Expansion of existing system with storage

[Tailele]

Good morning dear users, I would like to ask you a doubt. Currently I would like to expand my existing system with an off-grid system, making targeted interventions in several steps. I currently have a 3.2 kW photovoltaic system, to which I would like to add a first self-built storage tank. For this reason I purchased 16 Eve lf105 cells, a 150A 16S Daly home appliance BMS, and a 5A active Daly balancer. In this way I should have a nominal 5375Wh storage unit, to which subsequently if everything works as I expect, I would subsequently add another one. Now I need to replace my inverter with a hybrid one and my choice fell on a Victron energy Multrigrid II gx 5000. In fact, I thought that in the event of expansion of the photovoltaic modules, I could add another one in parallel, in this so if there were to be a fault with one of the two grills, I would always have one working in any case.
The first question I ask you for help with is whether you think the sizing is correct; reading the datasheets, I see that the inverter supports 4kW, therefore within the 3.2kW of the photovoltaic panels, and then supports 48V storage, in line with the 16S that I am building.
As a second doubt, I don't understand whether the inverter needs one or more Victron energy SmartSolar MPPT modules, also because the meaning of this tool escapes me, as well as the correct size.
Thank you infinitely for the support

 

[DIYrich]

The Multiplus handles the grid and batteries. You need the MPPT to handle the panels.

Panels, battery, inverter seems compatible. You need to provide:
Average daily electricity use (kWh), and maximum simultaneous use (kW) for help to see if you sized it right. Also helpful would be overnight use (kWh) to see if you have enough battery to last overnight.

 

[Tailele]

Thanks so much for your reply. In the last day i have done a deep dive in inside the photovoltaic world understanding MPPT technology.
I went to the roof to understand the type of system. My system consists of 8 panels in series and 2 strings. Each panel has a Vcc of 44.14V and an Isc of 5.59A for a WP of 185W. Probably with this information if I were not to touch the system it would be necessary to purchase a Victron MPPT RS Smart solar 450/100 MPPT, which would probably be wasted for the current supplied. Alternatively I could buy a Multi Rs Solar VA6000 dual tracker inverter/charger (or perhaps single tracker, this point is a bit obscure for me). So my initial idea of purchasing a multiplus is not possible without putting my hands on the system, dividing it into 4 series and 4 strings. In this way I could use the victron multiplus with a mttp 250/70.
Coming to the data required for sizing the storage, I take the busiest month (December or January, where we are more at home), consumption around 450kWh, with 210 kWh in the evening after 6 pm. So to be more precise 15kWh/day, 6.8kWh after 6pm.

 

[DIYrich]

Thanks so much for your reply. In the last day i have done a deep dive in inside the photovoltaic world understanding MPPT technology.
I went to the roof to understand the type of system. My system consists of 8 panels in series and 2 strings. Each panel has a Vcc of 44.14V and an Isc of 5.59A for a WP of 185W.

Vcc of each string of 8 panels is 353v at 5.6a for 1,973 watts (under the 4,000w limit of one tracker limit). 353 v is likely under the 450 Voc max, but you should check anyway.

Two strings is 3,947 watts, which is under the 5,760 max of the SmartSolar (using both trackers).

Probably with this information if I were not to touch the system it would be necessary to purchase a Victron MPPT RS Smart solar 450/100 MPPT, which would probably be wasted for the current supplied.

Max output of SmartSolar is 4,800 watts, which is under the 3,947 watts of your panels. Why do you say "wasted"?

Alternatively I could buy a Multi Rs Solar VA6000 dual tracker inverter/charger (or perhaps single tracker, this point is a bit obscure for me). So my initial idea of purchasing a multiplus is not possible without putting my hands on the system, dividing it into 4 series and 4 strings. In this way I could use the victron multiplus with a mttp 250/70.

The SmartSolar is Solar Charger only. The RS Solar combines a Charger and Inverter. If you get the RS Solar, you would not need the Multiplus. I believe the Multiplus is a transformer based low frequency inverter, whereas the RS Solar is a high frequency inverter with no transformer.

Coming to the data required for sizing the storage, I take the busiest month (December or January, where we are more at home), consumption around 450kWh, with 210 kWh in the evening after 6 pm. So to be more precise 15kWh/day, 6.8kWh after 6pm.

The 15kWh daily use could be provided by the 3.2kW of panels, But the 5kWh of battery is not enough to store the daily production for use when the sun goes down. The 6.8kWh of after 6pm usage is above the 5kWh capacity of the battery. For an off-grid system, you will need at least 10kWh of battery to match 1 days production with 1 days consumption.

For Off-Grid, you may want 3 days of consumption in batteries (45kWh) to buffer for rainy days. Or plan to use a generator (which you need anyway). Then up your production to charge the batteries in 1 day. 1 day of good sun will provide enough power to last for 3 days of rain.

 

[Tailele]

Vcc of each string of 8 panels is 353v at 5.6a for 1,973 watts (under the 4,000w limit of one tracker limit). 353 v is likely under the 450 Voc max, but you should check anyway.

Two strings is 3,947 watts, which is under the 5,760 max of the SmartSolar (using both trackers).



Max output of SmartSolar is 4,800 watts, which is under the 3,947 watts of your panels. Why do you say "wasted"?




The SmartSolar is Solar Charger only. The RS Solar combines a Charger and Inverter. If you get the RS Solar, you would not need the Multiplus. I believe the Multiplus is a transformer based low frequency inverter, whereas the RS Solar is a high frequency inverter with no transformer.



The 15kWh daily use could be provided by the 3.2kW of panels, But the 5kWh of battery is not enough to store the daily production for use when the sun goes down. The 6.8kWh of after 6pm usage is above the 5kWh capacity of the battery. For an off-grid system, you will need at least 10kWh of battery to match 1 days production with 1 days consumption.

For Off-Grid, you may want 3 days of consumption in batteries (45kWh) to buffer for rainy days. Or plan to use a generator (which you need anyway). Then up your production to charge the batteries in 1 day. 1 day of good sun will provide enough power to last for 3 days of rain.

Sorry, I wrote the data wrong, it's Voc=44.1V not Vcc because nominally the panels make 185Wp, so with both strings I get a maximum of 2960Wp with Vmpp=35.7V and Impp=5.18A. Today I informed myself even more in depth, and actually the best choice is the multi Rs Solar dual trackers. It gives me the possibility of managing two lines with 3kW each, with panels with a maximum rated current of 13A. In this way I can replace my current ones and increase the power from around 3kW to 5kW, making the most of the inverter/charger. I totally agree with you that you need to increase storage with two nominal 5120Wh units.