New DIY system for peak shaving and emergency backup

[jeremieb]

I live in Quebec, Canada and I am looking to install a small system with a inverter+battery that can peak shave and also be used during power outages. At the moment, I am not looking to add solar due to limited space and cost. I was looking to start small with a ~6kW inverter (EG4, Victron, Solark, or even Anker/Bluetti) and 5kWh of server battery (to be added on later). I am trying to keep cost low probably around 5k$ for now as realistically, I will never pay off the cost (due to cheap rates in Quebec) but having power during an outage is priceless !

I currently only have a house panel. I drew 3 possible wiring options. All options have their pros and cons. Personally, I think option 2 is the best compromise but I do not know what inverter would fit the bill.

Option 1​	Option 2​	Option 3​
Peak Shaving	- Only loads on critical panels can be load shed which may not be close to inverter capacity	- based on CT reading, house loads can be zeroed upto inverter capacity	- all loads through inverter - house loads can be zeroed upto inverter capacity
Emergency Backup	- Critical loads fully backup seamlessly	- All house loads can be fed by operating interlocked breakers - May need to load shed manually	- All house loads fully backup seamlessly
Cost	- New panel required - off grid inverter possible	- hybrid inverter may be required?	- hybrid inverter required

My house is relatively new and efficient. All appliances are electric (electric stove, conventional dryer, conventional water heater, heatpump for heat/AC, strip heaters as backup).

Is there a better way to do what I want? Am I overcomplicating this? What inverter would best fit each option

Thank you for the help!

 

[MisterSandals]

and 5kWh of server battery (to be added on later)

All appliances are electric (electric stove, conventional dryer, conventional water heater, heatpump for heat/AC, strip heaters as backup).

How long are you expecting any power outage to last? I'm thinking that a 5kWh battery would keep a refrigerator powered for 2-3 days. Any of the items listed would deplete the battery in hours not days.

install a small system with a inverter+battery that can peak shave

This is referred to as time shifting and is illegal in many areas. Are you planning on being permitted? If so, this would be a good thing to investigate early on in your process.

How much extra are the peak rates than the low rates? There are inefficiencies with charging and then inverting that will reduce any savings, have you done the math on this?

Having a backup system is a good security feature but with you peak shaving plan as well, you will be balancing using the battery with your state of readiness for an outage. You can prepare for storms and other increased likelihood of outage circumstances by maintaining high SoC at these times.

 

[jeremieb]

How long are you expecting any power outage to last? I'm thinking that a 5kWh battery would keep a refrigerator powered for 2-3 days. Any of the items listed would deplete the battery in hours not days.

Yes, I understand that duration would be limited with one battery hence the provision for a generator. Additional batteries can be added as required in the future.

This is referred to as time shifting and is illegal in many areas. Are you planning on being permitted? If so, this would be a good thing to investigate early on in your process.

I already have a system to time shift energy (before and after peak power demands) from the utility. Yes, I will check with the utility but my question first is what inverter would work and for what costs and then I can call the utility with a clear schematic.

How much extra are the peak rates than the low rates? There are inefficiencies with charging and then inverting that will reduce any savings, have you done the math on this?

The first need is for power outage backup. The peak shaving feature is a "nice to have" as the economics would probably not make sence. There is a dynamic rate that is 55c/kwh (peak) vs 5c/kwh (offpeak) that I may use in the future.

Having a backup system is a good security feature but with you peak shaving plan as well, you will be balancing using the battery with your state of readiness for an outage. You can prepare for storms and other increased likelihood of outage circumstances by maintaining high SoC at these times.

I understand this and this is why a generator would be there as well. I think a 3/4kW generator would be sufficient during an outage to recharge the batteries. I can load shed as well we pretty efficient.

 

[MisterSandals]

You have a good understanding of all aspects of this. On paper all 3 diagrams are valid, the tricky part is finding an inverter that does what you seek (your original question, sorry for the diversion).
I look forward to seeing the recommended solutions!

 

[jeremieb]

You have a good understanding of all aspects of this. On paper all 3 diagrams are valid, the tricky part is finding an inverter that does what you seek (your original question, sorry for the diversion).
I look forward to seeing the recommended solutions!

Thank you. For Option 1, I think a EG4 6000XP would work but not for Option 2 since it does not have any CT input. A Victron or Solark would work. For OPtion 3, I would need a much bigger hybrid inverter that can power all my loads.