Solar panels work best when there is no shade cast upon them. In fact, a shadow cast on even just part of one solar panel in your solar array can potentially compromise the output of the whole system. What are some strategies for dealing with potential shading of solar arrays?
Why does shading have such a dramatic impact on energy production?
In most instances, solar photovoltaic (PV) systems for homes and businesses consist of solar panels (the collection of which is referred to as the ‘array’) and an inverter. The solar panels catch sunlight and convert it into DC (direct current) electricity, and the inverter in turn converts the DC electricity into grid- and appliance-compatible AC (alternating current) electricity.
Most small-scale solar systems for homes and small businesses will include anywhere from 6 to about 30 panels, although the ‘size’ of a system is usually referred to by its capacity (in kilowatts – e.g. 5kW). For technical reasons related to the voltage requirements of the system’s inverter, solar arrays are usually divided into ‘strings’ of solar panels. Small systems may only have 1 string, while large systems could have many more. One string could consist of a single panel, but usually they have more.
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You can think of a string of panels as something like a piece of pipe, and the solar power is like water flowing through that pipe. In conventional solar panel strings, shade is something that blocks that flow. If, for example, shade from a tree or a chimney is cast on even one of the panels in the string, the output of the entire string will be reduced to virtually zero for as long as the shadow sits there. If there is a separate, unshaded string, however, this string will continue to produce power as per usual.
In extreme cases, a shadow does not necessarily need to fall on an entire panel – depending on the technology used in the solar panel in question, shading of even just one cell could flatten the output of the panel and in turn the entire string. Many modern panels, however, come equipped with devices called bypass diodes which minimise the effects of partial shading by essentially enabling electricity to ‘flow around’ the shaded cell or cells.
Strategies and technologies for dealing with solar panels in the shade
Although the performance and therefore the return on investment (ROI) from a solar power system can be severely affected by placing your solar panels in shade – especially shading that occurs regularly due to an object that casts a shadow at the same time every day as the sun passes through the sky – there are a number of ways to avoid or mitigate these effects.
Site your solar panel array where there will be no regular shading
This is the first and most obvious step to making sure your system does not suffer the consequences of being partially shaded. It is extremely important to consider all times of day for all seasons of the year when working out whether some nearby object might cast a shadow onto your roof. A solar system installer should be able to tell you if shading will be a problem using a range of mapping tools.
An example of a tree which has grown tall enough to cast a significant amount of shade on the solar array of a nearby roof – a situation that solar system owners will want to avoid.
Solar system owners should also be vigilant in making sure that there are no nearby trees which might grow tall enough to eventually cause shading issues. Solar system lifespans are typically expected to be 25+ years, during which time trees have plenty of time to grow.
Clouds are another source of potential shading. Clouds passing through the sky during the day may also result in fluctuations in system output, but these are basically unavoidable. Amorphous silicon solar cells are said to be better at handling shading than crystalline silicon solar panels, but generally speaking the relatively low overall efficiency of amorphous panels means that crystalline modules are generally a better choice.
There are some other technologies under development that may offer high efficiencies even in inclement weather, such as ‘super black’ solar cells, but most of these are still either expensive or not yet commercially available.
Use a string inverter that has MPP Tracking capability
Maximum Power Point Tracking (MPP Tracking or MPPT) is a technology that now comes standard in most quality inverters. An inverter equipped with an MPP Tracker (or several of them) is able squeeze the most usable energy possible out of a string of solar panels (even when shaded) by adjusting the voltage to always suit the inverter’s preferred input range. In a nutshell, an MPP Tracker helps to minimise output losses associated with partial shading and other panel output mismatches. Inverters without MPPT capability simply lose the output from the weaker string once it passes below the required output threshold.
An example of partial shading in a conventional multi-string inverter system (Image credit: pvsolarchina.com)
Get a system with microinverters or power optimisers
If it is unavoidable to not place your solar panels in shade, then microinverters or power optimisers might be the right option for you. These devices get around the problem of partial shading by eliminating the need for or importance of strings in the first place. Both microinverters and power optimisers essentially allow every solar panel in a system to operate independently, so that overall system energy production is not disproportionately affected by just one or two shaded panels. (Space to watch: A newer technology by Maxim being used in a line of JinkoSolar panels promises to deliver even more granular shade protection than conventional microinverters or power optimisers.)
The main downside to these technologies is that they tend to be a bit more expensive than a system with a standard system containing a central string inverter, so there’s no need to splash out on them in instances where shading is not an issue.
