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Comment by somat | Hacker News Reader

Almost no private solar installations give power during outage, for the most part they use something called a grid tied inverter. This uses the power grid to shape the waveform and costs about a tenth of what a self shaping inverter costs. the unexpected downside, no grid, no power.

I have yet to find conclusive evidence if it is possible to use a small full inverter to drive grid tied inverters, that is, have the grid off capability of a full inverter with the cheap cost of a grid tied inverter. It sounds reasonable, but I don't see anyone doing it.

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> and costs about a tenth of what a self shaping inverter costs

I'm using a Fronius GEN24 Plus (10 kW) which can be used off-line/off-grid (called 'Full Backup', to use it you need some extra switching gear between the inverter and the utility hookup, which gear that is differs from country to country) and provides single-phase power in its default configuration (they call it 'PV power', basically a 3 kW single-phase connection which comes alive when the utility hookup goes down). While this inverter was slightly more expensive than the Chinese alternatives the difference was more in the range of 30%, not '10 times'.

Are there any systems offered that don’t have all the extra switch gear but just provides a socket you can plug something into? I figure people would be happy plug their fridge/freezer in manually to tun during the day and charge some stuff.

Or is that what you’re suggesting with the Chinese inverters?

The extra switching gear is needed for a utility hookup to ensure the inverter does not feed power into the utility hookup during a power-out. If the inverter is only to be used in island mode - without a utility hookup - such switching gear is not needed. You need to configure the inverter for island mode and you'll want to connect battery storage - this is a hybrid inverter which can be connected to one or more high-voltage (150V-510V) batteries - to power the system when the sun is down/low/obscured.

There are Chinese inverters which support island mode as well, my reason for choosing a European manufacturer is not related to this type of functionality. He who controls a large fleet of inverters can control the grid - and bring it down. I prefer to keep sole control over what my inverter does and do not allow it access to the internet, keeping it on a separate wired network (wireless access to the inverter is disabled) which is only accessible by a dual-hosted container on the server-under-the-stairs. It is through this container that I control the inverter and extract data for power management purposes - turn on heavy loads when the sun is doing its thing and/or imported electricity prices are at the lowest rates for the day. While I could (and would) do the same with a Chinese inverter I'm not convinced that would be enough to keep third parties from accessing the device though either some embedded 2/3/4G, LoRa or similar device.

I installed the panels on a barn I built in 2019 and installed the inverter in 2022 - long before my suspicions about the potential for such covert control channels were 'proven' [1] so my initial caution turned out to be justified.

[1] https://www.reuters.com/sustainability/climate-energy/ghost-...

https://www.myenergi.com/product/libbi-battery-storage/

I have a rebranded kstar inverter which has a "backup" output and I had the electrician wire that output to 6 sockets around the house for fridge, well water pump, and internet connectivity. When the grid is on, the backup is fed by the grid. When the grid goes off, the panels deactivate and the backup is instantly (like a UPS) powered from the 5kWh battery. I can then manually switch off the grid connection to the inverter and re-activate the panels. It should be enough for backup loads more-or-less continuously although I should buy a better fridge and a winter storm might need us to reduce water consumption and disconnect internet.

Biggest disadvantage is that we don't have central heating during powercut - would require more invasive rewiring and more power than I care to draw from inverter with single battery. But gathering around wood stove and telling stories by candlelight is nice, eh?

I seem to recall almost two years ago when I was getting info on a possible solar install, we had the options of LG batteries or Powerwall, and one of the specific points of difference that the more expensive (and larger capacity) Powerwall battery install provided was stated to be power when the grid was down.

I can't speak to the accuracy of that, as I was speaking to a salesperson and I didn't go forward with the project so don't have any personal experience to add.

Please don’t spread misinformation. Every current Chinese inverter (Sungrow, Goodwe, you name it) can provide emergency power with or without installed battery. My all PV installations (10-20 kWp panels with 10-30 kWh batteries) provide emergency power for whole house. Battery has lower power than the grid connection, but clients agree to don’t charge their EVs during blackout. Starting cost 10000€ for 10 kWp panels and 10 kWh battery if installation is easy on single flat roof.

You mean something like feeding a grid fed inverter an artificially generated wave form from a Raspberry Pi and some relays or something?

I don't see why you can't flip a giant switch to go from grid to home power. It's not automatic, but this tech is well established for gas generator cutover in factories and remote homes.

The hardest part of that is regulatory compliance on whatever interlock you have installed that prevents you from connecting mains to your backup.

The most common solution to that is a switch that goes through fully disconnected in the middle, and I've even seen a sliding metal plate used that interferes with at least one or both circuit breakers.

You need a home backup battery with a transfer switch, specifically one that accepts solar input. There are a bunch of off-the-shelf solutions out there.

Or you unplug your fridge from the wall and plug it into your inverter, with or without battery backup. Or you just leave it plugged into your APC UPS. I think cheaper ones than this US$60 2000W inverter exist: https://www.temu.com/ar/-2000w-inversor-de--con-pantalla-dig...

In the US they cost a lot more, but they still exist; there's a 750-watt unit at Horror Fright for US$70: https://archive.fo/1pzdK

You can, you need something to form frequency if it isn't coming from the grid and you very much need to synchronize when grid frequency comes back or your equipment will generate expensive smoke and noise.

I thought the generators phase differently with the movement of the engine vs the type of inverter you nened for use with batteries. I do agree it should be trivial.

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