Use grid as backup instead of generator

nickdearing88

When using these larger 48v split-phase inverter/chargers that accept AC input, is is possible to use grid input in place of a backup generator without requiring an interconnection agreement? I'm still unsure on what "brand-route" I want to take: Schneider, Outback, Magnum, etc but I'm trying to avoid the purchase and use of a generator, if possible. I plan to support 90% of the loads with solar but would feel uncomfortable without some kind of backup.

The original property I was going to purchase did not have grid power available without a $25k - $35k extension from the power company. However, the final property I settled on is much closer to the road and already has grid available. I have ruled-out a GT system or any kind of net-metering specifically because I want to end up off-grid. Also, our local power company makes net-metering a COMPLETE hassle and seems to have very little knowledge of these systems.

I was hoping I could connect grid AC input directly to the inverter (or using an AC transfer switch) without any kind of interconnection/net-metering agreement. I have no desire to sell power back to the grid and would only get a few cents per Kwh anyway. In my area, one can install a backup generator system with no permits or utility approval, as long as everything meets NEC and ensures no power back to the grid while grid is down for safety, of course.

My question is: 1)Do these inverter/chargers ensure that no power can flow back to the grid? 2) That being said, I assume they have a built-in protection device to protect from islanding or is the only safe way to use an AC transfer switch for my loads? 3) I assume there are sufficient software settings to prioritize solar/battery use over the grid connection?

WaterWheel

Yes,     In my county (no building permit required for solar system install) with the Context XWs and probably many other inverters you can use the grid as a backup with no interconnect agreement assuming you program the inverter to not sell to the grid.

nickdearing88

Thanks for the reply WaterWheel. And when the grid goes down, the XW ensures no power can make the utility lines hot? Do you have your XW configured to be primarily off-grid and only use grid as a backup?

My thoughts are this will be a good (safe) way to test the waters off-grid for a few years, while ensuring it's a realistic goal.

Dave Angelini

The XW+ has consumption only mode that will  feed just about zero to the grid and use everything (solar) for your needs when the sun is out. I doubt it makes sense to use the battery to support the grid as every cycle is just more cost to you. Totally safe for utility workers also.

I think it makes sense for you if you really do go offgrid. If not, a generator is much cheaper and if run with propane or natural, much more reliable.

mcgivor

Check the basic charges associated with a grid connection, you know, the hidden fees like delivery charges , transportation levies and whatever other hidden "taxes" they always seem to add to the consumption and still charge them even if you consume nothing. Grid power is invariably cheaper than off grid, despite these fees, if grid was available to me, I would use it with solar backup to reduce the battery requiments. Going off grid to be green and eco friendly is not a reality either, considering the energy taken to manufacture, transport and recycle batteries. Just some thoughts.

nickdearing88

Thanks for the reply Dave. Are you happy with your XW+? I'm intrigued by the Schneider line because I like the integration of products and data collection. What logic can be used to decide when to engage grid power? I assume it can be based on battery bank voltage? Can the grid connection be made to the AC2/gen input for more "backup only" style options.

I also considered more of a manual strategy of connecting the AC but keep the AC breaker switched off and only switch on when needed to support loads and/or charge batteries. The goal is to be as off-grid as possible but have support for unexpected situations, long periods of bad weather, November & December, etc.

Dave Angelini

nickdearing88 said:

Thanks for the reply Dave. Are you happy with your XW+? I'm intrigued by the Schneider line because I like the integration of products and data collection. What logic can be used to decide when to engage grid power? I assume it can be based on battery bank voltage? Can the grid connection be made to the AC2/gen input for more "backup only" style options.

I also considered more of a manual strategy of connecting the AC but keep the AC breaker switched off and only switch on when needed to support loads and/or charge batteries. The goal is to be as off-grid as possible but have support for unexpected situations, long periods of bad weather, November & December, etc.

Probably very near 100 XW's in my client base. You can look at my web page.  I would suggest that you look at the Schneider Solar
 U-tube channel and look at their products. Make sure it is the Solar part of Schneider as the rest of the company is huge. Also consider Outback. 

mike95490

The larger XW inverters have a 60A AC transfer switch internally.  So I don't think you need another transfer switch.
If you use it with just batteries, you have made a whole house UPS
Then you can solar charge the batteries...

nickdearing88

For more of a manual/occasional backup as needed, could grid AC be wired to AC2/gen terminal? I was thinking perhaps a relay could even be used to switch on the AC current, rather than engaging a generator.

Back to individual equipment, it looks like we've got a couple of good reviews for XW's. What about the less expensive SW line? I've read mixed reviews. I've also considered the Magnum route but I am impressed with Schneider's data collection ability. I'm a sucker for data...

Ralph Day

With my Outback equipment I have the grid accepted as AC2.  Programmed to engage the utility when on cheapest rates...but only if it'sbreaker is on.  Lots of sun and wind, no breaker on, no utility power used.  This is not usually on charge mode, just load carrying (charger mode off, but utility power carries house loads).

Dave Angelini

You can also watch your system anywhere in the world with Schneider or Outbacks web portals. The difference in the SW is 3 years less warranty on the 5 year XW+. For Offgrid homes I always use the XW+ because it is built better for those who can't afford to lose power.
Take a look at the Bridge thread 
http://forum.solar-electric.com/discussion/351297/conext-bridge-for-xw-li-ions-from-lg-and-hoppecke-announced-for-2nd-half-2017/p1

nickdearing88

Great to know, thanks to everyone for their comments. I will post again when I have more exact specs put together.

Dave, I like the Bridge idea for sure when researching on the Schneider site. However, it's posts like this that scare me:
http://forum.solar-electric.com/discussion/351990/conext-xw-6848-during-grid-support-mode-waste-480watts-doing-nothing

Dave Angelini

I would say that if you have not been trained, a battery based inverter for grid homes is very hard to do. It is not a DIY project and really requires the knowledge. It is the value added of having a pro! You can search the site here for the many who have done it. One of the original beta testers for the XW was Solar Guppy. You can go over to Outback and find the same stories with their Radian.  I agree it should be easier but there are so many configurations to perform. It is pretty easy to do Offgrid.

nickdearing88

I think I've decided to keep the grid in the picture (for the next few years anyway) and for the non-essential loads like the mini-splits that I won't need to run if the grid is down. The majority of the loads will be wired through the inverter for primary off-grid use but easy access to grid power by the flip of a breaker.

Because I don't really want any of the "grid interaction" features, I'm leaning towards either the Magnum or SW route, simply due to the significant price difference. Since I'll be maintaining grid power, I won't be worried if the inverter needs to be down for service for short periods.

Quick question for users of the Magnum MS-PAE or Schneider SW -- Can it be configured to allow AC passthrough without charging? I imagine several occasions where I may need to enable grid power but want to hold off charging the batteries until the next day's solar power kicks in. I don't see this feature/setting listed clearly in either manual.

Estragon

If I didn't want to charge from grid, I would look for an inverter setting that limits charging current and set that to minimum (zero?).

Dave Angelini

Almost every inverter/charger can have it's charger disabled. The SW can go into self consumption mode and again you should look at the U-tube Schneider channel on the SW in zero export mode.