Repurpose grid-tie technology for local scalability?

[flippineck]

Could I connect together the outputs of multiple seperate grid-tie power inverters to get more power?

They'd all be fed off the same battery bank, charged by solar PV.

For instance say I have 5 identical inverters each rated at 1kW continuous, 240V 50Hz, with grid-tie capability.. could I use the grid-tie functionality to connect them all to one common bus without actually having a grid connection?

And then run a 5kW appliance off the bus?

I figure you couldn't do that with standard inverters because all the outputs would be randomly out of phase with each other and allsorts of wrong way currents could arise. But would grid tie inverters synchronise with each other ok, even without a grid connection?

I ask because I can find grid-tie inverters cheaply enough, but if I had to actually attach them to the grid, I'm not certified for that sort of thing & the expense wouldn't be worth it.

I guess I could just go out and buy an ordinary inverter that would be likely big enough to cover all and any future needs, and which was guaranteed to live up to it's continuous output rating. That would be very expensive though.

I'm currently struggling along with a Chinese ebay special which promises 2000W continuous pure sine wave, but has trouble powering a 950 Watt toaster. It's run off 2 parallel 12V 110Ah lead acid leisure batteries, maybe I just don't have enough oomph in those or something.

It does attempt to power the toaster and will happily sit there attempting to make toast forever and a day, so the batteries aren't going flat in short order.. but the elements never get really hot and the inverter is on it's warning beeps all the time (low input voltage) - seems to sit at 12.7V on load, dragged down from 13.8V idle.

 

[KrisBlueNZ]

would grid tie inverters synchronise with each other ok, even without a grid connection?

I have no experience with this but I imagine you might need one non-synchronising inverter to "lead the way". Otherwise you might have five separate inverters all playing follow-the-leader with no leader!

I'm currently struggling along with a Chinese ebay special which promises 2000W continuous pure sine wave, but has trouble powering a 950 Watt toaster. It's run off 2 parallel 12V 110Ah lead acid leisure batteries, maybe I just don't have enough oomph in those or something.

It does attempt to power the toaster and will happily sit there attempting to make toast forever and a day, so the batteries aren't going flat in short order.. but the elements never get really hot and the inverter is on it's warning beeps all the time (low input voltage) - seems to sit at 12.7V on load, dragged down from 13.8V idle.

That's really unacceptable. Have you contacted the seller? You should kick up a fuss.

If it's faulty, the seller should replace it. If they're just lying about its capability, other buyers should know.

If no one calls people on their lies, specifications start to become meaningless. And inverters aren't cheap.

 

[flippineck]

Just linking in another thread for me to come back to

https://www.electronicspoint.com/threads/diy-1kw-grid-tie.10664/page-2

One of the posters mentions an "anti-islanding circuit" in there, put there to prevent grid tie inverters zapping line repairmen.

Wonder if I could use my Chinese jobby as "the Leader".

maybe if i try this, I should wire them all up in a metal box outside with the hosepipe handy

 

[(*steve*)]

According to what I have read, inverters (as part of the anti-islanding) also check the impedance of the mains. A small group of inverters would probably fail this (I guess they're designed to).

 

[flippineck]

I've always found impedance a hard thing to understand. Could I build some kind of small device to make the impedance 'look' correct?

 

[(*steve*)]

I think it's called a power station

 

[flippineck]

I've got a little diesel generator?

 

[(*steve*)]

It *might* work.

The problem is that grid tie-in inverters rely on the grid to suck up any excess power they generate, and to supply it when needed.

If you have a light load and the sun comes out, the voltage will rise and the inverters will probably go off-line.

Similarly, if the load is heavy, and the sun disappears, the voltage will fall and the inverters will again drop out. This is the worst case because the solar isn't even helping.

And it will rely on you keeping a diesel generator running -- which is not ideal.

This is the sort of case where you really want solar panels charging batteries, and batteries supplying an inverter.

Of course, it's a more expensive and less efficient arrangement.