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Power outage backup

  • 25-07-2022 6:46pm
    Registered Users Posts: 226 ✭✭

    I've a 5.5kWH battery, ~5 usable. The inverter has two UPS sockets attached. Sadly it's in the attic so it's a bit of a pain to run an extension lead on the event of a power cut. 

    I typically stop discharging the battery at 20%. 

    If I avoid drying clothes and roasting dinner, the normal usage in the house drains the battery at about 7% per hour.

    It annoys herself indoors hugely that even after investing in solar we are not automatically backed up in the event of an outage. 

    We've had 3 power cuts here in the last 3 months. I can see that getting worse before I it gets better. 

    So I'm thinking of an isolation switch setup, and a second battery (usable total ~10kWH). That would give me, worst case ~6 hours of low load usage. Better of course when the battery is charged. 

    An added benefit is shifting a lower rate and feeding in during the bright days. Not the decider, but nice option. 

    Now the questions...

    Can the system be set up to continue generating during a power cut?

    Does an isolation switch interfere with the ability to feed the grid, and get compensated by the mythical FIT?

    What happens to surplus when the house load is met and the battery is full?

    If the battery drains completely, will the inverter 'wake up' with the sun?

    Each battery has a max output of ~2500W. The inverter, 5kW. With two batteries, I assume the load can be up to 5kW before tripping or protecting itself. 

    Finally, is there an easy way to know when the grid is down? I'm thinking an unprotected socket with a power failure alarm plug...

    🌞4.55 kWp, azimuth 136°, slope 24°, 5kW, 🛢️10.9kWh, Roscommon

Best Answer

  • Registered Users Posts: 113 ✭✭TerraSolis

    What's your current inverter make & model? It may have all the functionality built in already subject to some rewiring of the UPS.

    Your first question depends on the inverter.

    Isolation switch wouldn't interfere with FIT (although obviously you won't be exporting during periods that you are isolated).

    Surplus power depends on your inverter. If you have an offgrid enabled inverter it simply won't generate more power and your panels will sit on your roof doing nothing at all for a wee while. No biggie.

    Yes - if you have an offgrid enabled inverter and the battery is drained, it will wake when power generation resumes.

    Batteries combining to generate 5000W depends on the battery make & model. Google the datasheet and you should find your answer fairly quickly.

    Basically - it all depends on your kit!


  • Registered Users Posts: 2,504 ✭✭✭bullit_dodger

    I guess it also depends on how much effort you want to put into developing a solution.

    A relatively simple solution which should give you a decent bang-for-buck is to permanently run a cable from both those 2x UPS in the attic, to either 1 room with a 2 gang socket, or 1x gang socket in two rooms. Power your major devices from those when your experiencing a power cut (tv/wifi/few lights ?).

    Obviously that doesn't mean running the tumble dryer as you'd deplete your battery quick for one, but also you might be hitting the limit of what power you can draw.

  • Registered Users Posts: 226 ✭✭curioustony

    @TerraSolis The kit is Alpha ess smile 5. Cannot see from the specs of it is off-grid enabled. I think it is or can be configured as such...

    So the hope is that the inverter is smart enough to figure out when the grid is there or not, and if not just ignore the extra -- I guess that's off-grid

    @bullit_dodgerI did think about running a cable, but the stuff that I care about is all over the place. I also thought about just a couple of circuits. But at that stage it was close enough to whole hog. Electricity, DIY & I don't mix :-)

    The alarm is because the dryer is on the same circuit as the freezer

    🌞4.55 kWp, azimuth 136°, slope 24°, 5kW, 🛢️10.9kWh, Roscommon

  • Registered Users Posts: 113 ✭✭TerraSolis

    Alpha ESS kit is offgrid ready. You could have an electrician add a second busbar into your consumer unit and switch over all your backup essentials onto that. Then run a cable from the backup output of your inverter into that busbar as the supply. If you're putting in another battery, you'll need a reci anyway!

  • Registered Users Posts: 558 ✭✭✭idc

    @curioustony Did ******* install this? Did you just get them to install 2x UPS sockets. They also do a full backup with a changeover switch, this allows the panels to generate in a power cut as well. With your current setup in power outage you only have use of battery and no solar generation. With changeover switch you are isolated from grid and reenables the solar panel to feed battery/inverter

    [ edited to remove installer name ]

    Post edited by idc on

  • Registered Users Posts: 5,871 ✭✭✭Chris_5339762

    We were told that you can buy an inverter that works during a power cut - of course after we'd paid for ours, which doesn't.

    The poor mans solution is to plug the inverter into our emergency diesel generator!!! And see what goes bang first.

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  • Registered Users Posts: 226 ✭✭curioustony

    @idc yes indeed they did. And yes my mistake was not asking for the full backup on installing. I have a call in with them at the moment but they are a bit busy. I suspect a lot of installers are...

    @Chris_5339762 do you get fireworks before the bang?

    🌞4.55 kWp, azimuth 136°, slope 24°, 5kW, 🛢️10.9kWh, Roscommon

  • Registered Users Posts: 1,439 ✭✭✭DC999

    Hey. Remember first rule of Fight Club :) No naming installers. OK to name suppliers like midsummer

    Post edited by Jonathan on

  • Registered Users Posts: 558 ✭✭✭idc

    Doh forgot about that! I didn't even need to mention their name as they are the only installer for AlphaESS in Ireland to my knowledge!!

    Even if i edit my comment it will still be visible in your reply 🤣

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,141 Mod ✭✭✭✭Jonathan

  • Registered Users Posts: 226 ✭✭curioustony

    Fight club preserved for another day. In fairness, it's a good policy.

    I suspect more folk will consider the backup option, the way things are going...

    Now if only the mythical FIT would materialize!!!

    🌞4.55 kWp, azimuth 136°, slope 24°, 5kW, 🛢️10.9kWh, Roscommon

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  • Registered Users Posts: 1,439 ✭✭✭DC999

    Oops. I was both the protector and assailant there :)