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Very Small 3-Phase Systems


CCC Telecom
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I am coming across a lot of very small 3-Phase homes who want to go nearly off-grid aiming for 75% power bill reductions

They are low power users with have a bill of R2,000 per month, and usually have 2 * 3kW geysers, (they do not need a 3-phase supply)

So looking at their options, getting the 3-phase removed is not really an option due to admin delays

1) Put everything on phase 2 and run an unbalanced system - here it is not going to kill Eskom since most 3-phase users have a high imbalance on Phase 1, you could keep the geysers and ovens on Phase 1 and Phase 3 and just protect the rest of the house on Phase 2

2) Put in 3 small 3kW battery inverters and a small cheap PV inverter and load shed the geysers during non-solar hours

I would much rather be dealing with 90kW 3-phase systems, as these are relatively easy to configure when they actually need to be 3-phase

Anyone got any advice for these tiny 3-phase systems

 

Edited by CCC Telecom
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There's a 3 phase hybrid from Goodwe, and the Solis one has been announced. They work from HV batteries though which is potentially a problem (at least R80k for the battery bank).

Other option is to parallel 3 sunsynks (either 3.6kw or 5kw). I'm actually considering using 2 X 5kw sunsynks at my place and leaving the 3rd phase empty. 

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On 2021/02/06 at 4:38 AM, CCC Telecom said:

2) Put in 3 small 3kW battery inverters and a small cheap PV inverter and load shed the geysers during non-solar hours

I would much rather be dealing with 90kW 3-phase systems, as these are relatively easy to configure when they actually need to be 3-phase

Anyone got any advice for these tiny 3-phase systems

 

Axpert (Voltronic) has 3kW inverters. 3 of them can be configured to a 3-phase system. That would make a total of 9kW. What I don't like about them is that they are built for 24V battery. With 9kW potential power that implies a terribly high current on the battery. I would rather use 3 4kW units with 48V battery.

But I would suggest to think about rewiring the DP to single phase and use only one phase from Escom for backup. I suspect that you pay extra monthly fee for 3 phase. R2000 per month seems to me very high. Enduring the admin hassle to reduce to single phase may well pay off in the long run.

 

 

 

 

 

 

 

 

 

Edited by Beat
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On 2021/02/07 at 3:51 PM, Beat said:

Axpert (Voltronic) has 3kW inverters. 3 of them can be configured to a 3-phase system. That would make a total of 9kW. What I don't like about them is that they are built for 24V battery. With 9kW potential power that implies a terribly high current on the battery. I would rather use 3 4kW units with 48V battery.

But I would suggest to think about rewiring the DP to single phase and use only one phase from Escom for backup. I suspect that you pay extra monthly fee for 3 phase. R2000 per month seems to me very high. Enduring the admin hassle to reduce to single phase may well pay off in the long run.

 

 

 

 

 

 

 

 

 

The problem with the 3 *3kVA approach is obviously large power devices, and most of these customers want to be moving towards Off-Grid, we would be sending them down a dead end where this can not happen, hence installing 8kVA inverter and moving the DB board to single phase would be my preferred approach, I actually have 3 customers in the same street wanting the same thing, so they can use a different phase each, and eskom remains balanced.  But you are right, eventually it will be time to get around to moving them to single phase supplies

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Actually... not sure whether the Sunsynk 3.6kW units are available in South Africa, but if they are and spec wise they are following the 5kW and 8kW units, then you could put in 3 of them in phase rotation, synchronized for 3 phase and when you go off the grid single phase eventually, put them in parallel mode for 10+kW single phase power... but confirm the specs and availability before thinking this is a workable solution...

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The 3.6 does not have a fan, so at loads close to the max, the heat sink gets hot enough that you cannot keep your hand on it for more than10-15 seconds, also it comes with a single mppt, albeit, you can cantwo strings to it, in parallel.

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5 hours ago, Tariq said:

The 3.6 does not have a fan, so at loads close to the max, the heat sink gets hot enough that you cannot keep your hand on it for more than10-15 seconds, also it comes with a single mppt, albeit, you can cantwo strings to it, in parallel.

Although three of them give you three MPPTs

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  • 3 weeks later...
On 2021/02/10 at 1:13 PM, CCC Telecom said:

.........., hence installing 8kVA inverter and moving the DB board to single phase would be my preferred approach, I actually have 3 customers in the same street wanting the same thing, so they can use a different phase each, and eskom remains balanced.  But you are right, eventually it will be time to get around to moving them to single phase supplies

There is one thing however you must pay attention to: If the electric stove is in single or 3-phase connection. You find this out at the DB. If there are 3 breakers for the stove, then it is 3-phase connected. It then is most likely wired with 4x2.5mm². Simply connecting the 3 phase wire together to single phase would risk to overload the neutral wire. There are 2 possible solutions: Ether you pull in a stronger, 4 or 6mm² neutral wire.

Or you connect 2 and 2 of the 4 wires together, i.e. blue and black together for the neutral and red and white together for the phase. You also would have to jumper the 3 phases on the input terminals of the stove together. In the DB you would have to replace the 3 breakers by a single 30A breaker.

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