Adding a battery to existing grid tied system

DIY
, , , , ,
1

Hi I am looking at running batteries with our home solar system and would like some advice on hardware and the best way to add the batteries either via DC coupled or AC coupled or alternately removed the existing grid tied inverters and install multiplus II 48/5000 in parallel. I am a fan of Victron equipment so my intention is to stay with their products. I have recently installed a Victron 12 Volt system on my RV however, setting up a home I will definitely need help with. My existing grid tied system consists of a 6.6kw system with two strings into a Sungrow SG5K-D 5kw Inverter and a second 3.3kw system with two strings into another Sungrow SG5K-D 5kw Inverter. I am not ready to go off grid at this stage and wish to draw from the grid when required. I am hoping to install a 30kw battery.

What I would like is a system that:

· Will Run off batteries when the Grid goes down

· Will provide power assist when day time solar isn’t providing enough power

· Run off batteries at night to minimize grid draw

· Feed in any excess power (although the feed in tariff is becoming a bit of a joke)

Statistics for 2024

· Production 13.6Mwh

· Load 8.1 Mwh

· Feed in 9 Mwh

· Purchased energy 3.4 Mwh

I have a standard hot water system that runs on a timer at peak sun hours and we use Air Con during the summer months and don’t bother running the Air Con in the colder months. Any help would be appreciated

2

This would be a fairly standard AC coupled storage system. Assuming your peak house load is <5kW, then a 5kW Quatro or MP2 inverter would do, with the battery connected appropriately. The large grid tied system would be on the AC out side of the inverter, with the smaller on the AC in / grid side of the inverter (observing the 1:1 rule).

A Grid power meter will be required as well. The system will need a Cerbo for control, and interface to the BMS on the battery.

3

Hi Mike thanks for the response, I have just had a look at the Inverter history and the smaller pv system highest peak power was 3kwh throughout the year but mostly around 2kwh. The larger system peak power is 5.1kwh and this is consistent throughout the year. I didn’t think of connecting one system to the AC side MP2 or Quatro but I still have a lot to learn. Based on the info above would it be better to connect to the larger system and If so, would I have to go for a larger inverter?

4

Hi Kevin, without wanting to be pedantic, energy is in kWh, and power in kW. Confusing the units leads to further downstream confusion.

In answer to your question, I don’t think it matters too much about which system goes on which side of the inverter.

I did find a wonderful presentation by Victron as an introduction to how to arrange ess systems: 1. ESS introduction & features

perhaps you should give that a look?

5

Hi Mike thanks thanks for clearing up the terminology and the link. Very helpful and comprehensive

6

Hi @Doog,

could you provide some more details about your planed system?

120 vs 240V

1, 3 or split phase

Do you consider to use a heat pump to create hot water (500W) instead of several kW.

How do you measure maximum load? 1 minute interval?

Do you need to supply high current, e.g. welding? Than go for a MP2, else RS would be an option.

If 5kW AC single phase is sufficient , than a Multi RS 6k might be a good starting point. No humming, efficient. RS can be 3-phase, but cannot be paralleled.

You can add RS 450/200 PV charger for more PV2bat.

You can add Fronius PV inverters for more PV2AC.

General rules:

Serve your AC with PV inverter (Fronius) or hybrid (Multi RS).

Charge your battery from MPPTs or hybrid.

For special situations like many shadows and different direction, you could integrate grid tied micro inverters. But this is deep DIY :wink:

I have 4x 14,4.kWh (280A) Gobel Power batteries working as one stack of 56 kWh on 8,5 kWp PV. My daily consumption is ~12 kWh normal, 20 kWh on a cleaning day and with 12 kWh hot water I end up at 32 kWh max. Due to many shadows, I can collect up to 42 kWh PV.

NKON delivers 16 kWh quality (EVE) batteries at around 1,600 EUR.

In any case, a MP2 or Multi RS can be configured as ESS prioritizing PV and battery before grid and both can supply off grid power during grid failure and reconnect automatically.

Pls mind systems with more than 5/6k per phase need an external grid safety relais.

Maybe check if your loads (hot water, AC) can be controlled by Home Assistant. I control my 3x single Phase water heating Element with a Shelly 4pm via Home Assistant to use PC I straf of Gas during summer time.

BTW: a water heat pump Ariston NUOS EVO A+ 80-110 uses only 350W max. and 250W average.

1 Like
7

Hi Bjorn thanks for the reply. It is a 240v system (Australia) single phase. I am not considering a heat pump at this stage as having hot water on a timer has worked well for me to date.

The load is measured by existing AC inverters at 10min intervals.

We do use Air-conditioning and occasional welding with an inverter welder but only when the PV is working through the day.

If I where to consider the multi RS would this negate the need for the existing Grid tied inverters?

I am looking at 30kw eve batteries for the system.

The other issue is whether the multi meets Australian standards. I think the 48/3000 and 5000 have been approved recently and Quatro but RS isn’t approved for feed in as far as I know.

8

@Doog

pls check Andy’s Offgrid Garage on YouTube.

The Multi RS is high frequency hybrid inverter, though an PV charger, PV inverter, battery charger and battery inverter in one system. It has two MPPTs integrated, can handle 450V PV and 100A charge like the RS450. So you could replace one of your PV inverters.

For welding, the MP2 is better, as it can deliver higher impulse current. For black start, you should consider at least one small MPPT with one PV panel.

With the 10 minutes interval measurements, I expect a much higher peak load. Many appliances use PWM, e.g. they switch on 100% for a friction of the time. My coffee machine pulse every few seconds.

