Converting 3 phase system to use single phase for reduced cost off-grid system

[barnabyrees-jones]

I have a question regarding a new off-grid installation. The household currently has a mains 3-phase 40 amp supply. Its a domestic holiday home in South Africa and the loads are generally pretty low - underfloor heating, hot tub, air con, fridge, freezer, TV and lighting etc - nothing industrial or too power hungry.

Having researched various off-grid systems I think the most cost effective system to provide the peak power output needed is a 5kW solar array system coupled with a 8kW sunny island and 6.4kWh LG-Chem battery linked with an auxiliary generator that the sunny island can auto start should it need the extra power to meet the load.

The problem I have is because the house is 3-phase, I would need 3 sunny islands which doesn't make financial sense. Is it possible to just link the loads to a single phase and run a single phase PV and sunny island system on that phase (I take it a domestic property wouldn't unbalance the phases). Or would it generally be easier to rewire the distribution board to single phase?

Also, I am looking for input on possible alternatives to the sunny island should anyone have any other ideas? I have had a look at the viltrons, but their peak power output is quite low. Any help would be greatly appreciated.

Thanks,
Barns

[inetdog]

I think that the greatest concern is whether the existing three phase distribution wiring, including branch circuits, ever uses a shared neutral wire between two or more phases to save on copper.
With three phase supply such a neutral will never carry any greater current than any one of the hot wires.
If you convert to single phase supply those neutrals could end up carrying as much as three times the current of a single hot wire and would be badly overloaded.
Second, of course, would be whether any equipment in the home is set up to use the Line-to-Line voltage as its supply. To get that higher voltage with a single phase supply would require installing a transformer to step up the single phase voltage.

The only safe way to determine whether this can be done is to bring in a professional electrician to evaluate the situation. You will not get the safety advice you need over the internet.

[ButchDeal]

loads are generally pretty low - underfloor heating, hot tub, air con, fridge, freezer, TV and lighting etc - nothing industrial or too power hungry.

A/C, floor heating, hot tub..... But nothing too power hungry huh.

Well you might want to check your loads a bit more.
I would suggest the FlexPower3 from outback which can be configured for 3phase but it likely is not big enough for your needs

[jflorey2]

I have a question regarding a new off-grid installation. The household currently has a mains 3-phase 40 amp supply. Its a domestic holiday home in South Africa and the loads are generally pretty low - underfloor heating, hot tub, air con, fridge, freezer, TV and lighting etc - nothing industrial or too power hungry.

Having researched various off-grid systems I think the most cost effective system to provide the peak power output needed is a 5kW solar array system coupled with a 8kW sunny island and 6.4kWh LG-Chem battery linked with an auxiliary generator that the sunny island can auto start should it need the extra power to meet the load.

The problem I have is because the house is 3-phase, I would need 3 sunny islands which doesn't make financial sense. Is it possible to just link the loads to a single phase and run a single phase PV and sunny island system on that phase (I take it a domestic property wouldn't unbalance the phases). Or would it generally be easier to rewire the distribution board to single phase?

Also, I am looking for input on possible alternatives to the sunny island should anyone have any other ideas? I have had a look at the viltrons, but their peak power output is quite low. Any help would be greatly appreciated.

You're going to need a lot more than 8kw to run all that stuff. You might want to consider three Outback GTFX inverters; you'd get a bit more power (10kW) with three of them and they might be cheaper. Although with your loads you might need six.

One problem you will have is that some of your loads simply won't run on single phase. I doubt the air conditioning (if it's central) or the hot tub (if it's electrically heated) will be able to run on single phase power.

[Mike90250]

I have a question regarding a new off-grid installation. The household currently has a mains 3-phase 40 amp supply. Its a domestic holiday home in South Africa and the loads are generally pretty low - underfloor heating, hot tub, air con, fridge, freezer, TV and lighting etc - nothing industrial or too power hungry.......

You are dreaming. You are not going off grid with this, unless you are a billionaire. You have huge loads, and will need a huge system.

Try thinking about Grid-Tie Solar with a 3-phase backup generator. That's the only route that would save you money.

You did not say that you are in an area that experiences frequent blackouts, so batteries would be wasted.