An illustration showing how microinverters/power optimisers can help solve the problem of partial shading on solar panels (via now defunct microinverter manufacturer Enecsys.)
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Hi,
I live in a very shaded area of the Adelaide Hills so can I get a measure of how effective solar panels will be before getting quotes? South side of a slope and many trees around us and across the way which stops the sun.
Thanks
Stephen
Hi Stephen. Yes – happy to help. Please email james@solarchoice.net.au or call us on 1300787273 to discuss if you like.
I have a existing solar system that has been working for years, but a neighbor’s tree has grown and now causes a serious shadow problem, especially in the winter. Is there a legal action that can be used to remedy the problem?
Hi Robert,
Good question. The Queensland government has an excellent resource on this topic. While we should make fully clear that we are not legal experts, we think the below might be most relevant to your situation:
Interference with your use and enjoyment of your land
Your neighbour’s tree may be classed as unreasonably getting in the way of your use and enjoyment of your land if it … interferes with the proper functioning of solar panelling
Check out the link for further details – and best of luck with your system.
hi i am about to install 3 200w solar panels on my caravan how would i go about having 3 strings with by pass diodes so when free camping i still have some input when it is at times shady regards Wayne
What great site this is, Well done. Q If I have 6 panels in a row and each individual wire is connected to a Buzz bar junction box, and then elec cable enough to carry the amps down to the controller. Would that fix a problems with partial shade ?
Hi Stuart,
We’re not electricians here and would not want to give advice that we can’t stand behind. We do know that there are a number of companies who make products that get around this problem – usually in the form of microinverters & power optimisers. And yes, in essence they make it so that all panels are not all lumped into one string.
Power optimisers (particularly Tigo’s optimisers) can be retroactively installed onto an existing solar PV system.
Hope this helps!
Hi James,
I’m a gal from the other side of the planet (England), and just wanted to say a huge THANKS for your informative articles.
I’ve often come to your site to obtain (what seems to me to be) pretty unbiased and sensible advice.
Anyway, enough blowing smoke up your rear, just wanted to let you know that you are my number-one-go-to-guy when it comes to information about solar energy – from half a world away. :)
Oh, the reason for this visit?
Wanted more information regarding the different panel manufacturing processes/types for a maximum-efficiency (optionally portable) solar-powered NiMH/NiCad/L-ion/Ni-Zn intelligent charging station project I am designing.
Yes, there are other sites available, but yours always has the information all in one place. Now I know what to look for, I can research the exact specs of the panel(s) that would most suit.
The project’s main goal is to make something that actually works in less than optimal conditions (UK sun is often pathetic!), is lightweight, and where cost is not an issue.
I think I may have to use GaAs panels for the portable (backpack) version. Ouch! ;)
Thanks again,
Susi xxx
Hi Susan,
Thanks a ton for reading! I’m not really an expert when it comes to the different types of solar PV materials (we mainly talk about silicon around here). Sounds like you’d want something flexible but durable.
Good luck with your solar-powered backpack!
Your article is the first to explain the fact that a little shadow has a massive effect on the whole output. I have done several web searches in the last year and at last I understand with your article and by reading very carefully the spec of the panels (11 x 250W multi crystalline ET PP600250) and the inverter (Sunny Boy 2500 HF).
I had wondered from the outset, 2 years ago why the output showed a rise from 200w to 1200w in ten minutes on the best sunny days around 10 am. I now know the answer is a chimney shading one of the 11 panels by 30 to zero percent in that ten minutes. I had always assumed that it was just the low angle of the sun on 10 panels and not the complete shade of half of one panel. Do I have a design fault to confront my istaller with?
Peter
Hi Peter,
As long as the installer knew about the shading issue at the design phase and informed you about it, it’s not a problem. They may have made a justified, informed decision to install the panels as they are (e.g. knowing that the larger system size would offset the early morning losses due to the shading). You may want to get in touch with them directly with any questions you have about it.
Hi,
I live in Sydney and I got a 5KW system installed a couple of months back. The installer told us that he can’t fit 20 panels on the north side and divided the panels, 15 on north and 5 on west. But after installation was done I found that he installed 13 on North and 7 on the West and I was upset about it because I wanted atleast 15 panels on the north to maximise the output. There are some tall gum trees on the West and I feel it will not be that effective because of the shade of the trees after 4pm. I haven’t paid the installer yet and when I asked him to move 2 panels to the North as per the installation map he gave me initially, he says that if we have just 5 panels on the West then these western string of panels would not produce any power at all. This would reduce the overall output of the system. Increasing the number of panels on the northern string would overload the Fronius inverter causing damage that would not be covered by warranty because of the installation procedure. I don’t know what to do. Could you please give me your valuable advice. I would greatly appreciate it.
