Ladies next door asking what i thought...

alyaz

Our neighbours down the road asked what I thought of the quote they just received. Since a little knowledge is dangerous I thought I would ask the experts here...

Currently, wired into one Outback MX60 MPPT controller they have:
Three (3) Evergreen 110 watt panels wired in series to a combiner box. Also wired in series to this combiner box are two (2) Sharp 167 watt panels.
The quote they received says the installer is going to add Four (4) Hanwha 240 watt panels (quoted $2000 just for the panels w/o taxes :-/ ) and everything will run into the existing Outback MX60 MPPT controller.

The panel location and exposure is the same (one roof facing south). They have a 12 volt battery bank, u/k a/hr capacity.

My gut tells me that three different sets of solar modules are not going to match up very well, (within 5% right?) but then again i have been wrong many times before :-)

Evergreen specs (three modules):
110 watts
VP 16.4
IP 7.72
VOC 20
ISC 7.67

Sharp specs (two modules);
167 watts
VP 23.5
IP 7.1
VOC 29
ISC 7.91

Hanwha specs (four modules):
240 watts
VP 30
IP 8.02
VOC 37.3
ISC 8.58

All advice appreciated.

NorthGuy

Re: Ladies next door asking what i thought...

The old ones were matched perfectly.

The best (but not perfect) way to match new ones I can see is into two strings:

E-E-E-H-H
S-S-H-H

This gives V_OC about 135V, probably too high for the controller.

alyaz

Re: Ladies next door asking what i thought...

Thanks.

Soooo, safe to say, the worst case scenario is destroying the controller and best case is less than optimal solar performance and maybe burning out some cells?

They should be probably telling the installer they want the hanwhas on a new/seperate mppt controller, right?

NorthGuy

Re: Ladies next door asking what i thought...

alyaz wrote: »

They should be probably telling the installer they want the hanwhas on a new/seperate mppt controller, right?

I would rather try to find matching panels. They have V_MP of about 48V in their two strings. Any kind/brand of panels with V_MP around 16V, 24V or 48V should match perfectly.

bmet

Re: Ladies next door asking what i thought...

The controller should not be harmed, it will simply 'suspend' operation until the Voc drops below 125V. Northguy, if your figure of 135 is at namplate value, then chances are that real world performance won't be affected much. My question is whether the differences in Vmp would cause the string to operate at the value of the lowest panels.

ggunn

Re: Ladies next door asking what i thought...

bmet wrote: »

The controller should not be harmed, it will simply 'suspend' operation until the Voc drops below 125V. Northguy, if your figure of 135 is at namplate value, then chances are that real world performance won't be affected much. My question is whether the differences in Vmp would cause the string to operate at the value of the lowest panels.

Not if they are in series; in that case they would operate at the lowest module Imp.

bmet

Re: Ladies next door asking what i thought...

ggunn wrote: »

Not if they are in series; in that case they would operate at the lowest module Imp.

So then the entire string would operate at 7ish Amps per panel?

alyaz

Re: Ladies next door asking what i thought...

Thanks for the replies... couple more questions though. Running the voc that close to the controllers limit would not seem like good practice to me because I know there are discussions about controller efficiencies that come into play too. Regardless, the ladies tell me they have already signed and provided the installer with a deposit. Soooo, if they are stuck with the panels, would not adding a seperate controller for the 4 hanwahs be a reasonable alternative?

niel

Re: Ladies next door asking what i thought...

"Soooo, if they are stuck with the panels, would not adding a seperate controller for the 4 hanwahs be a reasonable alternative?"

no only a reasonable alternative, but in my opinion it is the best way to go when voltages or currents are too far mismatched for using just 1 controller.

alyaz

Re: Ladies next door asking what i thought...

Thanks Niel... i was hoping you would pop in...

Appreciate it...

:-)

NorthGuy

Re: Ladies next door asking what i thought...

alyaz wrote: »

Thanks for the replies... couple more questions though. Running the voc that close to the controllers limit would not seem like good practice to me because I know there are discussions about controller efficiencies that come into play too. Regardless, the ladies tell me they have already signed and provided the installer with a deposit. Soooo, if they are stuck with the panels, would not adding a seperate controller for the 4 hanwahs be a reasonable alternative?

Perhaps the contractors can pay for the new controller? They agreed to install and connect the panels and the new controller is the only reasonable way to do it.

alyaz

Re: Ladies next door asking what i thought...

It's like Hooterville around here when it comes to trying to get anything done properly... most 'installers' around here don't even have any courses under their belts...

Thanks for everyone's help. I will let them know about their options. :-)

westbranch

Re: Ladies next door asking what i thought...

If they are on line, do them the favour of sending them here, to read this and other threads.

alyaz

Re: Ladies next door asking what i thought...

Yes, I provided them the website. We spoke about an hour ago. I also showed off my systems that you guys helped me put together - which have worked flawlessly!

Thanks again! :cool:

ggunn

Re: Ladies next door asking what i thought...

bmet wrote: »

So then the entire string would operate at 7ish Amps per panel?

I don't know the specifics, but if you run current mismatched modules in series, the current in the string will be restricted to the current capacity of the lowest rated module in the string.

inetdog

Re: Ladies next door asking what i thought...

ggunn wrote: »

I don't know the specifics, but if you run current mismatched modules in series, the current in the string will be restricted to the current capacity of the lowest rated module in the string.

Or else the voltage of the string at the higher current will be a bit lower than the voltage of the higher current panels alone. Either way you lose power, often all the power than you could naively expect to gain by adding the lower current panel.

ggunn

Re: Ladies next door asking what i thought...

inetdog wrote: »

Or else the voltage of the string at the higher current will be a bit lower than the voltage of the higher current panels alone. Either way you lose power, often all the power than you could naively expect to gain by adding the lower current panel.

That's assuming that the current of the mismatched module is somewhat close to that of the others. If the Isc of the mismatched modules is, say, half of that of the others, there's no way that a change in voltage can make up for it.