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jackb avatar image
jackb asked

Inverter/Charger advise for Enphase solar excess storage

Hey


I currently have a 11.1kWh system on our house in NSW Australia, utilising 30x Enphase IQ7PLUS-72-2-INT inverters. Currently, this system is set up to provide power during the day when required and export the excess PV to the grid.


The majority of our power demands are at night so we are looking at battery storage. We are looking at a 48v 14.3kWh battery and would like the following to happen:


  • PV provides power for the house when sun is out
  • Excess PV is used to charge battery up to 100%
  • Once PV is unable to sustain house requirements, Battery is used for power consumption in the house until it reaches 10%.
  • At 10%, the grid takes over and provides power.
  • If power demands exceed the Inverter/charger limits, grid assist with power (e.g. 6.5kW load, 5kW from inverter and 1.5kW from grid)


If you could please recommend an inverter/charger for this, It would be greatly appreciated.


I was thinking the Multiplus-II 48/5000 if that would work, as well as a GX device for monitoring. I believe I will also require a current sensor with the Multiplus.


Thanks in advance for your assistance.

Multiplus-IIMultiPlus Quattro Inverter Charger48v batteryenphase
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3 Answers
shaneyake avatar image
shaneyake answered ·

Yes, the Multiplus-II 48/5000 is what I would recommend for this. The only thing to note is that you can't exceed the Multiplus rating if you would like to AC-couple. AC-Coupling allows you to use the solar power if there is no grid available but for every Watt of AC-PV you need a Watt of inverter capacity. 1:1 ratio or better. You could split up your enphase array and have some of it AC-coupled.


You can add more inverters at a later stage if this is something you want to do. Not supported by 48/8000 and 48/10000.

If the Solar only needs to work when there is grid. This isn't a problem all the AC-PV should be on the AC-Input side of the inverter.

Yes, CT or Grid Meter is required and for the GX I would get a Cerbo.

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jackb avatar image jackb commented ·

Thank you.


So I would be best off determining my max potential load (e.g water heater, air con, stove, oven etc.. all running at once) and size my inverter to suit?

Or am I reading it incorrectly, and instead this means that given my 11.1kWh system makes a max of 8.5kWh (that I have seen on Enlighten) at any one time, I need a Multi with at least 8500w capacity (e.g. 48/10000 or 2x 48/5000)?


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shaneyake avatar image shaneyake jackb commented ·

So the the 1:1 rule is for inverter size when not grid connected.

So since you have 30 x 290VA (IQ7PLUS OUTPUT) = 8700VA of AC-PV inverter capacity.
If you would like to connect all your solar so that in the event that you lost grid you could keep everything running you would need at least a 48/10000 or 2x 48/5000.

But as I said, if you are okay with PV turning off when you lose grid then you can use any size of inverter.

That is the first part, the second part is yes, You should figure out what your loads are so that you have enough capacity to run then off the battery. This is critical if you would like the Multiplus to run everything in the event of grid loss.

If you aren't going to use the system as a UPS or back-up power source but rather just reducing your grid consumption the sizing matters less. Since you have 8.7kw of Solar I wouldn't go smaller than a 5000VA inverter as this will limit how much power can go into or out of the battery.

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jackb avatar image jackb shaneyake commented ·

Thanks!


So I have 3 main options by the sounds of it


  1. Backup and storage with 48/10000 or 2x 48/5000 inverters, 30x enphase on the load side of the Multi
  2. Backup and storage with 48/5000 and splitting the enphase so 17x are on the load side of the Multi, and 13x are on the AC-Input side of the Multi.
  3. Storage only with 48/5000 and having all 30x on the AC input side


Option 1 allows me full UPS/Backup, so I can continue as normal when the grid is down (which is quite rare where I am)

Option 2 allows me some power when off grid, but not the full potential (allows lights, TV, fridge etc, but not air con or hot water heater)

Option 3 gives me storage only, and if the grid is down, the whole house is offline until the grid is back up.



How does the charging side of AC-Couple work? I am assuming that when the PV inverter sends power back to 'the grid', the Multi intercepts that and uses it to charge the battery? Once the battery is full, will this then continue feed the grid, or is this power now lost?



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shaneyake avatar image shaneyake jackb commented ·
Correct.


Option 3 does still give you some backup but only till battery is empty.

The CT or meter monitors your grid connection, if the multi sees you are pushing back it will start charging to keep your grid connection at 0W, this is done till the batteries are full. Once the PV dies down the multi will then invert and push power to your house to keen the grid usage at 0W, this happens till you hit the low SOC limit which you set.

There is obversely still the case that if you use more than 5000VA then the multi will ramp up to around 5kw depending on temperature but the rest of the power will have to come from grid. This is the case for both charging and discharging.

In a backup case if you draw more than 5000VA from the inverter for more than a few seconds it will Overload shutdown.

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jackb avatar image jackb shaneyake commented ·

Thank you.


So the way to install it for option 3 if understand correctly would be:


Grid <> Energy Meter ET112 <> Enphase PV Inverter > Multiplus II > Loads

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shaneyake avatar image shaneyake jackb commented ·
Correct.
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David avatar image
David answered ·

Hi @JackB

I'm in NSW and have a similar system. 33 Enphase Micro's - split across 3 phases (11 per phase)

I added a MultiPlus II - 5000VA and have a battery.

As you are in NSW, it really doesn't matter if you have 3 phase or Single phase - as we are billed on the net of the three phases - So you can consume on L2 and L3 while L1 exports and if the sum of all three is 0 this is what you are billed :-)

If you would like your enphase system to keep generating while the grid is out, you need them connected to the OUTPUT side of the Multiplus, and this is where the 1:1 rule comes in that others have talked about.

The multi effectively becomes the grid and keeps the enphase running to power your loads and charge your batteries even while the grid is out.

My enphase is on the input side thou, so is only operational while the grid is operating.

I also have DC-coupled solar - with a further 18 panels connected via three separate 150/35's MPPT's - so I get some charging and power out of the system when the grid is down.

With a system as big as yours, you could easily support a 30kwh battery.

Are you planning to do this yourself or get a qualified installer :-P

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jackb avatar image jackb commented ·

I think you and I will end up with a very similar setup.


I will be putting the PV inverter on the input side, so if the grid fails, the house will be powered from the battery and the DC solar (I will also be running some solar via Victron MPPT to the batteries). We rarely have grid failures here, and when we do it is usually at night during a storm, so the AC PV will not (in most cases) be generating anyway.


I will be building the system with futureproofing in mind, larger battery, second inverter etc.. if my power demands increase (EV for example).


This is roughly how I plan on running it (for now, as you know, plans always change)


The physical mounting of the hardware will be installed by myself, but I will be leaving anything that has the potential of letting some smoke out to the professionals :)


home-solar-battery.jpg


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David avatar image David jackb commented ·
Yeah cool - basically the same


Are you single phase or three phase?

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petere101 avatar image
petere101 answered ·

Hi David and Jackb,

I have the same system as you guys. Any chance of an update on how your installations are working? I'm in Sydney and would appreciate any 'heads up' info that you may have.

Thanks Pete

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