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Grid tied inverter with Generator backup.


Clement
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Hi.

This is my first time having a grid tied system and am still in the preparation and design stage.

My customer requirement is to have a grid tied system which will be run by generator when grid fails. I do understand that grid tied systems are mainly for eliminating or lowering down electricity cost and feed-in  into grid via net metering system. I have researched and so far all I am finding are grid tied systems which obviously shut down when grid is absent and one inverter luckily runs on pv or backup batteries when grid is absent and uses a bypass cabinet switch point to cut off power from going to grid (automatically).

Now my client does not need batteries instead needs a generator.how can I integrate Grid tied system and generator and not disturb the grid or feed into grid? And how can it be automated?

Regards.

 

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1 hour ago, The Terrible Triplett said:

Heard of a person who built his system so that when Eskom goes off a Victron inverter assumes the role of the grid so that the SMA continues uninterrupted.

That was my first line of thought but won't the power drawn be limited to the Victron capacity? 

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2 minutes ago, Clement said:

That was my first line of thought but won't the power drawn be limited to the Victron capacity? 

Jip, then get a bigger unit, 10kva, I recall that maybe up to 6 can be paralleled. Plonkster can confirm.

BUT, I am not saying it is the answer, just saying there are ways around grid tied with no grid. :-) 

And batteries are cheaper than diesel, not so?

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16 minutes ago, pilotfish said:

I would use a normal auto-start generator.

When grid fails and grid-tie inverter shuts off, then auto-start generator starts and runs loads as desired. When grid returns then generator will auto-stop after settlement period.

Thanks alot that settles the dust.i was thinking of incorporating ATS into the system .isolates the grid and generator picks up.

much appreciated 

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1 minute ago, The Terrible Triplett said:

Jip, then get a bigger unit, 10kva, I recall that maybe up to 6 can be paralleled. Plonkster can confirm.

BUT, I am not saying it is the answer, just saying there are ways around grid tied with no grid. :-) 

And batteries are cheaper than diesel, not so?

Ok great. Understood and yes batteries would be cheaper on a long term basis. 

Thank you.

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2 hours ago, Clement said:

That was my first line of thought but won't the power drawn be limited to the Victron capacity? 

There is a 1:1 rule. Your Multiplus/Quattro cannot be smaller than the GTI. It may be bigger though. It will charge the batteries using surplus solar power from the GTI, and if you install the right assistants in the inverter it can manipulate the frequency to cause the GTI to back off, thereby throttling it down when the batteries are full. You can combine the power of the GTI with that of the Multi, for example, if you have a 5kva gti tying with a 5kva quattro, you can do loads higher than 5kva. It is however possible that at that instant when the grid fails, the event will be picked up as an islanding event and the GTI might disconnect for a minute.

The GTI of choice is Fronius. I can find out if you want more info.

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Just to clarify, that doesn't mean the multi WILL carry the whole load. The Multi will pretty much carry only the shortfall, if more power is required than the GTI makes. If there is surplus power, the Multi will charge the batteries. If the batteries are full, the Multi will use GFPR to back off the GTI. The reason they Multi needs to be big enough to carry the whole load is because such a setup isn't 100% stable. The GTIs are ultra sensitive to conditions that might indicate an islanding condition, and large changes in load will sufficiently affect both a battery inverter and a diesel generator so that GTIs will disconnect and reconnect again after a minute.

It goes without saying that if you go with a generator instead, it would also h ave to be sized for the full load.

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1 hour ago, plonkster said:

It goes without saying that if you go with a generator instead, it would also h ave to be sized for the full load.

Not necessarily - you can have a Generator DB that only powers critical circuits if so desired. When grid fails then the Auto-start gen should start up and supply power to the load that is supplied via the ATS - this could be the entire load or a selected load depending on how wired.

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17 minutes ago, pilotfish said:

you can have a Generator DB that only powers critical circuits if so desired

Aaah yes, of course! Thanks for mentioning that. Of course you could do the same with an inverter, make it large enough to cover just the essential loads. The 1:1 rule would still apply though, it has to be at least as big as the GTI.

I question how much sense it would make to tie a GTI with a generator. Generators generally make the cheapest power when they are about 80% loaded down. Using the GTI with a generator actually increases running costs of the generator per unit of energy. I'm sure @Chris Hobson will agree with me here, when that engine is running you want to use the expensive energy as a priority, otherwise it is lost.

If you're going to involve batteries and a Multiplus, it might of course make sense to forget the GTI and just add some MPPTs on the DC side, then run ESS. That also gets you backup (on the output) and grid tie (on the input), and it is a lot more stable than using GTIs, though the efficiency is lower of course (double conversion).

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Ok that is understood.. Am learning from everyone and taking note of contributions.

In a case where we decide not to complicate the setup, would it be ok if we had this arrangement 

1.GTI

2.Auto start Generator 

The generator only kicks in when GTi is absent  I assume as long as the grid is present the generator remains on standby mode right? I should believe when Pv peak hours passes , the load draws power from grid unless grid fails will the generator come in. Though this setup makes panels useless when grid fails during the day it's pretty much easier to troubleshoot should I be out if site.

 

2nd option 

Setup 

1. GTI with backup battery 

2. Auto start Generator 

Operation.

A. GTI is first Priority to Supply load and if enough,feeds back into grid 

B. Should grid shut down during day time,Solar power continues to Supply power to the load and grid is isolated by A bypass cabinet switch point  (Found one in China) though expensive but allows me to use the Pv array during the day thereby saving on generator fuel costs. In this generator only kicks in when both grid and solar power fails completely. 

I have thought through and researched for some good hours and your contribution on these two options will help.

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Second option, that would basically be a Victron Quattro configured to start the generator on low battery. Such a setup is pretty common. It has two inputs on the inverter, one for grid and one for the generator. If you run the ESS (Energy Storage System) option, it can also feed back excess energy to loads that are not on the output (ie it operates like a GTI).

Option 1 is by far the least complicated though. Unless you have frequent failures, that would be the one I'd go for.

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3 minutes ago, plonkster said:

Second option, that would basically be a Victron Quattro configured to start the generator on low battery. Such a setup is pretty common. It has two inputs on the inverter, one for grid and one for the generator. If you run the ESS (Energy Storage System) option, it can also feed back excess energy to loads that are not on the output (ie it operates like a GTI).

Option 1 is by far the least complicated though. Unless you have frequent failures, that would be the one I'd go for.

Ok great I would go for option 1 too.

Will draw up the two options and settle for one which will be within our budget and most efficient. Thanks for your contributions

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35 minutes ago, Clement said:

Ok great I would go for option 1 too.

The beauty of that system is nothing is really wasted. Should outages become sufficiently irritating and/or frequent, you can add the Multi and some batteries later. You'll pay a little extra, but that's more than compensated for by buying extra time, something that is way underrated, money spent tomorrow is always worth less than money spent today, if it has to be spent at all!

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