Hello everyone. I am new here and hoping to tap into the wealth of experience in order to begin to develop a solution for my problem.
I have a large house in Greece. It receives three phase mains AC supply, 40A on each phase. The core issue is that the supply is variable and we suffer frequent voltage drops and imbalances across the phases. The grid supply to this area is weak and demand exceeds supply in the summer. The variability of the supply is slowly frying my electrical equipment which is expensive and irritating as you will imagine.
There is also a limit on how much solar I can have. Obviously we have a lot of sun but I am limited by law to 10kw of non-grid connected solar as the local distribution network cannot accept distributed generation.
I would like to know whether what I am proposing is possible. I have seen similar systems on large boats so I hope it is.
I would like to find a large enough three phase hybrid inverter/rectifier. Into this I would like to feed my mains AC supply, a back up generator supply and the supply from a battery. The battery would be supplied by the solar and topped up where necessary by the generator.
The inverter would convert the incoming AC supply to DC, that DC would be “topped up” as necessary from the battery and then the combined supply would be rectified to a nice steady 230v supply on each of the phases to the house.
Is this possible? While my electrician sees what I am trying to do he seems doubtful if this can be achived with 3 phase AC input and output.
Sorry for such a long post but I was keen to understand the experience of others here. Apologies if I am making some naive assumptions!
For this use-case you can use three Victron Quattro inverters, one per phase.
In case the grid is within the specified parameters, it will be directly connected to your loads. In case it deviates from any parameter, the inverters will disconnect the grid and supply the load from the battery. The generator can be started automatically below a certain state of charge.
Be aware that you need a three-phase generator in this setup.
As second option you could use three Multiplus-2 inverters (they don’t have a generator input, otherwise identical). The generator would then charge the batteries with a seperate charger (could be single-phase).
As for PV, you can choose to charge the batteries directly with a DC/DC MPPT or use a AC-coupled string inverter. I would recommend the first option in your case, it allows system startup even with depleted batteries and should be more stable. The 10kW grid limit can be set in the inverters, you don’t have to limit the amount of panels due to this.
Thanks very much for the helpful reply. I looked at the Quattro. In the scenario I have described however do I not need three inputs?
Input 1 AC from mains
Input 2 AC from 3 phase generator
Input 3 DC from battery (charged by the PV or the generator).
Maybe I am not understanding but I don’t see whereabouts in this system the DC feeds in and gets rectified to AC?
Also would you know whether in the event of voltage drop this system would simply switch off the mains AC so I’d be wholly reliant on battery power until te mains supply parameters were restored OR would I continue to receive the mains supply but this would be boosted back by the battery to the required specification? I think this last question might be important in battery sizing. We don’t often get fully cut off but brownouts are common.
The Quattro/Multiplus inverters do not have a solar input. You will need seperate solar chargers that directly supply 48V DC to the batteries (e.g. Victron MPPT 450/100).
Edit: I think I misunderstood your question. The Quattro along with every other inverter of course has a bi-directional 48V DC battery connection.
However, you could use the Multi RS Solar instead, but this doesn’t have a generator input. I’m not aware of a all-in-one unit that can do everything, not even from different manufacturers.
Regarding the brown-out behavior: The limits are defined by the grid-code that is required by your grid operator. Technically, it’s possible to deviate from that and allow the grid connection up to 185V I think. But this will not be boosted, you will see the grid voltage at your loads as long as the grid is connected.
In case the grid issue is just your individual connection to your house, you could define a maximum grid current, the rest would be supplied by the batteries/pv. This should then limit the voltage drop significantly. However, it sounds like the brown-out affects the whole grid section?
The only option I can think of that completely eliminates brown-outs at your loads is a dedicated charger with low input limits that supplies the batteries from the grid. Your loads will then be isolated from the grid. Be aware that you will have significant losses if you go this route (AC → DC → AC conversion for anything coming from the grid). Also PV feed back to the grid is impossible with this isolation.