Many Thanks,
Nishath
Hi Nishath,
That sounds like a tricky situation. Really, these are issues that the installer should have worked out at the design stage – not after the installation. The potential shading issues should have been identified at the outset, and the system designed accordingly. By the sound of it, it would have been better to have a smaller system only on the north side of the roof – this is again something that the installer should have suggested to you as an option. Perhaps you can suggest to the installer that they downsize the system to what can fit on your northern roof and ask for the overall price to be reduced? (They can take back the west-facing panels, of course.)
Best of luck working something out with them!
I have this current setup :
Bosch 4.6kw inverter with 2 strings 1×13 panels and 1×6 panels Hanhwa 260w Poly . How is the quantity of panels calculated on each string . Can i add more ?
Thanks
Hi Mark,
If you’re going to add panels to an existing string (as opposed to adding on a new string altogether, which would require additional inverter inputs), then you’ll want to make sure that the specifications of the new panels almost perfectly match those of the existing panels.
However, your current inverter would appear to be pretty close to being maxed out – you’ve got 4.94kW worth of panels and a 4.6kW inverter. It’s okay (and can be a good thing) to have a setup like this, where your total solar panel capacity is greater than the nominal inverter input capacity.
However, best practice is that the panel array should be no more than 30% ‘overclocked’. In your case, that would translate into about 6kW worth of panels. That might be worth your while in terms of additional energy yield, but it might not. I’d recommend speaking with an accredited installer who does panel retrofits to get a definite answer.
Is it expensive to have multiple strings? Why don’t they always make each panel a separate string?
Hi johnny04,
String inverters usually have a limited number of string inputs – 1x or 2x inputs in most cases. This is why you can just create more strings – most standard inverters can’t handle more than 1.
If the system uses microinverters or power optimisers, however, the shading problem is mostly averted because the panels are then basically on their own ‘string’. These sorts of systems tend to be a bit more expensive – especially with larger solar systems (e.g. over 5kW or so) because you’re paying for more components.
I have 10 sunpower 214 watt SPR cells in two strings, 5 each. One of the cells has turned a bright reddish brown. I can’t get a dealer out to look at it and my dealer went belly up. I’m considered measuring the current and voltage of that panel and compare it to the others. I’m a retired engineer and work on guitar tube amps so I know to be very careful doing this. Will that one cell lower the output of entire array in any significant way? Oh my system is going on 9 years old and I have an SPR2000 inverter. Older technology but still working.
Thanks
Hi,
Im getting 16 x 260w Q Cell (poly) panels 4.16kw system installed in a string of 2 rows facing north.
The 2nd row of 9 panels will be shaded atleast 200mm at the bottom during midday. I believe this will affect the output of the system. Is it possible to overcome this problem by having 2 strings instead of 1 string.
Thanks
Riaz
Hi Riaz,
You may want to look into microinverters or power optimisers for your system – these are generally recommended in situations where shading is an issue. A 2-string solution with a single string inverter may also do the trick (and be more cost effective), but speak to your installer about it to get more specific advice.
I am going to install the EVO+10PV mudule 4KW system, 8 panels north-facing an aggle at 5 degrees and 8 south-facing 175 degrees. I am not sure due to the roof orientation based on direction and angle of the roof the system gona generate the optimum amount of energy. Am I right? Help, help….., Please.
Hi James,
We are in the process of installing 12 x 250W panels on 2 strings (6 in a line facing North on tilting frames and 6 West on pitched roof)
They have installed the north facing array with two end panels tilted five to ten degrees lower than the other four. Could this be a problem regarding shading from other panels?
They said this was because of the screw line in the iron roof. Are they being lazy? Are there ways to adapt mounting systems?
Thanks,
Ariel
Hi Ariel,
This is a great question. So just to clarify – the installation company is installing your system with 2 strings of panels, and the last panel on the end of each string is at a different tilt angle from the rest of the panels? If I’m understanding this correctly, it does not sound right. Once you get back to me with a confirmation about the layout I will check with our in-house engineer.
