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Connecting hybrid in series with Grid tied


KobusK

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I have currently got a grid tied solution which works great when the sun shines and the grid is up. 

 

Can I install a Hybrid solution first and keep my grid tied? 

In theory the Hybrid will trick the grid tied that the the grid is still up. When the sun is down the grid tied will switch off and I will het back up power from Hybrid system.

Is my assumption correct?

 

Edited by KobusK
Wrong word
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27 minutes ago, KobusK said:

Can I install a Hybrid solution first and keep my grid tied? 

I have heard of people using a Victron inverter as the "grid" for the grid tied inverter.

So yes, probably with some T&C's on the technical side. 

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only if the GTI and the hybrid can do frequency shifting. i changed from my hybrid Goodwe  for this reason and have my GTI connected to my load outputs of my bi directionals, so it stays on but does not cook batteries.... and thereby creating a decentralized grid

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The grid tied can not feed back to the grid as it has a clamp on the municipality feed blocking the feed. 

This should then be a gatekeeper. So the idea is municipality into mecer inverter in and then the output going to the solis and this into the DB BOX.

Thanks for the responses thus far.

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15 hours ago, The Terrible Triplett said:

I have heard of people using a Victron inverter as the "grid" for the grid tied inverter.

Indeed. Victron inverters can have a PV inverter (aka GTI) on the output side. If the grid goes down, it will use frequency shifting to control the PV inverter. This means the PV inverter must support GFPR (Grid Frequency-dependent Power Reduction). Usually it uses a frequency between 50Hz and 53Hz, where 50Hz is 100% and 53Hz is 0%. The Victron inverter doesn't care about the exact calibration, it will simply shift the frequency up until the power reduces to an acceptable level. If the inverter does not support GFPR, it will still switch off when the frequency goes out of bounds (usually above 53Hz) so it still works... but not nearly as well, it becomes a hard-on/hard-off thing.

16 hours ago, The Terrible Triplett said:

So yes, probably with some T&C's on the technical side. 

Remember that when the grid fails and the Multi or Quattro takes over, or when a really large load switches on or off, there is usually a small dip or rise in the voltage which the PV-inverter will see as an islanding event, and it will switch off. So your Hybrid inverter must be able to carry the full load, you cannot rely on a combination of PV and Hybrid power to attain a larger total. Furthermore, there is a 1:1 rule (PV inverter may not be larger than the Hybrid), which I am sure will also apply to inverters other than Victron inverters.

Also, there are numerous issues to be careful of, for example some grid codes (I'm looking at you VDE AR N 4105, though I think AS4777 has something similar) mandates a ramp-up of power over several minutes, so islanding events are really irritating. The way the hybrid works often means that it has nowhere to go with the power other than the battery when the grid is out... so a slow-reacting PV inverter combined with a really full battery bank (especially lithium which switches off if there is an overvoltage condition), or any sort of feed-in restriction (people setting AC-input limits on their Quattros/Multis)... it can get really painful. In general... though it can be done, it is much more stable to bring your PV in on the DC bus using MPPTs.

15 hours ago, KobusK said:

The grid tied can not feed back to the grid as it has a clamp on the municipality feed blocking the feed. 

People tend to misunderstand this. The grid-limiter type solutions doesn't really prevent you from feeding in, they just try to keep it to a very low value, at or around zero. As the load changes (especially large loads coming and going), there is always a second or so where you're either pushing into the grid or drawing from it before the inverter actually backs off. The grid is a low-impedance place for the power to go and so it works well. When the grid isn't there, for that second or so while the PV-inverter backs off... it's going to push it into the batteries. If the inverter is designed to do it (The Victron's are). Others will either blow something up or overvolt their high-voltage DC-bus (if they use a bi-directional topology).

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That sounds like a potential bomb in the making.

 

is it feasible to to first put the GTI the the Hybrid gong to the DB. 

 

Should the mains then be interrupted the Hybrid will be the only one working. 

 

We dont have load shedding any more and at night this can get rid of the 500 w load throughout the night. I have checked this load comes from the security cameras routers.

 

or is it just better to split everything in parallel and put the essential loads on the Hybrid? 

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the GTI 1st on its own disconnect and then the hybrid. on outage the gti will then disconnect and the hybrid will take over the load. this is how i had mine before changing besides the fact that i had pv on bith the gti and hybrid and both returning to grid without issue....

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4 hours ago, KobusK said:

... at night this can get rid of the 500 w load throughout the night.

The cost per kw/h, in your case, which is more, Eskom or batteries?

 

Just putting a thought out there. Camera's, seeing that most surveillance camera systems are 12v, they make a good case for off-grid.

Take a large 12v battery bank to power the system for say up to 72 hours with no charging. Then add a dedicated panel and small controller to extend that to run indefinitely, completely off-grid.

Same logic can apply to all 12v systems that must be on 24/7.

No wastage with a PSU that takes 220v AC to 12v DC etc.

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On the topic of how hybrids/bi-directionals work, I always think of the Cahora-bassa electricity line. This is a DC distribution line. To tie it into the AC distribution on the other end, two massive parallel-series thyristors are used, essentially using the AC frequency to switch the DC into a two-winding transformer and thus turn it into AC of the exact required frequency to be fed into the AC line. Theoretically this arrangement will also work in reverse, with the transformer running the other way and the thyristors being a normal basic rectifier to make DC. So it's a fully bi-directional AC to DC bridge. As I understand it, that's how a grid-parallel inverter works as well, though it will likely use MOSFETs or IGBTs.

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Much in the same vein. I have a small hybrid UPS just being used for a little bit of backup. This is not connected to PVs and charges by the grid.

I'm having a 10kw/h PV grid tied system installed in the next week. If the grid goes down there will be no power because of the isolation from the main grid.

How can I use the small hybrid to fool the system into delivering power when the grid is down? The hybrid system is too small to route everything through it, thus my question is how to utilse the local 10kW/h system, with grid down, using the hybrid to give the 'signal'? I have the silly idea that once it is running, that the disconnected PVs will charge the hybrid and then deliver the perceived sync while the sun is shining, plus a little bit from the hybrid.

Ideas will be very welcome.

 

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3 hours ago, economode said:

I'm having a 10kw/h PV grid tied ... thus my question is how to utilse the local 10kW/h system, with grid down, using the hybrid to give the 'signal'? 

I think the answer lies here, from Plonkster ...

On 2018/07/07 at 1:14 PM, plonkster said:

So your Hybrid inverter must be able to carry the full load, you cannot rely on a combination of PV and Hybrid power to attain a larger total. Furthermore, there is a 1:1 rule (PV inverter may not be larger than the Hybrid), ...

For I myself would be over the moon if I can use a smaller system to "fool" a larger grid tied system, well, not grid tied, "inverter" tied. :-)

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2 hours ago, The Terrible Triplett said:

I think the answer lies here, from Plonkster ...

You're going to have to tie it to a 10KVA Quattro or similar. Or you will have to configure it to a max of whatever your hybrid can handle.

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  • 3 years later...

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