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COCT SSEG on three phases

The Bulldog

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Now that I am live with a legal COCT SSEG feed and a AMI meter I have got the first account and can clarify one of the questions nobody has been able to answer at COCT.

The AMI meter is setup by COCT to do PER PHASE metering. Not NET metering (like a old fashioned three phase meter would do). The AMI meter is perfectly capable of doing NET metering but parameterised by COCT not to do so.

This means if you feed out on one phase to use the power on another phase (a very common occurrence) you will get charged full tariff for your own power while getting a credit for the same power on the feed-in tariff. In other words COCT is selling you your own power at 2.6 times the rate it is giving you (The power has just moved between phases via the utility transformer up the road - COCT did not get that power anywhere else). 

In my setup this happens usually when house loads and generation are relatively close to each other, not a problem once power generation ramps up and each phase generation exceeds the house loads.

I'll have to investigate how to work around this - have some ideas.

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16 hours ago, The Bulldog said:

I'll have to investigate how to work around this - have some ideas.

What inverters are you using. The way you explain it, I guess you are using Victrons, if that is the case, switch off "Phase Compensation". The way i understand it, it will then "Move" the power around over the DC bus. Its less efficient but way better than paying those fees.

@plonkster, do i understand this correctly?


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1 hour ago, Jaco de Jongh said:

, do i understand this correctly?

Yes. But the "Phase compensation" thing (which we are changing, because the name is mucho confusing) does more of a phase balancing thing, making sure that all three phases are doing the same thing (not the same amount of the same thing, but the same thing). If two phases are exporting while another is importing, then power is taken away from the exporting phases and added to the importing phase until all three are exporting (or zero). Or not really zero... until the three phases all do the same thing AND add up to the ESS grid setpoint. The effect of that, when you have a small positive ESS grid setpoint (as you normally would ) is that it balances each phase to about a third of the grid setpoint, and power has to flow over the DC bus if there is a surplus on one phase and a shortage on another.

So long story short: Yes, that is the setting.

But, @The Bulldog previously reported that he was not using ESS. He may have changed that though. But the above feature is an ESS feature, so that has to be said.

Also, pushing power into one phase and using it on another (ie via the transformer down the street) is also inefficient, though less so than pushing it through the DC bus. That is one reason not to do "phase compensation" in the usual sense where you make them all equal. It is much better to let the Multi on each phase do the job of powering things on that phase than to attempt to somehow split the work and losing energy by pushing power through the transformer down the street. Again, just mentioning this for completeness: Both practices are slightly inefficient.

Pushing the power through the DC bus is at best 80% efficient, and possibly even less. In my experience a Multi running at 80% capacity is around 88% efficient, and 0.88^2 = 77%, let's call it a round three quarters.

Edited by plonkster
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Using ESS is unfortunately out of the question as that would violate my systems approval by COCT (My three Victrons are 5KVA Multiplus and not NRS-097).

I am only allowed to use them as UPS.

One way to solve my problem is to simply drop out the grid during the times when power shunting between phases is needed and let the Mutis take over the supply. During this time my Solis grid tie can still generate power and since I can throttle it (and have to) using its RS485 bus I know what the potential generation is (from the amount I have to throttle) so I know when to reconnect to the grid.

It's not a huge issue - in monetary terms it works out to perhaps R80 maximum loss to my side a month - it's more the principle of it. 

ESS with external control via a MK2-RS232  which I have is attractive as it opens up a lot of other interesting possibilities - but I don't think I'm allowed to use it. It strictly would not violate COCT's SSEG rules as it does not form part of the solar system anymore - but it would not be a UPS to NRS codes either.


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