Hi James,
Nice article first of all. I would have some questions though:
– do you have any information regarding different technologies ? I see you’re speaking about the shading for crystalline silicon. I would like to know if the Thin Film Technology has different results, especially CIGS. I know that Crystalline Silicon are connected in series and of course the shading will affect the whole system. I was reading lately that the Thin Film Technology may be/are connected in parallel and they are not that much affected – is that correct ? If yes, do you know at least how Thin Film would still be affected by a chimney or a tree let’s say ?
– if just a panel is shaded, the whole system will work as that panel ? or the system will just be affected loosing a % from its output?
Thank you,
Adrian
Hi Adrian,
Thanks for the comment and excellent questions. Yes, you’re right that some solar cell technologies are better at handling ‘microshade’ than others–namely thin-film cells like CIGS vs crystalline solar cells. But technologies such as bypass diodes within individual solar modules may counteract the effects of shading even in these types of solar cells. Things are changing quickly–check with any installers that you speak with and check the specs of individual solar panel brands.
The overarching issue, however, is that if you have an entire solar panel blocked out by the sun will knock out an entire string (if you have a centralised inverter and not microinverters or optimisers). This is the really crucial thing that individual panels–no matter how good they may be at dealing with shade on a module-to-module level–cannot generally overcome. Better to avoid the shading where possible.
Hello James; thanks a lot for this very interesting post.
I have a 2Kwp system, 20 x 100 kwp 12V panels; each 4 are connected in series, hence having 5 strings.
These 20 panels are installed on 2 lines, 10 units each, and they are equipped with diodes.
My system runs on a Steca Tarom 4055 MPPT charge controller, and it was installed 3 days ago. It’s an off-grid installation with 48V batteries.
After reading the above, I would assume that this entire system goes down because of a horizontal shade that blocks cells in multiple modules.
However I have noticed during the 2 tests I have made so far that the charger is displaying on its screen an overcharge message, with a voltage of 56V instead of 54 (the max I have set in Tarom).
And the output isn’t working.
I have to open the junction box and open / close all strings’ fuses to have it adjust and work again.
Did you encounter any similar situation?
Do you think this overcharge is due to the shade on panels?
Best,
Hi Adel,
If I were you I would get in touch with the installer who designed and set up the system–the overcharge warning doesn’t sound right, especially if you’ve just had the system installed a matter of days ago!
I have a 44 panel 11 kW single file PV array, and a neighbour is applying for planning permission for a wind turbine which will throw a shadow on to my array at certain times of the day. The turbine will be sited so the entire length of the array will be affected. Will this ruin my output completely? What can I say to the Planning to let them know this is very bad for my system?
Hi Sam,
Unless you’ve got dc-dc optimisers or microinverters the shading will definitely affect the whole array, which I’m assuming is a single string. Even if you have those, it sounds like the neighbour’s turbine could affect your system’s output.
You could check to see if your planning board/council area has any rules about not blocking a neighbouring property’s solar access (unlikely). Otherwise you could try to base your case on the damages that you would suffer if the turbine were to be built–I’m sure you could easily quantify what your losses would be.
In any case, hopefully you’ll be able to negotiate with your neighbors so that they can site the turbine in a different location that doesn’t block the sun for you.
Best of luck with your system.
Best,
James
Hi James
In your section titled “Use an inverter that has MPP Tracking capability” you said in line 4 “the difference between the current and voltage of 2 or more strings of inverters”. Should this say solar panels, not inverters?
Absolutely, Don. Thanks for pointing out the typo–fixed now.
Hi. I have a 2.2kW system made up of 9 panels in 1 row and in one array. However the 9th panel is in the shade to such an extent, and stopping the other 8 from working, that I am thinking I might actually be better without it. Is there anything else I could do?
Hi Tim,
As solar panels are connected through a ‘string’ shading on one panel will negatively impact all the others as you’ve seen. I would check your installer contract as some include a clause about moving panels for free if they are not generating the optimum amount of energy, but this would probably be if the panel has always been shaded. If the original installer placed the panels in an obviously shaded area it may be worth while paying an other installer to relocated them.
If the panel is shaded as the result of tree growth our suggestion would be to prune the tree allowing the light to get to your panels again. Alternatively you could have them relocated to a shade free part of your roof, this has to be done by a qualified installer or it may void the warranty.
A good installer should have accessed for any shading, we are aware of a few installers (who are not on our network) who actually have images on their websites of completed jobs wshowing the system in full shade or, in one case, shade created by placing mounted panels too close together! If you feel you may have an issue with the original installer you could talk to another company. Look out for evidence of a good company history (they will normally be happy to talk to you about this to reassure you), Clean Energy Council accredation and they may be able direct you other jobs they’ve done in the local area so you can speak to exisiting customers.
