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Headshot: Ironic that an article came up about the topic we were just discussing


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Paul

Adding Battery Backup to Your PV System with AC-Coupling

By: Justine Sanchez
Published In: Issue #168, July / August 2015

 

Batteryless grid-tied PV (GT PV) systems are affordable, efficient, and simpler than their battery-based counterparts. But when the grid goes down, the system goes offline, leaving the homeowner without electricity. Fortunately, there are solutions for those who don’t want their electricity access disrupted by utility outages.

 

There are two different approaches to integrating battery backup into an existing GT PV system—DC-coupling or AC-coupling. Both involve adding a battery bank and a battery-based inverter-charger; plus the associated disconnects and overcurrent protection, and a backed-up (or “critical”) loads subpanel for the appliances that need to continue operating during an outage.
 
The DC Approach
 
The conventional battery-based PV system is “DC-coupled”—all power generation is on the DC side of the system. All sources operate at the same system input voltage, typically 12 to 48 VDC.
 
This strategy avoids the compatibility, technical, or warranty issues of an AC-coupled system (see below). Benefits include having the preferred three-stage (tapered off) battery charge control during all conditions and being able to recharge the batteries during a utility outage, even after they have been drained beyond the low-voltage cut-out point.
 
To minimize wire size, which is more economical for long wire runs, PV arrays can be wired for higher DC voltage (commonly 150 VDC but up to 600 VDC) using a step-down charge controller to convert to battery bank voltage. Energy stored in the battery bank is converted to AC by an inverter–charger, which is usually set up to provide energy first to a critical loads sub-panel, then to the grid through the main distribution panel and utility meter. In the event of a grid failure, the critical loads will continue to be powered by the inverter.

 

(continued)

 

Link to full article

 

 

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angbumabasa

I  just run an inverter off our owner jeep battery with the engine running. From the US where I did similar immediately after Katrina. 120VAC. Here I reverse a 220 to 110 VAC transformer to get 220 VAC. Enough for computer, TV or small fridge. Just run at selected times of limited duration. Have real kerosene lamps for lighting.  Worked fine for Yolanda.

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Headshot

Yes. Ironic. It shows that it is possible to set things up so the tie to the grid opens while the tie to the house (or at least critical circuits) remains closed. I believe there is also a device that protects the battery bank from becoming overcharged (if you have a battery bank in the system).

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angbumabasa

Solenoid switches running off of line voltage open when voltage drops. Simultaneously closing backup power. AC/DC  transformer DC solenoid. Voltage regulator from line voltage to battery backup which which functions like vehicle systems. Solenoid switches there also. On our ships we had battery closets, can't recall how many, all 48 volt DC going to various regulated DC for various processing, data collecting, surveying and navigation systems. At our place similar but simpler.

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fred42

 

 

I believe there is also a device that protects the battery bank from becoming overcharged (if you have a battery bank in the system).

 

Yeah..Thats what the battery charge controller is for.

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thebob

 

 

AC/DC  transformer DC solenoid.

 

It's called a rectifier.

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Paul

Yes. Ironic. It shows that it is possible to set things up so the tie to the grid opens while the tie to the house (or at least critical circuits) remains closed. I believe there is also a device that protects the battery bank from becoming overcharged (if you have a battery bank in the system).

 

As Fred stated, the charge controller does this. It goes into different stages of charge, depending on the state of charge of the batteries. A battery monitor also keeps track of how much energy (DOD: Depth of Discharge) the batteries have remaining in them. 

 

charge_stages.png

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angbumabasa

As Fred stated, the charge controller does this. It goes into different stages of charge, depending on the state of charge of the batteries. A battery monitor also keeps track of how much energy (DOD: Depth of Discharge) the batteries have remaining in them. 

 

attachicon.gifcharge_stages.png

It's called a ';dead band'. Very simple.

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Paul

 

 

It's called a ';dead band'. Very simple.

 

Dead band?

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