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Heating water with excess power
#1
I’m not explaining how to do it. I’m asking what would be my best option.
solar array is 3660w max (no wind or hydro). My array is not oversized. The battery is 60v 16s Li-ion. I am using a grid tie inverter with limiter (GTIL2) that uses battery (if pv power itself isn’t enough) when needed throughout the day. Outback fm60 chargecontroller.

I’m wanting the excess power the array can produce to be sent to hotwater heater when battery is full-in float. Or for the hotwater heater to be turned on so GTIL2 can power the hotwater heater when excess is available and battery is full. The outback has a few aux options that might help to achieve this. I’ll put pics below of those options. I’m ok with changing one of the hotwater heater elements to dc, but would prefer to keep the elements AC so I can heat the entire tank of water if excess pv isn’t available for some reason.
Standard diversion controllers seem to use voltage only (not amps). I understand that they can be set to activate when float voltage is achieved. How do they make sure when there’s any excess pv power (that the LOADS ARE NOT USING) that the power goes to the hotwater heater. Also when there’s not excess because the loads need the available pv power how does the diversion controller allow the loads to use that power instead of the hotwater heater using that power?

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#2
I do like this
https://youtu.be/pJQOklaPntE
Or kind of.

But more efficient to use proper air to water heaters that is powered by excess electricity.
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#3
(08-30-2020, 10:43 PM)daromer Wrote: I do like this
https://youtu.be/pJQOklaPntE
Or kind of.

But more efficient to use proper air to water heaters that is powered by excess electricity.
Good video.
It’s not that simple for me. I have a limiter which keeps the solar from producing more than I need. The limiter is very precise and I need it to be so absolutely no power is put past the electric company meter. I’d assume that form of diversion in the video would still allow some power to go past the meter.

Other than that seems simple enough besides the micro controller. Never used one. I have the iotawatt so that info could be sent to a micro controller I think. But there’s no excess power shown on the iotawatt to send to a micro controller because the Inverter has limiter

Could I somehow divert the pv power before the chargecontroller?

Guess I’d have to have a dc element and dc thermostat then

I wouldn’t have enough excess pv power to do much air to water heating with. It takes 4Kwh every day to warm up my hotwater heater from tap cold to 120 degrees. I have atleast that much excess pv power available most days.
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#4
I have my RaspberryPi3 that logs BMS data also do that for me, commanding a Wifi SmartPlug to turn on/off the dumping load. My dumping load is small (750W) compared to my PV panels (10kWp), so I'm having it preemptively start dumping long before the batteries get full.
Every few minutes, I have it calculate a formula that takes into account the season (sunrise/sunset), time of day, battery SoC, charge current, to predict whether the battery is likely to get fully charged before sunset. If so, it starts to dump.
The dump load for me is actually a GTIL2 (no limit set) that feeds back to the grid - I get paid for that.
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#5
1) Why would that be too difficult? All you're doing is using a microcontroller to turn on/off heating elements. Fairly simple really.

2) You could also get a DC heating element. They are used in RV's. They cost about the same but are designed to run on 48VDC instead of 220VAC. The downside is if the amps required.
1000W @ 220VAC ≈ 4.5A.  1000W @ 48VDC ≈ 21A

You still need some sort of controller to know when the battery is full and go into bypass. Granted, some Solar Charge controllers have bypass circuitry. However, you do "not" want to run a heating element directly from that port. You'd want to use a relay that can handle the amps, like those in the diagram.

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#6
Sounds like a good setup ajw22. It would be nice selling to the grid if that was an option where I live. It is an option here but they make it impossible to save any money because they have every bit of the install done by a highly paid installer if I’d want the solar meter to sell back to them.
Bet that cheap little GTIL2 about paid for itself already with you flying the power into the grid.

(08-31-2020, 12:40 AM)Korishan Wrote: 1) Why would that be too difficult? All you're doing is using a microcontroller to turn on/off heating elements. Fairly simple really.

2) You could also get a DC heating element. They are used in RV's. They cost about the same but are designed to run on 48VDC instead of 220VAC. The downside is if the amps required.
1000W @ 220VAC ≈ 4.5A.  1000W @ 48VDC ≈ 21A

You still need some sort of controller to know when the battery is full and go into bypass. Granted, some Solar Charge controllers have bypass circuitry. However, you do "not" want to run a heating element directly from that port. You'd want to use a relay that can handle the amps, like those in the diagram.


Using a micro controller doesn’t seem to difficult. Never have used one is all. I’d use it if it would work for my situation. Like I said I use a limiter which keeps power from going past the electric company meter. The diversion in the video (I’d assume) allows power from the inverter to feed past the meter causing a negative amount of consumption. And then it reacts but only after the negative consumption has happened. I cannot do this because I do not have a solar meter from electric company so negative consumption isn’t allowed
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#7
The FM60 has a built in diversion controller which should work with solar. Even though the Fm60 manual only refers to wind/hydro power any excess power can be diverted. Starting on page 38 it explains how to set it up.
Once the battery voltage has reached a set level the FM69 will divert the power to the diversion load. and once battery dips below a set level the diversion is off . This is controlled by a simple relay on/off.
later floyd
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#8
(08-31-2020, 01:11 AM)floydR Wrote: The FM60 has a built in diversion controller which should work with solar. Even though the Fm60 manual only refers to wind/hydro power any excess power can be diverted. Starting on page 38 it explains how to set it up.
Once the battery voltage has reached a set level the FM69 will divert the power to the diversion load. and once battery dips below a set level the diversion is off . This is controlled by a simple relay on/off.
later floyd
I was hoping that aux option would work. Above is a pic of the outback manual that explains how it works. It (go figure) won’t work for my setup.

Floyd the diversion aux option you speak of uses volts to turn on/off a relay. When the relay-aux is active and the hotwater heater element is being powered by the GTIL2. What would happen when other loads come on that should be using the power the hotwater heater is using. I’m thinking the hotwater heater would continue to run and those other loads would be getting their power from the grid. I’m saying using volts doesn’t seem like a great way to assure that the hotwater heater is only using excess power because the volts might not be dropping while the hotwater heater is on so then hotwater heater won’t shut off when other loads come on. And they will use the grid power.

Or am I wrong, will the battery drop in volts? I guess it will if the available pv power is less than what the loads are using.. hmmm this might workSmile

I guess it would just take some tweaking of the HYST volt setting to try and get the hotwater heater element to shut off as quick as possible when the available pv power is less than the amounts the loads are using, that way the grid isn’t supplying power to loads because the hotwater heater was using the available pv power

Floyd, would the relay-contactor be on the AC power wire going to the hotwater heater?
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#9
I was talking about the dc side but let me look again.
later floyd
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#10
I believe, not entirely sure, that once the charge controller (as the FM60 above) detects current loads on the primary output (aka to the battery), then it turns off the Aux port and allows all power to flow to the primary output.
If it doesn't detect it, then it probably monitors voltage very closely and when a heavy load happens on the inverter side, that causes the battery voltage to drop enough that the controller will switch over to primary feed and turn off the aux
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