Off grid Islanding [RE-wrenches]

David Katz david at aeesolar.com
Fri Apr 15 15:19:41 PDT 2005


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Ray,
The SW is bi-directional. if you put ac into the output, it charges the 
battery. The AC in terminal is connected directly to the output through 
a relay. The inverter is quite amazing. If you connect the output of the 
SB and the SW to the same sub panel and turn off all loads you will see 
it charge the battery. If you turn on loads to the point you are drawing 
more than the SB is supplying, it will begin to draw power from the 
battery and supply the excess that the SB is not supplying. I use an 
outback for backup power on my grid connected house this way. As long as 
the SW in turned on, there is a sine wave present at the AC output. This 
makes the SB think the grid is present. I hope this answers your 
question. If not let me know and I will try to draw a diagram.
By the way, if you connect the AC input of the SW or (FX) to a breaker 
in the main panel in a grid connected system it will become your 
connection from the main panel to the sub panel (120VAC) and the 
inverter will turn on whenever the grid fails and keep the SB running. 
If you are using a 240 V SB, you will need an autotransformer or a 
second SW.
David

Ray Walters wrote:

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>> Dave;
>
>
>> I'm not sure I completely follow, are you saying both the SW output 
>> and the SunnyBoy feed the same AC subpanel? If so, how does the SW 
>> recharge the batteries? I thought you had to feed the SW AC in, to 
>> activate the charger, and if the you're feeding AC in what provides 
>> the sunnyboy with an AC waveform to synch to? Do you have a circuit 
>> diagram I could see? I wish we could post low res GIF files of 
>> diagrams to the wrenches list, I think it would save alot of 
>> misunderstanding.
>
>
>
> Thanks for your reply,
>
> Ray
>
>> Hi Ray,
>> I have connected Sunny Boy inverters directly to the output of 
>> Xantrex SW inverters and Outback inverters. It works well. The Sunny 
>> Boy operates when it sees the SW or Outback output. Sometimes it 
>> shuts off when a large load, like a pump is applied to the circuit, 
>> because it looks like a grid failure. If the SB shuts off, it waits 5 
>> minutes to turn on. If there is no AC load on the system and the SB 
>> is supplying power, you will charge the batteries connected to the 
>> SW. You need to put a voltage controlled switch to turn of the AC 
>> between the Sunny Boy and the sub panel if the battery voltage gets 
>> too high.
>>
>> Grundfos makes a BMQE booster pump which has an SQE pump inside of a 
>> stainless tube to allow inline operation. this pump has no starting 
>> surge and would not cause a big strain on the inverter. They make 
>> sizes up to 30 GPM at 20 PSI .
>>
>> Regards,
>> David Katz
>>
>>
>> Christopher Freitas --- OutBack Power wrote:
>>
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>>>
>>> Ray -
>>>
>>> I think your ideas good - but there is a lot of confusion out there 
>>> as to what the SMA Sunny Island inverter is capable of doing in a 
>>> system like this.
>>>
>>> The SMA Sunny Island is very similar to an OutBack FX or the old 
>>> Trace SW series inverter/charger. It is a battery-type inverter 
>>> which is Bi-directional. It is not able to "sell" power back to the 
>>> utility grid though - it can be used to "create" a local grid which 
>>> then you can connect SMA Sunny Boy grid-tie inverters to create an 
>>> "islanded" power system - i.e. an off-grid system with AC-coupled 
>>> power sources.
>>>
>>> I think what your considering is putting the PV array near the pool 
>>> and maybe using regular grid-tie type SMA Sunny Boy inverters to 
>>> allow long distance transmission of the power to the main SW based 
>>> system. This can work - in fact it has been done with using SW's as 
>>> the "utility grid" by a few with some success. I know it works with 
>>> the OutBack FX series as well.
>>>
>>> The real issue is that even with the Sunny Boys added to the system 
>>> the entire AC load needs to be able to run off the capacity of the 
>>> main battery inverter in case a cloud comes over or the Sunny Boys 
>>> shut down.
>>>
>>> In my opinion doing the DC pumps direct from the PV array makes the 
>>> most sense to me.
>>>
>>> Christopher
>>>
>>> Christopher Freitas
>>> OutBack Power Systems, Inc.
>>> cfreitas @ outbackpower.com
>>> www.outbackpower.com
>>> Arlington WA USA
>>> Tel 360 435 6030
>>>
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>>
>> -- 
>> David Katz
>> President, AEE Solar
>> formerly Alternative Energy Engineering
>> 1155 Redway Drive - Box 339
>> Redway, CA 95560 USA
>> (707) 825-1200
>> (707) 825-1202
>> email: david at aeesolar.com
>> web: www.aeesolar.com
>>
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>
> Ray Walters
> ray at solarray.com
> President, SolarRay, Inc.
> NABCEP Certified Solar PV Installer
> BS Mechanical Engineering, UT Austin 88
> Returned US Peace Corps Volunteer
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-- 
David Katz
President, AEE Solar
formerly Alternative Energy Engineering
1155 Redway Drive - Box 339
Redway, CA 95560 USA
(707) 825-1200
(707) 825-1202
email: david at aeesolar.com
web: www.aeesolar.com

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