Solar overflow to run water heater?

[Carv]

Thank you Inetdog, I read it and it sounds like everybody's trying to over complicate things I understand it better but I'm still a little lost.

Pnpmcnab,
I think I need to do something like you have set up, but I'm not sure exactly what that is. From reading the other thread I believe you take 60V panels, send that PV through your unavailable CC and convert it to 60V AC which raises your water tempature not to 60F, but raises you're water temp by 60F, so from 50F to 110F?


I checked my specs and my water heater does not have a 2nd port IIcould put a DC thermostat in to Although I might be able to put it in a extra incoming water port but it's 3/4 NPT so I don't think the 1" NPT DC element with thermostat will fit so I really don't think this is an option?

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

This leaves me having to configure a way to use the existing AC element for heating the water. My current AC element is 120V 1650W. So how do I take the current PV output or my DC output and convert it to use with the AC element & thermostat?

If I ran the existing element at 60V that would give me 412W which is enough to heat the water. I'm just not understanding how to go from what I have now to the AC element?


I did see the techluck converter thing but it's pricy and from people on that thread have said it seems a like dangerous.
http://techluck.com/index.php#buy

I also saw the PMW CC set up to run a WH but that's as much as the MPPT CC have now

https://www.ebay.com/itm/PWM-MPPT-Heater-Charger-Regulator-Solar-Photovoltaic-Solar-Panels-Hot-Water-PV/263523458861?pageci=68a96c3a-3217-4009-8a53-ac83f6df3921&redirect=mobile

[inetdog]

See also this thread.

[ewarnerusa]

I believe my Morningstar can deliver up to the entire solar input to the load output if state of charge of the batteries warrant that (i.e. they're fully charged). The program logic is current comes in from panels and first priority is to the charging lines. Current is routed there until batteries reach the voltage setpoint, either in absorption or float charging state. Once setpoint is reached, PWM does it's duty cycle thing except that instead of just on/off to the charging lines it is switch between charging line/load line so that charging line voltage stays constant at the setpoint. When in float charging mode, very little current is directed to the charging lines and most of it would go through the load lines.

[PNPmacnab]

I run 2,000W 120V elements in my system. These are common and cheap, used in point of use water heaters under 10 gallon in the US. Half the voltage gives 1/4 the rated power, an exact match.

[Carv]

Thanks ewarner, I'll look in to it.

I do have additional side ports on the WH but there for output spigots, with all the tubes and annode inside I'm not sure if I could get a 2nd element in there but it's something to check in to.

Did anybody know how many watts this EPever 3215BN outputs at the aux load port and when? The manual didn't tell me anything.

I have 2 x 255w, 30V, 8.49A wired in series (see attached). How big of an element could I run with these panels off the aux port on this CC?



Thanks

[bcroe]

You first need to work out a decent match up between panel output and heater consumption.
Otherwise the effort may only succeed in feeding some current through the heater, but burning
up most of the available energy in the panels. Bruce Roe

[ewarnerusa]

Several years ago when I first got our camper and interest in solar for it, I followed a forum post on rv.net about a guy with a truck camper that dumped his excess solar via the "load" output of his charge controller to a dedicated 12V element in his water heater. I seem to recall him fabbing something up so that he could use an existing part of the water heater to house the dedicated element. I was interested because it was the same model Morningstar Tristar controller that I have; the Morningstar Tristar controllers have programming options to due this very thing. It did exactly what the OP is asking about, something useful to do with solar harvest if his batteries do not need further charging. Unfortunately, I cannot find this forum post. Sorry! I keep thinking it will be easy to dredge up but I'm not having luck. I recall that this was in no way a replacement for the propane heating of the water, nor a claim to heat the water to the setpoint via solar alone. But it was something useful to do with power that could still be harvested during daylight hours if batteries were already floating.

My google searching found an ebay link to "12 Volt 200 Watt DC Low Voltage Submersible Water Heating Element or Dump Load" if you'd like to search for that on your own, I didn't want to post a direct link here.

[Carv]

So what am I missing here?

If transformers only work off AC then I'd have to wire it to run off the inverter as my CC only out puts DC, unless the Aux load is AC, does someone know on this CC?

This would mean I'm still pulling load off the batteries through the inverter and then stepping it down, basically doing exactly what I said won't work above.

So again what am I missing here?

[Mike90250]

> So if I was to do this I'd wire in the transformer to DC output side the CC

NO !! Transformers only work on AC. Put DC into a transformer and you get smoke and a boat anchor.

[Carv]

Pnb, yes the WH has a 110v standard US plug.
I'll get the element specs too.


So if I was to do this I'd wire in the transformer to DC output side the CC then plug the WH in when batteries hit float? Basically how would this system be wired based on the photo above of my system?

Thanks

[PNPmacnab]

Using the transformer method is probably your best method. The heating element is most likely 1400W and running it at 60V will produce 1/4 of that power. Like my 6 gallon heater you are never going to replace that element. I assume it plugs into something. Just plug it into a transformer when you want to heat water with solar. I didn't find anything cheap on ebay, 240V to 120V auto transformers rated at 750 to 1KW with cords and plugs already. What is your price point? My 6 gallon 1440W tank easily RAISES water 60F with only 900WH. That is two hours in mid day sun. If the water is somewhat warm it takes much less. Running off the panel voltage in an automatic system to harvest excess like I do is the way to go, but these systems aren't out there yet. Transformer is manual but doable.

https://www.ebay.com/itm/Simran-THG-...UAAOSwH2Ja0sfc

[Carv]

This is on a box trailer so there is no grid to tie into or feed back to

[inetdog]

Its a long read, but I did add an index at the bottom of the first post:

http://midniteftp.com/forum/index.php?topic=3881.0

While true, if you use a small enough water heater resistive load, it will run a good bit of the time and use up a good bit of the excess power from the panels. And if you have some kind of programmable setting from the CC it will only run at user defined charge level points. There are several ways to program the set up with a MidNite Classic, none of which is ideal, but each having its own pros and cons. Most of that is discussed in various places in the link above.

That makes it a good strategy if your goal is to avoid net export to the grid. It is less helpful when your goal is never to send power out to the net because of prohibitions or a single directional meter.
You can use a larger water heater load to consume more than your excess power to avoid feeding back into the net, but you cannot exactly match the power surplus.

[Matrix]

Its a long read, but I did add an index at the bottom of the first post:

http://midniteftp.com/forum/index.php?topic=3881.0

The fundamental problem is that the WH element is a fixed resistive load while the excess power from the panels will be essentially variable current (as a function of insolation (being shined on)) at a close to constant voltage. It can never be the correct resistance to suck up all excess power, when the amount of excess power will vary.

While true, if you use a small enough water heater resistive load, it will run a good bit of the time and use up a good bit of the excess power from the panels. And if you have some kind of programmable setting from the CC it will only run at user defined charge level points. There are several ways to program the set up with a MidNite Classic, none of which is ideal, but each having its own pros and cons. Most of that is discussed in various places in the link above.

[inetdog]

The fundamental problem is that the WH element is a fixed resistive load while the excess power from the panels will be essentially variable current (as a function of insolation (being shined on)) at a close to constant voltage. It can never be the correct resistance to suck up all excess power, when the amount of excess power will vary.