Adding battery backup to existing grid-tie PV system [RE-wrenches]

[William Korthof]

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Good points... the SI is a great match for these applications.
We used the outback because it's familiar, a little lower cost, and we 
had it in inventory.

We used the Deka sealed/deep cycle "solar" batteries... not flooded 
batteries, no maintenance.

/wk



Jeff Clearwater wrote:
> 
> Hi William,
> 
> Yes I would also recccomend you look at using a Sunny Island.  That way 
> you get all of the PV output available (well all one SI can handle which 
> is about 5KW of PV on SBs) and don't have to do relay control which is 
> iffy.  You'll find the price is not much more when you consider the SI 
> includes the DC disconnect.
> 
> Also you say 4 (8D) batteries.  I was under the impression that 8Ds 
> aren't true deep cycles - more of an industrial starting battery for 
> CATS and such.  And you might want maintenance free batteries for these 
> folks.
> 
> Hope that helps!
> 
> Best,
> 
> Jeff C.
> 
> 
> 
>> We have a customer from a several years back who bought a larger 
>> system (~7kW AC system) which used 3 SMA 2500 and 1 SMA 1800 
>> inverters... they always wanted battery backup, but given their high 
>> end, low maintenance lifestyle, I wasnot eager to throw a pile of 
>> batteries, miles of heavy 48 volt wiring, and dual SW inverters at 
>> this application. But when they called a couple months ago discussing 
>> their extended and unseemly LADWP power outage frequency, and apparent 
>> willingness to let go of the whirlpool, sauna, wine chiller, outdoor 
>> light show, and multi-level HVAC refrigeration system (at least during 
>> power outages), I took note.
>>
>> Rather than dig in and rewire the PV array (or alternately), install a 
>> backup power system that didn't use the PV system... we came up with 
>> an interesting compromise:
>> install (1) new Outback GVFX inverter with (4) 8D deep cycle batteries,
>> this inverter is directly grid-tied, like the existing SMA inverters.
>> On the (backed-up) load side of the inverter, we conneced the frige, a 
>> few lights, computers, and a couple other important items. In 
>> addition, we reconnected the (1) SMA 1800 inverter onto the load side 
>> of the outback. When the outback is online (whether grid-tied or 
>> standalone) the SMA inverter feeds in power to offset emergency loads 
>> (and even charge the batteries if the power draw is lower than solar 
>> output).
>>
>> This approach requires redundant inverter capacity (extra cost), but 
>> allows the PV array to be wired at high voltage, enabling a larger 
>> array and longer electrical feeder distances if needed.
>>
>> I'm thinking that this is a reasonable compromise solution (cost, 
>> labor, performance...) for us to use as a retrofit/upgrade on older 
>> systems, as well as a decent way for us to furnish battery backup 
>> power with systems that wouldn't otherwise be compatible (Sunpower).
>>
>> I'm sure others have already done this... were you satisfied with the 
>> results? Any issues of note?
>>
>>
>> /wk
>>
>>
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> 
> 
> 


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