diy solar

diy solar

Direct to water heating.

"Dry contact" may be the simple way to do it.
I think Outback and/or Midnight has that, programmable for something like voltage or SoC.

Considering the curves of lithium, if Growatt can switch a relay on and off part way up the voltage curve, it could cycle up and down a few percent near fully charged, diverting power to the heater without curtailing PV production.

Analog control could be most ideal. If the waveform didn't cause issues, a dimmer (uses SCR to cut in part way through sine wave) with servo circuit could hover at some battery voltage without charge/discharge cycling.

(AC not DC circuits feeding water heater, of course. Unless you buy the heating elements with DC thermostat built in. Would still need DC relays for timing or dump load functions in that case.)
There appears to be some voltage settings to control the dry contact switch, so if I can figure out how to utilize it I will use it to turn the water heater on via a relay. Probably once the charger hits float mode. And then off if voltage drops below whatever voltage I set. All of which I still need to determine. I would also like to avoid rapid on/off relay switching if possible.
If I can't figure out how to do that then my fall back is the timer.
 
Relay contacts, and therefore thermostat contacts, rated 120VAC might only handle 30VDC. Check the manufacturers DC spec.
Arcing while contacts opening is the issue. VAC goes through zero volts breaking the arc. Arcing can weld the contacts together. That's why there is a RED button high temp cutoff thermostat. Usually 1 per tank for both controllers. Splitting them to 2 circuits leaves 1 without the protection.
I'm not going to use DC. It's going to be 240v into lower wattage heaters so no danger of thermostat contacts welding and causing steam bomb. My goal is to safely heat my water from my excess solar power through my inverters and by using lower watt elements I hope to achieve that over several hours without draining my batteries or over taxing my inverters.
 
Is there any off-the-shelf stuff you guys know about that one could set up a mess of solar panels and magic box 1 and maybe a magic box 2 and directly drive a 240V 4,800W standard water heater element?

Any ideas welcome.
I am working on that project now. My plan is to use extra capacity of my solar after battery recharge to be directed to a 120v ac water to precharge the water to my propane hot water heater. I have started to talk to a inverter/ charger supplier to try to use the “grid feature” as a way of seamlessly make the transition back and forth between battery and demand as system demand changes. Thoughts are as inlet water temp increase to the propane water heater it takes less propane to reach delivery temperature.
 
In order to do that there would have to be something preventing the heater from back flowing into the mains
I am assuming there is a non-return valve in some jurisdictions that prevents legionella enriched warm water from returning back into the mains.
There is a valve before our HWS and this may be it??2020-12-24_10-43-38.jpg
 
I just have backflow preventers on irrigation valves. Vacuum relief so water in sprinkler pipes doesn't get sucked into the water line.
Laundry machines and dish washers have an air gap so prevent siphoning dirty water (for dish washer, appears to protect dishwasher from drain line but doesn't protect water supply.) When the water company shuts off some pumps for maintenance, they say we might experience reduced pressure. I'm up a hill so people below me get water but all I hear is gurgling as air is sucked into the pipes, through the meter, into the water main.

Here's another example of steam power.
Captain America's shield?

Captain America's Shield badday-13-768w.jpg
 
Thrust the force captain luke.
Yes steam is very powerful, i am happy to see the lid is in the ceiling and not thru a window or body part......
I hope you are all oke and only material damage is done
High pressure cooker?
 
Many water districts have been sued when water drained out of tanks due to a main break and elements then burned out. It is common to see weeping of the over temp valve. Yhis is due to expansion of water with no place to go. Pressures can easily go to 500 pounds unless you have some leaking faucets. For solar applications with wide temp swings an expansion tank is absolutely necessary.

Almost any control system can heat water. Most don't divert all that can be used, most CC diverters are don't work that well. Unless you consider "better than nothing" an acceptable goal.
 
Here is the way I've been looking at:

The magic box is a small circuit that modifies the DC solar into rough AC suitable to be directly plugged into an existing electric water heater without needing to modify the water heater safety systems or temperature control.
Resistive heating don't care about sine-wave so that side is good. Only downside is really cheap square wave (modified sine) inverters are noisy from an electrical standpoint. Could mess up radio and TV reception for you and your close neighbors.
 
You can use a DC rated solid state relay to switch the high current DC to the water heater, then just wire the water heater thermostat in series with the control circuit for the relay, so all it switches is a low voltage control signal when the water gets up to temp.
One example, it uses a 3-32 volt dc control signal, and can handle up to 220 volts DC and 80 amps of current on the output: https://www.amazon.com/Hoymk-AMR-10-Actually-5-220v-AMR-40A/dp/B07TVH6GZ9
Better mount that guy on a honking big heat sink if you are going to try to pass 80A through it.
 
