Two combiner boxes in series?

davidwillis

I am thinking about setting up a grid tie system. However I would like to be able to add battery backup later.

I am thinking about having two combiner boxes that combine to around 200V each. Then run these two boxes in series to my grid tie inverter (making it run at 400v). This way if I need to run off grid, I can just connect a clasic 200 charger to each combiner box and charge my batteries.

However I am not sure if you can run combiner boxes in series like that, and if I do, could they use 300V breakers, or do I need to go with 600V fuses?

Too bad 600v chargers are so expensive, otherwise I would just use them.

Aguarancher

Unless your grit tie inverter is hybrid, won't you still need an inverter to hook those batteries to?

davidwillis

Yes, I will need an off grid inverter.

ButchDeal

davidwillis wrote: »

I am thinking about setting up a grid tie system. However I would like to be able to add battery backup later.

I think you would be a lot safer, and automated to just add an AC coupled off grid inverter and not play with the DC side at all.

davidwillis

Can I use an off grid inverter as a grid tie without batteries or charge controllers? Maybe I am missing something, but it seems like it would cost a lot more to do an off grid system rather than a grid tie. The whole point is to get a grid tie system up and running (which will be saving me money), then later add an option for battery backup.

Are you saying that it is not safe to connect two combiner boxes into a series? I question if running 300V breakers would be safe, but I Don't see any danger to running them with 600V fuses. But I did want to run it past some people on here to make sure I am not missing something (I easily could be). Of course I would have to have some dissconnects to make it safe while switching over to off grid.

Thanks
David

ButchDeal

davidwillis wrote: »

Can I use an off grid inverter as a grid tie without batteries or charge controllers? Maybe I am missing something, but it seems like it would cost a lot more to do an off grid system rather than a grid tie. The whole point is to get a grid tie system up and running (which will be saving me money), then later add an option for battery backup.

Are you saying that it is not safe to connect two combiner boxes into a series? I question if running 300V breakers would be safe, but I Don't see any danger to running them with 600V fuses. But I did want to run it past some people on here to make sure I am not missing something (I easily could be). Of course I would have to have some dissconnects to make it safe while switching over to off grid.

Thanks
David

My point is that you can get a grid tie up and running then later add an outback system with AC coupling and not have to deal with the DC side.
http://www.outbackpower.com/index.php/flex-coupled-solutions

davidwillis

Ok, I see what you are saying now. However that would be a much more expensive option (at least if you don't go with it from the start). And since the backup power would just be on a rare occation, it seems like a waste of money.

I can get a small off grid inverter for under $1000, add a few golf cart batteries from sams club for $800, and add two classic 200's for about $1100. So for under $3000 I would be able to have a backup system to a 5kw grid tie sytem. For an outback system, I would need to put in a radian 8048 with all the panels, chargers and batteries... about $9000... or a flexpower 2 with chargers, batteries.... $7500 or a Conext XW+ 6848 with chargers, batteries, etc... about $7000. Yes it would be a better system, but for off chance I need it, it is not worth it to me.