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

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

Postby Tracker » Wed May 15, 2013 8:32 am

.
Perhaps as a means of helping searchers, I thought it might be good to ask a Dorothy-Dicks question..

How can I disconnect from the GRID.. :?:


We see comments in threads about AC & DC coupling, and these terms have crept into the renewable vernacular , in the last year or so. In another thread on "off grid - what would you do differently" and in other active threads with OFF GRID in the title, there are strong suggestions that AC Coupling was the future.

WHAT IS AC COUPLING, if other than "off topic" stuff from the bedroom

( newbies are reluctant to ask perceived dumb questions )

We are all faced with the reality that our power bills rise, and we seek relief and alternatives, and even the dream of suburban-off-grid and all that comes with it.
We likely all have Grid Connect PV Systems , and we wonder just how we can utilise that investment in extending our renewable contribution.

Almost embarrassingly, I think of all the past discussions as to how we can do unnatural things with our PV systems... :o ..
.. NOW, technology has answered those demands.. :mrgreen:
( but will the energy retailers move to prevent their use, and thus their profits being eroded )

I have started on the journey with a small PV/Battery/inverter setup, connected to the most consistent household power sink in the home.. ie.. a specially wired house circuit feeding refrigerators and some air-conditioning . :D
That has removed a significant load from the grid and our power bill... :P .... We also have two smallish Grid Feed Systems.. and space for more Insolared PV roof Insulators..

Now, I would like to look at what we have and in the most practical way, and move towards Grid-Isolation.

SO,
--- what is the technology that will allow us to integrate Grid-Connected PV and general OFF-Grid technology.
--- what is the cheapest and/or, the best technology that will allow this conversion.
--- what would be the most practical and affordable way of moving from basic grid connection, to off grid..

Time Line.... or perhaps Task Line. ... :?: ...
. Given the usual financial constraints of households, and the assumed PAIN, that will descend upon us all as we move towards repaying the past Federal Wastage, and the rising energy bills, what would YOU do ..?
..
.
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby bpratt » Wed May 15, 2013 10:04 am

I assumed AC coupling was using grid electricty (or generator power) to supplement an offgrid system.

Using a generator to my way of thinking is a pointless execise when you want to go offgrid, unless the supplementing was for when there are days and days of cloudy/rainy weather, or perhaps for plasma cutting (workshop heavy currrent stuff).

Those currently grid fed with panels could supplement their to be offgrid system from an off-peak circuit (if they are not on ToU tariffs), as I was considering with one of those powerstar inverters (although that one is not very efficient!).
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby davidg » Wed May 15, 2013 12:03 pm

bpratt wrote:I assumed AC coupling was using grid electricty (or generator power) to supplement an offgrid system.

That is one form of AC coupling, it is the simplest version of it. (no batteries) called typically Grid-connect. however it is really a form of AC coupling and the simplest way to start. Then move all loads you can to when the power is being produced "DAYtime". Get top brand grid-connect inverter/s they will last the distance.

It is not cheaper to run on batteries off-the grid at this point in time, depending on how much per kWh you pay, it's getting very close but it's not typically cheaper. It is worth doing grid-connect as it will save you money overtime.

bpratt wrote:Using a generator to my way of thinking is a pointless execise when you want to go offgrid, unless the supplementing was for when there are days and days of cloudy/rainy weather, or perhaps for plasma cutting (workshop heavy currrent stuff).

A bigger array will minimise generator use. PV is cheap compared to what it used to cost. An AC grid connected system can be used directly with appliable equipment directly and without modification.

bpratt wrote:Those currently grid fed with panels could supplement their to be offgrid system from an off-peak circuit (if they are not on ToU tariffs), as I was considering with one of those powerstar inverters (although that one is not very efficient!).

Don't, they throw away 20% of the power they produce from batteries, without even trying, also for what it's worth, before you buy ask for an SAA approval number then if you get one go check it out. It would be interesting to see what you get, assumming if you get one.
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby bpratt » Wed May 15, 2013 2:51 pm

davidg wrote:
bpratt wrote: as I was considering with one of those powerstar inverters (although that one is not very efficient!).

Don't, they throw away 20% of the power they produce from batteries, without even trying, also for what it's worth, before you buy ask for an SAA approval number then if you get one go check it out. It would be interesting to see what you get, assumming if you get one.


After reading all about them in here, I chose not to even bother with them. They did have that AC coupling feature though which was nice, but not at the expense of such a poor design.
Kaco 6600
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby davidg » Wed May 15, 2013 2:58 pm

bpratt wrote:After reading all about them in here, I chose not to even bother with them. They did have that AC coupling feature though which was nice, but not at the expense of such a poor design.


No they don't, they are a essentially a very cheap UPS, they are not designed for AC coupling period. They do not have bidirectional charging system built into them, you have to use DC coupled Solar direct to the batteries.
SPS Standalone Power System/Hybrid specialist - Store the Sun!
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby bpratt » Wed May 15, 2013 4:10 pm

davidg wrote:
bpratt wrote:After reading all about them in here, I chose not to even bother with them. They did have that AC coupling feature though which was nice, but not at the expense of such a poor design.


