Electrician Says I Need Two Inverters to Balance the Loads

Discussion about OutBack Inverters in Grid Tie Applications

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Electrician Says I Need Two Inverters to Balance the Loads

Post by NorthernWind » Wed Oct 09, 2013 2:18 pm

I recently bought a GVFX 3524 inverter to go with my 2000W wind turbine. I also have a 24V battery pack (4X6V), a charge controller and ample resistors. There will be an emergency sub-panel and an automatic transfer switch.

This is a very basic system with no solar panels, and meant for a country house where consumption is almost nil in the Summer, and considerable in the Winter because of the electric baseboards. Hence the grid tie approach to accumulate credits with my utillity in the Summer to spend during Winter.

My electrician is reluctant to wire the Outback in the main panel, because he says injecting in only one phase in the system will have the two phases out of balance, and that this will create a lot of problems in the long run. He is of the opinion that this could go against code, and suggests that a second inverter should be installed to complement for the other phase.

I want to avoid two Outbacks for obvious reasons, having such a small capacity for production

The utility staff I spoke to consider this to be a non-issue, as the system is too simple and modest to create any problem.

May I get some of your thoughts on this, please? Thanks !

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Re: Electrician Says I Need Two Inverters to Balance the Loads

Post by dhamilton » Fri Oct 11, 2013 3:20 pm

If the utility doesn't have an issue with this I would say its not a problem. The inverter matches to the utility phase before you ever start selling power so you shouldn't have any problem with injecting a phase different from the utility.

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Re: Electrician Says I Need Two Inverters to Balance the Loads

Post by watermanhfl » Sat Oct 12, 2013 5:28 am

I have had a single inverter running for 6 years without issues. 4,000 watts solar and some wind tied in. Houses use lots more energy on one leg vs the other all the time. As long as you have a good neutral all fine.
PS my wind turbine puts out lots in winter but not much in summer here in upstate NY. Suggest you add a or couple $200 PV panels to keep batteries up when wind is low or turbine is down. Panels are cheap now vs when I bought and you can go straight to batteries without controller for now.

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Re: Electrician Says I Need Two Inverters to Balance the Loads

Post by jnh » Sat Oct 12, 2013 7:11 am

My single GVFX-3524 has also been running in grid-tie configuration for several years now and has never given me the slightest trouble, either functionally, with county inspectors or with the utility. During this time there have been three different utility meters installed (smart-meter rollout), all of which correctly registered net flow when energy was being backfed on one leg and drawn on the other.

In accordance with NEC article 690.10(C), my protected loads subpanel is labeled, inside and out with a a sign reading

"WARNING: Single 120-volt supply. Do not connect multi-wire branch circuits!"

MWBCs (two circuits sharing a neutral) are often used in newer construction to feed the kitchen receptacles. Fortunately, our place was old enough not to have any. I had heard that some inspectors didn't like to see the two hot buses jumpered together within a panel using split-bolt connectors, etc., so I opted to instead just feed it with a 6/3 line, with each hot landing on the same AC-Out bus back at my inverter's E-Panel.

Back at the main load cener, to improve balancing I moved the few remaining 120-volt circuits to the opposite leg from the one supplying the inverter and subpanel, basically leaving every alternate row empty, although this isn't strictly necessary.

Even larger Outback G*FX systems with two inverters, one on each hot leg, will keep the second one in standby until the first has been loaded down at a reasonable fraction of its capacity, since this improves overall efficiency.

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Re: Electrician Says I Need Two Inverters to Balance the Loads

Post by LOLpsyentist » Wed Oct 16, 2013 7:35 pm

The inverter would need to be rated for grid tied/interactive applications, which this model is.

By having this rating it means that the inverter will synchronize with the grid waveform to prevent voltage micro-spikes or drops due to out of sync waveform (constructive/destructive interference).

The only reason you would need a second inverter would be if there was a large variance in the input voltage (ie, 2 different size turbines or arrays) but the charge controller and batteries would usually smooth that out as long as the inputs were in the operating range of the charge controller.

The only other reasons you would want two inverters would be if the loads were outside the operating specs of the inverter or if you wanted to configure one inverter to run intermittent loads and sleep for the rest of the time then have a bigger, more efficient inverter managing all the "always on" loads.

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