Adding more solar panels in parallel

[Spoonman]

i currently have a 150 watt ecoworthy solar panel on top of my boat , connected to a 30 amp epever solar controller. 

 

i would like to add two more 120 watt solar panels of the same make , to bring the total up to 390 watt which is the max total advertised for this controller.

 

i would just like to just ask a few questions to see if my understanding of this is right....

 

firstly please take a look at my very professionally drawn diagram ? and let me know if this is how the 3 panels would be connected in parallel (increasing the amps not the voltage)

 

1.

can i  use "3 to 1 " mc4 connectors to do this, attaching to the prexisting 6mm wire i already have going to the first solar panel? or is it better to use several " 2 to 1" mc4 connectors.

 

i have seen some " trident"looking ones and also ones that are more "whip" like, so 3 seperate mc4 connectors with seperate wires that are connected together.

 

2.

As the solar panels come with like 1 metre of 4mm already attached i am going to have to replace this with 6mm solar cable to account for the higher amps the wire will be handling

 

. is this simply a case of crimping terminals on to the 6mm wire i am going to be using, opening up the panel's junction box and unscrewing the 4mm wire , and reattaching the 6mm wire? 

 

3. being an economically minded chap ,is it possible to reuse the individual mc4 connectors that will come attached to panels, or will i have to buy new ones.

 

By my reckoning i will need two ( male and female ) " 3 way" mc4 connectors for the wires that attach directly to the controller , then three male and three female mc4 connectors for connecting the panels to the 3 way mc4 connectors?

 

am i on the right track with all this?

 

 

[matty40s]

14 minutes ago, Spoonman said:

i currently have a 150 watt ecoworthy solar panel on top of my boat , connected to a 30 amp epever solar controller. 

 

i would like to add two more 120 watt solar panels of the same make , to bring the total up to 390 watt which is the max total advertised for this controller.

 

i would just like to just ask a few questions to see if my understanding of this is right....

 

firstly please take a look at my very professionally drawn diagram ? and let me know if this is how the 3 panels would be connected in parallel (increasing the amps not the voltage)

 

1.

can i  use "3 to 1 " mc4 connectors to do this, attaching to the prexisting 6mm wire i already have going to the first solar panel? or is it better to use several " 2 to 1" mc4 connectors.

 

i have seen some " trident"looking ones and also ones that are more "whip" like, so 3 seperate mc4 connectors with seperate wires that are connected together.

 

2.

As the solar panels come with like 1 metre of 4mm already attached i am going to have to replace this with 6mm solar cable to account for the higher amps the wire will be handling

 

. is this simply a case of crimping terminals on to the 6mm wire i am going to be using, opening up the panel's junction box and unscrewing the 4mm wire , and reattaching the 6mm wire? 

 

3. being an economically minded chap ,is it possible to reuse the individual mc4 connectors that will come attached to panels, or will i have to buy new ones.

 

By my reckoning i will need two ( male and female ) " 3 way" mc4 connectors for the wires that attach directly to the controller , then three male and three female mc4 connectors for connecting the panels to the 3 way mc4 connectors?

 

am i on the right track with all this?

 

 

1. Use 3 to 1 connectors if possible, the less connections the better.

2. No point changing the panel cables really, a single panel will only produce the same A as it always does, you are just adding 2 more that produce the same A. But yes, use 6mm from the 3/1 connectors onwards.

3. It is almost impossible to re-use mc4 connectors, the internals are crimped, and the messing about isnt worth the pennies saved.

https://www.wish.com/gb/product/new-quality-mc4-solar-panel-connectors-25-6mm-with-crimping-pliers-spanner-set-5e1031695df5090bfed706df

 

[Jen-in-Wellies]

19 minutes ago, Spoonman said:

1.

can i  use "3 to 1 " mc4 connectors to do this, attaching to the prexisting 6mm wire i already have going to the first solar panel? or is it better to use several " 2 to 1" mc4 connectors.

3 to 1 should be fine.

20 minutes ago, Spoonman said:

2.

As the solar panels come with like 1 metre of 4mm already attached i am going to have to replace this with 6mm solar cable to account for the higher amps the wire will be handling

4mm² between each panel and 3-1 connector is perfectly good. Each panel only has roughly a third of the total current, plus the lengths are relatively short.

