Solar Panel Shading

[mark1882]

Hi How big an issue is shading of solar panels I have some heard some people say that only 10% shading can knock out a whole panel

I am in the process of fitting 2 x 80w solar panels on a gantry and have been reading some conflicting opinions about the impact on the performance on the panels of shading. I am also planning to fit a wind generator and numerous antenna including Wifi Bat, Navtex, Weatheman and GPS which will on a bar as part of the gantry that is upstanding at the rear of the gantry which means that when the sun is from the stern they will cast a shadow,albeit small over the solar panels. The 25mm upstand will run the full length of the panels so could potentially cast a small thin shadow over the length of the panels. The panels are polychristaline

I am not sure if this is going to be an issue or not and if it is i may need to redesign the gantry.

Any advice about how much shading is an issues on the performance od solar panels would be appreciated.

Many thanks

Mark

 

[telford_mike]

Some interesting info:

http://midsummersolar.co.uk/frequen...cles/26-the-effect-of-shading-on-solar-panels

 

[Beyondhelp]

Shading IS a big issue. Any cells not under light go high in resistance resulting in the whole panel dropping a great deal. If you covered 10% of the area I suspect output will drop by more than 50%. I have two 80w panels on my garden shed as an experiment, I may actually see what this does and report back later.

 

[duncan99210]

I recently fitted 80 watts of panels on to our bimini. Because there's rigging in the way, I used four twenty watt panels rather than one 80 watt panel. This cuts down the loss from shade as it mostly only affects one or two of the four panels. In due course, wheni come to fit an arch and panels to that, I'll use a similar strategy to minimise losses to shade.

 

[JumbleDuck]

Shading IS a big issue. Any cells not under light go high in resistance resulting in the whole panel dropping a great deal. If you covered 10% of the area I suspect output will drop by more than 50%.

It depends very much on whether it's full or partial shade (think eclipses) and the relative geometry of the shadow and the solar cell wiring. I understand that PBO may do an article on this soon.

 

[JumbleDuck]

I recently fitted 80 watts of panels on to our bimini. Because there's rigging in the way, I used four twenty watt panels rather than one 80 watt panel. This cuts down the loss from shade as it mostly only affects one or two of the four panels.

80W panels are normally configured internally as several smaller panels in parallel.

 

[sailaboutvic]

Reading the midsummer report , I may just as well throw my panels away . We have three panels , two 65 and a 75 unless the sun is direct on top at less one panel is always shaded , if it not the Bimini , it the wind gem or the radar , our battery banks is 400 house , 200 usable AH from March till oct we never have a problem with power , we can sit on our anchor for as long as we like and not have to start the engine , in the morning our battery are showing 75 % 12.8v within two hour of sun up in the sky their showing back upto 105 % never dropping less then 95% , our uses is heave , 3000w inverter , two iPads , two PC , two Phone , charging recharging able battery most of the time , that's with out all the normal stuff we have on boats these days , I have to say Nov last years we was still cruising and there was days when we just wasn't getting enough power .
I keep thinking that I am using all that space with small panels maybe I get rid of them and buy two 150w .

 

[RobbieW]

80W panels are normally configured internally as several smaller panels in parallel.

Given this an area where I found it very difficult to get hard information, in the form manufacturers spec sheets, do you have a link to support that view please - assuming that you're saying that feature mitigates the effect of shade.

We will almost inevitably get shade on panels mounted on boats, so trying to design an installation that minimises the effect seems important. For the sort of sizes most of us will fit, up to c. 100w, I've found none with more that one bypass diode per panel which is what I understand to be required to mitigate the effect of shade.

 

[JumbleDuck]

Given this an area where I found it very difficult to get hard information, in the form manufacturers spec sheets, do you have a link to support that view please - assuming that you're saying that feature mitigates the effect of shade.

It's a consequence of how they are made. Basically, all the individual cells are more or less the same size, which means that they produce the same voltage and the same current. To get the full voltage needed they are connected together in series and then to produce a more powerful panel these series strings are connected in parallel. Both 50W panels on my boat have two of these strings in them. Before I fitted them I did some experiments. As one cell in one string is progressively blocked, the output from that string reduces, but the other is unaffected. In my case the strings run fore and aft, so a hard shadow from the boom is unlikely to affect both and a soft shadow doesn't have very much effect. A hard shadow across the boat (and therefore across both strings) is much worse, but also more or less impossible.

