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Linking independent solar power sources together in a grid - what could possibly go wrong?  RSS feed

 
Jason Silberschneider
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I currently have 3 small, independent systems on my property for doing various tasks. They each consist of 3 panels going through a regulator to a small battery bank of 4 batteries, which then power a 240V inverter. (Australian voltage)

Recently I've been asking myself what would happen if I linked all the outputs on the inverters together in a kind of local "grid" in order to run more powerful tools, and be able to boost each other if one isn't quite up to the power requirements.

I haven't done this yet, because that little voice in the back of my head has been making that Marge Simpson grumbling sound that it normally makes to stall me from killing myself. But I can't work out what is wrong with this theory. Does anybody know what is wrong, and why it's wrong? And is there a non-lethal way of going about this? Or is it perfectly fine to do this?
 
Steve Farmer
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How would you get the separate AC sources to be in phase with each other?
 
Jason Silberschneider
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Exactly my point. Is this a problem? If so, how much of a problem? A laptop or other device with a bridge rectifier wouldn't care, but a purely AC powered device might. But would it matter?

What's the difference between 3 pure sinewave power sources being out of phase, and a single cheap and dirty squarewave inverter?
 
Steve Farmer
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I've never tried to connect a non grid tie inverter to a grid, but I'd imagine it would destroy it, or if it was intelligent enough at least it would shut down.

Running multiple sine waves out of phase... well depends how lucky you are. Imagine you have two sources 180 degrees out of phase and a way of not getting the inverters destroyed or shutdown, your appliance is going to prefer the squarewave.

You could use grid tie inverters, but the first one to power up would see the grid as down. When the second powers up it would see the grid as up and try to synchronise to the first. What I don't know is what the first one would then do, suddenly seeing the grid come back up, would they be stuck in an eternal handshake?

Assuming you don't already have grid tie inverters, its going to be cheaper to link the DC sources and get an inverter with 3X the power, than buy 3 grid tie inverters.
 
S Bengi
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Why not put all the solar panels in the same loacation, and all the batteries in the same location and then connect just one 'big' converter to the combined battery bank.
 
Jason Silberschneider
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1 is none, 2 is 1, 3's a guarantee. I don't like the idea of a big "centralised" system as much as dispersed smaller ones.

Then again, I probably wouldn't throw out the smaller inverters. They'd be in storage just in case.

Is there actually such a think as a device that would keep phase for anything that was dumping power into a micro-grid?
 
Steve Farmer
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Jason Silberschneider wrote:

Is there actually such a think as a device that would keep phase for anything that was dumping power into a micro-grid?


Yes, a grid tie inverter, just need to check with vendor its capable of running in your setup. Some will, some won't..

But - you will pay a big premium for grid tie. Far easier to tie the DC. You can have more than one inverter running off the same DC circuit
 
frank li
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Sma has systems that should do what you describe.
 
frank li
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This may be more appropriate though, truly unique permies should geek out on this!

http://www.transverter.com/
 
Jason Silberschneider
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Tying the DC is a great idea, but now the battery capacity is greater than a single regulator can deliver. Can multiple regulators feed a single bank, or will they psyche each other out?
 
frank li
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Yes, you can paralell the controllers onto one battery and set them all to the same set-point. They will get along together just fine.
 
Jason Silberschneider
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frank li wrote:Yes, you can paralell the controllers onto one battery and set them all to the same set-point. They will get along together just fine.


I'm totally going to try this. All 3 controllers going into a now-combined battery bank, with all 3 inverters on the other side. I now simply run the AC cables underground (in conduit!) to their destinations, as AC plays much better with distances.
 
Jason Silberschneider
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frank li wrote:This may be more appropriate though, truly unique permies should geek out on this!

http://www.transverter.com/


Regardless of how good the hardware is, when I read things like "We use deep cradle to grave Life Cycle Analysis of the Transverter to maximize beneficial environmental impact and promote Green Engineering" in their mission statement, I immediately smell a rat. That intro on the main page was painful to read.

Either it's all a scam, or their marketing department needs to be shot. Hopefully it's the latter, and the stuff actually works.
 
frank li
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Jason Silberschneider wrote:
frank li wrote:This may be more appropriate though, truly unique permies should geek out on this!

http://www.transverter.com/


Either it's all a scam, or their marketing department needs to be shot. Hopefully it's the latter, and the stuff actually works.


Ive yet to install or test one of these, but the guy has some serious street cred in RE. Basically he is the father of bulletproof off grid inverters for RV/Marine and as an inevitable extension, RE inverter-chargers. Heart was an RE inverter manufacturer when i was a toddler. They became Trace, Magnum and i think the story goes the young guys from his crew became Outback and now midnite solar! An epic story at the least and its on Midnite's web site.

These guys designed almost all of the heroic equipment that we have been using since the 80's! And it all started with stereo amplifiers and sailboats. We should be proud.
 
frank li
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Alright, i gotta post the link!

http://www.midnitesolar.com/pages/frontPage/nwHistory/history.php

A great story about the roots of off grid power electronics!
 
Jason Silberschneider
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Great to hear. So it's just the marketing department that needs to be shot. I can live with that. The website for transverter is just awful.
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