That seems like a problem with an super easy fix. There must be a lot more to it than that. Just build into the inverter a subsystem that syncs to the grid signal, then generates that signal to itself. Upon disconnect from the grid, the subsystem draws power from the solar to sustain the signal. - ThreadSky

eric-hainline.bsky.social • 6 days ago

That seems like a problem with an super easy fix. There must be a lot more to it than that.

Just build into the inverter a subsystem that syncs to the grid signal, then generates that signal to itself. Upon disconnect from the grid, the subsystem draws power from the solar to sustain the signal.

Comments

emgre.bsky.social•6 days ago

It's quite more complicated than that. To become grid-forming (to work in islanded mode), an inverter needs advanced control algorithms, it has to do protection with limited fault-current, it lacks inertia, etc. The transition between grid-forming and grid-following also requires precise timing.

robbak.bsky.social•5 days ago

The challenge is reliably re-synchronizing with the grid when the grid power comes back. This needs to be done very reliably, because reconnecting when not in sync is catastrophic.

againstkookery.bsky.social•5 days ago

The easiest thing to do is to require a manual reconnection, in the process cutting power to the house.

againstkookery.bsky.social•6 days ago

Yes, you need an extra piece of equipment to generate the signal in the absence of the grid and disconnects from the grid when the grid power stops. It's absolutely available, but it's an optional extra that many don't pay for.

carlchansen.bsky.social•6 days ago

The reason standard grid-tie inverters can't operate in island mode, is that UL standards require them not to (anti-islanding). It's for the safety of utility linesmen, so they can repair the lines without surprise sources of energization.

Backup power requires isolation by transfer switches.

crissakentavr.bsky.social•6 days ago

But then they could just work on an island, though.

The grid-tie inverters don't just do that because linesmen: It's because the ability to shed or boost power takes more electronics.

(Just like a portable generator doesn't have the ability to sync frequency, either.)

Battery systems tho...

carlchansen.bsky.social•6 days ago

There are inverters that can do that, it's called island mode. Usually battery inverters have the ability to grid-form and operate in island mode, and you can AC-couple them with the solar inverter to grid-follow like it usually does.

SMA makes the sunny boy/sunny island system to do exactly that.

eric-hainline.bsky.social•6 days ago

Thank you for this! It makes huge sense. When I installed my 1.3MWh/month system I was simply told that because I opted for no batteries, the power company would reach in and shut me down if there was an outage in my area. This seemed like nonsense to me.

eric-hainline.bsky.social•6 days ago

Of course, their reason was lineman safety. But I figured that is they could reach in and shut me down, they should be able to reach and simply disconnect me. Let me stay operational with all those panels on my roof.

They had no response. I just figured they wanted to upsell batteries.

carlchansen.bsky.social•6 days ago

Some grid-tied inverters have secure power supplies, that allow you to run a single outlet off grid, as long as there's sunlight available. They have an internal transfer switch to disconnect from the grid, and only run that one outlet. They are uncommon.

carlchansen.bsky.social•6 days ago

Utilities commonly require a blade disconnect, which linesmen in theory could shut off at every house with solar. But in practice, that's extra work, so anti-islanding is required to shut off all inverters automatically. Except for those that are isolated by transfer switches so they can island.

Comments

Posting Rules

Reply