# Waste not, or Diversion Control



## Montanarchist (Feb 24, 2005)

I added a second 50 gallon hot water storage tank to capture all the extra power goodness. Anyone else run















ning a diversion controller


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## Alice In TX/MO (May 10, 2002)

Please elaborate how that saves.


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## Montanarchist (Feb 24, 2005)

The easiest way to describe it is that instead of turning off the power from the panels to the battery with a conventional solar controller the excess power (after the battery bank is full) is ran through an electrical resistance heater elements(s). I have two 20A 48VDC elements installed in my last downstream water heater. The other tank just stores 50 gallons of hot water for domestic use. 

I designed my system as an open loop but you can do the same with heat exchangers.


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## Montanarchist (Feb 24, 2005)

And not wasting also includes after the 100gallons of domestic water is hot the system pumps any extra hot water produced through my infloor heating loops- Which is cooled with spring water I run through the floor in summer to keep the place cool.


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## painterswife (Jun 7, 2004)

Montanarchist said:


> The easiest way to describe it is that instead of turning off the power from the panels to the battery with a conventional solar controller the excess power (after the battery bank is full) is ran through an electrical resistance heater elements(s). I have two 20A 48VDC elements installed in my last downstream water heater. The other tank just stores 50 gallons of hot water for domestic use.
> 
> I designed my system as an open loop but you can do the same with heat exchangers.


You need to give more explanation. I think this info could be very valuable for some but it is pieces and bits right now.

1. Do you have a solar system that uses excess energy to heat water? Is that correct?
2. Your floor heat system is an open one? In other words directly from the hot water heater and through the floor not through a heat exchanger?
3. How is that second water heater piped in?


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## Alice In TX/MO (May 10, 2002)

This is AWESOME!!


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## Alice In TX/MO (May 10, 2002)

Are all plumbing connections inside/freeze protected?


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## painterswife (Jun 7, 2004)

I have no solar but I do have an open radiant floor system.  Cue the plumbers because we are about to get hammered on that one.

My floor is a couple of inches of concrete and no freeze protection. I have a propane stove in case of no power so things don't freeze.


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## Montanarchist (Feb 24, 2005)

Power comes in as 48VDC, it charges the battery bank. When the battery bank is full a diversion controller (not pictured) sends 48VDC to my retrofitted DC water heater. When the water heater reaches 130F a controller (pictured) opens a valve; and turns on a pump to circulate water between the 50 gallon heater and the 50 gallon water storage tank. When both tanks are 130F another valve opens and another pump turns on circulating water from the storage tank through the infloor loops and back to the water heater. 

I designed this system and use industrial controllers valves and pumps. 

It's been online for fifteen years. I rebuilt my original headers so I can isolate and blow empty any/all loops. The default is just a single loop that heats the bath and utility. 

I designed the house for passive solar gain and have all the active AE. Back in '17, I shut off the water to the kitchen and went to Puerto Rico for the month of February. The house dropped below freezing and I lost a few plants but the utility pantry, and bath stayed above 50F


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## Montanarchist (Feb 24, 2005)

My upper cabin I'm designing for 100% geobank heating. I have a dry mine and southern slope below it. I expect to be able to back enough heat inside the mountain in the summer to heat that cabin the winter. 

These are child's play and just practice for the day I go to Mars.


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## doc- (Jun 26, 2015)

It seems to me that most people with solar arrays don't have the luxury of "extra" power, and if you do have that much sun, then maybe a passive water hearting array would suffice without all the extra hardware.

In regards earth berm design-- its advantage is that inside air is always trying to equilibrate temps with the outside -- In summer, outside air might be 100* and in winter, -30*-- that's a strong gradient...With earthberm, the "outside" is always 55*-- a much more mild gradient for energy flow....OTOH-- heat is lost more quickly into a solid material than into a gas (air) so you still need good insulation.


