Matching Panels

System

Hi,
I currently have 3 panels hooked up to a Blue Sky MPPT (2512iX). I am looking to add more to bring the total close to the maximum it can support. I have heard that I should match the Vmp of the panels closely. How closely should they match ? What would happen if they don't "match"?

My current panels are as follows (128W total):

2 Hoxam H4810 48 Watt Vpmax=15.80
1 Unixolar FLX-32 32 Watt Vpmax=16.5 (?)

Is anyone aware of any panels that are about 10"-18" Wide that would match, I am looking to add about 150Watt to the array.

(This is on a sailboat)

Geoff.

crewzer

Re: Matching Panels

Geoff,

The followling is an excerpt from a previous post ot two:

Adding panels to an existing array, or reconfiguring an array, requires that you pay close attention to two basic rules. One is that the PV modules wired in series have substantially the same Imp specs. The other rule is that the PV strings wired in parallel have substantially the same Vmp specs.

For example, my “48 V” array consists of two series-strings wired in parallel. Each string consists of four BP (SX) 60 W modules (“6 V” configuration; 8.4 Vmp x 7.12 A Imp), one Kyocera 120 W module (16.9 Vmp x 7.10 A Imp), and one Sharp 123 W module (17.2 Vmp x 7.16 A Imp). Allowing for manufacturing tolerances, the Imp current specs for the different brand/model modules are “close enough”. Accordingly, each string spec ends up at 67.7 Vmp x 7.10 A Imp, and the total array spec is 67.7 Vmp x 14.2 A Imp. The revised 966 W spec is 99.5% of the nameplate ratings. Under clear and crisp mid-day skies (summer humidity is a problem in my area), my array easily produces 14.2 A.

Deftly applied, this mix ‘n’ match approach can be very handy. As illustrated above, it’s allowed me to gradually expand my array, although the BP 60 W modules and the Kyocera 120 W modules are now out of production. And, when the time comes to "grow" the array to a "60 V" configuration (there is a sorta-plan here), I can expand the array by adding one more ~125 W module to each string. Current options include the same Sharp 123, the Mitsubishi 125, and the Kyocera 130, which is the same form factor as the old KC-120.

To answer your questions directly, the closer the Vmp match of the parallel strings/modules, the better. If they don't match, then the array will operate at/near the lowest string/module Vmp under STC conditions. As a practical matter, STC conditions rarely occur, and array Vmp is invariably below STC spec. Nonetheless, the performance of the string or module with the lowest Vmp will pretty much drive the array votage.

HTH,
Jim / crewzer

niel

Re: Matching Panels

in addition a vmp of 15.8v is very low and makes me believe you may have pvs that were to be self regulating type that was out years ago by starving the voltage. get yourself some new pvs to replace the ones that you currently have. you can offer the old pvs up for sale here if you wish to. even the 16.5v from the unisolars are low compared to the 17-17.6v typically seen today for vmps.