Are these supply side taps?

[ggunn]

I appreciate the desire to only back up critical loads in a new sub panel (SP). More efficient.

However, customer wants at least 20 kwh of battery, and everything, including heat pump HVAC, backed up.

Really my reason is: I HATE the "spaghetti" ((#10 and #12 wires and wire nuts) and ton of labor involved with pulling and rebuilding a new back up SP. So many issues arise, starting with 3-wire circuits.
I have learned to put that money toward more battery and just backing up the whole damn house - if possible.

Whole home backup is simpler, that's for sure, and something customers do not realize is that if they get a partial home backup and later decide to add more batteries to back up the whole home, the system will need to be reconfigured.

 

[kwired]

Whole home backup is simpler, that's for sure, and something customers do not realize is that if they get a partial home backup and later decide to add more batteries to back up the whole home, the system will need to be reconfigured.

I do not deal with this sort of equipment but have to ask, wouldn't more batteries just allow longer run time but not more VA output from the inverter? Increasing inverter capacity I can see possibly needing reconfiguration.

 

[ggunn]

I do not deal with this sort of equipment but have to ask, wouldn't more batteries just allow longer run time but not more VA output from the inverter? Increasing inverter capacity I can see possibly needing reconfiguration.

Partial home backup systems are wired differently from whole home backups. When I was doing residential PV design, if we had a customer who wanted a partial home backup with the idea of adding batteries later to change to a whole home backup, we encouraged them to spring for all the batteries up front because the changeover would mean rewiring the system and possibly having to replace some equipment, which could get expensive.

 

[jaggedben]

I do not deal with this sort of equipment but have to ask, wouldn't more batteries just allow longer run time but not more VA output from the inverter? Increasing inverter capacity I can see possibly needing reconfiguration.

AC coupled systems like Enphase and Powerall increase both proportionally. And DC coupled inverters have limits; you generally can't keep increasing the batteries connected to a single inverter by a whole lot before you have to add more inverters, or in some cases at all.

 

[jaggedben]

Whole home backup is simpler, that's for sure, and something customers do not realize is that if they get a partial home backup and later decide to add more batteries to back up the whole home, the system will need to be reconfigured.

I find the distinction oversimplistic. It always depends. If I back up 2 out of 30 branch circuits or 28 out of 30 branch circuits they are both 'partial home'. I can imagine two different scenarios where each option is easiest and cheapest (namely one where the branch circuits are almost all in a meter/main, and another where they are almost all in a subpanel). It always depends. I've never technically done a 'whole home' because I don't think it's wise not to have the service equipment and overcurrent protection upstream of an MID that might need to be bypassed or replaced.

 

[ggunn]

I find the distinction oversimplistic. It always depends. If I back up 2 out of 30 branch circuits or 28 out of 30 branch circuits they are both 'partial home'. I can imagine two different scenarios where each option is easiest and cheapest (namely one where the branch circuits are almost all in a meter/main, and another where they are almost all in a subpanel). It always depends. I've never technically done a 'whole home' because I don't think it's wise not to have the service equipment and overcurrent protection upstream of an MID that might need to be bypassed or replaced.

Of course; "partial home backup" can mean a lot of different things, but a whole home backup means the ATS or gateway is on the service conductors, while a partial backup is usually a load side connection. Changing from one to the other can be costly, sometimes approaching the cost of the battery they want to add later.

 

[kwired]

AC coupled systems like Enphase and Powerall increase both proportionally. And DC coupled inverters have limits; you generally can't keep increasing the batteries connected to a single inverter by a whole lot before you have to add more inverters, or in some cases at all.

Again I don't deal with this sort of equipment I guess I can see what you are saying to some extent with AC coupled systems, but still seems to me on a basic level an inverter would have a max VA output rating and possibly even can be programmed not to deliver excess power, at least not for any extended time period. More battery would simply mean more run time before needing recharged again.

 

[jaggedben]

Of course; "partial home backup" can mean a lot of different things, but a whole home backup means the ATS or gateway is on the service conductors, while a partial backup is usually a load side connection. Changing from one to the other can be costly, sometimes approaching the cost of the battery they want to add later.

It just depends. Sometimes it's a lot more work to move loads than other times. I've also backed up entire homes (all the existing circuits) without making the MID (gateway, ATS) the service equipment.

 

[jaggedben]

Again I don't deal with this sort of equipment I guess I can see what you are saying to some extent with AC coupled systems, but still seems to me on a basic level an inverter would have a max VA output rating and possibly even can be programmed not to deliver excess power, at least not for any extended time period. More battery would simply mean more run time before needing recharged again.

Yeah, but what ggunn points out correctly is that what really matters cost wise is often the work relocating the loads or changing the location of the MID or the size of the feeders to it. (I suppose you could say that's not the 'system', but that's a finer point.)