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## JRHill02 (Jun 20, 2020)

I have thought about this. I have a Morningstar in the well pit and there are two 80g pressure tanks in there. The well water is COLD but gets much more so in the winter. I mean, really cold. I love the efficiency of the LP Rinnai water heater but its working against the cold water well temp. The volume of water even from one tank helps keep things from freezing up and with the 2nd tank the pump doesn't have to cycle near as much. There has never been a freeze up.

I have thought about using the Morningstar's diversion to fire off air resistance heat to add some heat to the pit. The set up would have to be on a thermostat - that's the easy part. The hard part is the heating element. Any resistance 'coil' is way too high a wattage. I have found 80 watt 48vdc sealed beam lights that would be perfect. But boy, those are EXPENSIVE. It's not worth much expense or I end up adding more complexity and expense than LP saved. So this ends up being one of those things I think about....

BTW, the batteries in the pit are 6v golf cart blocks. At six years old, one died earlier this year so the whole string is worthless (and old) so I just have the Grundfos pump plugged into the house 120v. I'm not going to buy a new bank of 8 GC batteries again. Way too much stored power for a 800w load. The well has its own panels - 800w. So I've been watching for this: Discover Helios battery, 48v 30ah. They are new and not available yet. And replacing the lead batteries with the LiFEPO4 would be just right. It's supposed to be a drop in replacement for lead so the Tri-Star will work fine with appropriate config. And it would get the well pump back off the house.

Any ideas for an inexpensive 48vdc heating element? Less than a few hundred watts?


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## Montanarchist (Feb 24, 2005)

You could add an old electric hot water heater after the last pressure tank and retrofit it to 48VDC like I did. A controller to dump the water if it gets too hot from not being used is a good idea too.


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## backwoodsman7 (Mar 22, 2007)

JRHill02 said:


> Any ideas for an inexpensive 48vdc heating element? Less than a few hundred watts?


You can get little 10a 48v-12v DC converters for under $20 on Ebay. That will run 2 (55w high beam) or 3 (35w low beam) old sealed-beam headlights, or anything else up to 120w. Or get a 30a one (under $30) and run one of the cheap little 12v 300w (25a) heaters that plugs into a lighter socket. The converters are pretty efficient, not that that matters if you're looking for heat anyway.


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## JRHill02 (Jun 20, 2020)

backwoodsman7 said:


> The converters are pretty efficient, not that that matters if you're looking for heat anyway.


I have more than a little bit of stuff that needs/can use 12vdc. So I bought a decent 48-12vdc converter. It was on its own shunt. Whoa, it wasn't very efficient at all. I don't have the numbers close at hand but at idle with no load it was a hog. With a small load it was, eh, acceptable and the power was pretty clean. I determined it was easier to use a 120vac wart or power supply as needed.

But for this thing I'm thinking about here is some math to use a resistive load at 48vdc (thanks to Bill at the NAW&S Forum):

You can use 120 or 240 VAC heating elements too... Just derate them for running on 48 VDC.​​P=V*I=I^2*R=V^2/R​P=V^2/R​V240^2/R=V120^2/R​R=240^2 / 48^2 = 25 ratio of power for 240 VAC element on 48 VDC source​R=120^2 / 48^2 = 6.25 ratio​​P=V^2/R​R=V^2/P = 200 Watts = 48V^2 / 200 Watts = 11.52 Ohm heater or higher resistance​P=V^2 / R = 240 VAC ^2 / 11.52 Ohms = 5,000 Watt (or smaller) 240 VAC heating element​​Basically, for a 240 VAC element on 48 VDC will have 1/25 the Wattage.​​For a 120 VAC element, you will have 1/6.25 ratio:​​200 Watt @ 48 VDC * 6.25 = 1,250 Watt rated @ 120 VAC element.​​Note that AC vs DC rating does not matter for the element. HOWEVER, whatever you use to switch 48 VDC needs to be rated for (at least) 48 VDC.​​DC power will sustain can arc beautifully on a switch/breaker/fuse not rated for 48 VDC (technically, 60 VDC minimum rated as the battery charging voltage--But 48 VDC rating should work too).​
Fun stuff, eh?


