Choosing Equipment for Hybrid System

[cods4]

I'm looking to build a hybrid system at my home, with the goal of reducing my power bills and learning a lot in the process.

I have managed to source some batteries for very cheap through work. They are VRLA and were about 45kWh when new and I'm banking on them being about half that now. I plan to replace them with LiFePo4 cells once they are totally worn out.

I plan to install 6-8kW of solar panels in the next year or so (need to replace my roof first), but because I'm getting these batteries in the next few weeks I want to design my system now as I need to purchase something to keep these batteries charged in the mean time.

I have been trying to work out the best way to design my system, and have come up with the two different arrangements below..
I quite like the idea of going with all Victron equipment as it seems fairly popular in my country and I like the attitude of the company (they have published lots of useful information, and their interface software seems to be open source)

I have a few questions I was hoping someone could answer for me.
Would either of these work? I'm not 100% sure if the Multiplus inverter can be grid tied or not?
Which arrangement would be the most efficient or most optimal?

I am an electrical engineer so I have a good understanding of the theory etc, so I'm just trying to get familiar with the capabilities of all the different equipment.

 

[newbostonconst]

Arrangement 2 looks like it will be more efficient under daily power making and be easier on batteries.

 

[mrzed001]

I'm looking to build a hybrid system at my home, with the goal of reducing my power bills and learning a lot in the process.

I have managed to source some batteries for very cheap through work. They are VRLA and were about 45kWh when new and I'm banking on them being about half that now. I plan to replace them with LiFePo4 cells once they are totally worn out.

I plan to install 6-8kW of solar panels in the next year or so (need to replace my roof first), but because I'm getting these batteries in the next few weeks I want to design my system now as I need to purchase something to keep these batteries charged in the mean time.

I have been trying to work out the best way to design my system, and have come up with the two different arrangements below..
I quite like the idea of going with all Victron equipment as it seems fairly popular in my country and I like the attitude of the company (they have published lots of useful information, and their interface software seems to be open source)

I have a few questions I was hoping someone could answer for me.
Would either of these work? I'm not 100% sure if the Multiplus inverter can be grid tied or not?
Which arrangement would be the most efficient or most optimal?

I am an electrical engineer so I have a good understanding of the theory etc, so I'm just trying to get familiar with the capabilities of all the different equipment.


View attachment 66642

So your question is if you should use DC coupled (1) or AC coupled (2) system ?
Both work. Both have advantages and disadvantages.
You even can make them both on the same time

And yes, Multiplus II has a limiter and with that it can be used AC coupled. Also has a protected load AC output (really 2 ) where equipment always got power. To give power to Fronius Grid-tie inverter you need to separate your system from the grid.

 

[cods4]

Arrangement 2 looks like it will be more efficient under daily power making and be easier on batteries.

Agreed it would probably be easier on batteries. However I don't know if it will be more efficient unless I was able to consume most of the energy during the day.
My baseline load is about 500-700W at the moment so most of the generated power will be flowing into the batteries during the day. And with arrangement 2 I'd be converting the energy to AC 50hz and then back to DC to charge the batteries which I thought would be more lossy.

 

[cods4]

So your question is if you should use DC coupled (1) or AC coupled (2) system ?
Both work. Both have advantages and disadvantages.
You even can make them both on the same time

And yes, Multiplus II has a limiter and with that it can be used AC coupled. Also has a protected load AC output (really 2 ) where equipment always got power. To give power to Fronius Grid-tie inverter you need to separate your system from the grid.

Thanks for giving me the correct terminology. Yes I'm trying to decide between DC and AC coupled.

When you say I can use both AC and DC coupled at the same time. Do you mean I could have both a solar inverter (I.e fronius) and solar charge controller in the same system to get the best of both worlds? That actually sounds like a very good idea.

Regarding having the multiplus grid tied. I'm just a bit confused about how it would be connected. I see it has an AC input and two AC outputs. Just ignoring AC Out 2 as I don't think I have a use for it. Would I connect both the AC input and the Output together and to my main switch board so that power can flow both into and out of the grid?

