question

Paul Lapierre avatar image
Paul Lapierre asked

2 controllers one array question again....

I apologize if this has been asked and answered before but I did see similar posts and the answers were "no" hoping my variation may be more acceptable.

I have one PV array and one set of underground wires coming to house. I used the Victron MPPT calculator and chose the appropriate MPPT (150/35) what I did not realize is that in my current PV configuration (6 panels 480W 2S3P) am I running about 500% over paneled but this was allowable (I had selected the go over 130% option on webpage). I am a newbie and now realize my mistake. As I can not easily run another set of PV wires (beside I prefer to run them at a higher voltage - less drop).

My question is: if I purchase another 150/35 MPPT controller and link the two MPPT on the same Victron network (VE.Smart Networking) . Would they not work together and choose the same optimal voltage etc.... and not "compete". They would still each be about 200% over paneled but I could live with that.

Can I also have them charge the same battery bank? Alternatively, I could divide my bank in two as I have 2 inverters already.

I understand this setup may not be optimal but would it work?

Thanks for your help.



MPPT Controllers
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

5 Answers
Justin Cook avatar image
Justin Cook answered ·

It is not possible to connect two controllers to a single PV array; the array needs to be split, or an appropriate single controller selected.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

kevgermany avatar image
kevgermany answered ·

Charging the same bank isn't a problem.

Working back from your over panelling comments, looks as if you're already on a 48V battery bank. If I'm wrong and you're on 24V, it doesn't help to increase as you already have inverters.

If you do buy a second MPPT and it doesn't work, as has been said often, you're still going to be laying extra cable.

It hurts, but best do the job properly. Lay extra cable. And to maximise things, consider a bigger second controller to take 4 panels, keep 2 on the existing one. Or reconfigure better. Be aware that the current limit for MC4 connectors is 30A.


2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Michelle Konzack avatar image
Michelle Konzack answered ·

You have 2880Wp of solar panels a MPPT 150/35 and 500% overpowered.


This suggest, that you run a 12V System and also 12V inverters which you do not want to replace with a 24V or even 48V version.


Question: what is the size of the cable (crossection and lenght)


I think, you should use a SmartSolar MPPT 150/100 and configure the Modules as 3S 2P at least but you will still waste the half of the energy your Panels produce.


If you have s 24V system, the 3S 2P is very Perfect


However, make sure, your solarwiresvfrom the panels to the MPPT support the current.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Paul Lapierre avatar image
Paul Lapierre answered ·

Hi and thanks for answering.

To answer your questions:
I run a 12V system (battery bank and inverters)
I have 6 Qcell Duo 480W panels connected in 2S3P configuration
I have 10awg (5.26mm2) wire rated at 300V running 210ft (70m)
I live in Canada so temp can go down to -40C. (at lowest temp voltage would not exceed 150V)

I used the Victron MPPT calculator to determine proper MPPT unit (150/35 is acceptable according to website calculator) however failed to notice that only about 20% of available array power would be converted to battery bank

I am not sure I understand correctly how a MPPT works but my thinking is if I have two in parallel they would each see 50% of the voltage and 100% of the amperage. They do not actually change the output of the solar PV array but use the best combination of V and A to maximize output to battery bank. So in essence, both MPPT units would see the same input current and would choose/aim for the same output current to charge the batteries most efficiently.

If the 2 MPPT units are identical and programed in the same manner and connected via VE.smart connect would this not work?

Both MPPT units would be connected to same battery bank (I could separate this if if is easier but I think this would confuse things as both bank would have different SOC and MPPT would need different output parameters to function)

In addition, as the 150/35 MPPT model is able to accept the power output of my PV array alone (albeit only 20% of power is used) in case of failure of one unit, the other wold be able to function.

I am simply wanting this to avoid re-wiring my PV array and to limit my cost to upgrade to recoup more of the power my array produces.

2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

kevgermany avatar image kevgermany ♦♦ commented ·

Actually the MPPT does change the panel output. Panels have a potential power depending on irradiance. Actual power depends on operating voltage and current. The MPPT regularly adjust these to maximise panel output (tracking). Then applies the battery charging algorithm to the power from the panels. It's a very clever piece of kit. But it's designed to operate as a single unit.

The issue is synchronisation. To work the way you describe they need to enter the tracking process in synch and adjust their settings together. What happens is that they adjust in isolation and de-optimise each other.
0 Likes 0 ·
Michelle Konzack avatar image Michelle Konzack commented ·

Since the MPPT 150/35 can not deliver more then 500 in a 12V System. and with 70m cable you have the hell of power loss on the neck, you should definitiv go with a 150/100 (3 modules in series) which will give you up to 1400W.


Hence if your Batteries support this current, install a second 70m cable oand put the second array on this one too. Buy a second MPPT 150/100 and enjoy charging your Batteries with up to 2800W.


3 Panels in series reduce the current on the 70m cable enorm. Because with one string (roughly 80V) you get around 15A, with two strings 30A and with three strings 45A.


Having two cables with each 15A and roughly 120Vmpp is the much better solution. It can be, that you get much better power output from three series panels as 2S3P. Also the 250/100 version can help you enorm, especially in Autumn to Spring, because of the 200Vmpp it start much earlier producing Electricity.


And the Power loss with 200V and 15A is nothing at all. Only you can not use the full power of the solar panels which would be twice as big as the MPPT support at 12V.


IF YOU HAVE THE POSSIBILITY, you should consider switching to a 24V system which allow you to use MANY 24V Devices, including wellpumps and lighting. No Inverter needed.


Note:

I am Off-the-Grid in Estonia at 59deg Latitude (should mostly match yours right?) and we get also here -42C.

My system voltage is 24V and I use currently 70,5kWp SOPzS cells but waiting for the upgrade in spring to 175kWp (Unfortunately I had to delay the order, because I could not get my power station ready which need a new and better Underfloor Heating System and some door are broken from the stormy wind we get here.)

I run a 3S2P System with 1860Wp (SmartSolar MPPT 150/70) and get in some days two new 5S Systems with each 2050Wp (Smart Solar MPPT 250/100) and the difference 250V vs 150V version is enorm. it is only 190Wp more power, BUT the energy output over the year nearly double.

0 Likes 0 ·
Paul Lapierre avatar image
Paul Lapierre answered ·

Hi All,

Thanks for the input

To close this....

I tried running two MPPT 'sand it worked kinda ..... They both had a hard time synchronizing... But not wanting to run another cable and wanting to maximize my solar input, the solution I chose was to purchase a Growatt "battery less" inverter/charger. They happened to be on sale and about half price of a new larger Victron MPPT (which would still only use about 50% of solar input). I essentially converted my system into a battery backup in that I run my AC battery chargers using th e Growatt to charge my 12V battery bank which runs my loads.

I can upgrade my batteries later on to 48V it I want to. For now,this serves my purpose in that I maximize solar input without adding wire etc..... and I now have an extra MPPT controller (100/35) as a backup.




2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.