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offgridpete avatar image
offgridpete asked

Can I double the number of panels I have?

Hi

I would like to double the number of panels I currently have on my off grid system. I looked at the information on the Victron site and am even more confused than before. I don't want to increase my batteries but just want to increase the amount of energy to run more things during the day and not decrease the power generated to fully top up the batteries that I would use at night.

I have the following setup:

1 x Quattro 48/10000/140-100/100

2 x Smartsolar MPPT 250/100-Tr

10 x 3.4Kw Lithium batteries

22 x 330W solar panels

1 x Octo GX

1 x 17Kva diesel generator.

If I double the number of panels, what extra equipment would I require, if any?

Thanks

P

Solar Panel
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4 Answers
Louis van der Walt avatar image
Louis van der Walt answered ·

The battery limits are only for when you also add a PV inverter like a Fronius to the mix.

If you only use the SmartSolar 250/100s to charge the batteries you can increase the amount of panels any way you like, as long as you stay within the limits of the MPPT. (Never go over the voltage, but you can do a bit more current, which the MPPT 250/100 will clamp to it's limit). Remember the 100A are on the battery side of the MPPT and not on the PV side.

But then you can just add more MPPTs as well. It will recharge your batteries faster and then the panels will be throttled until there is usage.

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offgridpete avatar image offgridpete commented ·

Thanks for the reply. So if I read you correctly and add another SolarSmart 250/100, I could extra panels. How do I determine the limit to what I can add? What are the governing factors? The Quattro?

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Louis van der Walt avatar image Louis van der Walt offgridpete commented ·

Yes, if you add an extra MPPT 250/100 then you can add another 22 x 330W of the same type of panels.
There is no limit to the amount of extra MPPTs you can add, and you can mix and match them. So you can add a 100/20 or 150/75 to the 250/100. The MPPTs convert this to the voltage your battery use (I would guess you would be on 48V batteries).

Your batteries will have a charge limit, so if you reach that the MPPTs production will also be limited to what you use at the inverter.

Just check as each PV panel model has different voltage and current it work at and this might not be the same as your old panels. So you might see that you can only add 20 newer panels vs the 22 you now have.

Most PV panels would be around 50V and 10A each. So the general rule would be a string of 4 panels in serie to reach 200V @ 10A (or even 5panels to 250V if the max voltage of each panel is below 50V) and you could have a few strings like this to get more current.

Perhaps an example will help. Say I use PV panels that give me 50V 10A each. With the 250/100 if I have 2x strings of 4 panels each that would give me 200V 10A for each string, so 200V 20A or 4000W PV power. Your MPPT will use the 4000W and convert it to your battery voltage that will give 4000W / 48V = 83.3A (or your 100A limit).
If you add a third string that will give you 125A, but the MPPT will limit the PV power when you reach 100A which you will reach earlier in the morning.

There is a excel calculator on the Victron download site that you can look at that has all the little details included like temprature in your area, you wire thinkness and length, etc.

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offgridpete avatar image offgridpete Louis van der Walt commented ·
Thanks Louis, that's a great help.
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Phil Gavin avatar image
Phil Gavin answered ·

As @Louis van der Walt says adding an extra MPPT to cater for more panels is one way to go.

That will still only let you service the load limit of the Quattro though.

Another way is to add a PV inverter (for example a Fronius) instead of an MPPT, as this will have 2 MPPTs already built in. This will allow you to have more AC power available during the day for loads.

The Quattro is a bi-directional inverter/charger so excess (unused) AC power from the PV inverter will also charge your batteries faster than previously.

Another advantage is the string voltages are higher so cabling expenses are less. The PV inverter itself is also very efficient.

There are limits to the size of PV inverter that is suitable for the Quattro and existing size.

(Search for the 1:1 rule & battery sizing for PV inverters).

Unless I am mistaken, you are within these limits to add 22 similar panels and suitable rated PV inverter (say 8kW ish) without other equipment as is.

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offgridpete avatar image offgridpete commented ·
Thank you for the reply. The Fronius is more than I can afford right now. Maybe another MPPT 250/100 and extra panels. How many panels could I safely add?
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larsea-dk avatar image larsea-dk commented ·
Hi


just want to say...I have too much MPPT power compared to my Multipluspower. I have 2pcs 250/100 SmartSolar and 7.2kWp panels. My Multiplus can't take all excess power when battery is full, so due to the high current flowing and the Multiplus that cant transfer all excess power, I get overvoltage alarms on my battery. Max voltages is set, but MPPTs do not slowly ramp down. So I have to ramp down my MPPTs manually or do set a permanent max Amp for the MPPTs. Very strange that the system do not ramp down by it self, but it simply doesn't.

So just remember to what the current flow and the battery voltage and check if you need to manually set the maximum charge amp for your MPPTs.

BR,

Lars

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alexander-uhde avatar image
alexander-uhde answered ·

Hi Pete,


I think the way to go is highly dependent on your location, temperatures and orientation of your panels.


My system (reffering to the solar chargers, I have two other AC-Inverters running as well) consists of 1x MPPT 250/100 and 16 panels 360Wp.

I am running this in a 4s4p configuration. Highest voltage on the MPPT I observed in 2 years now was roughly 170V.

Since the "critical" limit is mainly the voltage (250V in this case), it might be also possible to use a 5s4p configuration, which would end roughly at 212V (calculated) on the MPPT.

In this case, I would use 20 panels with one MPPT 250/100


But as I said, this is highly dependent on your individual situation.

My solar generator is located on a flat roof, the panels are on a 10° slope.

Half of them facing to the East, half of them to the west. I suppose, if all of them were facing directly south with a higher slope, I would get over the critical 250V.


The above 170V are typically observed in winter on very sunny days (this does not happen very often here in my place in Germany) with temperatures around -10°C.


So I guess you could add more panels without needing another MPPT.

Doubling them (22 panels on each MPPT, 44 in total) seems a bit too "ambitious" to me.


However, if you live in an area where it does not get "cold" your voltage levels will not rise that much.

Did you see Victron`s MPPT calculator?

You can put the values of your panels to calculate what is possible: https://www.victronenergy.com/mppt-calculator


Regards

Alex

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offgridpete avatar image
offgridpete answered ·

Thanks Alex

We are in Andalucía, Spain and our 22 panels face due south, ground mounted. The array is within 5 metres of the battery room and victron setup and the house is 10 metres away from the battery room. Having sufficient sun is not a problem. My question relates to the fact I have a 420 sq metre house with underfloor heating/cooling and hot water provided by 2 Toshiba Estia air to water heat pumps. They are efficient but are energy thirsty during winter especially. Therefore the reason for wanting extra panels. I have sufficient batteries to see me through the night comfortably but sometimes struggle to recharge them fully without turning on the generator. The price of diesel has also gone through the roof since the terrible war in Ukraine.

As I said, I only want to know if I can double the number of panels to 44 with as low a cost as possible.

Regards

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