Heating water with excess power

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Cheap 4-life

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Im not explaining how to do it. Im 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 isnt enough) when needed throughout the day. Outback fm60 chargecontroller.

Im 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. Ill put pics below of those options. Im 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 isnt 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 theres any excess pv power (that the LOADS ARE NOT USING) that the power goes to the hotwater heater. Also when theres 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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daromer

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I do like this
Or kind of.

But more efficient to use proper air to water heaters that is powered by excess electricity.
 

Cheap 4-life

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daromer said:
I do like this
Or kind of.

But more efficient to use proper air to water heaters that is powered by excess electricity.
Good video.
Its 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. Id 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 theres 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 Id have to have a dc element and dc thermostat then


I wouldnt 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.
 

ajw22

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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.
 

Korishan

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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.


image_aixjwo.jpg
 

Cheap 4-life

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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 Id 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.


Korishan said:
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.


image_aixjwo.jpg

Using a micro controller doesnt seem to difficult. Never have used one is all. Id 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 (Id 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 isnt allowed
 

floydR

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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
 

Cheap 4-life

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floydR said:
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) wont 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. Im thinking the hotwater heater would continue to run and those other loads would be getting their power from the grid. Im saying using volts doesnt 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 wont 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 work:)

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 isnt 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?
 

Korishan

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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
 

Cheap 4-life

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One of the down sides to doing it with ac elements is if the available solar is below the amount the hotwater heating element is using then the battery volts would drop out of float because power would be used from the battery and shutoff the aux signal to the relay till the battery raises back to float again. On a day theres not much available pv due to clouds then the relay could be kicking on/off a lot.. doing it with dc elements would just divert the excess and the element would use only the amount of power diverted to it.
 

ajw22

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If you're going to use AC for heating, I think you need some sort of microcontroller with a logic that takes into account:
* battery SoC (Is it near full?). Can probably use one of the MX60 outputs
* real time power output of the GTIL2 (Is there enough excess capacity to power the heater?). Can be fetched from IotaWatt.

If using DC for heating, you only need the battery SoC, so could probably use just the MX60 output
 

floydR

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It appears that the diversion of PV isn't allowed via the OB because PV is routed though the controller. my bad
"External DC sources (wind, hydroelectric) are directly connected to a battery bank" missed this part
later floyd
 

Cheap 4-life

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Korishan said:
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

I dont think the aux is actually for diverting the current. The aux just sends a low voltage signal that can trigger a relay.
 

Korishan

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From the MX60 Manual:
https://www.altestore.com/store/media/pdfs/outback/Americas_and_Mobile_manual_rev_7.pdfPage12 said:
AUXILIARY OUTPUT ( AUX + / AUX - )The Auxiliary output system uses the AUX + and AUX terminals and is able to be programmed through the MATE to do a variety of tasks. The default use for these terminals is to drive one 12-volt fan for external cooling. The power available at these terminals is 12 VDC at 0.7 amps (8.4 watts) maximum. These terminals should not be connected to any type of DC load which has a high inrush current requirement. The FX includes internal electronic overcurrent protection for this 12 VDC output circuit which auto resets if it is short circuited. No additional fuses are required. Use the OutBack FX Turbo Kit or DC12-FAN for cooling. For automatic or advanced generator start functions, the Auxiliary Output can drive a 12V automotive relay for the 2-wire starting circuitry of a generator. OutBack Power Systems does not support 3-wire start generators, however, a 3-wire to 2-wire conversion kit is available from a different source.

and from the FM60 Manual:
http://www.outbackpower.com/downloads/documents/charge_controllers/flexmax_6080/owner_manual.pdfPage30 said:
The AUX (Auxiliary) is a secondary control circuit essentially, a small power supply that provides a 12 Vdc output current (up to 200 milliamps / 2.4 watts) to an isolated load. It is either ON (Active High) with 12 Vdc available at the output or OFF (Active Low) with 0 Vdc at the output. It can also be set to AUTO, so that it activates when certain criteria are met. The AUX output can respond to specific criteria and control cooling fans, vent fans, load diversion, fault alarms, and automatic generator control. In some cases, such as the PV Trigger, Night Light, or Diversion:Relay applications, the polarity of the output can be reversed so that a lack of power activates the output. This function is controlled through the Aux Polarity screen in the ADVANCED MENU. (See page 56.) NOTE: Diversion:Relay and Diversion:Solid St can be used for AC coupling applications. The AUX output can also be controlled externally through the system display. See the literature for the system display (if used) for details.

So with both of these, you can use a relay to trigger other devices. This would work for dealing with diversion control. Considering that they are activated with "certain criteria", including diversion control, it should be easy to configure this option.
 

daromer

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Simplest is to use my design with a controller that turns on a heating element powered by the battery when you deem the battery to be above 90% or whatever. Or when the solar voltage is above its maximum tracking point. Then you know you have excess power.
 

Korishan

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Using the graph I showed earlier (from daromers video), you could just as easily use a DC element instead of an AC element and power directly from the batteries instead of the inverter.

