bad enough energy-wise, but two was unacceptable.
Redesigning and re-piping followed with the kitchen waterheater removed and the whole house worked off one unit. I did add a hot water return line and a small circ pump so the kitchen had hot water quick.
For off grid water heating the initial plan was a 24v bank of four 200ah batteries running my oldest powerjack, my 24v/8kw. These batteries are separate from my main bank for powering the house. I put in a manual transfer switch so I could select inverter or grid to power the water heater.
I guess I didn't really grasp how much power an electric water heater draws. Switched to inverter and when the water heater tried to run the pj went immediately into overload and shut down. 4500w elements were just too much for an 8000w pj. Plan B was to hook up just 110v instead of 220v from the inverter. Now it ran but of course only heated half as fast with about 2500w measured by the powerjack meter. Also I only had half the solar hooked to it so far that I had planned, so after 2 days use I had to switch the waterheater back to grid to let the batteries come back up. So solar water heating 2 days of each 3. It was a start.
Next, I moved that extra water heater next to the main one and piped it in as a preheat tank for the main tank. Planned to heat this wh with dump load controller from the main battery bank. I installed 2 double 1000w 48v elements into the preheat tank. Got one of these;
Wired it up to power one 1kw upper element and one 1kw element lower. Planned to get a second controller and hook to the other two elements after trying this one out. It seemed to work fine. The tank heated up nicely, using excess solar the batteries didn't need. Then ran the circ pump to heat the whole loop up and keep the main tank hot enough to not turn on its elements. Eventually, the circ pump will be on a timer and temp switch control.
That all worked well enough for about a month. Then that solenoid relay cooked. I bought it because it was 48v and rated for 440 amps. Figured that was exagerrated but should still be enough to handle the 30-45 amp load I needed handled. Only about 10% of rated. So much for optimism.
While messing with the solenoid while it was failing, I realized the 48v elements were frying too. What the heck? The upper element had opened and was doing nothing, and the lower was cooking. One connection started glowing red hot! More junk overrated parts apparently.
Back to the drawing board.
Time to rethink this whole deal.
After much thought, I decided to put two 2000w 120v elements in place of the 48v elements. Ordered a dc controlled ac relay. I now plan to control the new relay with the same style voltage controller as was used with the bad solenoid. The relay will switch regular ac 120v from my main powerjack as an ac dump load into the water heater elements. Switching ac is much easier on contacts than switching dc.
As of today, I'm still waiting on delivery of the new relay.
Hopefully, this will solve the water heating issues but now I need to think about a real dump load. I want protection for my batteries that I can depend on. Eventually, I will have 3 times the solar that I'm using now. Dump load becomes a must! The water heater setup described above should usually use up the excess solar, but if the inverter isn't working for some reason or the tank is up to temp, ac dump load doesn't dump. So in addition to ac dump, will add a dc dump set a trifle higher voltage using this guy;
Its a dc contactor rated 500 amps! This one looks like its actually got a chance of meeting its specs. 60vdc contact rating and a 60vdc coil. I won't be doing anywhere near that of course. I like to use a space heater for my dump load. The heater that looks like an old style steam radiator except on wheels. I pick them up at flea markets and garage sales for $5. They are oll filled and don't have a fan. You need to bypass the thermostat because it can't handle the dc. I just remove the slide connectors from the thermostat and use a large size 30a fuse. The tabs on the fuse match the slide connectors. Connect the slide connectors to the fuse instead of the thermostat. This also gives some short ckt protection. The heater's switches let me use one or both elements. The switches don't much like the dc either, but work ok.(probably shortened lifetime) With one element engaged I see about 5 amps at 55vdc. Different brands of heater are slightly different.
So for cold weather I'll have a heater or two in the basement or back room. In summer I'll probably put some regular dump resistors outside on the chimney out of hands reach.
Back to water heating; (What! Me ramble?)
The 120v 2000w elements are installed and wired and ready. The controller is installed and ready. Just waiting for the ac relay to arrive. Supposed to hit 100 deg F today so hot water without the preheat tank won't be a problem.
That's where it stands. I'll report progress when I have some
