Do solar panels work in the shade?

Yes, but… Solar panels do work in the shade (they will generate some electricity), but the real question should be ‘how well do solar panels work in the shade‘? The answer to that is different and depends on a lot of factors.

Let’s dive in a bit deeper…

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Apologies in advance – this a text-heavy post. I could drop in some lovely images, but essentially there’s a fair amount of technical stuff to understand, so bear with…

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Solar panels turn light waves (solar radiation) into electricity. The more intense the light (which is a form of energy) the more electricity the panel will generate, up to its maximum.

The best light is direct sunlight, but any light will work do an extent. If clouds are in the way, some light gets through, but it’s less intense so that will have an effect on the electricity produced by the solar panel.

This is a very relevant and important question if you’re in UK (or places with a similar climate) where the weather is one of the most popular topics of conversation! I’m not knocking solar panels, but I am being realistic about what they will and won’t do when the sun isn’t shining directly on them.

The full answer is complicated because we need to understand what type of shading we might experience and what effect that can have, coupled with some understanding of they way solar panels are manufactured and how that can be affected by shadows from trees, buildings, or even telegraph poles or even wires.

Just to reference my answer (in case you landed here from some random search engine), I’m discussing and explaining this with relevance to small, simple solar systems for off-grid locations. Typically this means one or two panels that will be charging a 12v battery.

Grid-connected systems, where your house roof has several kW of solar panels and inverters are feeding back to the grid etc are beyond this discussion, although they will still have the same broad issues so you can glean some relevant information.

How cloud cover affects solar panels

Solar panels have a maximum stated output, usually expressed as watts, so you might have a 100 watt panel or a 250 watt panel.

The watt value is the maximum electrical output that panel can produce under ‘perfect’ conditions, in other words, when the sun is shining directly and equally over the whole panel, there’s no cloud cover, the panel is pointing directly at the sun and that it’s not too hot (heat can reduce the performance), and that the panel is new.

If there is some light cloud cover, then that cloud will affect the amount of sunlight energy (known as solar irradiance) hitting the panel. If the cloud is blocking 50% of the light, then a 100 watt solar panel may only product 50 watts of electricity. Denser cloud may block 90% of the sun energy, so your 100 watt panel will now be producing 10 watts.

So whilst it’s true to say that a solar panel will work on a cloudy day, it’s more accurate to include the caveat that its performance will be reduced.

In summary, these factors will broadly determine the output from a solar panel at any given moment:

• Amount and density of cloud cover, if any
• Intensity of sun (winter is less intense due to lower sun angles, conversely summer is more intense)
• Angle of panel, relative to the sun
• Any partial shading (from trees, leaves, buildings and so on)
• Temperature (hotter will reduce efficiency, that’s why many panels have an air gap underneath)
• Age of solar panel (the performance slowly deteriorates over time)

Different types of solar panel

In very broad terms, there are two types of solar panel (in the <200 watt range) on the market – rigid and flexible (sometimes referred to as semi-flexible).

Rigid solar panels

Although there are slightly different technologies available in rigid panels (mono crystalline, poly crystalline etc), they are usually all encased in an aluminium frame, under a sheet of glass. Barring any debris falling on them, and the odd bit of moss growing, the glass, being glass, will remain clear and will not affect the amount of light coming through.

Some companies may advertise that their type of solar panel performs better in shade than others. Whilst to some extent this is true, if you have shade on your panel, you won’t be getting anywhere near the stated capacity, so a few percent better isn’t going to make that much difference, in my opinion.

Rigid panels can be mounted to various roofing types using a mounting bracket. This ensures an air gap under the panel, which will help keep it cooler and improve the overall performance on a hot day.

Flexible Solar Panels

Flexible or semi-flexible panels are an attractive option because they are lower profile and can follow the contours of a surface, looking much less obvious or obtrusive. They are popular on yachts and camper vans for obvious reasons, and are comparatively light too.

However, there are a few of potential downsides to consider: 1) you won’t have an air gap under the panel, which may affect it’s performance on a hot day (it may also transfer a lot of heat through the surface you’re mounting it on as well), 2) the protective covering isn’t glass (because they need to flex), and that coating/surface may loose some clarity over the years due to UV damage, which in turn will decrease the light transmission and hence performance, and 3) they are typically larger and more expensive than a rigid panel of the same capacity.

Partial shade from trees, bushes, buildings, & poles

You can’t do anything about the weather, or the amount of cloud cover, but you can ensure that your solar panel is positioned optimally for when the sun does shine. I’ve written more about positioning your solar panel in the Solar PV knowledge section.

Now let’s talk about shadows and the resulting partial shading cast from other things like trees, buildings and telephone poles.

When I was learning about solar electric systems, I started with a 10 watt panel on my old shed. In the spring, summer and autumn, it was fine for my simple requirements, but in the winter no sunlight fell directly on the panel. My garden was north facing and the shadow of the house together with low sun angles meant it was essentially useless- perhaps producing 0.5 – 1 watt of power at best.

There was very little I could do to counter this – I could have put the panel higher up, but it might look very obtrusive, or I could have fitted a larger panel, but I’d still be struggling to generate much power because of the lack of direct sun the winter. In the end, you have to accept that there some places and/or times of the year, where it’s simply not feasible to have a solar panel.

Trees, telegraph poles and the like present a slightly different issue. Obviously in the summer, trees will have lovely leaves, which will cast a shadow. But, the sun is generally higher from the horizon for more of the day, so that might not be an issue.

So if you’re assessing a potential site for a panel in winter, do consider what will happen in summer in terms of blocking sunlight, and vice versa, when assessing a site in summer, remember that the sun will be lower on the horizon in winter – are there any landscape features that might block direct sunlight with the low sun of winter?

And don’t forget that trees and bushes will grow over time. A location that’s just clear of the shadow of trees now, might not be in 5 years time as the tree grows.

Telegraph poles and to an extent, the their wires can also cause an issue as the shadow moves across your panel, resulting in partial shading. Solar panels are usually made up from a series of smaller ‘cells’ which are connected in groups. A typical panel may have three groups (usually running top to bottom) of cells. If a shadow blocks one of the individual cells, the whole group will produce nothing whilst that shadow is there.

If the shadow falls across at least one cell in all three groups, the panel will produce nothing. Hopefully the shadow won’t be there all day, but it’s something to think about, and it’s therefore best to try to avoid your panel being partially shaded.

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You can minimise some the shadow and shading effects by having more than one panel, but the way you connect them together is important – see my post on connecting multiple panels for more information and ideas.

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As with all the other words on this website, this has been written by a human from their individual experience and not Ai.