Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

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Load Diversion

Postby Tracker » Tue Jun 18, 2013 8:00 pm

.......I think if you had land, sticking them outside on a concrete slab would be the way to go, fenced off of course...


Surely, not that critical... we are only talking about the equivalent of one or two stove elements.
There are a great many air heaters available from the appliance industry.
Some fancy ones have integrated fins, to disperse the heat better..
You could remove one from an old clothes dryer..

Thanks for the input guys...
I think that I am particularly interested in considering how you use what you now have, and how you can look to selectively purchase used technology to complement what you have..
We know that there are systems worth killer-bucks, like the SP-Pro and even the SMA/Sunny like combinations.
..
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby davidg » Tue Jun 18, 2013 9:18 pm

FarmerJohn wrote:Is it acceptable for a diversion load to be fan cooled?

I wouldn't it is an inductor, not ideal, what if the fan stops? - does the diversion load overheat?

Diversion loads are the LAST resort

BTW - I note no one has mentioned them but - here you are an excellent diversion device, are stove elements. I make them up using them, they don't take up much space at all, they consume a lot of power in a small space, just keep them out of the rain, put them in a cage with metal mesh and fly-wire as well keep away from anything flammable make it at least 35% larger than the maximum amount of power that can be produced by the solar system/s on the GCInverter/s, use a high current SSR on a suitable heat-sink and there you are that's about all there is to a decent diversion load unit that is not big. Trigger with either a digital output switch in the SP-Pro and it's done.

For any inverter that can be A/C coupled if you cannot do the digital switch like the SP-Pro. A Voltage monitor on the batteries themselves and using an SSR to turn the A/C diversion load on/off and then set top voltage point and your bottom voltage set point, that will cycle the diversion load on and off based on the battery voltage very effectively, the voltage variation can be as small as .1 of a Volt using this style of system, that's is pretty fine power control. The rate the it will or can be switched on and off can be very fast indeed any Electro-Mechanical Relays must not be used, this is basically PWM power control. 8-) 8-)
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby FarmerJohn » Tue Jun 18, 2013 9:31 pm

Tracker wrote:Surely, not that critical... we are only talking about the equivalent of one or two stove elements.
There are a great many air heaters available from the appliance industry.
Some fancy ones have integrated fins, to disperse the heat better..
You could remove one from an old clothes dryer...


My thinking was really because it was stated that you have to have something that can work without a thermostat. So it must be able to dissipate that power for hours on end - day after day in already hot weather. If not done right, it could get hot enough to melt things, start fires, and roast small children and animals :)

It strikes me that 7.5kw is a lot of power to get rid off and the first choice of places to dump it into is the atmosphere because it is always going to be there; but safely.
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Re: Load Diversion

Postby davidg » Tue Jun 18, 2013 9:42 pm

Tracker wrote:Surely, not that critical... we are only talking about the equivalent of one or two stove elements.

My personal diversion load has 3 dual elements in it for our 7.2kW system the 6 elements = 10.8kW of load in small package. I think I'll have to double it later on once on the farm because there will be an increase of solar up to at least 15kw of arrays maybe more. :)

Diversion loads are last resort way of using power so outside heating air is really the only place to have them, you can have indoor heaters, aircons whatever but if someone turns it all off or only uses some of the power the excess power must go some place that's what a diversion load is for, it's the some place to go device. that's why no thermostat and why it must be bigger than the maximum amount of power that can be produced.

BTW they make great outdoor toasters you can make a lot of toast one top of one on a sunny morning. :lol:

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Load Dumping.. how it helps planning an integrated system..

Postby Tracker » Wed Jun 19, 2013 7:54 am

:cry: .
........My personal diversion load has 3 dual elements in it for our 7.2kW system the 6 elements = 10.8kW of load in small package. I think I'll have to double it later on once on the farm because there will be an increase of solar up to at least 15kw of arrays maybe more.....


Oh so much of your valid observations are based on your intimate knowledge of the SP-Pro system, and clearly you would like to promote their use, but most of the thought behind the thread is how to make it happen with what one has or plan to have.. and preferably, on the cheap..
SP-PRO, and other specialised packages are likely not in the field of on-the-cheap .. :idea: although, technically and clearly the better but costly choice..

In your above observation, is an implicit suggestion that you will end up with perhaps 15kW of power to dispose of.. one would think that this would happen via multiple PV/GCInverter combinations. I do note the comment about dump-load being an absolutely last choice.

