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Excess power sell back


leaves
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Hi Guys, I live on a farm in close proximity to the neighbors.

I belive all three houses are on the same electricty supply line if ai can call it that.

If I connect my GTI up and push excess into the grid, will the neighbours recieve the solar power first before the eskom? How does this work?

Many thanks

L

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I believe so. Depends where the meters are. In town, assuming you have an old analog meter, what happens is a) your meter runs backwards, so Eskom "pays" you for the electricity, B) it takes the shortest path through your neighbour's appliances via his meter, where Eskom sells him that power again at the same price. If the meters are upstream from the neighbour, then of course he will benefit from your surplus.

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Awesome, thanks for the info. Please take a look at my rough finger drawing,

I am house B. The eskom is supplied from the eskom transformer market.

A and C are my neighbors homes. I would like to discuss a few scenerios.

If me at house B is producing more solar than I am consuming and pushing back power.

Will the solar flow to house C first and the makeup come from the grid?

If house C is shutdown, will the power then be divereted to house A?

Thanks Guys we on a plaas here :)

L

post-121-0-71593500-1442969225_thumb.jpg

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Janee, die manne op die plaas maak altyd 'n plan.  :D

 

Leaves, I will be very careful here if I was you.

 

With grid-tie, if Eskom is off, then grid-tie units also go off. Reason for this is that if Eskom is say doing maintenance somewhere, and you keep on supplying, someone can be shocked / killed working on the lines that are supposed to be off.

 

There are rules and regulations that you need to adhere to in order to connect to the grid legally.

 

So if your intention is to handle load shedding, it is not going to work.

If your idea is to save costs, then go for a off-grid scenario with Eskom as backup, as many users on this forum has done.

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A certified GTI will shutdown when the power is off?

 

Yes, that is a requirement - the GTI will stop feeding the grid when the grid fails. If you get a hybrid however, the grid exporting will stop when the grid fails, but your load will still be supplied by the hybrid.

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Hybrid needs batteries, and in your case leaves, having a big generator, you can lessen the batteries you need if Eskom takes too long to come back, by starting the generator to feed the hybrid inverter to power the load and re-charge the batteries.

 

And/or, with a hybrid inverter, get enough panels to power the load daytime (savings), with the min batteries because you have a generator.

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Hehehe I see that "benefit" is ambiguous here. As others have said, if the grid goes down, so does the GTI.

Will others get a cost reduction? That depends entirely on where the meters are. The supply line may run point-to-point from one house to the next, but that is no guarantee. It might be a big-old 4-wire 3-phase line with each house on a different phase, in which case it's not going to help if you feed back on just the one phase. Even if one or more houses are on the same phase, if the meter is on the house side, there is no financial benefit, because your neighbour's meter simply spins forward by the same amount yours spins backwards. You save money, the neighbour doesn't.

Other interesting things to note, on a three phase system that is properly balanced, the current on the ground wire is zero (now that's some counter-intuitive black magic at first glance), so generally when a three-phase system is connected it is done in a way that roughly balances the loads. Adding a very large solar GTI to one phase is probably not a good idea :-)

 

Long story short: It's difficult to say whether it will help the neighbours, but in almost all configurations except one the answer is probably no.

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Also, re the reason the GTI goes down when the grid goes down. Of course there is a practical reason (not killing line workers), but there is also a technical reason. The technical reason is that the line frequency itself is used to drive the final grid driver part of the circuit. Essentially the GTI creates a high-enough DC voltage using high-frequency conversion components, and then that is switched onto the line using some kind of high-voltage capable power transistor, using the grid frequency itself to drive this process.

 

When the grid goes down, you lose this signal. Of course you CAN use another frequency generator as a reference... but that's not how a pure GTI is designed :-)

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