 

[mrzed001]

Thanks for giving me the correct terminology. Yes I'm trying to decide between DC and AC coupled.

When you say I can use both AC and DC coupled at the same time. Do you mean I could have both a solar inverter (I.e fronius) and solar charge controller in the same system to get the best of both worlds? That actually sounds like a very good idea.

Using both means that you can have at the same time
- solar panels with MPPT charging battery + giving power to Multiplus (DC coupled) -> generates power for AC in (with limiter) and AC out ports
- Fronius (or other Grid-tie inverter) with other solar panels -> generates power to house and grid (AC coupled with Multiplus)

Regarding having the multiplus grid tied. I'm just a bit confused about how it would be connected. I see it has an AC input and two AC outputs. Just ignoring AC Out 2 as I don't think I have a use for it. Would I connect both the AC input and the Output together and to my main switch board so that power can flow both into and out of the grid?

No you have to separate the multiplus AC in from AC out.
AC out goes directly to protected circuit panel. No other line goes into that panel


Multiplus AC in is connected to your main like the grid-tie Fronius.
Before them in the main there goes the meter for the limiter (so Multiplus do not produce to the grid)
Multiplus AC out should be connected to loads that always has to run: PC, server, alarm system, IP camera system ... coffee machine

If you want you can put a separation device in the main, so in a blackout multiplus will run and manage the Fronius Grid-tie inverters to.

Here is a simple AC coupled system:



If battery inverter is a Multiplus, then that can have MPPTs connected to other solar panels too.
Here is the DC coupled part:



Also I do not know if you from US or EU or ... For US there is Sol-Ark hybrid inverter too.

 

[cods4]

No you have to separate the multiplus AC in from AC out.
AC out goes directly to protected circuit panel. No other line goes into that panel

Thats what I was worried about. So that means I can't connect any loads to the Multiplus that are going to exceed the rating (i.e 5kVA), or I need to install enough Multiplus units to cover my whole peak load (15kVA).

What I would really like is a charger/inverter that can be truly grid tied. So if I have 10 or 15kW of load, my battery inverter will supply its peak output (say 5kVA/4kW) and the remaining 6kW are supplied from the grid. (And it would be nice to be able to feed back into the grid from my batteries too). But if thats going to be very expensive or not available in my country then I think I can live with the below system.

Also I do not know if you from US or EU or ... For US there is Sol-Ark hybrid inverter too.

I am in New Zealand (we use 230VAC 50Hz like Australia)

Also, thanks so much for all your help. It is starting to make more sense now.

 

[mrzed001]

Thats what I was worried about. So that means I can't connect any loads to the Multiplus that are going to exceed the rating (i.e 5kVA), or I need to install enough Multiplus units to cover my whole peak load (15kVA).

If you want them to have uninterrupted power, and work even on a blackout.
The Multiplus can give power out on the AC in and the AC out port too
See, here is a diagram for it



In the right protected panel you can add the circuits you want to have UPS power.
In the left main panel is your Grid-tie and all the not protected loads connected.
And yes, if you want your 15kW unit to have power in the middle of the night in a blackout, then you need 15+kW inverter power

What I would really like is a charger/inverter that can be truly grid tied. So if I have 10 or 15kW of load, my battery inverter will supply its peak output (say 5kVA/4kW) and the remaining 6kW are supplied from the grid. (And it would be nice to be able to feed back into the grid from my batteries too). But if thats going to be very expensive or not available in my country then I think I can live with the below system.

With Victron you can not feed back to grid I think. I am not sure but I think they do not have the needed VDE/AS certificates your grid company wants from your inverter.
So it has to be used with an outer meter and limiter to limit its production (to only what your house uses).
Every other thing you wrote it can do.
Except if you have a grid-tie system too and that sells power, then your Victron will not give power to the left panel (already power going out your house). Only after sunset when grid-tie does not produce anymore.

