Comments on: Optimal solar panel angle

By: davea0511

davea0511 — Sat, 06 Mar 2010 13:26:09 +0000

The best value is the Xandex sunMizer MPPT modules. You only put them on the panels that get shaded. they’re $160 each. Looking at your picture though it seems like you have a lot of roof space not being used in bright sunlight. I’d move as many of your panels there as possible, then sell the few left over, and with that money but the Xandex SunMizers, and my guess is that you’ll see a significant improvement right away without it costing you a thing.

By: Bill Sr

Bill Sr — Fri, 05 Mar 2010 04:08:11 +0000

{Blue Locktite}

By: Ken Krugler

Ken Krugler — Sat, 12 Dec 2009 01:07:21 +0000

Hi Dave,

Thanks for the ref to power point tracking. I’ll definitely follow up on that.

– Ken

By: davea0511

davea0511 — Fri, 11 Dec 2009 13:05:10 +0000

So what you need is called “power point tracking”. Google it. Should cost about $800 but it will solve all your shading problems and based on you image I’m thinking it would pay for itself within 3 years.

By: James R Potts

James R Potts — Sat, 12 Sep 2009 03:13:44 +0000

The panels look great

By: davea0511

davea0511 — Sat, 13 Jun 2009 22:12:53 +0000

Sorry … wordpress seems determined to shrink my line of periods or dashes. I think you get the idea though. Each graphs is supposed to be symmetric.

By: davea0511

davea0511 — Sat, 13 Jun 2009 22:10:52 +0000

Those graphs turned out bad. What I meant was this:

4strings of 4:
——-#######
—###############
#####################

2 strings of 9:
——#########
——#########
#####################

By: davea0511

davea0511 — Sat, 13 Jun 2009 22:08:07 +0000

Oops … I just hit “submit” on that last reply when I realized I was getting my math mixed up. Ignore the info about mismatch … that occurs if your voltage is mismatched not current (which is your case).

Nevertheless I still think you’ll get more power overall if you wire as 4 strings of 4 than 2 strings of 8, just because you’ll be going down in 2 smaller steps than one huge step. like this:
………#######
….#################
#########################
instead of this:
……..#########
……..#########
#########################

where “#” represents your power. You’ll notice you have less power at the peak of the day, but it’s more than compensated once shade kicks in.

Note you’ll want to double up on your existing wiring coming from the combiner box to the inverter.

By: davea0511

davea0511 — Sat, 13 Jun 2009 21:59:03 +0000

With regard to efficiency … greater parallelism (what I suggested) almost always results in higher efficiencies, because all the panels of a string will assume the lowest voltage of any panel on the string (that’s just how it works).

With that in mind since you can’t do 6 strings of 3 panels each your next best bet is probably to rewire them as 4 strings of 4 (16 panels) and you’ll get more juice than with 2 strings of 9 (18 panels), and it will be easier on your panels. As it is right now when the shade is moving across your panels you are getting a lot of mismatch between the two strings and that’s docking your power by up to 25% more than it would if both strings were always balanced.

By: davea0511

davea0511 — Sat, 13 Jun 2009 21:56:23 +0000

I’ve been thinking more about the bypass diode idea and I think it may help, but not by much (because they are in series, not parallel), and in fact the internal diodes may be working correctly already, though they do get ruined by spikes and over heating, etc. If they’ve ever been wired wrong, for example, they could be shot.

Try this: when our first panel starts getting shaded get a ladder and stick your hand on the shaded cells. Are they hot to the touch? Then your diodes aren’t working. If they aren’t hot then they are.