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Niko Järvinen avatar image
Niko Järvinen asked

Recommended setup for weak 3x16A grid + solar + batteries

We're in the process of starting a new house build. The idea is to have smallest possible grid connection to save on initial + recurring costs and then have batteries + solar to both help with the peak loads (ESS) as well as have a possibility of everything working as normal when the grid is down. The building location is quite far from anything and it's expected to have few days of issues per year after storms. Additionally we will want to feed all extra solar power back to grid due to local insentives.

As the house will have heat pump as the main heat (3kW peak) source, inductive cook top (7kW peak ) and electrical DHW heaters (2x2kW or something) things start getting a bit complicated quickly. In theory I'd guess going with something like 1 phase 64A (220V..) might actually be simplest but that would mean we would lose out on the day/night pricing for electricity.

That leaves going with something like 3x16A grid connection. We don't have any equipment that needs 3 phases so in my head I'm thinking each phase as a separate 16A grid connection right now... Since we have few quite powerful loads and would love to have the solar power available for each phase, I've understood I would basically need to have multiplus or quattro for each phase? This gets a bit pricey and creates a situation where I have to optimize each phase for the peak load for that phase which leaves quite a lot of wasted capacity.

The main question is that is there better way of doing things? Could I for example use one quattro and have phase 1 & phase 2 fed into the quattro as AC1 & AC 2 IN and basically combine two phases to be one stronger phase. This would negate the need to buy a second quattro plus make the load management easier since I can then have a simple load control for the DHW for example and turn them off if peak load is approaching due to other loads in the house.

This is based on the assumption that quattro would be able to pull 2x 3.6kW from the grid and then the inverter would be able to add another 4kW on top of that in peak load scenarios which would be plenty enough for our needs. And of course in a grid failure situation we would be limited to the 4kW which feels like a good compromise as it's enough to keep the basics running.



MultiPlus Quattro Inverter Chargersystem design
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matt1309 avatar image matt1309 commented ·
I can't really offer much advise on having say 1 to 3 small quattros/multis to take grid input into the battery and then another larger inverter to cover single phase house loads (quite a complex setup). Pretty sure it's possible but above my understanding (mainly because i'll never be able to afford a system that cool, so I'm very jealous if you go this route)

Or like you suggest using different phases on ACIN 1 and 2 of quattro.


However if the above isn't possible you may be fine anyway with just a single phase grid connection. And just have a larger battery/inverter with some schedule charging/peak shaving as the buffer be able to get around your problem of having a smaller grid connection.

ie rather than (2 x 3.6kw from grid) + 4kw solar

You'd instead have

3.6kw grid + 3.6kw battery + 4kw solar.

And then in non peak load time just have 3.6kw continue from grid into battery even if loads are not on say overnight, to top up the battery again. (Just realised I've just poorly described peak shaving essentially)

And if you are using huge amounts of power you could just leave grid charging battery 24/7 using grid setpoint to be 3.6kw 24/7. That would give you 86.4kwh of grid power per day.


Saying that if you are using over 85kwh per day the inverter/battery size you'd need would be substantial. You'd probably have at least 3 if not 4 quattros/multis in parallel in which case you may as well setup 3 phase for each 16amp supply from grid as you originally planned.




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slowmo avatar image
slowmo answered ·

Why not heat DHW using heat pump? And heat pumps are available in 3 phases as well. But anyway, you might get away with 16A per phase if you carefully distribute loads between phases. Cooktops are usually 2 phase. 2 zones per phase max 16A each.

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Niko Järvinen avatar image Niko Järvinen commented ·
Yep it will be doing that but usually COP starts falling off at the 55-60 degree mark (especially in the winter) so it's usual that you end up having some kind of extra heating system to push it it above that in the hot water tank. Additionally have to have enough heating capacity for the DHW & under floor heating tanks to get over a situation when the pump is not working or is broken..


Good point about the cooktop. Have to see if I can find one that can work with single phase for the full power.

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Niko Järvinen avatar image Niko Järvinen Niko Järvinen commented ·
Also since quattro has 2 outputs, I guess you could program those as two phases for the cooktop?
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mvas avatar image mvas Niko Järvinen commented ·

No, a single Quattro does not supply 2 different phase. They are single phase.

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Niko Järvinen avatar image Niko Järvinen mvas commented ·
Ok thanks. Good to know. I guess KISS wins once again...
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janieronen avatar image
janieronen answered ·

Quattro two inputs are just controlled relays and you can't use two inputs same time. Meant. only for example IN1 for Grid and IN2 for Genset type use. So one inverter can handle only one phase.


I have 3x Quattro II 5k 230 in three phase setup and do use system to limit grid power which it does well. I would lift some additional questions which may give you guidance for deciding how to continue.

What is grid code/ region ?

Does your grid operator compensate phase usage based on phase netting? So If you use ph1 1kwh, ph2 -1kwh and ph3 0kwh during netting period (usually 15min or 60min) You don't need to pay anything to grid company or electricity company? If you don't have net balancing then you need to optimise loads.


With phase compensation you can also misuse grid by installing only one phase inverter and just measure all phases. Sure then your max charge power is maximum 3600W (16A230V). Also if you have phase compensation in place you can have three smaller inverters and doesn't harm if loads are not balanced between phases as grid phase compensation will net this issue away.


Hope you can understand something from my quick writing. Please ask if my text is not clear :)

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Niko Järvinen avatar image Niko Järvinen commented ·
Thanks. Sounds like there's no easy way to combine those phases so the only setup remains to have 3 multis or quattros.


The region is Latvia. All I know currently that their solar is some kind of "Long term netting" system.. so basically all you input to the network during summer, you'll be able to use for free during the winter. It's about to change during the end of the year however so have to study a bit.

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