For EU/Australia there is also the Voltronic Infinisolar / MPP (real) hybrid inverter


It can sell to grid, has all the certificates. But I think this inverter can not AC coupled with a Grid-tie inverter.
So they can work on the same line, no problem. But in a blackout if you disconnect your house from the grid the Victron can give power to Grid-tie inverters, control them using frequency raising. (to lower or stop they production). I do not know if Infinisolar can do it.
The big question is: do you need it ?
So first you have to decide what equipment should get UPS power.

View attachment 66748


I am in New Zealand (we use 230VAC 50Hz like Australia)

Also, thanks so much for all your help. It is starting to make more sense now.

Of course. I am just writing a post about all the hybrid systems, so the pics are from that

 

[cods4]

If you want them to have uninterrupted power, and work even on a blackout.
The Multiplus can give power out on the AC in and the AC out port too
See, here is a diagram for it

Ah thankyou! Just what I wanted to hear. I now see what you were meaning about the meter for the limiter.

Except if you have a grid-tie system too and that sells power, then your Victron will not give power to the left panel (already power going out your house). Only after sunset when grid-tie does not produce anymore.

Although if I connect it like in the below diagram, I think I might not have this limitation. But I am on the fence about whether I need a grid tie solar inverter. I might just stick to the Victron MPPT charge controllers for all my solar.

For EU/Australia there is also the Voltronic Infinisolar / MPP (real) hybrid inverter

Thanks for the suggestion, I cant find it available locally, but it looks good.
I also found the Selectronic SP-PRO which sounds like the ideal inverter and ticks all my boxes. However I then discovered it is about 3 times the price of a Victron Multiplus for a similar capacity http://download.selectronic.com.au/brochure/BR0002_10 SP PRO Data Sheet LR.pdf


Updated diagram:

 

[mrzed001]

Ah thankyou! Just what I wanted to hear. I now see what you were meaning about the meter for the limiter.


Although if I connect it like in the below diagram, I think I might not have this limitation.

Yep, correct The diagram is perfect

But I am on the fence about whether I need a grid tie solar inverter. I might just stick to the Victron MPPT charge controllers for all my solar.

If you want to sell power to utility then you need the grid-tie inverter.
If not ... then not

Thanks for the suggestion, I cant find it available locally, but it looks good.

Yep, it is like all MPP Solar inverter. You have to order it from China/Taiwan.
It is cheaper than Victron, but not as good warranty. A 10kW 3phase hybrid costs as much as the 5kW 1 phase Multiplus II.
And it has grid-tie like 900Voc MPPT on it. Victron MPPT's are a joke sadly. The strongest is 150Voc. So not for big systems (or have to buy a bunch of these very expensive MPPT)

I also found the Selectronic SP-PRO which sounds like the ideal inverter and ticks all my boxes. However I then discovered it is about 3 times the price of a Victron Multiplus for a similar capacity http://download.selectronic.com.au/brochure/BR0002_10 SP PRO Data Sheet LR.pdf


Updated diagram:
View attachment 66759

 

[Skipr]

One question I have been wondering about Is why go for a 5kW inverter if you are only expecting 700W of load… granted you will see some peak on startup, but everything you list will have low peaks. 3kW would be more than enough? The battery bank really defines how much load you can run without having to drop back to the grid. Granted expansion is always useful for the future, but tech is changing so fast in this area, not sure I would optimize for that.
just curious what your thinking is?

 

[mrzed001]

One question I have been wondering about Is why go for a 5kW inverter if you are only expecting 700W of load… granted you will see some peak on startup, but everything you list will have low peaks. 3kW would be more than enough? The battery bank really defines how much load you can run without having to drop back to the grid. Granted expansion is always useful for the future, but tech is changing so fast in this area, not sure I would optimize for that.
just curious what your thinking is?

Inrush is a b..ch ?
A simple PC power source can pull a lot and fast when connected.
An electric motor start pulls also 2-7x power of the continuous consumption.
So you can not have "to much" inverting power. But if too few then sometimes it is hard to go bigger (like sell small inverter if you can, and buy a bigger one)
Also there is some 3kW 48V inverter (Victron has one). But most 48V (all-in-one) inverters are 5kW.