Whilst I can appreciate the need, I do wonder why you would bother.
I can almost hear others groaning about the waste of power that is being suggested.
I hear their comments being made that they would be heating something or pumping something or thinking outside the square as to how to semi-productively, use that power..
On top of that I wonder why, if there is "multiple PV installations", you only allow to Dump-Load for say one system equivalent , and simply disconnect unnecessary generation.
Naturally, if one is blessed with a large property with multiple buildings and PV-Systems and are hell bent on demonstrating distributed AC-Coupling, then that is fine as an exercise.

So I can't see too many being concerned with providing for such power dumping.. although it is massively easy to achieve... just pick up an old stove after a kitchen Reno's.... that could be 12kW .. in a ready made device, just waiting for simple cage over the top..

With my property, I can see my eventually having up to five discrete and small PV Systems. As Off Grid...
Eg... 1.8kW, 1.52kW, 1.36kW, and 1+1kW (proposed E/W). Plus a true 1.4Kw Island
I think that when that happens, then I will simply have SSRelays on each and a control cable, allowing me to turn on and off different GCI's.
THEN, I will feed excess power to the HW tank and then, perhaps use a change over contact thermostat to switch the dump load to something like a solid stove hotplate, IF, and only if I have no possible use for that power..
PS.. you could change elements and fit a 4.8kw and better, have a dual element tank, and have twin elements, and perhaps of different size ... eg. 2.4 and 4.8kW this could provide a reliable short term dump..

A curiosity, if I might indulge myself... Why have you stressed the absolute need for a resistive Dump-Load.
Given an assumption that I need to dump large amounts of power, then I assume the sun is shining very well, and it is thus HOT, then, I would be using an Air Con. As a load shed..
What is the technical preference for completely resistive load..

Thanks for your thoughts... ;) ;)
.
PS... I again acknowledge that a SYSTEM, like the SP-Pro, does provide a commercially preferable home owner's power solution.. and one that is more easily administered by both the owner and the agent, who will likely be the one being asked the questions "..but why...".

PPS.. Part of my thinking in suggesting dumping generation as compared to dumping load, is that a CGI might last longer if it is not fully utilised.
I do recognise that technically, it's easier to just shed load, than developing a complex system to determine which generators should be disconnected, and in what order..
.
..
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Re: Load Dumping.. how it helps planning an integrated system..

Postby Gordon-Loomberah » Wed Jun 19, 2013 8:39 am

Tracker wrote:A curiosity, if I might indulge myself... Why have you stressed the absolute need for a resistive Dump-Load.


If you are using an SSR to regulate the amount of power dumped, the high frequency switching will destroy inductive loads such as air conditioner compressor motors.
If you weren't so concerned about balancing to export the absolute max power, you could use a timer that was triggered by a signal from the SSR to turn an inductive load on for a certain miniumum time, and not come on for a certain amount of time/duration of signal etc. You could do that with a Morningstar relay driver.

It all sounds a lot more complicated than it needs to be though- just use DC coupling and let the MPPT charge controllers do their thing- open circuit the panels, rather than powering us towards the heat death of the universe with a backyard full of stoves dissipating heat! :lol:

A more sensible thing to do with the excess energy would be energy storage for when the sun isnt shining- flywheel UPS type systems take a few hundred watts to maintain the energy store (friction losses etc), and that energy could be used after sunset to minimise import from the grid. Electrolysis of water to produce H2 and O2 for use in a fuel cell at night is another possibility, as would be compressed air energy storage or pumped stored hydro. Some of these are not particularly efficient, but when compared with powering a stove for no good reason, they look pretty good!
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Re: Load Dumping.. how it helps planning an integrated system..

Postby FarmerJohn » Wed Jun 19, 2013 9:45 am

Gordon-Loomberah wrote:A more sensible thing to do with the excess energy would be energy storage for when the sun isnt shining- flywheel UPS type systems take a few hundred watts to maintain the energy store (friction losses etc), and that energy could be used after sunset to minimise import from the grid. Electrolysis of water to produce H2 and O2 for use in a fuel cell at night is another possibility, as would be compressed air energy storage or pumped stored hydro. Some of these are not particularly efficient, but when compared with powering a stove for no good reason, they look pretty good!


You could do all those things but still need a dump load - even if it never got used due to your other storage options it would be needed to terminate your "grid" safely if they ever "filled up". (This comment only applies to the davidg AC coupled off grid solution above)
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby davidg » Wed Jun 19, 2013 9:58 pm

Ignore an SP-pro for a minute. Some of this comes from an earlier post of mine.