Resistive heating don't care about sine-wave so that side is good. Only downside is really cheap square wave (modified sine) inverters are noisy from an electrical standpoint. Could mess up radio and TV reception for you and your close neighbors.
In the video he called that an MPPT controller, but no inductors so can't be. Might be PWM.
He mentioned that PV panels directly feeding DC to water heater would burn up thermostat (true).
If the controller always chops the power at least 60 Hz or higher (square wave), then thermostat has as chance to interrupt it.
PWM ought to just connect and remain connected (DC) unless voltage exceeds a setpoint. If it simply reverses polarity 60 times a second and varies duty ratio (still PWM) that ought to work.

Thermostat could be wired for pilot duty to enable transistors in the controller, or a DC rated relay.
But I would want something beyond transistors (which can overheat and fail shorted) to turn off the heat.)
 
In the video he called that an MPPT controller, but no inductors so can't be. Might be PWM.
He mentioned that PV panels directly feeding DC to water heater would burn up thermostat (true).
If the controller always chops the power at least 60 Hz or higher (square wave), then thermostat has as chance to interrupt it.
PWM ought to just connect and remain connected (DC) unless voltage exceeds a setpoint. If it simply reverses polarity 60 times a second and varies duty ratio (still PWM) that ought to work.

Thermostat could be wired for pilot duty to enable transistors in the controller, or a DC rated relay.
But I would want something beyond transistors (which can overheat and fail shorted) to turn off the heat.)
I was thinking about a home brew circuit using an H-Bridge and a 555 timer circuit to convert Solar DC into Chopped DC (60Hz). Wire this to a DC heating element that is rated for a lower voltage than your panel voltage and configure the chopper control to provide the max power the heater element is rated for at max solar power. The chopped DC output would mean your tank thermostat contacts won't have any problems switching power to the water heater. Or you might prefer to have the thermostat control just disable the timer circuit instead. I think I would rather make the controller self contained and just let the thermostat interrupt power to the heater (simpler and less chance to screw it up).

This could be a really inexpensive solution. I would think 24V panels and 12V heater elements would make the most sense since this minimizes potential safety issues. Basically just a fixed PWM circuit that doesn't have to worry about overcharging a battery.
 
Probably constructed of the purest crapolium, but I wonder how well something like this would work in the application. $18...

 
Magick box 1 would be to series connect panels to make 240v to heat the element direct from panels. I would use a breaker and a fuse or 2 somewhere along the line.

I do not know if a heating element with a thermostat would work as I am not sure what the thermostat control will do with DC
the thermostats don't work well for very long , using DC you blow the contacts, unless the thermostat is solid state which only works on AC. You didn't mention how long a recovery rate you were looking for, but there are people out there that use the power direct from the solar but you run the risk of over temping the tank.
 
You can use DC if the control board has an off interrupt cycle at least every 10ms. They will extinguish the arc as it normally does with AC line voltage. There is no need to totally eliminate the arc, just keep it from continuing.

From what little has been learned by most, an inductor is always need. This is wrong. Dumping power by pulses into a resistor is highly efficient for heating using a capacitor for storage during off times. if the voltage swing is only a few percent. A deep discharge is very inefficient.

Using a DC speed control is part of the circuit. It still needs a much larger capacitor on the panel side and some way to control the duty cycle to keep the panel voltage constant. There is nothing out there you can buy which can be easily modified. I found only one thing one thing which was suitable and nobody in solar could do the modification for the past three years. So, buying something off ebay is a fools errand and a waste of your money.
 
Rheem makes plastic hot water tanks, wire direct from panel to tank.. I just installed a rheem heat pump unit...
I have been looking at the heat pump water heaters. Did you just wire yours into standard AC power or somehow power it through the solar? Thanks!!
 
Yep, they sure do move heat. I managed to catch the Rheem ProTerra 50 on sale for $699 and now I must report my garage is frozen. At least it's my garage and not the house. Meets my needs otherwise.
 
Just be sure to by-pass the thermostats. They are safe only for AC, never DC.
It is easy to rewire a standard water heater to operate with high/low capabilities by operating a single 4500w element on 115 v. Yields about1100 watts. 2 4500 watt elements in series is about 600 watts. High/low, hence.
Have done this for years and works great.
 
Don't use contacts for high voltage DC use a DC solid state relay. SSR. They're an isolated transistor that doesn't have to deal with arcs at all.
 
What I would like is a 4 panel microinverter like APSystems QS1 to be instructed to operate by the grid, but not backfeed the grid. I just want to use it to feed the bottom element of my hot water tank. Cheap simple reliable and now it's AC that won't burn up my hot water tank thermostat.
Preventing the microinverter form backfeeding the grid made me think of diodes. Then I found this.
Anyone see this engineer team working on the ACdiode?
I don't think it accomplishes what I want, but it seems like that would be cool.
 
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