Adding a panel

8n-bob

Here is a question that I just want to make sure that I am thinking correctly

I have 2 Canadian solar panels
235 watts
VMP 29.8
IMP 7.9
Voc 36.9
Isc 8.46
Mod EFF 14.61%

They are hooked up in series so voltage is doubled. I know my electrical math

I was thinking of adding another panel to the mix but they do not have that panel any more

I found a 240 watt Light Way panel
VMP 29.8
IMP 8.05
Voc 37.4
Isc 8.56
Mod EFF 14.7%

Can I add this in series with the other pannels. Are they close enough to the same electrically that it does not matter. They are physically the same length and width dimensions.

Total mp voltage should be 89.4
Total oc voltage should me 111.2

My MPPTcontroller can handle 150 volts input.

And correct me if I am wrong but this is under ideal conditions so my max power is probably never getting to 235 per panel. since on the Canadian Solar they are saying Nominal Max. Power is 170W per panel. I have a Tirstar MPPT 45 45 amp controller and on max theroetcial power at (704 watts, 235 per panel) that the panels will put out the charge current would be
@ 12 volts 58.75 amps
@ 13 volts 54.23 amps
@ 14 volts 50.35 amps

I was told that it would just clip the current at 45 watts out put.

But since things are not 100 percent the (3) panels at 170 Watts each would be 510 watts total so that means
@ 12 volts 42.5 amps
@ 13 volts 39.3 amps
@ 14 volts 36.4 amps

So I should be fine with very little "lost power" over 45 amps.

Hopefully you understand all that I said.

Thanks

BobO

BB.

In series, the current is no problem--A 5% to 10% difference between high/low ratings should work fine (Imp for series connections, Vmp for parallel connections).

Vmp-array / Voc-array-cold should all be fine.

MorningStar has a string/array sizing tool--You can double check your numbers there:

http://www.morningstarcorp.com/string-calculator

The one issue with MPPT controllers, the larger the "spread" bettween Vmp-array and Vbatt -- The lower efficiency of the MPPT controller. You will find that the controller runs hotter--So you want to make sure you have good air movement around the controller and it is not stuck in a "hot closet".

See page 61 of manual:

http://www.morningstarcorp.com/wp-content/uploads/2014/02/150V-TS-MPPT-Operators-Manual.pdf

-Bill