What effect does shade have on a solar panel output?

[coopec43]

I've mounted two 80W solar panels (in series 24V) on the aft cabin roof (under the mizzen boom) I've noticed the panels only get about 2 hours per day completely unshaded but this morning I noticed the Port panel (10 cells X 3 cells) was shaded diagonally by one of the mizzen mast stays and I wondered if the output of the panels was destroyed. I did a bit of research and it seems the shade would have very little effect at all.

I don't know how reliable the figures are from the amateur test. Are these results somewhere near to what you would expect?

(My panels do have some diodes but let's leave that out of the equation to keep it simple.)

My computer is playing up and I'm trying to find the link to the test results. HOPE THIS WORKS!

https://www.builditsolar.com/Experim.../PVShading.htm

[pcmm]

Even a small amount of shading can have a serious impact on the output of the panels, depending on where and what cell(s) sees shade. Diagonally across the panel could (depending on the panel) basically shut it down. Easiest way to check is to check the voltage of that panel by itself when you see the shading on the panel. Some panels have blocking diodes to help with this. Its always best i you can arrange it, to have the panels as unobsructed as possible. I have my 400watt panel on my parch away from my mizzen mast and clear of the rig.

[coopec43]

I installed these panels just to keep the batteries "topped up".

I do plan to install X2 150W (1.2M X .9M) for charging the house bank

Incidentally do you keep your bilge pumps on "auto" all the time? (I think it makes sense but the X3 pilot lights do consume power)

[pcmm]

Originally Posted by coopec43

I installed these panels just to keep the batteries "topped up".

I do plan to install X2 150W (1.2M X .9M) for charging the house bank

Incidentally do you keep your bilge pumps on "auto" all the time? (I think it makes sense but the X3 pilot lights do consume power)

Yes, my bilge pumps are wired so that they (and their panel) are active all the time, even when the battery switch it turned off. the LEDs (4 in total, 2 per panel) consume milliamps of power so no real draw on the batteries. To me its a safety thing to have the pumps available all the time, even when I'm not around.

My current solar "farm" is a 400watt panel on my arch and 2 x 160watt panels that I can swing out on my lifelines (solid tube at the top) so right now I'm capable of a bit over 700watts of production, but I usually leave the 160's at home as the single 400 watt can easily keep up with my needs through out the day and I have enough battery (today) to last a few days if the weather is cloudy. I no longer plug in to shore power, even when I'm at my home yacht club, I just don't need to.

[rslifkin]

Definitely bilge pumps on auto at all times. I don't have full time pilot lights for the auto position on any of mine (only pilot lights to indicate if they're running), so no parasitic draw from that.

As far as shade, any shade will reduce a panel's output. How much depends on the panel in question, how much it's shaded, and how the shade is distributed across the panel. Keeping solar totally un-shaded is hard to do on a boat, so generally you just want to have enough that you get enough daily output even with some shading.

[coopec43]

Originally Posted by rslifkin

Definitely bilge pumps on auto at all times. I don't have full time pilot lights for the auto position on any of mine (only pilot lights to indicate if they're running), so no parasitic draw from that.

As far as shade, any shade will reduce a panel's output. How much depends on the panel in question, how much it's shaded, and how the shade is distributed across the panel. Keeping solar totally un-shaded is hard to do on a boat, so generally you just want to have enough that you get enough daily output even with some shading.

Did you have a look at "Build it Solar" test results? Any thoughts? If you can go by their results a shadow from a mast stay wouldn't have much effect at all?

https://www.builditsolar.com/Experim.../PVShading.htm

[rslifkin]

Originally Posted by coopec43

Did you have a look at "Build it Solar" test results? Any thoughts? If you can go by their results a shadow from a mast stay wouldn't have much effect at all?

https://www.builditsolar.com/Experim.../PVShading.htm

A stay is generally going to cause a very narrow shadow, so in most cases it won't have a huge effect (as they found). It's likely to be measurable, but not huge.

[thomm225]

My 65 watt panel is in the shade much of the morning when the boat is in the marina due to the mast and dodger.

The 65 watt panel is lying flat on the aft lazarette.

Boat is bow to the Sun in the slip.

Batteries get recharged or topped off later in the day through a Victron Smart Solar Controller.

This is my Wintertime set up.

The panel charges two 6 volt Golf Cart Batteries of 220 ah each.

I have no shore power or alternator.

During the Sailing Seasons, I add a 50 watt panel, but it faces the horizon. The panels are in parallel.

I have 115 Watts total for the panels.

Bilge pump is on auto.

I run fans at night when at anchor.

Power is for lights, autopilot, inverter, depth, VHF, computer, fans, and phone charging.

[coopec43]

Originally Posted by rslifkin

A stay is generally going to cause a very narrow shadow, so in most cases it won't have a huge effect (as they found). It's likely to be measurable, but not huge.

My two panels are in series but at one point the Port panel was shade free but the Starboard panel had one corner cell completely shaded by the boom.

The Build it Solar didn't test for that sort of shading. (I suppose that is where the diodes come in)

Now I have just read:

"Shading just one cell in a module to half causes the output power of the whole module to fall to half. No matter how many cells there are in the string, completely shading one cell will cause the output power of the module to fall to zero."

The Effects of Shading on Solar Panels

https://www.deegesolar.co.uk/solar_panels_shading/

[rslifkin]

Originally Posted by coopec43

My two panels are in series but at one point the Port panel was shade free but the Starboard panel had one corner cell completely shaded by the boom.


The Build it Solar didn't test for that sort of shading. (I suppose that is where the diodes come in)


Now I have just read:


Shading just one cell in a module to half causes the output power of the whole module to fall to half. No matter how many cells there are in the string, completely shading one cell will cause the output power of the module to fall to zero.
The Effects of Shading on solar panels


https://www.deegesolar.co.uk/solar_panels_shading/

If you can see what the solar output is doing you'll start to get a sense of what shading is most problematic and what has a minimal effect. When we're traveling and at a dock without shore power it's not unheard of for me to orient the boat based on what will give better solar performance.