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# Mismatched panels on string

• 13-03-2023 9:13am
Registered Users Posts: 1,406 ✭✭✭

Have 14 Amerisolar 340W facing SW on one string and 7 Longi 380W facing SE on another string.

Was reading on some thread here last night that 14 panels is a bit much on the one string as the voltage would be over 600v and as my Inverter died last year I am considering moving 2 of the Amerisolars to the SE side. I figure that it would give me an extra boost in the morning also

But what will be the effect on the SE string I am wondering ?

• Moderators, Sports Moderators Posts: 18,431 Mod ✭✭✭✭

Moving 340w panels into a 380w panel string will drop all panels on that string to 340w

• Moderators, Sports Moderators Posts: 18,431 Mod ✭✭✭✭

According to the spec sheet, the Open Circuit voltage is 46.1 so you are over voltage at 645.4 currently, just disconnect one panel from the string is the easiest solution

• Registered Users Posts: 519 ✭✭✭

would it also work to split the 14 panels in half and connect the two halves in parallel instead. so two strings in series connected in parallel and that going to one MPPT ?

• Moderators, Home & Garden Moderators Posts: 5,467 Mod ✭✭✭✭

Inverters* aren't rated for the double current. I think the solis is about 11 amps. A paralleled string is about 20ish amps

*The sunsynk 8kw is rated for it, but it has 2 pairs of inputs per mppt

• Registered Users Posts: 519 ✭✭✭

yes, but with double the current is that not where the MPPT will adjust the voltage of the panels thus reducing the current to acceptable value, similar to how it reduces the current when you limit you set an export limit - if i limit my inverter to 50% export the MPPT adjusts the voltage to change the current returned?? hence the same would happen in this scenario as the current increase to 11amps the MPPT adjusts the voltage so as not to exceed 11amps ?

• Moderators, Home & Garden Moderators Posts: 5,467 Mod ✭✭✭✭

If it causes no issue having more current there, putting them in a parallel string would limit to about 2.8kw (37.5 (working voltage of panels) x 11x 7)

• Registered Users Posts: 1,406 ✭✭✭

I think that's what I'll do

• Registered Users Posts: 1,406 ✭✭✭

And following on from this thread I am now thinking that i should cut from 14 on the string back to 12 https://www.boards.ie/discussion/comment/116585187/#Comment_116585187

Will have two spare panels then which I was thinking would it be possible I could have them both in parallel and then connect to the SW string?

• Registered Users Posts: 64,285 ✭✭✭✭

You can't parallel panels on most inverters as they would only take 12-13A max. Only possible exceptions I can think of are if you have a very steep east and west roof as the combined current of both would never be much more than the max of one of them. Or if your inverter can handle double that amperage per MPPT like the Sunsynk 8.8kW can

I would just connect those 2 panels to a micro inverter

• Registered Users Posts: 1,406 ✭✭✭

A micro inverter is going to cost €200 or thereabouts and I will never see that back so what am I going to do with those two panels at all is the problem.

Its paralleling two 340w panels to make one 680w panel then the current will be limited anyways as those two panels will be in series with the rest of the string so in effect they should b downgraded to 380w which is what the panels are on the rest of the string ?

Post edited by Big Lar on

• Registered Users Posts: 1,406 ✭✭✭

Or now I am thinking that if I put in the two 340w panels in series with the 7 380w panels that I would only lose 7X40w=280w

So instead of the current 7 X 380w = 2660w

I would end up with (2 X 340w) + (7 X (380w - 40w)) = 3060w

Think thats a better plan

• Registered Users Posts: 2,331 ✭✭✭

Not saying you should go any specific route, but why would you never see the money back on a Micro-inverter?

200 euros ~ (say) €0.30/kWh means that once the 2x panels have produced 666kWh, your in the positive. Assuming of course that you consume every single unit. Gets a bit more complicated if your exporting some, putting it into batteries (losses) etc,

From PVGIS 800watts of panels, south facing with slope 35deg will do approx 750kWh per year, so after 1 year you'd be in the clear and have recouped the cost of the device? Again, not saying this is "better", only letting you know that it's an option. Course you'd have to weigh that against the output of the other option your considering, but I'd probably just micro-inverter it if it was me.

• Registered Users Posts: 64,285 ✭✭✭✭

And if you buy well, you will have zero or negative depreciation on your hardware, I have done this numerous times over the years. So if you change your mind in a year or two and upgrade, sell the microinverter and with hindsight it will have been making you a profit from day one