Solar panel shading

[Itinerant1]

With 1,280 watts of solar I don't worry to much about getting enough solar. This time of the year with the days getting shorter and we're in the national forest boondocking catching light shadows from some pines I would expect some drop off in amps going to the battery (can see it on the display).
Yesterday morning while I was walking the dog I was checking the shadowing on the panels from the trees from the hill behind the 5th wheel and noticed that the crank up antenna was casting a good shadow on 2 panels (each in a different series string). This morning at 10am I remebered about the antenna shadow and before cranking it down there was 25-26amp reading, after lowering it down 36-37amp. That's a pretty fair boost just lowering the antenna, during the day seeing we're not watching it anyways. I'll have to pay attention to the tv antenna during the winter so not I'm losing any possible power.;) We know about shadowing on the panels but seeing it yourself is a little eye opener.

[Almot]

Itinerant1 wrote:
... battery bank normally gets back to 95-100% even after a couple/ few days of playing catch up but in this location it's been getting to 70% (350ah) by sundown ...
That's what seemed odd to me that I wasn't gaining back the lost power after a couple days of heavy overcast and snow. The way I'm parked and the path of the sun is enough for the antenna shadow to stay on the panels a fair amount of the day.

Hard to tell why it couldn't catch up to 95% when changing the location. Antenna shade could've contributed, or this location had some trees/mountains blocking the early sun when you needed it the most, or there is less sun in late October than it was in August :). Or you changed the time pattern of loads. Increased current is needed only until you get to Absorb, then you can get by with very little charging current - until you turn some heavy loads on. If battery can't catch up past 70% - change the way you run loads, avoid running heavy loads after sunset.

Most solar systems require a fair amount of self-discipline, charging all the tools and running other loads is better in daytime - especially after the battery went to Float. Then you could use the energy from the sun directly, rather then discharging the battery. Battery stays in Float, sun runs your devices.

[Almot]

MEXICOWANDERER wrote:
Where I have to park to eliminate solar-oven effect, I imagine I hear an occasional Tarzan, yell. Turning the entire roof of Quicksilver into an "Aircraft Carrier" would help reduce solar heating.

I thought it was my imagination - trailer was suddenly getting hotter when sun moved to the area not covered by 2 big panels. Panels really help against over-heating, if installed with couple inches clearance off the roof.

[time2roll]

CA Traveler wrote:
Solar Panel Bypass Panel Example

Three 60 cell 30V panels with 3 bypass diodes in each panel. Each panel can be viewed as composed of 3 subpanels each with a bypass diode. As shown below the output would consist of 20+30+20 = 70V at the given amps. The amps depend upon the given light conditions.

Assuming 8A the output would be 8*70 = 560W for the serial panels. For parallel connected panels the output would be 8*30 = 240W.

With shadows on 7 of the 9 subpanels there would be 8*20 = 160W available for charging with serial panels.


Click For Full-Size Image.

Unfortunately an antenna can take out all three strings and the panel produces nothing. Only part of a string needs shade for it to drop out. Of course the other three panels in series can push on through.

[CA_Traveler]

If you had serial panels and a MPPT controller then the bypass diodes were not working. As you can see from my link above serial panels with bypass diodes work very well.

[liborko]

That is exactly what I was doing when I did initial testing of my panels. How do you explain total loss of output when only one cell shaded on the panel that had 3 by-pass diodes. Seems that things are not that simple when it comes to solar panels.

[CA_Traveler]

liborko wrote:
Solar panel is a CURRENT source. How much power(watts) does it produce when short circuit amps are say 8A and voltage is 0V?

Panel short circuit is one way to test for Isc and along with Voc is a good indication of expected panel performance. I preform these tests on all of my new panels.

Vmp is the expected maximum MPPT voltage/power output and Isc is used for PWM controllers.

[liborko]

Solar panel is a CURRENT source. How much power(watts) does it produce when short circuit amps are say 8A and voltage is 0V?

[liborko]

Solar panel is a CURRENT source. How much power(watts) does it produce when short circuit amps are say 8A and voltage is 0V?

[CA_Traveler]

pianotuna wrote:
Itinerant1,

The problem is the shaded panel (if in series) limits the amperage of the entire string. Even if you only had the upright part of the antenna casting shade through put would be reduced. The only "fix" is bypass diodes between each and every cell.

So far as I am aware, only Unisolar ever did that--and they are no longer in business.

Activation of a bypass diode does not change serial panel amps, they do reduce the panel voltage. The MPPT CC controller output amps/power is reduced.

[CA_Traveler]

Solar Panel Bypass Panel Example

Three 60 cell 30V panels with 3 bypass diodes in each panel. Each panel can be viewed as composed of 3 subpanels each with a bypass diode. As shown below the output would consist of 20+30+20 = 70V at the given amps. The amps depend upon the given light conditions.

Assuming 8A the output would be 8*70 = 560W for the serial panels. For parallel connected panels the output would be 8*30 = 240W.

With shadows on 7 of the 9 subpanels there would be 8*20 = 160W available for charging with serial panels.


Click For Full-Size Image.

[MEXICOWANDERER]

Where I have to park to eliminate solar-oven effect, I imagine I hear an occasional Tarzan, yell. Turning the entire roof of Quicksilver into an "Aircraft Carrier" would help reduce solar heating. Lessee.... seven feet by thirty eight feet = ...

...A $olar Farm

Bankruptcy.

Ladders and exotic extendo-handle squeegees.

Naaaahh

400 amps x 28 volts = 11,200 watts
Wish I had money for $1,00,0000,000 worth of Lithium batteries
And a proxy to rob a few banks to get that dough.

Then I could C A M P !!!

Or check into the Acapulco Princess hotel and ring down for room service.

Compromises......compromises...

[CA_Traveler]

Almot wrote:
30% drop, and antenna shade probably didn't cover 28-29 sq.ft. (30% of 1,280W).

When I posted about this oddity in series panels few years ago, nobody believed me. People were talking about magical powers of bypass diodes, sheesh...

There is nothing magical about bypass diodes in solar panels.

But clearly they are often not understood so perhaps that qualifies as having "magical powers". :@

Click here to see the magical powers of my bypass diodes in leafy shade. :B

[BFL13]

Itinerant1 wrote:
With the inverter and misc charging of phone, laptop or tablet there is always some small load (2-8ah). The battery bank normally gets back to 95-100% even after a couple/ few days of playing catch up but in this location it's been getting to 70% (350ah) by sundown and after the evening dinner, tv and morning breakfast/ coffee making the bank could be down to 35-40% (175-200ah).
That's what seemed odd to me that I wasn't gaining back the lost power after a couple days of heavy overcast and snow. The way I'm parked and the path of the sun is enough for the antenna shadow to stay on the panels a fair amount of the day.

This is where the Li batteries come into their own--they can get by without being fully recharged. "Normal" batteries would be in trouble. Big bucks for Li though.

[pianotuna]

Itinerant1,

The problem is the shaded panel (if in series) limits the amperage of the entire string. Even if you only had the upright part of the antenna casting shade through put would be reduced. The only "fix" is bypass diodes between each and every cell.

So far as I am aware, only Unisolar ever did that--and they are no longer in business.

[liborko]

Typical 12V nominal solar panel has 36 cells connected in series. Before I installed my solar system in 2006 I did testing of effect of shadowing on the output from the panel. Complete shading of as little as one cell would completely kill the output from the whole panel. Connecting panels in series makes situation even worse when any of the cells in chain are in shadow. That is why I prefer parallel connection of panels.