If you don't want to alter your existing water heater, you could do a pre-heater setup. This would use a second water heater tank that is plumbed "before" the existing system. This one would have the elements replaced to use DC elements. If it's not used, there'd be no difference between it being not used and be cold water, or it not being there at all, as cold water would enter your primary tank just as usual.
The pre-heater tank could be much smaller, too.
 

Redpacket

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I like daromer's idea of using the array voltage & when this rises above max power point voltage, it means you have spare energy. As soon as the array voltage drops to MPPV again, it would cut off again.
 

Cheap 4-life

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Using a preheater tank. Lets say main tank cooled to 100 degrees over the night. When a shower is started hotwater will come from preheater tank to main tank. The preheated water will begin to warm the main tank but that will take a while. The first couple people showering will have water that is only 100degrees or slightly warmer from the little bit of preheated water that has come into the bottom tank that mixing with the colder bottom water during the duration of the shower.

Right now I wait till battery is full and then I start the AC hot water heater and fully heat the tank. I do this when no other loads are on (actually like 300w are still on) so its all free water heating but the battery Are still drawn from when available pv power is lower than the 3000w ac element. The water in the tank is almost completely full of tap cold water each day once showers are done. Right now I only heat the entire tank once. Id assume using the preheating tank would make the entire main tank as hot as the preheater tank temp settings but only once everyone has showered because it would take that much flow to put the preheated water into the main tank. Then the main tank would cool over the night, maybe to 100 degrees. And then the first couple showered will only be with close to 100 degree (or whatever the tank cooled to overnight) water.

The preheater tank would keep the main tank from running as much as it would if preheater tank wasnt installed. But for the first couple people showering it would only be as hot as the water cooled to overnight. Unless I keep the main tanks power supply on all night to keep the tank up to temp at night but then Id be using battery or grid power for that, which doesnt work cause only excess pv should be used.


Without a preheater. Using a dc element in the bottom of my existing tank. If there wasnt enough excess pv that day due to clouds or to many loads. Then the bottom element wouldnt have heated the water. Then Id need to turn on the hotwater heater to have hotwater and if the bottom element being dc means that I cant fully heat the tank. Id need to fully heat the tank because thats just enough hotwater for the whole fam to shower. If I kept the ac power available to the top element- hotwater heater 24/7 then the tank would turn on at night when someone showered, which would drain the battery.
 

Korishan

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Cheap4-life said:
Using a preheater tank. Lets say main tank cooled to 100 degrees over the night. When a shower is started hotwater will come from preheater tank to main tank. The preheated water will begin to warm the main tank but that will take a while. The first couple people showering will have water that is only 100degrees or slightly warmer from the little bit of preheated water that has come into the bottom tank that mixing with the colder bottom water during the duration of the shower.

Not entirely so. The preheater tank regardless of temp wont change the temp of the main tank. The way cold water is introduced into the hot water tank is to make it not dilute the hot water as the cold water replaces what was used. As the cold water level rises on the bottom of the tank and passes the lower thermostat, it triggers that element to turn on (altho, it's not enough to heat the water on its own and will eventually be overloaded by cold water)
A preheater tank would basically be turning an 80gallon tank into 120 (if using a 40g preheater tank, for example) tank. It would extend the run time of hot water.

So yeah, what ever the main tank cooled down to overnight, that's what they'd get. You could put extra blanket material around the tank to extend temp longevity.

Cheap4-life said:
Right now I wait till battery is full and then I start the AC hot water heater and fully heat the tank. I do this when no other loads are on (actually like 300w are still on) so its all free water heating but the battery Are still drawn from when available pv power is lower than the 3000w ac element. The water in the tank is almost completely full of tap cold water each day once showers are done. Right now I only heat the entire tank once. Id assume using the preheating tank would make the entire main tank as hot as the preheater tank temp settings but only once everyone has showered because it would take that much flow to put the preheated water into the main tank. Then the main tank would cool over the night, maybe to 100 degrees. And then the first couple showered will only be with close to 100 degree (or whatever the tank cooled to overnight) water.

Since you heat the water with solar/battery, why not switch over to using DC elements anyways. You'd save efficiency conversion. Save energy from being wasted by going through the inverter. Unless your water heater is a long run from the battery.

Cheap4-life said:
Without a preheater. Using a dc element in the bottom of my existing tank. If there wasnt enough excess pv that day due to clouds or to many loads. Then the bottom element wouldnt have heated the water. Then Id need to turn on the hotwater heater to have hotwater and if the bottom element being dc means that I cant fully heat the tank. Id need to fully heat the tank because thats just enough hotwater for the whole fam to shower. If I kept the ac power available to the top element- hotwater heater 24/7 then the tank would turn on at night when someone showered, which would drain the battery.

What you could do is do some replumbing of the heating elements. Something I've thought of before, tho not sure if it'd really be to any advantage. You'd take the elements out, put a piece of piping with a T at the bottom, and put the element down there. Turning on the element would cause water convection and the whole tank would get hot as it circulated.

Kinda like this:

image_ebgxqs.jpg


Would be interesting how well it'd work. I suppose it depends on the demand, too.
 
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