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Author Topic: off grid spec for chewing  (Read 27268 times)
billi
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« Reply #15 on: June 30, 2012, 08:57:56 AM »

Personally  , if i would start again  , i would use both "AC coupling"  and MPPT controller  and somehow  try to match the AC coupled part  close to the energy consumption used during the day ( or the base load)  and the rest (or the bigger part) of the Modules  connected to a MPPT controller 


In a Wind /PV  hybrid  system  surely the windturbine AC coupled   , cause the turbine will work more efficient and not in relation to Battery voltage

Billi
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« Reply #16 on: June 30, 2012, 09:31:50 AM »

Personally  , if i would start again  , i would use both "AC coupling"  and MPPT controller  and somehow  try to match the AC coupled part  close to the energy consumption used during the day ( or the base load)  and the rest (or the bigger part) of the Modules  connected to a MPPT controller 


In a Wind /PV  hybrid  system  surely the windturbine AC coupled   , cause the turbine will work more efficient and not in relation to Battery voltage

Billi

so ineffect your splitting the array into two. one to power directly and the other to supply the storage. would that offer benifits over say having all the array ac coupled.   
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camillitech
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« Reply #17 on: June 30, 2012, 10:33:08 AM »

Hi Paul,

supplying the loads direct is more efficient with AC coupling and storage, you are in effect 'double handling' your power and at every conversion there is a loss of efficiency. Probably works well in Greece as many of your loads coincide with PV production, like air con and pool pumps. Here in Scotland it's the opposite, or at least is unless you alter your lifestyle. The main advantage of AC coupling is flexibility, you can have multiple power sources great distances apart of different voltages and combine them easily.

My 'mini grid' is about a mile from one end to the other so it works well but in many circumstances it is not an efficient way of doing things.

Good luck, Paul
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billi
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« Reply #18 on: June 30, 2012, 10:48:51 AM »

I cannot tell you the efficiency  in exact detail
But for sure AC -coupled  is more efficient when  consumed direct as well it adds AC power to the off grid inverter
Mppt     charge-controller will charge the battery better than AC coupled ...

Sure  one ads  another component to the system  and that adds costs

One thing i have not found out yet , is the efficiency of the internal charger of the off grid inverter in relation to the Watts that come from the Grid tie inverter

In my case , i have only a 300W GTI  as a trial  connected (wind)    ....... it basically  supplies the house loads direct , but seldom manages to backfeed  into my offgrid inverter to charge , even when i switch of most loads in the house
I can watch the amps on my laptop that would flow into the battery  and in good wind , when one expects more coming than consuming , the Amps just  sit most of the time at 0 , jumping to  one or two Amps (so 24-48 Watt)  .
This tells me (not sure if i am right)  that i need  more power  to even start the internal charger of the off grid inverter , and i assume that there is some sort of an efficiency  curve  for the internal charger  and that it is less efficient ,when only small power reaches the internal charger ,
I  guess also only ,that AC-coupling promoters , use efficiency  ratings   , when internal charger efficiency is the highest or working with lots of watts coming in  , but that is not always the case  Roll Eyes

But on the otherhand  a MPPT controller has a efficiency curve as well , here my one





Just a few thoughts   and i would like to see a performance  curve  of an internal charger of the off grid inverter , when converting 230 volt  to battery DC

Billi
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« Reply #19 on: June 30, 2012, 11:32:22 AM »

Billi those cheap Chinese GTI's are notoriously inefficient, sure much better than what you had and a great economical solution for what to do with a small poorly sited wind turbine but I would not read too much into how yours performs when compared to a proper GTI.

On Utube, I saw inside of them, Those troublesome GTI, they use High frequency switching FE-transfomers, ( Widely use in low cost Computer power supply), One FE-Transfomer = 300W, 2 fe-transformer = 600W and 4 fe-transformer = 1200W, They are very light weight and inexpensive but with many problems.

Good Grid tie inverter use high quality low frequency transformer, They are much heavier but their efficiency reach 95% at full rated power and meet CEC standard.


and

you can buy cheap Ebay Chinese GTI invertor, That "Power Jack" model is very low quality and dominated EBay.
For example:

3000Watts "Power jack" GTI inverter
- $900 Ebay

3000 Watts Germany "Sunny boy" GTI inverter
-$1600

Although Power Jack is much cheaper than Sunny boy, It is not UL1471 listed, and overated it power rating, One user mentioned that 6 of his Power Jack GTI was burned out within one year, Real world power efficiency is between 82% to 85% while Sunny Boy is near 90+% range, Waste energy = Waste money = over heated = GTI burned out.


from a thread here http://www.solarpaneltalk.com/showthread.php?6388-Grid-tied-inverter-110V-VS-220V

Cheers, Paul
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« Reply #20 on: June 30, 2012, 02:19:02 PM »

Another interesting advantage of the SMA AC coupling solution is that if you have a large distributed system then you can easily control loads based on the frequency.  E.g. turn on pool pump only when there's surplus PV power.  Granted you can do this with the relays built into some charge controllers and inverters, but then the load has to be close enough to the device to make this practical.  With the AC coupled system, you just need a frequency dependent relay and you can control any load anywhere on the AC bus.

