how to set up a battery based PV system with GRID BACKUP

Without going into a lot of detail, what you need is an automatic transfer switch.  (Some inverters have this functionality built-in).  I have a separate automatic transfer switch, configured to use my inverter as the primary source of AC.  My inverter is configured to shut-down when battery voltage drops below acceptable levels.  When the inverter shuts down, the automatic transfer switch connects grid-power to the loads. 

Your equipment will be different than mine, but basically you need two things:  1.  A way to shut down the inverter when batteries get low.  2.  A way to switch to grid-supplied power when the inverter shuts down.

You might look into an IOTA automatic transfer switch.  I have more information about my system on my blog:  http://solarjohn.blogspot.com

Hope this helps.

John
 

Thanks for the kind words Rene.  If you'll check through my blog archives, you'll find a diagram of my system in my 2/25/2008 post.  You're welcome to duplicate my work, but you'll have to make some adjustments if you're using equipment that is different than mine. The heart of my system is a Morningstar Relay Driver.

My goal is to use as much of the available energy as possible (minimize waste).  I'm constantly monitoring performance, and tinkering with potential system improvements.  I'm working on diversion load control enhancements right now. 

If you have any specific questions, I'll be happy to respond.

   

Actually, the relays came from my spare parts box.  They were bought many years ago from Radio Shack.  You can use any relay with a dc coil voltage that matches your battery bank, 12volts dc for example.  Try Jameco, Digikey, or some other on-line source of electronic parts. 

 hi jerry,

 i like the idea that xantrex had with those power hub all in one units. looks like a good way to get your feet wet in renewables.

 that model you have has a 20amp automatic transfer switch built in so when the line (ac) power goes down it goes into battery backup mode.

  what we need here is a voltage sensitive relay driver like the one john mentioned in this post.
http://search.altenergystore.com/search?p=R&srid=S1%2d3&lbc=altenergystore&w=reley%20driver&url=http%3a%2f%2fstore%2ealtenergystore%2ecom%2fEnclosures%2dElectrical%2dand%2dSafety%2fMiscellaneous%2dElectrical%2dParts%2fSwitches%2fVoltage%2dControl%2dSwitches%2fMorningstar%2dRelay%2dDriver%2dLogic%2dModule%2dAccessory%2fp792%2f&rk=2&uid=270843492&sid=2&ts=v2&rsc=ULTGZRdh:BHmmanU&method=or&isort=score&ref=MORRELAYDRIVER

or if you are handy with an iron heres a kit.
http://www.jaycar.com.au/productView.asp?ID=KC5377&CATID=&keywords=Voltage+Switch&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=

 with a driver like this we can power a relay to shut the line power off to that power hub and go into battery mode at a user settable (high) battery voltage and back to the ac pass thru/charge mode at a settable (low) battery voltage.


 i like the idea of using that generated power in some useful way rather than diverting it to a dump coil (wind) or shutting down production (solar).

 we did not see what you are using for a solar charge controller but some of them have a built in settable trigger for this sort of thing.

 yikes! i'm in the middle of this post and i see that this setup won't work with this application...when the ac power comes back on line it will keep triggering the cycle!!(due to the built in charger)oops.

 how about this. we set a timer to shut off that line power to the power hub for a few hours every afternoon and watch the results and adjust the timer/load accordingly?

 back to the charge controller, we may be able to grab a trigger source from a (charging indicator) on the controller? or right from the pv input..not sure?

best regards,