This point. Diversion loads are a LAST resort If it all goes wrong this can save things and keep it nice.
Tracker wrote:Oh so much of your valid observations are based on your intimate knowledge of the SP-Pro system, and clearly you would like to promote their use.

Sure I do, I like them, I like other products as well, such as SMA for many of the same reasons.
Tracker wrote: is an implicit suggestion that you will end up with perhaps 15kW of power to dispose of.. one would think that this would happen via multiple PV/GCInverter combinations. I do note the comment about dump-load being an absolutely last choice.

Yes and yes.
Tracker wrote:Whilst I can appreciate the need, I do wonder why you would bother. I can almost hear others groaning about the waste of power that is being suggested. I hear their comments being made that they would be heating something or pumping something or thinking outside the square as to how to semi-productively, use that power..

Yes all true, So a classic scenario that really could happen. A Circuit breaker pops because one of the irrigation pumps systems goes into overload because it gets too hot or there's a blockage, in a few milliseconds there's now 5-8hp of excess power, the batteries are in full float there is no place for the power to go? What do you do with it? Hello dump load everything stays in control no nasty surprises or problems.

Tracker wrote:THEN, I will feed excess power to the HW tank and then, perhaps use a change over contact thermostat to switch the dump load to something like a solid stove hotplate, IF, and only if I have no possible use for that power..

Got them already 700 litres of hot water services waiting to be used for just that, 4 x 4.8kW elements in them.
Tracker wrote:PS.. you could change elements and fit a 4.8kw and better, have a dual element tank,and have twin elements, and perhaps of different size ... eg. 2.4 and 4.8kW this could provide a reliable short term dump..

Dual elements tanks have the second element near the top it will turn off the top section when it hot enough. Once it is all hot what then? or what if an element fails? Tanks splits? A Diversion load of last resort will save you and consume the difference.

Tracker wrote:but most of the thought behind the thread is how to make it happen with what one has or plan to have.. and preferably, on the cheap..

I also mentioned how to do it WITHOUT an SP-pro, so here it is again

For ANY inverter that can be A/C coupled if it does not have digital switching internally to support this, then a peak voltage monitor device connected to the battery bank/pack and an SSR to turn the AC diversion load, the on/off the rate will be pretty fast and gives fairly fine grain control.

There you go a generic fine grain load diversion control of last resort. The rate that it will or can be switched on and off can be very fast indeed any Electro-Mechanical Relays must not be used, this is basically PWM power control. Cheap to do.

Gordon-Loomberah wrote:rather than powering us towards the heat death of the universe with a backyard full of stoves dissipating heat! :lol:

I'm only using 300mm x 300mm x 500mm for the 7.2kW one here (Gross 10.8kW). That's got to be small enough. Any heat it produces is no more or less than the sun produced or is supplied. It's a carbon and heat neutral device.

:mrgreen: :mrgreen: :lol: :lol:
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Re: Load Dumping.. how it helps planning an integrated system..

Postby Tracker » Thu Jun 20, 2013 12:48 pm

Gordon-Loomberah wrote:......If you are using an SSR to regulate the amount of power dumped, the high frequency switching will destroy inductive loads such as air conditioner compressor motors.......


Sorry - I was not thinking in terms of FINE control... Naturally, if you are trying to fine tune the consumption, then it will be pulsing and switching to suit, and anything other than a resistive load, would be a problem..

I was more thinking of just switching in an AirCond, for a set time... or an energy storage device of another kind..
YES, I agree that you would have to be careful, as to how you used a load like an RAC..

It's all VERY much determined by exactly what your system is made up of... That is why I want MY voltage control to include a TIME function as standard..

So, David's comment is completely correct, if the Dump-Load device is a final protection..
But I still wonder if it is not better to use that SSR, to drop out a solar system itself.. assuming we have various PV systems, AC-Coupled... Dropping power to an SSR would instantly kill that solar power, and it could then cycle on and off (60Sec) doing start ups and then drop out again..

Again - it's all academic and determined by the whole system design.. Nothing clear-cut right or wrong.. :roll:
..
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby franks » Thu Jun 20, 2013 2:28 pm

Will change to a AC load dump, use a hard wired 1500 watt ceramic heater element, controlled by dirvert output aux signal from DC inverter-charger, when battery voltage is over 28.8v
Can also use a PWM dirvert control from the MidniteSolar MPPT charge reg, Im thinking to have a fail safe control of 2 solid state relays from both DC inverter charger & charge reg divert controls.
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