Mixing solar panels

[Scottish dan]

Can anyone help please.
I have an off grid system in my summerhouse where my current 3 solar panels are linked in series(195 watt each)

I was looking at buying 3 very similar panels to connect in series(190watt each) also but to connect in parallel to each other.

I am using a 24 volt, 60 amp mppt solar charge controller

Will this be manageable

 

[FilterGuy]

I usually advise a different SCC for different panels....

Having said that:
Your current SCC is plenty large enough to handle the extra current.

You could try your plan and see how well it works but I would be concerned that whichever string has the higher voltage would dominate and the lower voltage string would not be able to contribute very well.

 

[Scottish dan]

I usually advise a different SCC for different panels....

Having said that:
Your current SCC is plenty large enough to handle the extra current.

You could try your plan and see how well it works but I would be concerned that whichever string has the higher voltage would dominate and the lower voltage string would not be able to contribute very well.

Thanks for your help
When you say not contribute very well. Do you think they would produce there given wattage or would it be considerably less
Also would my 60 amp mppt solar inverter handle these strings

 

[FilterGuy]

When you say not contribute very well. Do you think they would produce there given wattage or would it be considerably less

My *guess* is that the would contribute considerably less than they would on their own controller.

Also would my 60 amp mppt solar inverter handle these strings

Probably.
I assume the resulting OC voltage of the two strings will not be much different than they are now... so I assume the input voltage will be OK.

Your total possible panel wattage is 3*195 + 3*190 = 1155W. That means on a low battery the current output will max out at 770W/24V=48A.... and that assumes full power from all 6 panels.

Is your MPPT built into an all-in one or is it a separate device?

 

[Scottish dan]

My *guess* is that the would contribute considerably less than they would on their own controller.


Probably.
I assume the resulting OC voltage of the two strings will not be much different than they are now... so I assume the input voltage will be OK.

Your total possible panel wattage is 3*195 + 3*190 = 1155W. That means on a low battery the current output will max out at 770W/24V=48A.... and that assumes full power from all 6 panels.

Is your MPPT built into an all-in one or is it a separate device?

My mppt controller is an all in one . In your opinion would this be worth trying or am I just throwing money away by adding the the new string

 

[FilterGuy]

When you say not contribute very well. Do you think they would produce there given wattage or would it be considerably less

My *guess* is that the would contribute considerably less than they would on their own controller.

Let me explain a bit more.
Your MPPT controller is going to try to find the best Voltage-Current point for maximizing the output of the two strings. Unless the the best voltage for both sets is the same, the MPPT will find a point that is not quite the best for both but is the best for the pair of strings.

Depending on how far off the point is from optimum, the output could drop considerably.

 

[time2roll]

My concern would be the differential in the Vmp of 1.7 volts. The controller will find something in the middle and each set will produce a bit less power than what is possible. My guess would be close to 5% loss but I am no expert. Will you get more power for adding the additional panels.... absolutely. Worst case you could get a second controller but the price may not make up for the gain in the harvest. The panels are fairly close.

 

[FilterGuy]

My mppt controller is an all in one .

Quick question: What All-in-one do you have? Does the All in One have more than one MPPT? (Some of them do) If so, then you 'just' have to hook the new string to the 2nd MPPT.

In your opinion would this be worth trying or am I just throwing money away by adding the the new string

It is really hard to say. It would not be a complete waste, but it might not be a large gain either.

If you make the purchase and the gain is too small you have a few options:
* Live with it and call it a lesson
* Try to return the panels
* Try to sell the panels
* Buy an independent MPPT to wire in parallel with your All-in-one.

BTW: Will has recently done videos where he mixes panels, but the reports he gave are not detailed enough to tell how much extra he gets verses the rating of the panels.

 

[FilterGuy]

My guess would be close to 5% loss

If 5% is all the loss, it would definitely be worth doing..... Do you have any reasoning behind that guess or is it a SWAG? The roll-off of the power curves for solar panels is really steep so I could imagine it being a lot more....


As you can see, the panels that are operating below their optimal voltage will loose some power, The panels operating above their optimal voltage could loose a lot of power.

Any % guess I give would be a SWAG.

 

[Scottish dan]

Thanks for your help, I will go ahead and purchase them . Worst case scenario, sell the panels and a lesson learnt

 

[time2roll]

If 5% is all the loss, it would definitely be worth doing..... Do you have any reasoning behind that guess or is it a SWAG? The roll-off of the power curves for solar panels is really steep so I could imagine it being a lot more....

View attachment 59294
As you can see, the panels that are operating below their optimal voltage will loose some power, The panels operating above their optimal voltage could loose a lot of power.

Any % guess I give would be a SWAG.

Need a graph with actual current and voltage. Move about 1 volt from the peak power. One set in each direction. The controller should still find the point of max power. Or pull your horizontal ruler down on the blue curve until you have 1.7 volts differential and calculate power.

 

[time2roll]

Here is an exaggerated graph moving voltage up 7 volts or down 18 volts. The OP panels should stay within 1 volt of MPP

 

[FilterGuy]

Here is an exaggerated graph moving voltage up 7 volts or down 18 volts. The OP panels should stay within 1 volt of MPP

OK. Good analysis.

@Scottish dan: Please post the before and after results. It will be educational for all of us!

 

[iamrich]

Thanks for your help, I will go ahead and purchase them . Worst case scenario, sell the panels and a lesson learnt

How much are the panels? You may be able to replace them all with used panels of the same brand/specs for less than 3 new panels.

 

[FilterGuy]

How much are the panels? You may be able to replace them all with used panels of the same brand/specs for less than 3 new panels.

That thought crossed my mind as well....

 

[Scottish dan]

How much are the panels? You may be able to replace them all with used panels of the same brand/specs for less than 3 new panels.

These panels are already used. Only cost me 150 gbp for all 3

 

[iamrich]

These panels are already used. Only cost me 150 gbp for all 3

Ah! Disregard my post then. We can get 250w panels here for about $50 each (plus shipping), six panels becomes very affordable ($450ish USD) which is close to what you already paid.

Maybe hook up the second string but face it in a completely different direction so that when the first string starts to fall off, the second string kicks in? Say South and West maybe? (I don't know how the sun shines in your part of the world though?)