Unstable grid... considering options for battery backup

mjs44

New Member
Hello All,

I did a quick peruse of the forums and didn't find exactly what I'm interested in, but feel free to redirect me!

Our family has a place in the Bahamas, where brownouts occur very frequently and blackouts occur almost weekly. Typically these events are short-lived (~2hr blackouts; <1min brownouts), and I'm talking to my family about a grid-tied battery backup path to start with potential inclusion of solar in the future. So the priority would be to maintain charge on the batteries (~85%? for lifetime considerations) from the grid, then have some sort of smart subpanel that can quickly handoff to the batteries in brownout or blackout conditions, then switch back to the grid supply (and charging) when the power comes back.

Watching some of the videos posted here, I gather a slightly different set of priorities... I'm not trying to shift grid power consumption to different times. Down the road, if we add solar, perhaps I'd envision prioritizing using the solar to charge the batteries and then feed AC back to the house after battery charge is reached.


So the main component I'm not sure of is the smart subpanel that can quickly switch from grid power to battery-fed AC. Do any exist that would help with the brownout conditions?

Thanks,
Mike
 

snoobler

Solar Honey Badger
Moderator
Welcome to the forum.

Most inverter/chargers can pass through grid and then act as a UPS when grid is lost with a ~20ms switchover time. They can keep the batteries charged when not in use. You would literally place the device between your mains and your AC panel.

You need to determine:
Type of power: 120V single phase, 60Hz; 120/240V split phase, 60Hz; 230V single phase, 50Hz
Your peak power demand, i.e., how many Watts will you need at one time.
You total number of items, their Watts consumption, and the total hours of use of each.

Link #1 in my signature is a good place to start. Download the energy audit spreadsheet and populate it with your items.
 

mjs44

New Member
Thanks!
To be clear though, the placement between the mains and panel would then take on the full house electrical load. I presume I could alternatively place the inverter/charger between the main panel and a subpanel to only supply a sub-portion of the full house?

I'll start looking at your info!

Cheers,
Mike
 

snoobler

Solar Honey Badger
Moderator
Correct. That scenario is often referred to as a "critical loads" panel and would work as you describe.

Mains -> AC panel -> branch to inverter -> critical AC loads panel.
 

wattmatters

Solar Enthusiast
To be clear though, the placement between the mains and panel would then take on the full house electrical load. I presume I could alternatively place the inverter/charger between the main panel and a subpanel to only supply a sub-portion of the full house?
Yes, or as I have done, have a cutover switch and exclude non-critical or high powered appliances from the backup side of the switch which would not be suitable for running while on backup power.
 

mjs44

New Member
@wattmatters, the cutover switch is manual? I am looking for an automated system that's as hands off as possible, since it needs to work reliably when I'm not there... I could see how some form of automated switch could save on idle power draw(?)
 

mjs44

New Member
Also, if I did go the route to power the whole panel (90A, 240V), I'm wondering... If I get something like this: https://watts247.com/product/hybrid-lv6048-split-phase-120v-240v/?wpam_id=3

It's rated at 6kW (vs 90A * 240V = 21.6kW for the panel capacity)... would this unit be able to pass the full 90A of utility current when not pulling from the battery? Looking at the datasheet, there's something listed as bypass current... 40A... that kind of sounds like what I'm talking about, but I'm not sure.
 

wattmatters

Solar Enthusiast
@wattmatters, the cutover switch is manual? I am looking for an automated system that's as hands off as possible, since it needs to work reliably when I'm not there... I could see how some form of automated switch could save on idle power draw(?)
It is, however if the all in one inverter which supplies the backup circuit is set to line mode, it passes through the grid supply, only cutting over to battery energy when grid supply goes off. Cutover is like a UPS, mine has a 10ms cutover.

So if I leave the manual cutover switch in the "backup" position, this means the AIO inverter and battery operates like a big a UPS power supply.

I don't typically use it this way (with cutover switch in the "backup" position) because my AIO is limited to 4kW output.

While most high power draw devices are not on the backup side and only connected to the grid side of the switch, there is still a chance of occasional over draw (which is far less likely when we are on a known outage backup scenario and being a little more careful about usage). We have three buildings, two of them dwellings, and so there is always the chance of two electric kettles being on at the same time which would be enough to trip the AIO supply. But if we were just one smaller home, or the AIO was rated to supply higher power output, then leaving it in this mode would be fine, indeed that's probably what I would do. That way if ever there is a problem with the AIO which needs sorting, we can always just flip the manual cutover switch back to direct grid supply.

I have this option for a specific scenario - if we are away and my elderly mum will be in her home alone for a couple of days, then this is an option to ensure she has power security.
 

snoobler

Solar Honey Badger
Moderator
Yep. 40A bypass current, that's what it will feed through to power the house, 9600W. You can parallel them and get 80A, but that would mean buying two.
 
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