Off Grid Backup to Grid

[Boogarweed]

I am a total solar newbie. I have watched a lot of Youtube “how tos” on solar and I THINK I know what I want to do but would really like a gut check from those of you who know what you’re doing. Thanks in advance for the help! I purchased the following equipment:

1ea EG4 6.5kW Off-Grid Inverter

3ea EG4-LL Lithium Batteries - 48V 100AH

1ea DC Disconnect

1ea DC Circuit Breaker

10ea 455 watt solar panels

Various cables

I would like to move my critical loads from my existing panel to a new critical loads panel. Then use the EG4 inverter to power the critical loads panel. I would like to use solar first, then battery and then grid power. I have 2 questions; First, is this doable? Then, if so, is this what I should do since my goal is to cut grid usage as much as possible and have a backup in case of grid down for critical loads. I will upload a drawing of what I am planning.

 

[Bobert]

First I will mention that I don’t have experience with your specific AIO so what I am sharing is based on my experience with AIOs in general.
The short answer is it should work fine. A few things you should be aware of if you haven’t thought of it already.

Make sure your grounding is correct . The neutral should be bonded to ground in your main service panel and no other place. Be sure your ground and neutral are separated in your critical loads panel and not bonded in the AIO either.

Be sure your grid power coming into your AIO is of sufficient amperage to supply both your loads and the load from the Battery charger in the AIO.

The reality is that from a mechanical standpoint the most likely point of failure in your house electrical system will be your AIO it’s self. Flooding, lightning strikes, power surges and the like can all take out your AIO and leave the rest of your house electrical system intact and functioning properly. You need to have your critical loads panel mounted in such a way that it can be connected directly to the main panel without requiring new wire or special tools. So for instance let’s say a freak storm comes through and damages your roof water gets into your AIO and destroys it. Supply chains are disrupted and travel is impossible for days. It’s possible you could have grid power back in days but not be able to get another AIO for the better part of a month. Being able to wire the critical loads panel back into the mains in thirty minutes without purchasing anything could be a lifesaver. Even better a manual transfer switch could accomplish that in seconds.

 

[12VoltInstalls]

So for instance let’s say a freak storm comes through and damages your roof water gets into your AIO and destroys it.

On Thursday a lightning ground strike 600’ away made all my lights (none were on at the time) flash, the MPPSolar AIO relays clicked, and my fridge clicked/snapped simultaneously. I didn’t know that second that it was lightning but in half of a second the crash/thunder peeled and I knew.

So stuff can happen. And I wasn’t grid connected. Surprisingly everything is fine other than my nerves.

 

[Boogarweed]

First I will mention that I don’t have experience with your specific AIO so what I am sharing is based on my experience with AIOs in general.
The short answer is it should work fine. A few things you should be aware of if you haven’t thought of it already.

Make sure your grounding is correct . The neutral should be bonded to ground in your main service panel and no other place. Be sure your ground and neutral are separated in your critical loads panel and not bonded in the AIO either.

Be sure your grid power coming into your AIO is of sufficient amperage to supply both your loads and the load from the Battery charger in the AIO.

The reality is that from a mechanical standpoint the most likely point of failure in your house electrical system will be your AIO it’s self. Flooding, lightning strikes, power surges and the like can all take out your AIO and leave the rest of your house electrical system intact and functioning properly. You need to have your critical loads panel mounted in such a way that it can be connected directly to the main panel without requiring new wire or special tools. So for instance let’s say a freak storm comes through and damages your roof water gets into your AIO and destroys it. Supply chains are disrupted and travel is impossible for days. It’s possible you could have grid power back in days but not be able to get another AIO for the better part of a month. Being able to wire the critical loads panel back into the mains in thirty minutes without purchasing anything could be a lifesaver. Even better a manual transfer switch could accomplish that in seconds.

Thanks for the reply and info! I thought about having a transfer back from the main panel to the critical loads in case of failure. I will have an electrician help me do just that. Thanks again!

 

[Boogarweed]

On Thursday a lightning ground strike 600’ away made all my lights (none were on at the time) flash, the MPPSolar AIO relays clicked, and my fridge clicked/snapped simultaneously. I didn’t know that second that it was lightning but in half of a second the crash/thunder peeled and I knew.

So stuff can happen. And I wasn’t grid connected. Surprisingly everything is fine other than my nerves.

Thanks for the reply! Good info.

 

[meetyg]

First I will mention that I don’t have experience with your specific AIO so what I am sharing is based on my experience with AIOs in general.
The short answer is it should work fine. A few things you should be aware of if you haven’t thought of it already.

Make sure your grounding is correct . The neutral should be bonded to ground in your main service panel and no other place. Be sure your ground and neutral are separated in your critical loads panel and not bonded in the AIO either.

Be sure your grid power coming into your AIO is of sufficient amperage to supply both your loads and the load from the Battery charger in the AIO.

The reality is that from a mechanical standpoint the most likely point of failure in your house electrical system will be your AIO it’s self. Flooding, lightning strikes, power surges and the like can all take out your AIO and leave the rest of your house electrical system intact and functioning properly. You need to have your critical loads panel mounted in such a way that it can be connected directly to the main panel without requiring new wire or special tools. So for instance let’s say a freak storm comes through and damages your roof water gets into your AIO and destroys it. Supply chains are disrupted and travel is impossible for days. It’s possible you could have grid power back in days but not be able to get another AIO for the better part of a month. Being able to wire the critical loads panel back into the mains in thirty minutes without purchasing anything could be a lifesaver. Even better a manual transfer switch could accomplish that in seconds.

Why do you advise against N-G bonding in the critical loads panel ?
Of course there should be only one N-G bond at a time, but unless the inverter he is using is a "common neutral" inverter (which most aren't), his critical loads will also need N-G bonding (preferably dynamic by the AIO, when grid is not in use / not available).
Or am I missing something ?