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## backwoodsman7 (Mar 22, 2007)

JRHill02 said:


> I have more than a little bit of stuff that needs/can use 12vdc. So I bought a decent 48-12vdc converter. It was on its own shunt. Whoa, it wasn't very efficient at all. I don't have the numbers close at hand but at idle with no load it was a hog. With a small load it was, eh, acceptable and the power was pretty clean. I determined it was easier to use a 120vac wart or power supply as needed.


Must've been an old design. The newer IC stuff is at least 90% efficient under load, and no-load consumption is basically zero. But if you still have that one, this seems like the perfect application for it since you're trying to create heat anyway, and if I understand correctly, it'll be powered down when you're not trying to turn extra power into heat.



> 200 Watt @ 48 VDC * 6.25 = 1,250 Watt rated @ 120 VAC element.


I didn't check his math, but assuming it's correct, the element from a 1500w heater would get you just about where you want to be.


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## JRHill02 (Jun 20, 2020)

I am hung up on the relay at this point. I have searched widely for a relay whos _contacts_ can handle 60vdc safely and reliably - even as low as 6 amps. But the searches keep revealing relays whos trigger control is 60vdc but the contacts are for AC. Ultimately I'd love to find a relay whos trigger AND contacts are rated 60vdc. Its kind of illusive at this point.

I actually have a similar problem with the main battery breaker in the solar on the house. When I originally spec'ed out the components for the house 48vdc system I built it with a 100a flat mount DC breaker. I intended that the breaker would be sufficient for a nominal 48vdc. That was an error on my part as the flat mount breaker is actually rated at a MAX of 48vdc. If the breaker were to ever trip during the absorb or EQ stages, 58-62VDC, it could become a one time fuse  I can't find a flat mount 100a 60vdc replacement. The only option is an additional box with a plug in breaker and have to recable and add the stuff in a spot that has no room. The breaker has never tripped from load, only as a switch when shutting the system down and minimum load. But I have heard of DC breakers that have literally exploded. Not good.


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## backwoodsman7 (Mar 22, 2007)

JRHill02 said:


> I am hung up on the relay at this point. I have searched widely for a relay whos _contacts_ can handle 60vdc safely and reliably - even as low as 6 amps. But the searches keep revealing relays whos trigger control is 60vdc but the contacts are for AC. Ultimately I'd love to find a relay whos trigger AND contacts are rated 60vdc. Its kind of illusive at this point.


Your charge controller's diversion output can't handle the current directly?


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## JRHill02 (Jun 20, 2020)

backwoodsman7 said:


> Your charge controller's diversion output can't handle the current directly?


It can, But I need a relay


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## backwoodsman7 (Mar 22, 2007)

JRHill02 said:


> It can, But I need a relay


I must be missing something. If it can handle the current, why do you need a relay?


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## JRHill02 (Jun 20, 2020)

backwoodsman7 said:


> I must be missing something. If it can handle the current, why do you need a relay?


To shut down when needed.

All this AC/DC stuff.... Is there a relay to shut down the wife? What can handle the load? A D68 cat?


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## backwoodsman7 (Mar 22, 2007)

JRHill02 said:


> To shut down when needed.


Oh... well that aspect at least would be simplified by converting down to 12v or even 24v. Do you not still have the 48-12 converter you mentioned? Another simple solution would be a small thermostatically controlled vent fan.



> All this AC/DC stuff.... Is there a relay to shut down the wife? What can handle the load? A D68 cat?


 Haven't found a solution for that yet, sorry. I'll only say solutions involving voltage may be contraindicated.


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## JRHill02 (Jun 20, 2020)

Actually, I'd like to have the Cat. I'd even take a smaller one. And the wife. I'm a guy, can't I have it all?


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