Hope this helps!
My question re shading comes from the opposite side. I currently have 12 x 170W panels and a 2kw inverter. Inefficiencies result in generation way below inverter capacity – especially in winter. Physically I can add a further 6 x170W panels which will boost me in winter (but not exceed the inverter capacity). However in summer with, say, 80% efficiency my 18 panels will produce about 400W OVER inverter capacity. Can I bring the output down below inverter capacity by deliberately covering,say, two panels during extreme summer generating periods ? I envisage eg a sheet of ply, sarking or the like.
Hi Tony,
I’ve spoken to our in-house Solar Engineers and they have advised me that adding extra panels would be very detrimental to your current set up. Although most inverters are set up to cope with energy production over the official capacity this essentially a safety measure and should not be used on an ongoing basis.
They also strongly advise against covering your panels. Shaded or covered panels will heat up, this in addition to the sun hitting your roof heating up and drying out what ever material you have used to cover the panels could result in a fire.
If there is some way you can remove the source of the winter shade this would be a less costly and safer alternative.
We hope this answers your question
we have a 1.5k solar system facing west vitally unshaded until late afternoon.in 18 months we are credited by supplier with about one(1)kw per month.how do we know that the feed in system is working?the installer seems to think we have the best system due to the higher tariff credit.if it isn’t working correctly it is a poor return on cost.is there a display in the metering system we can access?we would be more comfortable if we were able to assess any savings other than the lousy 1k.per month.
Hi William,
the fact that you’re feeding out 1 kilowatt-hour (kWh) per month could mean either that your system isn’t producing, or that you’re using all the power that your system is producing as it is being produced. If it’s the latter, that’s not necessarily a problem, as it means that your system would still be saving you money on your electricity bill.
If there is somewhere to see what your system is producing, it would likely be on your inverter. Some inverters even have wireless access so that you can see how your system is performing online. Do you have a user’s manual for the inverter?
If you believe that there is indeed a problem with your system, you’d be best advised to contact your installer to come out and have a look.
Best of luck!
Hi, What an excellent website. 2 questions please.
Q1 My shading problem appears minor. I have 4 rows of north facing panels on angle brackets all at 10 degrees. As we approach the winter solstice I notice about 100mm of shading falling on row four from the elevated edge of row three. It is a result of the morning slant sun angle and by 10am the shadow has gone. Would shadow shut off the panel or array whilst shaded? I have a Sunny Boy SB 3000TL-20
Q2 If I increase angle of row 4 to 20 degress will the aimed improvement be held back by other rows which remain at 10 degrees?
PS I don’t follow your solar-tilt drawing as it seems to suggest that increasing tilt angle from 10 degrees will decrease performance. Probably I am not reading it correctly? Help!
Hi Ron,
Thanks for your questions.
Q1. This narrow band of shading could be affecting the output of your array depending on a) how your panels are arranged (i.e. how many strings) and b) the specifications of panels you have.
a) If you have multiple strings, the shading may only affect one of them–i.e. the panels in row 4, if they constitute a single string. If rows 3 and 4 are on the same string, however, the shading could potentially be cutting into the output of all of them, as in most conventional panels the ‘weakest link’ breaks the chain.
b) Some panels have bypass diodes that handle the problem in solar panels where even partial shading has a disproportionate effect on overall array output. Such panels will only see a loss equivalent to the number of cells that are shaded (or possibly slightly more depending on the number of bypass diodes) instead of knocking out the entire string.
A couple more comments: Do you have a means of monitoring your system output? If you do, you should be able to see what effect this partial shading is having on your system’s output. Additionally, consider yourself lucky that the shading is coming from a lower row of panels instead of from a tree on a neighbour’s property, which would keep growing!
Q2: Changing the angle of row 4 will again depend on how many strings your array is divided into. If it is in its own string and plugged into the MPP tracker on your inverter just like that, it shouldn’t be a problem to change the angle. I don’t know where you’re located, but I would assume that you’re in a tropical area given the low angle of your array? Was it a flat roof originally? If you’re anywhere outside a tropical area (and still in the southern hemisphere), it’s generally better to have the panels tilted at around 20-30 degrees from flat, facing north. If you do increase the angle of the last row of panels and it happens to be on the same string as row 3 and you latitude below about 30 degrees south, this should actually improve the output of that string–albeit only slightly. A 20 degree angle will catch more sun further south.
Hope this make sense. Good luck!