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

3 Posts
Oct 20, 2008 03:25 am
how to set up a battery based PV system with GRID BACKUP

Yes, you read that right. I live in Hawaii, where the utility rates are .$.40-$.50/kWh. I want to design a system that relies on batteries, but backs up with the grid (instead of a generator) I'm hoping that a good outback GTFX can be programmed to do this(and that it will be easy?)...but it's not a typical application, and to boot, I have no experience.

There are a number of reasons I want to do this; (1) I'm not confident in the long term viability of the grid, and (2) we can no longer net meter here, so if I grid-tie, I have to buy at $.40-$.50 and sell at $.20-$.30. (3) I run a B&B out of my home so I can't go completely off-grid yet (people bring hair dryers) and a generator would be too loud.

I just picked up a used PV system - (20) 24v BP panels, but it came with a sunny boy grid tie (swr2500U, wanna buy it?)

One more thing...I may add a wind turbine in a year or two.

Am I crazy? Beyond help? What should I read first? Thanks for any and all help

Aloha from Kauai

 
184 Posts
Oct 20, 2008 10:36 am
Re: 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
 
 
27 Posts
Oct 20, 2008 02:14 pm
Re: how to set up a battery based PV system with GRID BACKUP

Loved your blog ,have any detailed schematics you would like to share.I think you have hit on a great idea.
I'm getting to the point of being able to do such a thing and would need detailed instructions.
If you can't help with this, I truley enjoyed your blog and your idea.
Thanks
Rene
 
184 Posts
Oct 20, 2008 03:52 pm
Re: how to set up a battery based PV system with GRID BACKUP

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.

   
 
27 Posts
Oct 21, 2008 02:27 pm
Re: how to set up a battery based PV system with GRID BACKUP

Ok 1 Iota transfer switch
1 morningstar relay driver
what did you use for relays ??
Thanks
Rene
 
184 Posts
Oct 21, 2008 06:45 pm
Re: how to set up a battery based PV system with GRID BACKUP

Ok 1 Iota transfer switch
1 morningstar relay driver
what did you use for relays ??
Thanks
Rene
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. 
 
4 Posts
Dec 25, 2008 09:40 am
Re: how to set up a battery based PV system with GRID BACKUP

I stumbled across this posting and what the person here wants to do is same as me. I have a xantex 1800 power hub with solar and wind to charge batteries. I want to use the hub when power is available and the grid when it is not. I thought the xantrex would do that for me but when got it, it does not. Sounds like the lota transfer switch is me answer. Thanks for sharing this.
 
220 Posts
Dec 26, 2008 05:26 pm
Re: how to set up a battery based PV system with GRID BACKUP


 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,
 

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