I would recommend a MP2 10k.

9

thanks Bjorn, I will do a bit more research on the Multi RS and Multi II. Thanks for the Youtube link

10

Hi Mike just a few questions while I try and get my head around what will work for me before I commit to purchasing a battery. I think at this stage here in Australia the Multi II 3000 and 5000 are approved although I still haven’t been able to confirm this. I would have like to go the 8000 but will have to settle on the 5000. As mentioned earlier I would like the system to operate when the grid fails but have to ensure that there is no grid feed in taking place. It seems the only way to turn off feed in on the Sungrow is to change the setting to micro grid or alternately place a disconnect device of some sort.

· Looking at the diagram the 3.3kw system inverter will feed into the grid independently of the Multi?

· The 6.6kw system will operate as a micro grid?

· Is a disconnect device and anti Islanding the same thing?

image.png
image.png417×480 66.1 KB

11

If there is data coms from the GX device to the 3.3kW Sungrow, then the GX can reduce the output of the sungrow to prevent export.

A microgrid is completely independent of any grid, and there is a central inverter (of any size) that ‘forms’ the grid of the microgrid. This is not one of those cases, it is a grid connected ESS system (To the purists, yes a microgrid can use an external grid as backup, instead of a generator). However, the Solar output from the 6.6kW system will primarily be used to supply local loads, and charge the battery with any surplus. As the frequency is controlled by the external grid, again there must be datacoms from the Gx to the 6.6kW grid inverter for control.

A disconnect can be simply a manual switch, whereas an anti-islanding device will detect grid failure (by several methods) and disconnect your device grom the grid to prevent feedback.

12

Hi Mike, thanks again for your help.

13

I might also suggest that you consider running 2 5000W inverters in parallel if you want more power and are facing certification issues.

Then both PV systems can go on AC out, and the grid side energy meter would not be required.

14

that was my next question re running both systems on the AC side, thanks for the update

15

Hi Mike with both inverters connected on the AC side will the
Multiplus use the PV systems to charge the batteries before charging
from the grid?

16

The ESS system will do this, even if one of the inverters is on the AC in side, provided it can see the grid consumption.

That’s why the ESS schemes with grid tied inverters on the AC in side also have a grid power meter, while those with PV inverters on the AC out side don’t need this. In the latter case, the ‘AC in’ current sensing of the multiplus is used instead.

17

Thanks again for your help I think I am ready get started

18

With the MP2 all AC-ports are connected by the internal AC bus bar, though AC-in, AC-out1 “critical load” and AC-out2. The internal battery charger and the inverter are connected to the same bus bar.

AC-in can be disconnected is two relais in series to prevent uncontrolled backflow in case of grid failure. AC-out2 can be disconnected by an additional relais via “relais assistant” e.g based on SoC.

If an energy meter is connected on the grid side before parallel AC-loads, the Venus OS (Cerbo, Ekrano) will try to hold a grid set point, e.g. 0W import or export.

To achieve the goal Venus OS will instruct to charge energy to batteries, discharged and invert energy, throttle down MPPTs or grid inverters (Fronius) while connected to the grid.

In case of grid failure, frequency shifting is used to throttle PV in case the battery is full.

With latest Venus OS there is the unofficial possibility to manage PV inverters compliant to SunSpec via IP.

Venus KS does not care if you use one big MP2 or several parallel MP2. The Multi RS cannot be paralleled at the moment.

In most countries the MP2 5K can be used without external safety relais due to the build in two in series on AC-in.

A parallel system is more difficult to administrate like a 3-phase system.

I have a 3-phase system with Hoymiles micro inverters on AC out and one MPPt for black start.

If you plan to go mostly offgrid and need a generator as second AC-in, than the Quattro is you choice.

19

Reading through this post reminds me of my research stage for my setup. I installed a Victron ESS with two power meters (with roles as a grid meter and the second as a PV inverter to monitor) to collect the PV production from my Huawei grid tied 3kW inverters in a 14kWh battery. My final setup includes DC coupled Smartsolar MPPT 150/35 charge controller and 2 Multiplus II, 120V 48/3000/35 configured in splitphase (for my local grid). It’s working like a charm, detecting grid feed in from the Huawei PV inverter and using the battery charger on the two Multiplus II to charge the battery in addition to the mppt charger.

image
image1469×634 99.2 KB

I wanted to migrate at least 1 of the Huawei Inverters to be AC coupled, however, my original Huawei installer does not know how to do it and the hazzle of navigating the horrible Huawei UI to program it makes me just want to decomission one of them and just install a Smartsolar MPPT RS 450/100 instead and stick to Victron equipment.

My loads were split. Main load panel has the biggest loads that go offline when the grid goes down(which happens so often is frustrating). the rest of the house, 2 AC units, all plugs and lights are backed up to a critical loads panel. The Multiplus II’s are connected between the main panel and critical load panel. basically, AC IN comes from a 50 amp breaker from the main load panels, and AC OUT goes to a 50 amp breaker that backfeeds the Critical loads panel.

Edit to include a simplified diagram of the ESS instal and connection:

image
image1792×1007 45 KB

20

@icdeadppl2 I have my PV inverters on AC-out1 continuously proving energy whilE grid is going down.

Consumers are split to AC-out1 und AC-out2. Relais for AC-out2 is programmed to open in SOC below 25% and close again above 30% SoC.

Maybe a setup which could ease your life with frequent power cut offs…