Maybe I am just overcomplicating this! Thanks for your very helpful reply.
My main issue in low voltage on one or more phases.
To reduce this to the simplest level, I think you are suggesting that I could have three Quattros or Multiplus (one for each phase) and I could then connect a battery to each inverter. I could I guess keep this battery topped up from the mains supply (when that is in specification) and switch to battery when the mains supply is out of specification (ie <220v). This would address my core issue.
Everything else is an optional extra. I could add a generator to top up the battery/supply the house directly (to reduce risk associated with longer duration issues).
I also could add PV as a cheaper (over time) way of charging the battery.
Is this correct?!
What I don’t completely understand (becuase I am a newbie to this!) is the extent that the battery can feed in power to the house alongside the mains supply. I think I understand you to be saying that that is not possible and the supply source must at any one moment be 100% mains OR 100% battery. Is that correct or I have I misunderstood? Thanks for your continued help!
What you’re describing is a double conversion system. Thats not how a typical Victron system works.
As long as there is an AC source available, this also means voltage and frequency within specs, then that is connected directly to the load. The inverter/charger sits parallel to that, either supplying additional power or taking power to charge the battery.
If the incoming voltage is not good enough, the system simply disconnects from the mains and supplies the loads from DC/batteries.
Yes you can create a double conversion system with victron components, but you would be looking at using twice the amount of devices. A set of three MPs/Quattros which only charge the battery/supply DC, and another set of three MPs/Phoenix inverters which create AC again. Loosing 10-20% of energy in the process.
A standard victron ESS, with either DC or AC coupled PV would possibly be enough for you.
Yes, you misunderstood. In normal conditions the grid is connected and the system tries to regulate the inverter power to 0W at the grid input. The inverters supply exactly the amount of power that the loads use in this moment. The grid is connected, but no current is flowing.
Grid power is only used in these circumstances:
the loads demand more power than the inverters can provide
the battery is empty
there is excess PV (and it’s configured to feed back this power to the grid)
you configured the system to always keep the batteries topped up
In case of a brown-out of the grid, the inverters disconnect the grid and everything is supplied by the batteries/pv/generator. When the grid is back at normal conditions, the inverters connect it automatically.
You can configure a minimum SoC of the battery, below which the battery will only be discharged in case the grid disconnects. This can be anywhere between 0-100%
You connect all inverters to the same battery (or to multiple batteries in parallel)
Just another question though. I understand your explanation that the inverter system set up parallels the grid supply.
You say that “the system tries to regulate the inverter power to 0W at the grid input”. I take from this that you mean that the system will always prioritise power from the battery over power from the grid. This makes total sense if the battery is charged through PV.
However my priority is voltage stability. So (assuming I keep it simple and don’t add a generator or PV myself), I’d want the grid to charge my battery but once charged I’d want the grid powering my home unless and until the grid power goes out of specification when the battery would kick in.
If I understand correctly this is the opposite of the quotation I have taken from your post. But (again from what you helpfully explain above) I deal with this by setting a minimum SoC of 100%. Is this correct?!
If I then decided to add some PV I would then need to decide what should be the minimum SoC - that is I would need to choose one high enough always to keep sufficient battery power in reserve to deal with voltage fluctuations but low enough to get some value out of having PV.
You dont need to set an SOC, since what you want to achieve, without PV, is just a regular Victron install without ESS.
As long as mains is available, it will keep the battery charged. Once the voltage/Frequency is out of the acceptable window, it will disconnect itself and feed the load from batteries.
This is a function of ESS, which is not standard functionality but needs to be enabled/added as an assistant to the MP.
You can add DC PV easily to a regular install, but it will never feed back to grid. But once you install PV, you can then change to ESS, and simply use the “optimized” mode, section 4.3.1.
You could also use ESS without PV and keep the mode on “keep batteries charged” which would be virtually identical to a regular victron system without ESS. So no real benefit in using ESS without PV.