Hot Water by Solar Electric direct via MPPT ?

[Carv]

The those who want to avoid a lot of home made hassle.

Missouri wind & solar has DC water heater elements

https://mwands.com/store/index.php?route=product/search&search=Dc%20water%20heater%20element

This one is 200watt DC and has a thermostat built in to it and it $72 shipped on ebay

http://mwands.com/store/adjustable-water-heating-element?search=Dc%20water%20heater%20element

https://www.ebay.com/itm/12-Volt-200-Watt-DC-Adjustable-Water-Heating-Element-with-Built-In-Thermostat/291645422913?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649&redirect=mobile

Since this element is DC it could be ran off the batteries, off the PV direct, or off the dump load depending on your CC programming.

This would work good if you have 2 thermostats and can replace the lower one or if you're willing to swap out your single AC thermostat with this one.

[inetdog]

An important thing to recognize is that for this application a unique operating mode is required for the output stage of the inverter:

Instead of delivering as much current as is available at voltage of the current grid connection (grid tie) or delivering as much current as is available at the relatively constant, known battery bank voltage (Charge controller) or as much current as demanded up to the limit of the input power, at a fixed voltage (stand alone inverter), this unit must recognize that the load is a fixed resistance, and to get it to absorb the available PV power it must regulate the output voltage such that the resistive load consumes exactly the available power. This is totally independent of the MPPT operation on the input side.

[PNPmacnab]

That appears to be a better deal than the techluk and not an unreasonable price. The fotobooster appears to be a capacitor bank. I've built my own system that works this way and it works great. At least when the sun shines. Love to hear your results after it is installed. The manual is crap and it is hard to figure out what they are doing. Besides MPPT, t appears you might be able to set a fixed power point voltage so it could operate in parallel with an existing controller.

[cretch]

thanks, I've looked into these and may use one, But they are expensive and require a large amount of battery power. My thought is that if I could store a portion of the energy produced as heat ( hot water) then I could get by with a smaller system to power second-biggest users, the frig. and dryer.

[jflorey2]

In Durango Colorado, my power company won't let me and others hook to the grid, they say they have too much solar power, so directly powering a hot water tank or heater has piqued my interest.

Look into net-zero systems. They will also allow you to power your water heater without new wiring - and without sending any power back to the grid.

[cretch]

In Durango Colorado, my power company won't let me and others hook to the grid, they say they have too much solar power, so directly powering a hot water tank or heater has piqued my interest. Here is an in-depth study found that may be of interest: https://www.hindawi.com/journals/ijp/2017/7540250/ . In the spring, I'm definitely going to install a system. So far the German controller (https://www.ebay.com/itm/263523458861) looks best to me.

[bcroe]

The design of the controller's special CPU is programmed for Maximum Power Point Tracking (MPPT) and also makes the DC into a form of high frequency AC and stops any arcing within microseconds, just like the zero crossing of AC does. The rapidly changing waveform inhibits arcing of the thermostat contacts. Unlike any other MPPT controller, this one is specifically for use in solar water heating using the original factory thermostat.

Sounds like a cool product, but I wonder if it causes radio interference? That could be contained. Bruce Roe

[psablo]

I have been reading the TechLuck FAQ's and he says:

Q: Why can't I hook up my solar panels directly to the hot water heater?

A: If you are using more than 150 watts of solar power the AC thermostat contacts can arc, weld, burn up or melt together. The thermostat will no longer function properly to prevent overheating of the tank, creating a dangerous condition.

The design of the controller's special CPU is programmed for Maximum Power Point Tracking (MPPT) and also makes the DC into a form of high frequency AC and stops any arcing within microseconds, just like the zero crossing of AC does. The rapidly changing waveform inhibits arcing of the thermostat contacts. Unlike any other MPPT controller, this one is specifically for use in solar water heating using the original factory thermostat.

As for heat sink, he says, use a bigger junction box to mount the controller if you get above 750W PV.

[psablo]

I saw the one from TechLuck and it appears to be real, though I have concerns over their heat sync (a wall-mounted electrical box).

Thanks for finding that, it looks interesting I might try one.

[bcroe]

I work on some HVAC equipment that uses SCR controllers for reheat (480V AC electric resistance heating.)
These heaters pulse to maintain setpoint, and I have not had any failures yet. I don't know if they would work
with DC line voltage but it's worth a check. The control circuit is usually DC .

SCRs are tough, but they can't be used to control pure DC line. Once they are on, they stay on until the
line power is removed. Bruce Roe

[LucMan]

1. It has two elements: the upper is 3800 W and lower 5500 W, with a max of 5500 W (wired so only one element on at a time)

2 & 3. I didn't log water temperature or electrical performance for the few weeks I was testing it. I was just glad to have hot water at night and again in the morning - and it did that much well.

4. Actually, I used it for weeks without connecting the water heater to POCO - and it always had hot water for me (until the SSRs overheated). This whole discussion has me more interested in resuming where I took off ...

5. I know the reliability of using a PV solar system, but have read of problems with pumps & leaks in other systems. Does anybody here have personal experience living with one?

Also: I'll have to put in a plug for my YouTube video on a solar irrigation system: Solar Irrigation

I work on some HVAC equipment that uses SCR controllers for reheat (480V AC electric resistance heating.) These heaters pulse to maintain setpoint, and I have not had any failures yet. I don't know if they would work with DC line voltage but it's worth a check.
The control circuit is usually DC .

I have a 84 sq ft flat plate solar thermal HW system that has been in operation since 2008. It is a drain back system and has had 0 issues. No glycol so minimum maintenance required. I change the anode rods in the storage tank every 3 years.
The first 15 ft of piping from the collectors is copper, the rest back to the storage tank is Pex.

[Tgriff]

I hadn't done a search in a while but WOW, did I find some on Alibaba:

https://www.alibaba.com/showroom/solar-charge-heaters.html

Sorry, guys - most of these are cheap controllers for charging batteries, nothing to do with water heaters. Those that do have incomplete/contradictory specs.

Yes - I'd be interested in the names/models and any experience with any *real* such devices.

I saw the one from TechLuck and it appears to be real, though I have concerns over their heat sync (a wall-mounted electrical box).

[Tgriff]

At least two companies I know of offer MPPT trackers for this purpose. (DC out to heating element) One of them also provides batteryless 120VAC for emergency use.

I hadn't done a search in a while but WOW, did I find some on Alibaba:

https://www.alibaba.com/showroom/solar-charge-heaters.html

[jflorey2]

If an MPPT control is to be used, it could also handle the job of turning power on and off. Bruce Roe

Exactly what I was thinking. (True of MPPT _and_ PWM.)

[psablo]

Going way down, does MPPT still matter?

That's what i was thinking; thanks for input.

I can't speak for Tgriff but I'm just trying to keep pipes from freezing in a well insulated pump control house which will probably never freeze, but just in case...
And, I'm in SW Co at 8500 ft where we rarely have more than 2 days without crystal blue skies and intense sun.

Re: jflorey2, correct me if I'm wrong, but don't Diversion Load Controllers require a battery bank? I was under the impression this discussion was based on not having any batteries.