No they don't, they are a essentially a very cheap UPS, they are not designed for AC coupling period. They do not have bidirectional charging system built into them, you have to use DC coupled Solar direct to the batteries.


Now that part I didn't realise, I thought they could charge the batteries up from the mains as well as PV.

Makes it even a worse buy now.
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New house build :-
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby davidg » Wed May 15, 2013 4:37 pm

bpratt wrote:Now that part I didn't realise, I thought they could charge the batteries up from the mains as well as PV.

Makes it even a worse buy now.


Um I appear to have not made myself clear, I'm not a sales person, If I was a real sales person I would have made a fortune, I build or design and install stuff that works.

Those units can use a generator or grid power on the "input side".

AC coupling is when as they are best known a "grid-connect" inverter is connected on the output side of a battery inverter, the Powerstar units are not designed for this at all.

I have not tried it but I think bad things would occur if you tried it, without being able to use ALL the power being produced by the "grid-connect" inverter, because they are NOT designed to be a bi-directional charger. That takes much more smarts than they certainly have in them.

A grid-connect inverter will not function without a suitable 50Hz frequency signal being available to sync to, which the battery inverter must supply it also needs to a stable frequency. E.g. SMA Sunny island or Sunny Backup, Selectronics SP-pro, etc.
Last edited by davidg on Wed May 15, 2013 5:34 pm, edited 1 time in total.
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby bpratt » Wed May 15, 2013 5:31 pm

Don't worry about it, all the previous posts about that inverter had long ago put me off buying one, so it's not just your recent comments about it. :)
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby Tracker » Fri May 17, 2013 9:17 am

bpratt wrote:Don't worry about it, all the previous posts about that inverter had long ago put me off buying one, so it's not just your recent comments about it. :)

W7 -Having one, and tried it, And blown it up, I have to agree with this comment.
At best, they might be used on a boat or similar, where the occasional use would warrant the cost savings..

Two years ago, you had trouble finding alternatives. Today, you can find older Latronics and Selectronic devices on EBay And Gumtree.. clearly, they are available because the owners are migrating from more complex discrete components to fully integrated off grid systems that near completely emulate normal GRID performance..
The average punter does not want to spend their lives hovering over the bloody power system ( like I do - but enjoy it )

I WOULD be confident that connecting a PV system to the W7 (AC Couple )p, would have dire results.
The other thing eluded to is that they are uni-functional... either an inverter or a charger and BOTH very inefficient.. too inefficient for real off grid function, other than for that boat or camper or bush shack..
Ie. You must have something else to charge the batteries properly.. the first w7 that I saw was actually labeled as Shore Power and Boat power.. ie. 240v charge and discharge..

As we see from SOoo many threads , we have all thought about how we can hybridise our PV system, to approximate Off Grid living... We dreamt of ways of AC coupling as it is now called ...

The thoughts were there, but the consistent claim was ----- " no way, magic smoke "
And the bottom line was no one wants to blow expensive inverters etc. trying.... nor this little black duck. ;)

So we have an expectation that DC coupling is easy to do..
DC coupling..?
We assume this is feeding multiple DC sources to a battery system .. easy to do today, with mppt charge controllers, having a master..slave function. AC then comes from inverter(s)...
So multiple PV's can supply the DC that can effectively skip off a fully charged battery, resulting in direct AC from DC.
Naturally, when the sun dies, the batteries provide the a DC..
Naturally, if you can't use the power and the batteries are charged, then the remaining PV power is simply lost.

AC coupling carries more unknowns, and that is the greater unknown..
ie. How we can connect AC sources in parallel, and produce electricity, without that magic smoke..
And.. how we can assemble a system with the smallest battery and the maximum PV input.
Here, we are specifically talking effective off grid.. ie. No grid power being used, but available as a backup resource.

The cheapest package system seems to come from Aussie Solar..
http://www.aussiesolar.com.au/services-tariff-management.html

How does this system compare to other energy management systems, and otherwise, what is the most practical method and the cheapest means of assembling a hybrid AC coupled system..
..
.
Last edited by Tracker on Fri May 17, 2013 10:01 am, edited 1 time in total.
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Re: Going Off-Grid.. AC / DC Coupling - What, How, Why - A Plan?

Postby davidg » Fri May 17, 2013 9:57 am

Tracker wrote:AC coupling carries more unknowns, and that is the greater unknown.. ie. How we can connect AC sources in parallel, and produce electricity, without that magic smoke..
Here, we are specifically talking effective off grid.. ie. No grid power being used, but available as a backup resource.
..
.


Sorry beg to differ on the unknown, it's just newer and for most less understood, The principle is easy enough and has been done for decades, Phase syncing is not new. We have been missing the equipment to be able to leverage it, until recent times, now we have it, some manufactureers are early adopters of being able to provide it equipment that can take advantage of it, or leverage it.
Now we have ways of being able to do what has been done only in DC coupling or we can use both at once if we really want, on and off grid. A great step forward in flexibility for off-grid or hybrid systems. It's just too 8-). Clients really love it because they are such clean installations particularly wiring wise.

:D :D
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