 

[Zee]

I find the distinction oversimplistic. It always depends. If I back up 2 out of 30 branch circuits or 28 out of 30 branch circuits they are both 'partial home'. I can imagine two different scenarios where each option is easiest and cheapest (namely one where the branch circuits are almost all in a meter/main, and another where they are almost all in a subpanel). It always depends. I've never technically done a 'whole home' because I don't think it's wise not to have the service equipment and overcurrent protection upstream of an MID that might need to be bypassed or replaced.

Yes, sure does depend.
1. Sometimes an existing sub panel (SP) has the critical loads we want to backup. I love these jobs. Then we just back that SP up.
2. Rarely an (E) SP has all the loads already, so we do a partial home backup..... but really it is a whole house backup.
3. Sometimes we put in a new SP and move some/all loads into it. But I HATE doing this if there are more than 3 load circuits...... the MSP and SP is far away from each other, and/or opening up walls required.

 

[Zee]

Again I don't deal with this sort of equipment I guess I can see what you are saying to some extent with AC coupled systems, but still seems to me on a basic level an inverter would have a max VA output rating and possibly even can be programmed not to deliver excess power, at least not for any extended time period. More battery would simply mean more run time before needing recharged again.

Whether adding add'l batteries increases capacity (kwh) only.... or capacity and power (kW) depends on whether it is an AC or DC battery system.
AC coupled essentially parallel connects add'l battery inverters, boosting your power available (kW).
DC will just increase capacity (kWh) as the inverter is the bottleneck.

E.g. in this case just 3 @ 5 kWh Enphase batteries (AC coupled) will boost the KW and Amps so much that it will start a 5 ton HVAC heat pump A/C unit.

 

[Zee]

Then this panel doesn't help.

Wait, doesn't Enphase tie in like that?
Been a while, and i have been installing DC BATT systems (Solaredge BUI's) that do need to re-route the service conductors........ but i thought Enphase just needs to tap the service conductors.
I will be studying the new Enphase IQ5P this week in any case.

 

[ggunn]

3. Sometimes we put in a new SP and move some/all loads into it. But I HATE doing this if there are more than 3 load circuits...... the MSP and SP is far away from each other, and/or opening up walls required.

Wait till you have to convert a service panel to a protected loads subpanel and there are a bazillon neutrals and grounds all mixed up on the ground and neutral bars.

 

[jaggedben]

Wait, doesn't Enphase tie in like that?
Been a while, and i have been installing DC BATT systems (Solaredge BUI's) that do need to re-route the service conductors........ but i thought Enphase just needs to tap the service conductors.
I will be studying the new Enphase IQ5P this week in any case.

No they are not really different, the MID always needs to be in series between the grid and the backed up loads. You could tie in an Enphase System Controller to those lugs but the branch circuits won't be on the load side and therefore won't be backed up unless you move them to a subpanel.

 

[kwired]

Whether adding add'l batteries increases capacity (kwh) only.... or capacity and power (kW) depends on whether it is an AC or DC battery system.
AC coupled essentially parallel connects add'l battery inverters, boosting your power available (kW).
DC will just increase capacity (kWh) as the inverter is the bottleneck.

E.g. in this case just 3 @ 5 kWh Enphase batteries (AC coupled) will boost the KW and Amps so much that it will start a 5 ton HVAC heat pump A/C unit.

Thanks, that answered my question. Don't deal with this equipment so don't know all the finer details that can come up.
My knowledge of these things was mostly just considering what you mentioned about DC coupling and the inverter being the bottleneck - could never exceed the power rating of the inverter but could in theory infinitely extend run time at that level with infinite number of batteries.

 

[Zee]

No they are not really different, the MID always needs to be in series between the grid and the backed up loads. You could tie in an Enphase System Controller to those lugs but the branch circuits won't be on the load side and therefore won't be backed up unless you move them to a subpanel.

Thank you.

 

[Zee]

Thanks, that answered my question. Don't deal with this equipment so don't know all the finer details that can come up.
My knowledge of these things was mostly just considering what you mentioned about DC coupling and the inverter being the bottleneck - could never exceed the power rating of the inverter but could in theory infinitely extend run time at that level with infinite number of batteries.

Exactly.
Just one correction: inverters limit how many batteries can be connected to the inverter.

 

[kwired]

Exactly.
Just one correction: inverters limit how many batteries can be connected to the inverter.

By physical design? Electrically all they should care about is input volts and you should be able to put unlimited number if they are all same volts in parallel and it wouldn't know the difference.

 

[jaggedben]

By physical design? Electrically all they should care about is input volts and you should be able to put unlimited number if they are all same volts in parallel and it wouldn't know the difference.

Short circuit current ratings matter. But perhaps more importantly, these kinds of energy storage systems aren't banks of dumb batteries these days. They are connected either through BMS with DC-to-DC converters, or they have inverters and connect to AC. They require comms to operate with each other and are engineered for a certain max number the system can support.

 

[ggunn]

Exactly.
Just one correction: inverters limit how many batteries can be connected to the inverter.

And PowerWalls have a limit on how much PV can be connected to them when they are operating off grid.