Hello, while not quite a solar question this forum seems to have all of the expertise I need to weight in on my problem.
Problem: I would like to add a “utility first” “battery backup” to selected critical circuits in my house-mainly the refrigerator and freezer, potentially also the sump pump. Though the sump is already with an attached extension backup pump with a 12v 100Ah battery.
Details: Ignoring the sump pump for a moment, using a kill-a-watt meter I have measured the refrigerator and freezer to be 1.2kW per 24 hours and 1.1kW per 24 hours respectively. I have been using a 2.5kW per day figure for planning purposes, really 3kW to allow for some other usage/planning factors. Adding solar panel generation is an eventual goal but should not be highly considered for this problem as that will likely occur at the next house. Also I plan on moving to a new house in 2 to 4 years so this setup must be transferable for the major components.
I have a small 2500watt inverter generator so for now the scheme during a “long term outage”, which I will coin as anything past 24 hours, would be to use the generator to recharge the batteries. Assuming this scheme would allow me to run the generator maybe 6 hours a day to recharge the batteries, I should have well over a weeks worth of fuel on hand to tackle an outage of at least that length.
Price:
I am looking for one step above the cheap stuff. Ideally not the cheap Chinese hardware, though made in the USA is not strictly required but would be preferred. I would prioritize reliability and proven track record just above low cost, though of course am also budget focused so don’t want to stray too far towards the expensive nice things. In my mind this will “not get used very often” being a utility first design so I don’t want to risk the hardware not working when the time comes.
What I am thinking so far:
Design:
Mount a sub panel and pull the freezer, refrigerator, and maybe one more circuit just for some outlets from the main panel over to the sub. Hook up an “off grid” inverter that would accept AC mains in and this inverter feeds the sub panel.
Buy battery bank. Ideally 1.5 to 2 days worth of power so I can recharge once a day. I believe that puts the math at 4.5 to 6kW total capacity.
I am looking at a 48v system since I will surely expand usage (and battery bank size) in the future. This means a single 48v 100Ah would just barely cut it over 36 hours, and 48v 200Ah should be a more comfortable 2+ days.
Hardware specifics:
-Outback vfxr3648 which is a 48v 3600w inverter, about $2k for this inverter so hopefully twice as good as the cheaper $1k ones.
-still deciding on batteries whether to get 4x 12v AGM batteries of 100Ah (or larger) or to spend more and get lithium. The soon-to-be released SOK server rack looks good to get one or two of.
Questions I have:
1) General “does this sound feasible/reasonable”?
2) Any hardware recommendations?
3) battery bank sizing seem adequate?
4) how to charge the batteries-I believe I will need a separate charger to charge from the generator, not sure if some kind of switch could be installed to accept generator into the AC main in of the inverter for when needed or if this is a bad idea.
Problem: I would like to add a “utility first” “battery backup” to selected critical circuits in my house-mainly the refrigerator and freezer, potentially also the sump pump. Though the sump is already with an attached extension backup pump with a 12v 100Ah battery.
Details: Ignoring the sump pump for a moment, using a kill-a-watt meter I have measured the refrigerator and freezer to be 1.2kW per 24 hours and 1.1kW per 24 hours respectively. I have been using a 2.5kW per day figure for planning purposes, really 3kW to allow for some other usage/planning factors. Adding solar panel generation is an eventual goal but should not be highly considered for this problem as that will likely occur at the next house. Also I plan on moving to a new house in 2 to 4 years so this setup must be transferable for the major components.
I have a small 2500watt inverter generator so for now the scheme during a “long term outage”, which I will coin as anything past 24 hours, would be to use the generator to recharge the batteries. Assuming this scheme would allow me to run the generator maybe 6 hours a day to recharge the batteries, I should have well over a weeks worth of fuel on hand to tackle an outage of at least that length.
Price:
I am looking for one step above the cheap stuff. Ideally not the cheap Chinese hardware, though made in the USA is not strictly required but would be preferred. I would prioritize reliability and proven track record just above low cost, though of course am also budget focused so don’t want to stray too far towards the expensive nice things. In my mind this will “not get used very often” being a utility first design so I don’t want to risk the hardware not working when the time comes.
What I am thinking so far:
Design:
Mount a sub panel and pull the freezer, refrigerator, and maybe one more circuit just for some outlets from the main panel over to the sub. Hook up an “off grid” inverter that would accept AC mains in and this inverter feeds the sub panel.
Buy battery bank. Ideally 1.5 to 2 days worth of power so I can recharge once a day. I believe that puts the math at 4.5 to 6kW total capacity.
I am looking at a 48v system since I will surely expand usage (and battery bank size) in the future. This means a single 48v 100Ah would just barely cut it over 36 hours, and 48v 200Ah should be a more comfortable 2+ days.
Hardware specifics:
-Outback vfxr3648 which is a 48v 3600w inverter, about $2k for this inverter so hopefully twice as good as the cheaper $1k ones.
-still deciding on batteries whether to get 4x 12v AGM batteries of 100Ah (or larger) or to spend more and get lithium. The soon-to-be released SOK server rack looks good to get one or two of.
Questions I have:
1) General “does this sound feasible/reasonable”?
2) Any hardware recommendations?
3) battery bank sizing seem adequate?
4) how to charge the batteries-I believe I will need a separate charger to charge from the generator, not sure if some kind of switch could be installed to accept generator into the AC main in of the inverter for when needed or if this is a bad idea.