Efficiency wise, you need to be careful, because the smaller transformer based GTIs tend to be not that great when it comes to efficiency.  The SB 3000 for example comes in at 93% I think, which is WORSE than most battery based inverters.
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« Reply #21 on: June 30, 2012, 06:21:33 PM »

I know Paul , my experimental GTI is  not top class  Grin , but in regards to battery charging through an inverter/charger  -AC coupled-
it does not really matter 


But still my point is  , that i would like to know the efficiency  of the internal charger of the off grid inverter  , not only the  efficiency of  whole unit or the inverter part

In the Studer  Whitepaper http://www.studer-innotec.com/upload/temp/Partial%20AC-coupling%20in%20Minigrids.pdf

 they base the charger being as well at 93 % efficient,  like  the whole unit  , and i personally doubt this , especially when only a small amount of power reaches the charger





But perhaps peanuts

Billi
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« Reply #22 on: June 30, 2012, 06:48:06 PM »


 they base the charger being as well at 93 % efficient,  like  the whole unit  , and i personally doubt this , especially when only a small amount of power reaches the charger






Yes Billi, I very much doubt that too but it is a good and flexible system for certain applications. It would be good to know the true efficiency as I am toying of doing away with the transformer on my Stream Engine and 'AC coupling' that using a bridge rectifier and GTI as transformers are also notoriously inefficient.

It does not actually make a great deal of sense to do it that way for the improved efficiency but does for the flexibility. At the moment The transformer takes it from AC wild 3 phase to DC 48v battery charging. If I AC couple it I could use it on a 24v forklift battery bank that I have if I could get hold of a 24v inverter/charger cheaply.

I'm just thinking if we sell the house and have to move into the caravan quickly, instead of having to shell out now for the SI5048 and all those Rolls Cells I could just use this second hand 400ah bank of cells I have for now. The Powerspout is already coupled and the Stream Engine would make a useful contribution to some dump loads for heating.

Cheers, Paul

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'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
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« Reply #23 on: July 01, 2012, 09:15:50 AM »

But still my point is  , that i would like to know the efficiency  of the internal charger of the off grid inverter  , not only the  efficiency of  whole unit or the inverter part

In the Studer  Whitepaper http://www.studer-innotec.com/upload/temp/Partial%20AC-coupling%20in%20Minigrids.pdf

 they base the charger being as well at 93 % efficient,  like  the whole unit  , and i personally doubt this , especially when only a small amount of power reaches the charger

I think the efficiency of the inverter part and the charger part will be the same because I believe it's the same electronics that does both (This why it can't invert and charge at the same time).  The efficiency graph of the 5kW SI is attached.  Looks like better than 93% between  250W and 3500W.  The efficiency of the sunnyboy is also going to be not-so-great at the low levels.  I'm waiting for the micro-inverters SMA are supposed to be releasing this month  Smiley




* Screen Shot 2012-07-01 at 10.15.37.png (25.36 KB, 430x274 - viewed 590 times.)
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« Reply #24 on: July 01, 2012, 09:43:56 AM »

Quote
This why it can't invert and charge at the same time

Oh , i did not know this ........ , so the Sunny Island can not add power to a second AC source ?  Or do i understand it wrong ?
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« Reply #25 on: July 01, 2012, 12:08:59 PM »

Quote
This why it can't invert and charge at the same time

Oh , i did not know this ........ , so the Sunny Island can not add power to a second AC source ?  Or do i understand it wrong ?

It can add power to second AC source, but while doing so it's not charging Smiley   All inverter/chargers work in a similar way, none of them can charge and invert at the same time AFAIK.
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« Reply #26 on: July 04, 2012, 12:55:35 AM »

Just to add to the mix here.

The use of an EMMA to manage extra production is a possibility.

The TL SMA units are very good eff at lower power ratings than older transformer based units (3000, 3300 and 3800)

I see AC coupling being the best way to manage the power and it does allow for extra capacity to be added later at much less cost.  The load is mostly in the day is what i would expect and extra capacity may be needed whilst extra storage not needed and the off grid unit will not need to be increased to cope with extra production if extra demand is produced.

Intresting thread.

Cheers and gone.

Jon


« Last Edit: July 04, 2012, 01:00:53 AM by Other-Power » Logged

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« Reply #27 on: August 08, 2012, 03:12:06 PM »

If the 5kwp array was split what % for charging and what % for ac? As a thought an outback 80amp could handle 3000w (3x250w panels in series x 4 strings=12panels) and a sma 2000 for the remaining 2000w.
 
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« Reply #28 on: August 08, 2012, 03:50:25 PM »

If the 5kwp array was split what % for charging and what % for ac? As a thought an outback 80amp could handle 3000w (3x250w panels in series x 4 strings=12panels) and a sma 2000 for the remaining 2000w.
 

Seems like a good plan to me but don't forget you'll still need to be able to dump 5Kw as your Sunny boy won't throttle the panels unless you use it with an SI. I don't think that the Studer will 'frequency shift' or will it??

Good luck, Paul
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'Off grid' since 1985,  Proven 2.5kW, Proven 6kW direct heating, SI6.OH, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup,
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« Reply #29 on: August 08, 2012, 09:07:50 PM »

will be using the 5048sma so this will help with the sunny boy? 
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