All this was a bit unscientific, but I am planning to do some proper tests soon and will share the results. Overall I think the answer is probably "Unshaded is best, but shadows along the direction of cell connections aren't as big a problem as people think."

Watch this space ...

 

[RobbieW]

It's a consequence of how they are made. Basically, all the individual cells are more or less the same size, which means that they produce the same voltage and the same current. To get the full voltage needed they are connected together in series and then to produce a more powerful panel these series strings are connected in parallel. Both 50W panels on my boat have two of these strings in them. Before I fitted them I did some experiments. As one cell in one string is progressively blocked, the output from that string reduces, but the other is unaffected. In my case the strings run fore and aft, so a hard shadow from the boom is unlikely to affect both and a soft shadow doesn't have very much effect. A hard shadow across the boat (and therefore across both strings) is much worse, but also more or less impossible.

All this was a bit unscientific, but I am planning to do some proper tests soon and will share the results. Overall I think the answer is probably "Unshaded is best, but shadows along the direction of cell connections aren't as big a problem as people think."

Watch this space ...

I'd certainly be interested in your results. I also understand the electrical theory, what I hadnt found when looking for panels was anything that suggested some panels have an internal serial/parallel design where others have a serial design - perhaps because I wasnt looking for it. I bought 50w Victron BlueSolar, partly because they fitted the space and partly because thats what I could get supplied. The specsheet, http://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-Monocrystalline-Panels-EN.pdf, describes them as 36 cells in series - suggesting theres no //ing in there. What panels do you have and how did you find them ?

 

[RobbieW]

I'd certainly be interested in your results. I also understand the electrical theory, what I hadnt found when looking for panels was anything that suggested some panels have an internal serial/parallel design where others have a serial design - perhaps because I wasnt looking for it. I bought 50w Victron BlueSolar, partly because they fitted the space and partly because thats what I could get supplied. The specsheet, http://www.victronenergy.com/upload/documents/Datasheet-BlueSolar-Monocrystalline-Panels-EN.pdf, describes them as 36 cells in series - suggesting theres no //ing in there. What panels do you have and how did you find them ?

There are some supplemental questions I have based on research done overnight. So far as I can see a solar cell has a nominal output of 0.5v, so a 36 cell series array will provide a nominal output of 18v. It also seems that standard sizes for cells are 150x150mm or 125x125, on that basis I cant see how 36 cells fit on the panels I have let alone multiples of 36 cell arrays. Assuming a manufacturer uses standard cells for their range of panels (to reduce cost) what is the variable I cant see or dont know?

 

[noelex]

To get the full voltage needed they are connected together in series and then to produce a more powerful panel these series strings are connected in parallel. Both 50W panels on my boat have two of these strings in them.

Most panels have all the cells in series. There are bypass diodes fitted (anywhere from about 2-8 is common). This diodes have an impact on the performance of the panel in shade and could be thought off as separating the panel into "strings", but the cells are still still connected in series.

 

[ribrage]

Hi How big an issue is shading of solar panels I have some heard some people say that only 10% shading can knock out a whole panel

I am in the process of fitting 2 x 80w solar panels on a gantry and have been reading some conflicting opinions about the impact on the performance on the panels of shading. I am also planning to fit a wind generator and numerous antenna including Wifi Bat, Navtex, Weatheman and GPS which will on a bar as part of the gantry that is upstanding at the rear of the gantry which means that when the sun is from the stern they will cast a shadow,albeit small over the solar panels. The 25mm upstand will run the full length of the panels so could potentially cast a small thin shadow over the length of the panels. The panels are polychristaline

I am not sure if this is going to be an issue or not and if it is i may need to redesign the gantry.

Any advice about how much shading is an issues on the performance od solar panels would be appreciated.