21 minutes ago, Spoonman said:

3. being an economically minded chap ,is it possible to reuse the individual mc4 connectors that will come attached to panels, or will i have to buy new ones.

Yes, leave the existing ones on, if you can.

[Alan de Enfield]

47 minutes ago, Spoonman said:

would like to add two more 120 watt solar panels of the same make , to bring the total up to 390 watt which is the max total advertised for this controller.

They may be the same make. but are they the same voltage ?

(Just as an extreme example my panels are 120v others are 19v)

[matty40s]

9 minutes ago, Alan de Enfield said:

They may be the same make. but are they the same voltage ?

(Just as an extreme example my panels are 120v others are 19v)

I've not seen 120v panels Alan.

[Alan de Enfield]

16 minutes ago, matty40s said:

I've not seen 120v panels Alan.

 

 

 

Purchased from Bimble.

 

96.9V output @ 1.6a - sorry picture is a bit bluuuuury.

91.6v output

103.1v output

 

Never yet seen 120v.

 

170w 'low light' panels designed for Northern latitudes where the angle of the Sun is much lower

 

 

 

Edited January 18, 2021 by Alan de Enfield

[ditchcrawler]

1 hour ago, Alan de Enfield said:

They may be the same make. but are they the same voltage ?

(Just as an extreme example my panels are 120v others are 19v)

Never mind what the voltage is, are they ALL THE SAME? (you can argue about 19 120 or 96 all day)

[Spoonman]

3 hours ago, Jen-in-Wellies said:

 

4mm² between each panel and 3-1 connector is perfectly good. Each panel only has roughly a third of the total current, plus the lengths are relatively short.

 

 

3 hours ago, matty40s said:

 

2. No point changing the panel cables really, a single panel will only produce the same A as it always does, you are just adding 2 more that produce the same A. But yes, use 6mm from the 3/1 connectors onwards.

 

thanks for clarifying this, I've obviously misunderstood , thinking everybit of wire in the array needs to be able to handle the total current of all the panels combined.

 

would it still be worth using 6mm cable from the 3/1 connector to each of the solar panels preinstalled mc4 connectors,to account for any voltage drop( i guess given the nature of a narrow boat roof , 1 panel is going to be perhaps 10- 15ft further away from the controller than the nearest panel  is) or could i just use 4mm aswell.

 

 

[Jen-in-Wellies]

5 minutes ago, Spoonman said:

would it still be worth using 6mm cable from the 3/1 connector to each of the solar panels preinstalled mc4 connectors,to account for any voltage drop( i guess given the nature of a narrow boat roof , 1 panel is going to be perhaps 10- 15ft further away from the controller than the nearest panel  is) or could i just use 4mm aswell.

Plug the numbers in to a voltage drop calculator like this one. Assuming the panel voltage is 19V, A panel 4m away in 4mm² will drop 0.377V, or 2%. Up the cable size to 6mm² and it goes to .251V, or 1.6%. Not worth going to the bigger size in my opinion.

Jen

[Spoonman]

the panels i am looking at both have  an advertised Vmp of 18 volts.

 

however for the 120 watt panels it says a Voc of  21.6 volts and for the 150 watt 20.3 volts ?

 

is it the voc or vmp which is significant here?

4 hours ago, Alan de Enfield said:

They may be the same make. but are they the same voltage ?

(Just as an extreme example my panels are 120v others are 19v)

 

[Jen-in-Wellies]

Voc = voltage open circuit, which will be higher than the Vmp, Voltage at maximum power for any panel, so the numbers are what I'd expect. The are probably all reasonably compatible and have the same number of individual cells strung together in series inside. The important thing is that one, or two of them isn't Voc 58V or something.

Jen

Edited January 18, 2021 by Jen-in-Wellies

[Alan de Enfield]

1 hour ago, Spoonman said:

the panels i am looking at both have  an advertised Vmp of 18 volts.

 

however for the 120 watt panels it says a Voc of  21.6 volts and for the 150 watt 20.3 volts ?

 

is it the voc or vmp which is significant here?

 

 

As long as they are roughly the same they'll be OK, its just if you have 1 at 90 volts and 2 at 21 volts, they will start to get 'upset' and won't play together nicely,