 

[cods4]

One question I have been wondering about Is why go for a 5kW inverter if you are only expecting 700W of load… granted you will see some peak on startup, but everything you list will have low peaks. 3kW would be more than enough? The battery bank really defines how much load you can run without having to drop back to the grid. Granted expansion is always useful for the future, but tech is changing so fast in this area, not sure I would optimize for that.
just curious what your thinking is?

6-700W is just my constant 24/7 load. I also have HVAC, oven, TVs etc, that I'd like the inverter to mostly supply. Ideally the grid should only be used when I'm exceeding the capacity of the inverter, or the batteries are empty.

 

[cods4]

And it has grid-tie like 900Voc MPPT on it. Victron MPPT's are a joke sadly. The strongest is 150Voc. So not for big systems (or have to buy a bunch of these very expensive MPPT)

I found this larger capacity Victron MPPT charge controller which I think should work ok. Maybe it is new to the market?

SmartSolar MPPT RS 450/100-Tr

Shipping, taxes, and discounts will be calculated at checkout. This product must be installed by a qualified electrical installer.Victron Energy SmartSolar MPPT RS solar charge controller. Victrons solution for systems with large series connected PV arrays charging 48 V DC battery banks. This...

victronenergy.co.nz

 

[mrzed001]

I found this larger capacity Victron MPPT charge controller which I think should work ok. Maybe it is new to the market?

SmartSolar MPPT RS 450/100-Tr

Shipping, taxes, and discounts will be calculated at checkout. This product must be installed by a qualified electrical installer.Victron Energy SmartSolar MPPT RS solar charge controller. Victrons solution for systems with large series connected PV arrays charging 48 V DC battery banks. This...

victronenergy.co.nz

Wow ... for that price you get 2 complete all-in-one inverter. ?

 

[cods4]

Wow ... for that price you get 2 complete all-in-one inverter. ?

The price is in NZ dollars and is equivalent to 1363USD, plus we seem to pay a premium for everything here.

A 5kW Fronius Primo costs about 2677NZD (1840USD) here.

Are there any others I should be looking at? Are the alibaba options worth considering?

 

[cods4]

With Victron you can not feed back to grid I think. I am not sure but I think they do not have the needed VDE/AS certificates your grid company wants from your inverter.
So it has to be used with an outer meter and limiter to limit its production (to only what your house uses).

I have done some more research, and it sounds like I can use the Victron Multiplus II to feed into the grid as it meets the correct standards for Australia and New Zealand. So it therefore meets all my requirements I think.

 

[Skipr]

6-700W is just my constant 24/7 load. I also have HVAC, oven, TVs etc, that I'd like the inverter to mostly supply. Ideally the grid should only be used when I'm exceeding the capacity of the inverter, or the batteries are empty.

Ah, I am looking at something similar. But expect that I will need the split phase 240 to run the AC. I am collecting data from “sense” to see what my real load is. Very helpful.

 

[Skipr]

Inrush is a b..ch ?
A simple PC power source can pull a lot and fast when connected.
An electric motor start pulls also 2-7x power of the continuous consumption.
So you can not have "to much" inverting power. But if too few then sometimes it is hard to go bigger (like sell small inverter if you can, and buy a bigger one)
Also there is some 3kW 48V inverter (Victron has one). But most 48V (all-in-one) inverters are 5kW.

agreed. I am collect data with a sense clamp monitor on the main incoming lines and I can see the inrush for everything. Going to put a posting up with my observations and see if it is consistent with what others have seen.

 

[cods4]

Ah, I am looking at something similar. But expect that I will need the split phase 240 to run the AC. I am collecting data from “sense” to see what my real load is. Very helpful.

Nice, our electrical system uses just 1phase 230V so no split phase 240V to worry about.

I have done the same thing, using a Shelly EM on my main supply which feeds my power consumption into Home Assistant and gives me a nice graph.