Many thanks

Mark

Mark

ALL of my panels have some shade on them , its almost impossible to rig them without shade at some point in time, my take on it was to go over size on the number and size of the panels, our fully charged light is on for most of the time, go big on charging systems and little on output (LEDS etc ) and you won't have any worries re shading

 

[vyv_cox]

My experience is similar to sailaboutvic's. Due to the layout of my arch, radar scanner and antennae there is almost no time when my 80 + 45 watt panels are shadow free. Despite this relatively small array for running a fridge full time there is never a time in May - August when we need to charge batteries using engine, and not very often outside those months. We see 8 amps at midday during those months, not reducing a lot even when the mast shadow is across a panel.

 

[TQA]

WARNING This theoretical knowledge on my part and is a product of perusing manufacturers sales blurbs.

The effects of shading can be reduced by using panels with a higher output voltage than normal - say 28 volts and feeding a [GENUINE] MPPT controller which takes the high voltage and transforms it to a lower voltage but higher amperage.

If this is really happening then it would seem to mitigate the effects of shading.

I am a little smug as I have a rear arch with my panels clear of shade by 8.30 am with 22 to 26 amps pouring into my battery bank if the sun is shining. I can tilt the panels to follow the Caribbean sun if, like today, there is overcast reducing output. Still getting 10 to 15 amps though.

3 x 135 w Kyocera panels in parallel with a BlueSky MPPT controller.

WARNING This one I have checked myself. Some of the controllers claiming to be MPPT are not, they do not do the clever transforming bit regardless of the overvoltage supplied.

 

[blampied]

WARNING This theoretical knowledge on my part and is a product of perusing manufacturers sales blurbs.

The effects of shading can be reduced by using panels with a higher output voltage than normal - say 28 volts and feeding a [GENUINE] MPPT controller which takes the high voltage and transforms it to a lower voltage but higher amperage.

If this is really happening then it would seem to mitigate the effects of shading.

I am a little smug as I have a rear arch with my panels clear of shade by 8.30 am with 22 to 26 amps pouring into my battery bank if the sun is shining. I can tilt the panels to follow the Caribbean sun if, like today, there is overcast reducing output. Still getting 10 to 15 amps though.

3 x 135 w Kyocera panels in parallel with a BlueSky MPPT controller.

WARNING This one I have checked myself. Some of the controllers claiming to be MPPT are not, they do not do the clever transforming bit regardless of the overvoltage supplied.

Agree, we have 4 x 100 semi flexible panels and MPPT controller (all cheep Chinese) at least one will be in shade at any one time, (Radar dome, Antennas, nav lights) We can easily see 25 Amp output during the day, (but only when running a heavy load like firing up the air conditioning through the inverter) a 25 amp output just for charging would soon cook my 340 ah of house batteries.
In short 400w of semi flex able solar will provide many many times more power than we can use during the day.
The panels are flat on the roof (we are a motor boat) output falls off drematically about 2 hours before sunset to the point where they struggle to even keep up with powering the fridge, and of course provide nothing at night.
What is needed is bigger batteries to store all the excess during the day.

PS.
If anyone interested, (we have one of the smallest marine Air con units) the solar panels won't provide more than 25% of power required to run the Air-conditioning.

 

[OldBawley]

Big difference summer / winter.

In summer, shade or no shade, the bulk charge is mostly finished by noon. Our solar brings 9 Ah, consummation is only 3 Ah.

In winter, and not using marina or town electricity, things are very different. Lots of days solar is not sufficient to charge bulk, let alone equalise. Panels have to be orientated and free of shade.
Wind power is a must during winter.
I do realise not many Med liveaboards live in winter on the hook.

 

[sailaboutvic]

Big difference summer / winter.

In summer, shade or no shade, the bulk charge is mostly finished by noon. Our solar brings 9 Ah, consummation is only 3 Ah.

In winter, and not using marina or town electricity, things are very different. Lots of days solar is not sufficient to charge bulk, let alone equalise. Panels have to be orientated and free of shade.
Wind power is a must during winter.
I do realise not many Med liveaboards live in winter on the hook.

I think you would be surprise how much do . Just on Meganisi There was five this year that I know off