Different panels/wattages in same array?

Re: Different panels/wattages in same array?

Roughly, you could parallel the second string if their Vmp was within ~10% (or less mismatch) with the existing array.

If the mismatch is too far apart, the MPPT controller will have a hard time picking the maximum power point (there may be three MPP locations in the power curve, low Vmp, High Vmp and a middle Vmp).

And for adding series connected panels, again within ~10% of Imp between the different panels.

Also, when adding parallel strings of large and small panels--you should have a series protection fuse (per data sheet rating) for each string (big string can overheat small wattage string if there is a short otherwise).

-Bill

Re: Different panels/wattages in same array?

adam1984 wrote: »

1) So, if i understand correctly, you can take 3- Evergreen 200's in one string, at 17.5Vmp and add a string of 3- 100W panels roughly the same voltage say, 17.8V, in PARALLEL, without losing efficiency or wattage? (and adding a breaker for that string) .... (voltage matching, current not matching)

That is correct... Your first string is:

• 3x 17.5 volts = 52.5 volts Vmp (nominal)
• +/- 10% or +/- ~5.25 volts
• 3x 17.8 volts = 53.4 volts
• 52.5/53.4= ~0.98 or a match within ~2% -- Not a problem at all

If you look at the Power Curves of typical solar panels, you see that the Pmp is fairly wide and does not change much over a 10% range of voltage/current.

Normally, for a matched pair of parallel connected panels (or strings of panels), a series fuse per parallel connection is not needed for one or two parallel connected strings. A short circuit anywhere does not draw any more than Isc--which is the same for each parallel string...

However, if you match 40 watt panels with 200 watt panels in parallel--one string can output 5x the current which could cause the smaller 40 watt string to overheat in the case there is a short circuit somewhere.

2) If i had same Example, 17.5 Vmp 3-Evergreen 200's, with and Imp of 11.5, i could add in SERIES 3 - 280W panels at 26 Vmp and 11 Imp? ....... (current matching, voltage not matching)

Yep--That is it.

You can also, add one 11 amp panel in series with a smaller pair of parallel connected 5.5 amp panels (which add up to ~11 amps).

Because solar panels are current sources and not voltage sources, they "share loads" pretty nicely (each contributes its available current as long as Vpanel is somewhere between 0 volts and Vmp).

That is what i got but coots comment makes sense:
"It doesn't take much imagination to see what would happen if you hook 35 Volts to 17.5; current would try to flow from the higher panel to the lower one."

That could be a problem with extreme miss-match of voltage (or current). Normally, if the miss-match is not too great--then it is just a loss of power (the 35 volt panel runs at ~17.5 volts -- for example paralleled to a PWM controller--P=I*V so the 35 volt panel running at 1/2 the voltage only outputs 1/2 the power).

The other thing to watch out for--Typically solar panels (and older used panels) were built for the day of 12-48 volt battery banks. And they have a maximum working voltage of around 75 volts (DC?).

The modern panels (typically over 100 watts) were designed to operate with Grid Tied Power supplies with Vmax system voltages of 600 VAC (typical house wiring ratings) or 1,000 VDC (in Europe).

So mixing old/small panels on a MPPT charge controller with Voc approaching 150 VDC could violate the max voltage ratings of older/smaller solar panels (designed for older/off grid battery systems).

Many older panels don't even list the Vmax rated system voltage.

-Bill