12 kPV with grid interlock (to avoid a critical loads panel)?

[Free_Sun_Power]

Hello. Newbie here. The timing was right and I finally justified purchasing a pair of 12 kPV EV4 inverters + an indoor EG4 PowerPro wall-mount battery + around 20 kW of Hyperion 400W panels. I am in the planning/ implementation phase currently. I purchased the 12kPV inverter over the 6000XP assuming that the 12 kPV had a better (easier) 200A panel interconnection system with full house back-up. But now I'm faced with the reality that accomplishing a whole-house backup with grid interconnect is more challenging and costly than I anticipated (mostly due to grid-feed in case of power outage). My goal in this order is: Offset my current energy use with solar; 2). Charge the battery daily to utilize that power at night (sprinklers, etc.) 3). Sell the excess power to my utility (above-and-beyond when my battery is full). My utility interconnect is in-progress (planning-stages).

However, after reading some other forums, it seems there is an easier way being floated. I tried to draw-up what I can imagine being an easier way to accomplish this task. First, the details: I have a 200A panel but according to an hour-by-hour download of my energy usage for the past year per my utility, my highest hourly average load was 5 kW. So I want to avoid a critical loads panel if possible since in case of a power outage, I can turn-off non-critical appliances at my main panel with high start-up loads to keep within the 12 kW of surge load and 8 kW continuous load. What I read is that generator interlocks are legal in the US (perhaps vary from local municipality to local municipality). So, as you can see from the attached diagram, (assuming my local municipality doesn't disallow), would such a interlock design cause issues? This would remove the need for a critical loads panel and also manual transfer switch.

 

[TM48]

How do you intend to feed grid power to your inverter? Also I predict you will be buying a second 12kpv and battery.

 

[Free_Sun_Power]

During normal times when the grid is 'up', the inverter is grid-tied through the supply side-tap (per EG4's recommended "12kPV with Supply Side Tap and Partial Home Backup" reference diagram).

During rare times of a power-outage, I would utilize the PV + battery power through the inverter's Load output and to my main 200A panel through a generator interlock (to avoid back-feeding the grid) or essentially as an off-grid system temporarily.

To your second point, I did purchase a second 12 kPV inverter since I have 2 electric meters - one for household power/ appliances and a second on a geothermal time-of-day rate which takes-care of my home heating/cooling. The 14 kWh PowerPro will be paralleled between the 2 inverters and will suffice for now and for the forseeable future until I pay-off this system and battery prices get even lower. (this set-up is a whole different subject, but my main question is whether the above 2 paragraphs present any unseen issues that I may be overlooking).

 

[TM48]

You may have issues trying to supply two 12k's with one 280ahr battery. The recommendation is 200 ahr each.

 

[Free_Sun_Power]

You may have issues trying to supply two 12k's with one 280ahr battery. The recommendation is 200 ahr each.

Yeah, I'm going to have to probably play with this in the settings in the 12 kPVs. I haven't gotten there yet. The main goal would be to prioritize battery for the household loads since that rate is much higher rate than the geothermal rate. I may only use battery power for the geothermal if we had a significant power outage and in that case I would dial-back my household usage to almost nothing.. The main advantage to paralleling the battery is really for PV charging. My 20 kW PV array will need more than one 12 kPV inverter during the best PV days but I plan on adjusting the battery charge rate down in both inverters for when I have significant surplus PV minus loads, then just sell more back to my utility. (but then again thinking about it more, I see your point about the battery size)

 

[Free_Sun_Power]

I wanted to bump this thread to see if I can get a few more sets of eyes on what I'd like to do. (and opinions)

When I contacted EG4 technical service last week, they shied-away from advising on grid interconnecting - other than of course the literature they have currently published. That's why I wanted to get help from the community and potentially avoid an unnecessary critical loads panel and manual transfer switch if I can.

 

[TM48]

I have a critical loads panel which is separate from the grid supplied load center. I do however have a grid bypass circuit which is interlock protected from the grid to the CL panel. This was used prior to commissioning the solar system and remains in case of catastrophic failure of the solar system. My AHJ had no problem with it. The biggest problem for this method for you is the inability to offload heavy loads individually. In my case I left the range and heat strips on my heat pump on grid which was easy with the second LC. You might consider adding a small LC that is grid supplied for any similar purpose.

 

[Free_Sun_Power]

Thanks for the advice with regard to the interlock and an explanation of your set-up. I'm trying to avoid a CL panel if all possible since I really don't have any heavy loads. My range is gas and my heating/ cooling is done by the geothermal heat pump which is dedicated to inverter #2. The only exception is I have an electric tankless water heater which I could just switch-off in the case of a power outage when I use the generator interlock.

 

[p5k6]

You know - I think Jesse Muller may have done something like what you’re thinking about. Check out this video -

(No affiliation btw - I’ve just been watching/reading a lot of videos/info as I’m prepping my own system)